Internet Engineering Task Force Y. Oiwa Internet-Draft H. Watanabe Intended status: Standards Track H. Takagi Expires: May 3, 2012 RCIS, AIST B. Kihara T. Hayashi Lepidum Y. Ioku Yahoo! Japan October 31, 2011 Mutual Authentication Protocol for HTTP draft-oiwa-http-mutualauth-10 Abstract This document specifies a mutual authentication method for the Hyper- text Transport Protocol (HTTP). This method provides a true mutual authentication between an HTTP client and an HTTP server using password-based authentication. Unlike the Basic and Digest authentication methods, the Mutual authentication method specified in this document assures the user that the server truly knows the user's encrypted password. This prevents common phishing attacks: a phishing attacker controlling a fake website cannot convince a user that he authenticated to the genuine website. Furthermore, even when a user authenticates to an illegitimate server, the server cannot gain any information about the user's password. The Mutual authentication method is designed as an extension to the HTTP protocol, and is intended to replace the existing authentication methods used in HTTP (the Basic method, Digest method, and authentication using HTML forms). Status of this Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." Oiwa, et al. Expires May 3, 2012 [Page 1] Internet-Draft Mutual Authentication Protocol for HTTP October 2011 This Internet-Draft will expire on May 3, 2012. Copyright Notice Copyright (c) 2011 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Oiwa, et al. Expires May 3, 2012 [Page 2] Internet-Draft Mutual Authentication Protocol for HTTP October 2011 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 6 1.2. Document Structure Overview . . . . . . . . . . . . . . . 6 2. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 7 2.1. Messages Overview . . . . . . . . . . . . . . . . . . . . 7 2.2. Typical Flows of the Protocol . . . . . . . . . . . . . . 8 2.3. Alternative Flows . . . . . . . . . . . . . . . . . . . . 11 3. Message Syntax . . . . . . . . . . . . . . . . . . . . . . . . 12 3.1. Tokens . . . . . . . . . . . . . . . . . . . . . . . . . . 14 3.2. Numbers . . . . . . . . . . . . . . . . . . . . . . . . . 14 3.3. Strings . . . . . . . . . . . . . . . . . . . . . . . . . 15 4. Messages . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 4.1. 401-INIT . . . . . . . . . . . . . . . . . . . . . . . . . 16 4.2. 401-STALE . . . . . . . . . . . . . . . . . . . . . . . . 17 4.3. req-KEX-C1 . . . . . . . . . . . . . . . . . . . . . . . . 17 4.4. 401-KEX-S1 . . . . . . . . . . . . . . . . . . . . . . . . 18 4.5. req-VFY-C . . . . . . . . . . . . . . . . . . . . . . . . 20 4.6. 200-VFY-S . . . . . . . . . . . . . . . . . . . . . . . . 21 5. Authentication Realms . . . . . . . . . . . . . . . . . . . . 22 5.1. Resolving Ambiguities . . . . . . . . . . . . . . . . . . 23 6. Session Management . . . . . . . . . . . . . . . . . . . . . . 24 7. Validation Methods . . . . . . . . . . . . . . . . . . . . . . 26 8. Authentication Extensions . . . . . . . . . . . . . . . . . . 27 9. Decision Procedure for Clients . . . . . . . . . . . . . . . . 28 10. Decision Procedure for Servers . . . . . . . . . . . . . . . . 33 11. Authentication Algorithms . . . . . . . . . . . . . . . . . . 35 11.1. Support Functions and Notations . . . . . . . . . . . . . 36 11.2. Default Functions for Algorithms . . . . . . . . . . . . . 37 12. Application Channel Binding . . . . . . . . . . . . . . . . . 38 13. Application for Proxy Authentication . . . . . . . . . . . . . 38 14. Methods to Extend This Protocol . . . . . . . . . . . . . . . 39 15. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 40 16. Security Considerations . . . . . . . . . . . . . . . . . . . 40 16.1. Security Properties . . . . . . . . . . . . . . . . . . . 40 16.2. Denial-of-service Attacks to Servers . . . . . . . . . . . 40 16.3. Implementation Considerations . . . . . . . . . . . . . . 41 16.4. Usage Considerations . . . . . . . . . . . . . . . . . . . 42 17. Notice on Intellectual Properties . . . . . . . . . . . . . . 42 18. References . . . . . . . . . . . . . . . . . . . . . . . . . . 43 18.1. Normative References . . . . . . . . . . . . . . . . . . . 43 18.2. Informative References . . . . . . . . . . . . . . . . . . 44 Appendix A. (Informative) Generic Syntax of Headers . . . . . . . 45 Appendix B. (Informative) Draft Remarks from Authors . . . . . . 46 Appendix C. (Informative) Draft Change Log . . . . . . . . . . . 47 C.1. Changes in Revision 10 . . . . . . . . . . . . . . . . . . 47 C.2. Changes in Revision 09 . . . . . . . . . . . . . . . . . . 48 Oiwa, et al. Expires May 3, 2012 [Page 3] Internet-Draft Mutual Authentication Protocol for HTTP October 2011 C.3. Changes in Revision 08 . . . . . . . . . . . . . . . . . . 48 C.4. Changes in Revision 07 . . . . . . . . . . . . . . . . . . 48 C.5. Changes in Revision 06 . . . . . . . . . . . . . . . . . . 49 C.6. Changes in Revision 05 . . . . . . . . . . . . . . . . . . 49 C.7. Changes in Revision 04 . . . . . . . . . . . . . . . . . . 49 C.8. Changes in Revision 03 . . . . . . . . . . . . . . . . . . 49 C.9. Changes in Revision 02 . . . . . . . . . . . . . . . . . . 50 C.10. Changes in Revision 01 . . . . . . . . . . . . . . . . . . 50 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 50 Oiwa, et al. Expires May 3, 2012 [Page 4] Internet-Draft Mutual Authentication Protocol for HTTP October 2011 1. Introduction This document specifies a mutual authentication method for Hyper-Text Transport Protocol (HTTP). The method, called "Mutual Authentication Protocol" in this document, provides a true mutual authentication between an HTTP client and an HTTP server, using just a simple password as a credential. The currently available methods for authentication in HTTP and Web systems have several deficiencies. The Basic authentication method [RFC2617] sends a plaintext password to a server without any protection; the Digest method uses a hash function that suffers from simple dictionary-based off-line attacks, and people have begun to think it is obsolete. The authentication method proposed in this document solves these problems, substitutes for these existing methods, and serves as a long-term solution to Web authentication security. It has the following main characteristics: o It provides "true" mutual authentication: in addition to assuring the server that the user knows the password, it also assures the user that the server truly knows the user's encrypted password at the same time. This makes it impossible for fake website owners to persuade users that they have authenticated with the original websites. o It uses only passwords as the user's credential: unlike public- key-based security algorithms, the method does not rely on secret keys or other cryptographic data that have to be stored inside the users' computers. The proposed method can be used as a drop-in replacement to the current authentication methods like Basic or Digest, while ensuring a much stronger level of security. o It is secure: when the server fails to authenticate with a user, the protocol will not reveal any bit of the user's password. Users can discriminate between true and fake Web servers using their own passwords by using the proposed method. Even when a user inputs his/her password to a fake website owned by illegitimate phishers, the user will certainly notice that the authentication has failed. Phishers will not be successful in their authentication attempts, even if they forward the received data from a user to a legitimate server or vice versa. Users can input sensitive data to the web forms after confirming that the mutual authentication has succeeded, without fear of phishing attacks. The document, along with [I-D.oiwa-http-auth-extension], also Oiwa, et al. Expires May 3, 2012 [Page 5] Internet-Draft Mutual Authentication Protocol for HTTP October 2011 proposes several extensions to the current HTTP authentication framework, to replace current widely-used form-based Web authentication. The extensions provided include: o Multi-host single authentication within an Internet domain (Section 5), o non-mandatory, optional authentication on HTTP (Section 8), o log out from both server and client side (Section 8), and o finer control for redirection depending on authentication status (Section 8). 1.1. Terminology The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. The terms "encouraged" and "advised" are used for suggestions that do not constitute "SHOULD"-level requirements. People MAY freely choose not to include the suggested items regarding [RFC2119], but complying with those suggestions would be a best practice; it will improve the security, interoperability, and/or operational performance. This document distinguishes the terms "client" and "user" in the following way: A "client" is an entity understanding and talking HTTP and the specified authentication protocol, usually computer software; a "user" is a (usually natural) person who wants to access data resources using "a client". The term "natural numbers" refers to the non-negative integers (including zero) throughout this document. This document treats target (codomain) of hash functions to be natural numbers. The notation OCTETS(H(s)) gives a usual octet- string output of hash function H applied to string s. 1.2. Document Structure Overview The entire document is organized as follows: o Section 2 presents an overview of the protocol design. o Sections 3 to 10 define a general framework of the Mutual authentication protocol. This framework is independent of Oiwa, et al. Expires May 3, 2012 [Page 6] Internet-Draft Mutual Authentication Protocol for HTTP October 2011 specific cryptographic primitives. o Section 11 describes properties needed for cryptographic algorithms used with this protocol framework, and defines a few functions which will be shared among such cryptographic algorithms. o The sections after that contain general normative and informative information about the protocol. o The appendices contain some information that may help developers to implement the protocol. 2. Protocol Overview The protocol, as a whole, is designed as a natural extension to the HTTP protocol [I-D.ietf-httpbis-p1-messaging] using a framework defined in [I-D.ietf-httpbis-p7-auth]. Internally, the server and the client will first perform a cryptographic key exchange, using the secret password as a "tweak" to the exchange. The key-exchange will only succeed when the secrets used by the both peers are correctly related (i.e. generated from the same password). Then, both peers will verify the authentication results by confirming the sharing of the exchanged key. This section describes a brief image of the protocol and the exchanged messages. 2.1. Messages Overview The authentication protocol uses seven kinds of messages to perform mutual authentication. These messages have specific names within this specification. o Authentication request messages: used by the servers to request clients to start mutual authentication. * 401-INIT message: a general message to start the authentication protocol. It is also used as a message indicating an authentication failure. * 200-Optional-INIT message: a variant of the 401-INIT message indicating that an authentication is not mandatory. * 401-STALE message: a message indicating that it has to start a new authentication trial. Oiwa, et al. Expires May 3, 2012 [Page 7] Internet-Draft Mutual Authentication Protocol for HTTP October 2011 o Authenticated key exchange messages: used by both peers to perform authentication and the sharing of a cryptographic secret. * req-KEX-C1 message: a message sent from the client. * 401-KEX-S1 message: a message sent from the server as a response to a req-KEX-C1 message. o Authentication verification messages: used by both peers to verify the authentication results. * req-VFY-C message: a message used by the client, requesting that the server authenticates and authorizes the client. * 200-VFY-S message: a successful response used by the server, and also asserting that the server is authentic to the client simultaneously. In addition to the above, either a request or a response without any HTTP headers related to this specification will be hereafter called a "normal request" or a "normal response", respectively. 2.2. Typical Flows of the Protocol In typical cases, the client access to a resource protected by the Mutual authentication will follow the following protocol sequence. Oiwa, et al. Expires May 3, 2012 [Page 8] Internet-Draft Mutual Authentication Protocol for HTTP October 2011 Client Server | | | ---- (1) normal request ---------> | GET / HTTP/1.1 | | | | <---------------- (2) 401-INIT --- | | 401 Authentication Required | WWW-Authenticate: Mutual realm="a realm" | | [user, | | pass]-->| | | ---- (3) req-KEX-C1 -------------> | GET / HTTP/1.1 | Authorization: Mutual user="john", |--> [user DB] kc1="...", ... |<-- [user info] | | | <-------------- (4) 401-KEX-S1 --- | | 401 Authentication Required | WWW-Authenticate: Mutual sid=..., ks1="...", ... | | [compute] (5) compute session secret [compute] | | | | | ---- (6) req-VFY-C --------------> | GET / HTTP/1.1 |--> [verify (6)] Authorization: Mutual sid=..., |<-- OK vkc="...", ... | | | | <--------------- (7) 200-VFY-S --- | [verify | 200 OK | (7)]<--| Authentication-Info: Mutual vks="..." | | v v Figure 1: Typical communication flow for first access to resource o As usual in general HTTP protocol designs, a client will at first request a resource without any authentication attempt (1). If the requested resource is protected by the Mutual authentication, the server will respond with a message requesting authentication (401-INIT) (2). o The client processes the body of the message, and waits for the user to input the user name and a password. If the user name and the password are available, the client will send a message with the authenticated key exchange (req-KEX-C1) to start the authentication (3). Oiwa, et al. Expires May 3, 2012 [Page 9] Internet-Draft Mutual Authentication Protocol for HTTP October 2011 o If the server has received a req-KEX-C1 message, the server looks up the user's authentication information within its user database. Then the server creates a new session identifier (sid) that will be used to identify sets of the messages that follow it, and responds back with a message containing a server-side authenticated key exchange value (401-KEX-S1) (4). o At this point (5), both peers calculate a shared "session secret" using the exchanged values in the key exchange messages. Only when both the server and the client have used secret credentials generated from the same password will the session secret values match. This session secret will be used for the actual access authentication after this point. o The client will send a request with a client-side authentication verification value (req-VFY-C) (6), generated from the client- owned session secret. The server will check the validity of the verification value using its own session secret. o If the authentication verification value from the client was correct, it means that the client definitely owns the credential based on the expected password (i.e. the client authentication succeeded.) The server will respond with a successful message (200-VFY-S) (7). Contrary to the usual one-way authentication (e.g. HTTP Basic authentication or POP APOP authentication), this message also contains a server-side authentication verification value. When the client's verification value is incorrect (e.g. because the user-supplied password was incorrect), the server will respond with the 401-INIT message (the same one as used in (2)) instead. o The client MUST first check the validity of the server-side authentication verification value contained in the message (7). If the value was equal to the expected one, the server authentication succeeded. If it is not the value expected, or if the message does not contain the authentication verification value, it means that the mutual authentication has been broken for some unexpected reason. The client MUST NOT process any body or header values contained in this case. (Note: This case should not happen between a correctly-implemented server and a client.) Oiwa, et al. Expires May 3, 2012 [Page 10] Internet-Draft Mutual Authentication Protocol for HTTP October 2011 2.3. Alternative Flows As shown above, the typical flow for a first authenticated request requires three request-response pairs. To reduce the protocol overhead, the protocol enables several short-cut flows which require fewer messages. o (case A) If the client knows that the resource is likely to require the authentication, the client MAY omit the first unauthenticated request (1) and immediately send a key exchange (req-KEX-C1 message). This will reduce one round-trip of messages. o (case B) If both the client and the server previously shared a session secret associated with a valid session identifier (sid), the client MAY directly send a req-VFY-C message using the existing session identifier and corresponding session secret. This will further reduce one round-trip of messages. In such cases, the server MAY have thrown out the corresponding sessions from the session table. In this case, the server will respond with a 401-STALE message, indicating a new key exchange is required. The client SHOULD retry constructing a req-KEX-C1 message in this case. Figure 2 depicts the shortcut flows described above. Under the appropriate settings and implementations, most of the requests to resources are expected to meet both the criteria, and thus only one round-trip of request/responses will be required in most cases. Oiwa, et al. Expires May 3, 2012 [Page 11] Internet-Draft Mutual Authentication Protocol for HTTP October 2011 (A) omit first request (2 round trips) Client Server | | | --- req-KEX-C1 ----> | | | | <---- 401-KEX-S1 --- | | | | ---- req-VFY-C ----> | | | | <----- 200-VFY-S --- | | | (B) reusing session secret (B-1) key available (B-2) key expired (1 round trip) (3 round trips) Client Server Client Server | | | | | ---- req-VFY-C ----> | | --- req-VFY-C -------> | | | | | | <----- 200-VFY-S --- | | <------- 401-STALE --- | | | | | | --- req-KEX-C1 ------> | | | | <------ 401-KEX-S1 --- | | | | --- req-VFY-C -------> | | | | <------- 200-VFY-S --- | | | Figure 2: Several alternative flows on protocol For more details, see Sections 9 and 10. 3. Message Syntax The Mutual authentication protocol uses five headers: WWW-Authenticate (in responses with status code 401), Optional-WWW-Authenticate (in responses with non-401 status codes), Authentication-Control (in responses), Authorization (in requests), and Authentication-Info (in responses other than 401 status). These headers follow a common framework described in Oiwa, et al. Expires May 3, 2012 [Page 12] Internet-Draft Mutual Authentication Protocol for HTTP October 2011 [I-D.ietf-httpbis-p7-auth]. The detailed syntax definitions for these headers are contained in Section 4. These headers use some common syntax elements described in Figure 3. The syntax is denoted in the extended augmented BNF syntax defined in [I-D.ietf-httpbis-p1-messaging] and [RFC5234]. The following elements are quoted from [I-D.ietf-httpbis-p1-messaging] and [I-D.ietf-httpbis-p7-auth]: auth-scheme, quoted-string, auth-param, SP, BWS, header-field, token and challenge. Mutual-auth-scheme = "Mutual" bare-token = 1*(%x30-39 / %x41-5A / %x61-7A / "-" / "_") extension-token = "-" bare-token 1*("." bare-token) extensive-token = bare-token / extension-token EQ = BWS "=" BWS extension-param = extensive-token EQ value value = extensive-token / integer / hex-fixed-number / base64-fixed-number / string integer = "0" / (%x31-39 *%x30-39) ; no leading zeros hex-fixed-number = 1*(%x30-39 / %x41-46 / %x61-66) string = quoted-string base64-fixed-number = quoted-string ; see main text for limitation Figure 3: BNF syntax for common elements used in protocol In relation to the definitions in core HTTP, Syntaxes for bare-token, extension-token, extensive-token, integer, and hex-fixed-number are subsets of token. Syntaxes for string and base64-fixed-number are subsets of quoted-string. Notes: o The syntax of challenges and credentials used in this protocol are conforming to (more precisely, subsets of) a generic syntax provided in [I-D.ietf-httpbis-p7-auth]. See Appendix A for more details. o In HTTP, the WWW-Authenticate header may contain more than one challenges. Client implementations SHOULD be aware of and be capable of handle those cases correctly. o In many HTTP implementations, syntax elements of headers are often handled very rudely. Especially, they often use both tokens and quoted-strings interchangeably. Implementations of this specification SHOULD NOT send such mis-formated headers. However, implementations MAY accept tokens in places where a quoted-string (or its subtypes) is expected, and MAY accept quoted-strings in Oiwa, et al. Expires May 3, 2012 [Page 13] Internet-Draft Mutual Authentication Protocol for HTTP October 2011 places where a token (or its subtypes) is expected. If did so, a token SHOULD be treated as a equivalent to a string whose content before backslash-quotation is equal to the octets of the token representation. 3.1. Tokens The tokens (bare-token and extension-token) are case insensitive; Senders SHOULD send these in lower-case, and receivers MUST accept both upper- and lower-cases. When tokens are used as the (partial) inputs to any hash or other mathematical functions, it MUST always be used in lower-case. All hexadecimal numbers are also case- insensitive, and SHOULD be sent in lower-case. Extensive-tokens are used in this protocol where the set of acceptable tokens may include non-standard extensions. Any non- standard extensions of this protocol MUST use the extension-tokens with format "-.", where is a validly registered (sub-)domain name on the Internet owned by the party who defines the extensions. 3.2. Numbers The syntax definition of the integers only allows representations that do not contain extra leading zeros. The numbers represented as a hex-fixed-number MUST include an even number of characters (i.e. multiples of eight bits). When these are generated from any cryptographic values, they SHOULD have their "natural length": if these are generated from a hash function, these lengths SHOULD correspond to the hash size; if these are representing elements of a mathematical set (or group), its lengths SHOULD be the shortest for representing all the elements in the set. For example, any results of SHA-256 hash function will be represented by 64 characters, and any elements in 2048-bit prime field (modulo a 2048- bit integer) will be represented by 512 characters, regardless of how much 0's will be appear in front of such representations. Session- identifiers and other non-cryptographically generated values are represented in any (even) length determined by the side who generates it first, and the same length SHALL be used throughout the all communications by both peers. The numbers represented as base64-fixed-number SHALL be generated as follows: first, the number is converted to a big-endian radix-256 binary representation as an octet string. The length of the representation is determined in the same way as mentioned above. Then, the string is encoded using the Base 64 encoding [RFC4648] without any spaces and newlines, and then enclosed by two double- Oiwa, et al. Expires May 3, 2012 [Page 14] Internet-Draft Mutual Authentication Protocol for HTTP October 2011 quotations. Implementations decoding base64-fixed-number SHOULD reject any input data with invalid characters, excess/insufficient paddings, or non-canonical pad bits (See Sections 3.1 to 3.5 of [RFC4648]). 3.3. Strings All character strings outside ASCII character sets MUST be encoded using the UTF-8 encoding [RFC3629] for the ISO 10646-1 character set [ISO.10646-1.1993]. Both peers are RECOMMENDED to reject any invalid UTF-8 sequences that might cause decoding ambiguities (e.g., containing <"> in the second or later byte of the UTF-8 encoded characters). To encode character strings to header values, they will first be encoded according to UTF-8 without a leading BOM, then all occurrences of the characters <"> and "\" will be escaped by prepending "\", and two <">s will be put around the string. These escaping backslashes and enclosing quotes SHALL be removed before any processing other than when using them in a header field. If strings are representing a domain name or URI that contains non- ASCII characters, the host parts SHOULD be encoded as it is used in the HTTP protocol layer (e.g. in a Host: header); under current standards it will be the one defined in [RFC5890]. It SHOULD use lower-case ASCII characters. For base64-fixed-numbers, which use the string syntax, see the previous section. 4. Messages In this section we define the seven kinds of messages used in the authentication protocol along with the formats and requirements of the headers for each message. To determine which message are expected to be sent, see Sections 9 and 10. In the descriptions below, the type of allowable values for each header parameter is shown in parenthesis after the key names. The "algorithm-determined" type means that the acceptable value for the parameter is one of the types defined in Section 3, and is determined by the value of the "algorithm" parameter. The parameters marked "mandatory" SHALL be contained in the message. The parameters marked "non-mandatory" MAY either be contained or omitted in the message. Each parameter SHALL appear in each headers exactly once at most. Oiwa, et al. Expires May 3, 2012 [Page 15] Internet-Draft Mutual Authentication Protocol for HTTP October 2011 4.1. 401-INIT Every 401-INIT message SHALL be a valid HTTP 401 (Authentication Required) message containing one (and only one: hereafter not explicitly noticed) "WWW-Authenticate" header with a challenge in the following format. WWW-Authenticate: Mutual algorithm=xxxx, validation=xxxx, realm="xxxx", stale=0, version=-draft10 challenge-401-INIT = Mutual-auth-scheme 1*SP 1#param-401-INIT param-401-INIT = version / algorithm / validation / auth-domain / realm / pwd-hash / stale / extension-param version = "version" EQ extensive-token algorithm = "algorithm" EQ extensive-token validation = "validation" EQ extensive-token auth-domain = "auth-domain" EQ string realm = "realm" EQ string pwd-hash = "pwd-hash" EQ extensive-token stale = bare-token Figure 4: BNF syntax for challenges in 401-INIT header The header SHALL contain all of the parameters marked "mandatory" below, and MAY contain those marked "non-mandatory". version: (mandatory extensive-token) should be the token "-draft10" in this specification. The behavior is undefined when other values are specified. algorithm: (mandatory extensive-token) specifies the authentication algorithm to be used. The value MUST be one of the tokens specified in [I-D.oiwa-http-mutualauth-algo] or other supplemental specification documentation. validation: (mandatory extensive-token) specifies the method of host validation. The value MUST be one of the tokens described in Section 7, or the tokens specified in other supplemental specification documentation. auth-domain: (non-mandatory string) specifies the authentication domain, the set of hosts for which the authentication credentials are valid. It MUST be one of the strings described in Section 5. If the value is omitted, it is assumed to be the "single-port" type domain in Section 5. Oiwa, et al. Expires May 3, 2012 [Page 16] Internet-Draft Mutual Authentication Protocol for HTTP October 2011 realm: (mandatory string) is a UTF-8 encoded string representing the name of the authentication realm inside the authentication domain. pwd-hash: (non-mandatory extensive-token) specifies the hash algorithm (hereafter referred to by ph) used for additionally hashing the password. The valid tokens are * none: ph(p) = p * md5: ph(p) = MD5(p) * digest-md5: ph(p) = MD5(username | ":" | realm | ":" | p), the same value as MD5(A1) for "MD5" algorithm in [RFC2617]. * sha1: ph(p) = SHA1(p) If omitted, the value "none" is assumed. The use of "none" is recommended. stale: (mandatory token) MUST be "0". The algorithm specified in this header will determine the types and the values for K_c1, K_s1, VK_c and VK_s. 4.2. 401-STALE A 401-STALE message is a variant of the 401-INIT message, which means that the client has sent a request message that is not for any active session. WWW-Authenticate: Mutual algorithm=xxxx, validation=xxxx, realm="xxxx", stale=1, version=-draft10 The header MUST contain the same parameters as in 401-INIT, except that the stale parameter contains token 1. 4.3. req-KEX-C1 Every req-KEX-C1 message SHALL be a valid HTTP request message containing an "Authorization" with credentials of the following format. Authorization: Mutual algorithm=xxxx, validation=xxxx, realm="xxxx", user="xxxx", kc1=xxxx, version=-draft10 Oiwa, et al. Expires May 3, 2012 [Page 17] Internet-Draft Mutual Authentication Protocol for HTTP October 2011 credentials-KEX-C1 = Mutual-auth-scheme 1*SP 1#param-req-KEX-C1 param-req-KEX-C1 = version / algorithm / validation / auth-domain / realm / user / kc1 / extension-param user = "user" EQ string kc1 = "kc1" EQ value Figure 5: the BNF syntax for the header in req-KEX-C1 message The header SHALL contain the parameters with the following keys: version: (mandatory, extensive-token) should be the token "-draft10" in this specification. The behavior is undefined when other values are specified. algorithm, validation, auth-domain, realm: MUST be the same value as it is when received from the server. user: (mandatory, string) is the UTF-8 encoded name of the user. If this name comes from a user input, client software SHOULD prepare the string using SASLprep [RFC4013] before encoding it to UTF-8. kc1: (mandatory, algorithm-determined) is the client-side key exchange value K_c1, which is specified by the algorithm that is used. 4.4. 401-KEX-S1 Every 401-KEX-S1 message SHALL be a valid HTTP 401 (Authentication Required) message containing a "WWW-Authenticate" header with a challenge of the following format. WWW-Authenticate: Mutual algorithm=xxxx, validation=xxxx, realm="xxxx", sid=xxxx, ks1=xxxx, nc-max=x, nc-window=x, time=x, path="xxxx", version=-draft10 Oiwa, et al. Expires May 3, 2012 [Page 18] Internet-Draft Mutual Authentication Protocol for HTTP October 2011 challenge-401-KEX-S1 = Mutual-auth-scheme 1*SP 1#param-401-KEX-S1 param-401-KEX-S1 = version / algorithm / validation / auth-domain / realm / sid / ks1 / nc-max / nc-window / time / path / extension-param sid = "sid" EQ hex-fixed-number ks1 = "ks1" EQ value nc-max = "nc-max" EQ integer nc-window = "nc-window" EQ integer time = "time" EQ integer path = "path" EQ string Figure 6: the BNF syntax for the header in 401-KEX-S1 message The header SHALL contain the parameters with the following keys: version: (mandatory, extensive-token) should be the token "-draft10" in this specification. The behavior is undefined when other values are specified. algorithm, validation, auth-domain, realm: MUST be the same value as it is when received from the client. sid: (mandatory, hex-fixed-number) MUST be a session identifier, which is a random integer. The sid SHOULD have uniqueness of at least 80 bits or the square of the maximal estimated transactions concurrently available in the session table, whichever is larger. See Section 6 for more details. ks1: (mandatory, algorithm-determined) is the server-side key exchange value K_s1, which is specified by the algorithm. nc-max: (mandatory, integer) is the maximal value of nonce counts that the server accepts. nc-window: (mandatory, integer) the number of available nonce slots that the server will accept. The value of the nc-window parameter is RECOMMENDED to be 32 or more. time: (mandatory, integer) represents the suggested time (in seconds) that the client can reuse the session represented by the sid. It is RECOMMENDED to be at least 60. The value of this parameter is not directly linked to the duration that the server keeps track of the session represented by the sid. Oiwa, et al. Expires May 3, 2012 [Page 19] Internet-Draft Mutual Authentication Protocol for HTTP October 2011 path: (non-mandatory, string) specifies which path in the URI space the same authentication is expected to be applied. The value is a space-separated list of URIs, in the same format as it was specified in domain parameter [RFC2617] for the Digest authentications, and clients are RECOMMENDED to recognize it. The all path elements contained in the parameter MUST be inside the specified auth-domain: if not, clients SHOULD ignore such elements. 4.5. req-VFY-C Every req-VFY-C message SHALL be a valid HTTP request message containing an "Authorization" header with a credentials in the following format. Authorization: Mutual algorithm=xxxx, validation=xxxx, realm="xxxx", sid=xxxx, nc=x, vc=xxxx, version=-draft10 credentials-req-VFY-C = Mutual-auth-scheme 1*SP 1#param-req-VFY-C param-req-VFY-C = version / algorithm / validation / auth-domain / realm / sid / nc / vkc / extension-param nc = "nc" EQ integer vkc = "vkc" EQ value Figure 7: the BNF syntax for the header in req-VFY-C message The parameters contained in the header are as follows: version: (mandatory, extensive-token) should be the token "-draft10" in this specification. The behavior is undefined when other values are specified. algorithm, validation, auth-domain, realm: MUST be the same value as it is when received from the server for the session. sid: (mandatory, hex-fixed-number) MUST be one of the sid values that was received from the server for the same authentication realm. nc: (mandatory, integer) is a nonce value that is unique among the requests sharing the same sid. The values of the nonces SHOULD satisfy the properties outlined in Section 6. Oiwa, et al. Expires May 3, 2012 [Page 20] Internet-Draft Mutual Authentication Protocol for HTTP October 2011 vkc: (mandatory, algorithm-determined) is the client-side authentication verification value VK_c, which is specified by the algorithm. 4.6. 200-VFY-S Every 200-VFY-S message SHALL be a valid HTTP message that is not of the 401 (Authentication Required) type, containing an "Authentication-Info" header with the value of the following format. Authentication-Info: Mutual sid=xxxx, vks=xxxx, version=-draft10 auth-info-200-VFY-S = Mutual-auth-scheme 1*SP 1#param-200-VFY-S param-200-VFY-S = version / sid / vks / logout-timeout vks = "vks" EQ value logout-timeout = "logout-timeout" EQ integer Figure 8: BNF syntax for header in 200-VFY-S message The parameters contained in the header are as follows: version: (mandatory, extensive-token) should be the token "-draft10" in this specification. The behavior is undefined when other values are specified. sid: (mandatory, hex-fixed-number) MUST be the value received from the client. vks: (mandatory, algorithm-determined) is the server-side authentication verification value VK_s, which is specified by the algorithm. logout-timeout: (non-mandatory, integer) is the number of seconds after which the client should re-validate the user's password for the current authentication realm. The value 0 means that the client SHOULD automatically forget the user-inputted password for the current authentication realm and revert to the unauthenticated state (i.e. server-initiated logout). This does not, however, mean that the long-term memories for the passwords (such as the password reminders and auto fill-ins) should be removed. If a new timeout value is received for the same authentication realm, it overrides the previous timeout. If logout-timeout parameters are specified both in an Authentication-Info header and an Authentication-Control header ([I-D.oiwa-http-auth-extension]), the client SHOULD Oiwa, et al. Expires May 3, 2012 [Page 21] Internet-Draft Mutual Authentication Protocol for HTTP October 2011 handle the parameter with the smaller value. The header MUST be sent before the content body: it MUST NOT be sent in the trailer of a chunked-encoded response. If a "100 Continue" response is sent from the server, the Authentication-Info header SHOULD be included in that response, instead of the final response. 5. Authentication Realms In this protocol, an "authentication realm" is defined as a set of resources (URIs) for which the same set of user names and passwords is valid for. If the server requests authentication for an authentication realm that the client is already authenticated for, the client will automatically perform the authentication using the already-known secrets. However, for the different authentication realms, the clients SHOULD NOT automatically reuse the usernames and passwords for another realm. Just like in Basic and Digest access authentication protocols, Mutual authentication protocol supports multiple, separate protection spaces to be set up inside each host. Furthermore, the protocol supports that a single authentication realm spans over several hosts within the same Internet domain. Each authentication realm is defined and distinguished by the triple of an "authentication algorithm", an "authentication domain", and a "realm" parameter. However, server operators are NOT RECOMMENDED to use the same pair of an authentication domain and a realm for different authentication algorithms. The realm parameter is a string as defined in Section 4. Authentication domains are described in the remainder of this section. An authentication domain specifies the range of hosts that the authentication realm spans over. In this protocol, it MUST be one of the following strings. o Single-server type: The string in format "://:", where , , and are the corresponding URI parts of the request URI. Even if the request-URI does not have a port part, the string will include one (i.e. 80 for http and 443 for https). The port part MUST NOT contain leading zeros. Use this when authentication is only valid for specific protocol (such as https). Oiwa, et al. Expires May 3, 2012 [Page 22] Internet-Draft Mutual Authentication Protocol for HTTP October 2011 o Single-host type: The "host" part of the requested URI. This is the default value. Authentication realms within this kind of authentication domain will span over several protocols (i.e. http and https) and ports, but not over different hosts. o Wildcard-domain type: The string in format "*.", where is either the host part of the requested URI or any domain in which the requested host is included (this means that the specification "*.example.com" is valid for all of hosts "www.example.com", "web.example.com", "www.sales.example.com" and "example.com"). The domain-postfix sent from the servers MUST be equal to or included in a valid Internet domain assigned to a specific organization: if clients know, by some means such as a blacklist for HTTP cookies [RFC6265], that the specified domain is not to be assigned to any specific organization (e.g. "*.com" or "*.jp"), the clients are RECOMMENDED to reject the authentication request. In the above specifications, every "scheme", "host", and "domain" MUST be in lower-case, and any internationalized domain names beyond the ASCII character set SHALL be represented in the way they are sent in the underlying HTTP protocol, represented in lower-case characters; i.e. these SHALL be in the form of the LDH labels in IDNA [RFC5890]. All "port"s MUST be in the shortest, unsigned, decimal number notation. Not obeying these requirements will cause failure of valid authentication attempts. 5.1. Resolving Ambiguities In the above definitions of authentication domains, several domains will overlap each other. Depending on the "path" parameters given in the "401-KEX-S1" message (see Section 4), there may be several candidates when the client is going to send a request including an authentication credential (Steps 3 and 4 of the decision procedure presented in Section 9). If such choices are required, the following procedure SHOULD be followed. o If the client has previously sent a request to the same URI, and if it remembers the authentication realm requested by 401-INIT messages at that time, use that realm. o In other cases, use one of authentication realms representing the most-specific authentication domains. From the list of possible domain specifications shown above, each one earlier has priority over ones described after that. Oiwa, et al. Expires May 3, 2012 [Page 23] Internet-Draft Mutual Authentication Protocol for HTTP October 2011 If there are several choices with different domain-postfix specifications, the one that has the longest domain-postfix has priority over ones with a shorter domain-postfix. o If there are realms with the same authentication domain, there is no defined priority: the client MAY choose any one of the possible choices. If possible, server operators are encouraged to avoid such ambiguities by properly setting the "path" parameters. 6. Session Management In the Mutual authentication protocol, a session represented by an sid is set up using first four messages (first request, 401-INIT, req-KEX-C1 and 401-KEX-S1), and a "session secret" (z) associated with the session is established. After sharing a session secret, this session, along with the secret, can be used for one or more requests for resources protected by the same realm in the same server. Note that session management is only an inside detail of the protocol and usually not visible to normal users. If a session expires, the client and server SHOULD automatically reestablish another session without informing the users. Sessions and session identifiers are local to each server (defined by scheme, host and port) inside an authentication domain; the clients MUST establish separate sessions for each port of a host to be accessed. Furthermore, sessions and identifiers are also local to each authentication realm, even if these are provided from the same servers. The same session identifiers provided either from different servers or for different realms SHOULD be treated as independent ones. The server SHOULD accept at least one req-VFY-C request for each session, given that the request reaches the server in a time window specified by the timeout parameter in the 401-KEX-S1 message, and that there are no emergent reasons (such as flooding attacks) to forget the sessions. After that, the server MAY discard any session at any time and MAY send 401-STALE messages for any req-VFY-C requests. The client MAY send two or more requests using a single session specified by the sid. However, for all such requests, each value of the nonce (in the nc parameter) MUST satisfy the following conditions: Oiwa, et al. Expires May 3, 2012 [Page 24] Internet-Draft Mutual Authentication Protocol for HTTP October 2011 o It is a natural number. o The same nonce was not sent within the same session. o It is not larger than the nc-max value that was sent from the server in the session represented by the sid. o It is larger than (largest-nc - nc-window), where largest-nc is the maximal value of nc which was previously sent in the session, and nc-window is the value of the nc-window parameter which was received from the server in the session. The last condition allows servers to reject any nonce values that are "significantly" smaller than the "current" value (defined by the value of nc-window) of the nonce used in the session involved. In other words, servers MAY treat such nonces as "already received". This restriction enables servers to implement duplicated nonce detection in a constant amount of memory (for each session). Servers MUST check for duplication of the received nonces, and if any duplication is detected, the server MUST discard the session and respond with a 401-STALE message, as outlined in Section 10. The server MAY also reject other invalid nonce values (such as ones above the nc-max limit) by sending a 401-STALE message. For example, assume the nc-window value of the current session is 32, nc-max is 100, and that the client has already used the following nonce values: {1-20, 22, 24, 30-38, 45-60, 63-72}. Then the nonce values that can be used for next request is one of the following set: {41-44, 61-62, 73-100}. The values {0, 21, 23, 25-29, 39-40} MAY be rejected by the server because they are not above the current "window limit" (40 = 72 - 32). Typically, clients can ensure the above property by using a monotonically-increasing integer counter that counts from zero upto the value of nc-max. The values of the nonces and any nonce-related values MUST always be treated as natural numbers within an infinite range. Implementations using fixed-width integers or fixed-precision floating numbers MUST correctly and carefully handle integer overflows. Such implementations are RECOMMENDED to accept any larger values that cannot be represented in the fixed-width integer representations, as long as other limits such as internal header-length restrictions are not involved. The protocol is designed carefully so that both the clients and servers can implement the protocol using only fixed-width integers, by rounding any overflowed values to the maximum possible value. Oiwa, et al. Expires May 3, 2012 [Page 25] Internet-Draft Mutual Authentication Protocol for HTTP October 2011 7. Validation Methods The "validation method" specifies a method to "relate" the mutual authentication processed by this protocol with other authentications already performed in the underlying layers and to prevent man-in-the- middle attacks. It decides the value v that is an input to the authentication protocols. The valid tokens for the validation parameter and corresponding values of v are as follows: host: hostname validation: The value v will be the ASCII string in the following format: "://:", where , , and are the URI components corresponding to the currently accessing resource. The scheme and host are in lower-case, and the port is in a shortest decimal representation. Even if the request-URI does not have a port part, v will include one. tls-cert: TLS certificate validation: The value v will be the octet string of the hash value of the public key certificate used in the underlying TLS [RFC5246] (or SSL) connection. The hash value is defined as the value of the entire signed certificate (specified as "Certificate" in [RFC5280]), hashed by the hash algorithm specified by the authentication algorithm used. tls-key: TLS shared-key validation: The value v will be the octet string of the shared master secret negotiated in the underlying TLS (or SSL) connection. If the HTTP protocol is used on a non-encrypted channel (TCP and SCTP, for example), the validation type MUST be "host". If HTTP/TLS [RFC2818] (https) protocol is used with the server certificates, the validation type MUST be either "tls-cert" or "tls-key". If HTTP/TLS protocol is used with an anonymous Diffie-Hellman key exchange, the validation type MUST be "tls-key" (see the note below). If the validation type "tls-cert" is used, the server certificate provided on TLS connection MUST be verified to make sure that the server actually owns the corresponding secret key. Clients MUST validate this parameter upon reception of the 401-INIT messages. However, when the client is a Web browser with any scripting Oiwa, et al. Expires May 3, 2012 [Page 26] Internet-Draft Mutual Authentication Protocol for HTTP October 2011 capabilities, the underlying TLS channel used with HTTP/TLS MUST provide server identity verification. This means (1) the anonymous Diffie-Hellman key exchange ciphersuite MUST NOT be used, and (2) the verification of the server certificate provided from the server MUST be performed. For other systems, when the underlying TLS channel used with HTTP/TLS does not perform server identity verification, the client SHOULD ensure that all the responses are validated using the Mutual authentication protocol, regardless of the existence of the 401-INIT responses. Note: The protocol defines two variants for validation on the TLS connections. The "tls-key" method is more secure. However, there are some situations where tls-cert is more preferable. o When TLS accelerating proxies are used, it is difficult for the authenticating server to acquire the TLS key information that is used between the client and the proxy. This is not the case for client-side "tunneling" proxies using a CONNECT method extension of HTTP. o When a black-box implementation of the TLS protocol is used on either peer. Implementations supporting a Mutual authentication over the HTTPS protocol SHOULD support the "tls-cert" validation. Support for "tls-key" validation is OPTIONAL for both the servers and clients. 8. Authentication Extensions The HTTP authentication extensions described in [I-D.oiwa-http-auth-extension] is a definitive part of this protocol. Interactive clients (e.g. Web browsers) supporting this protocol are RECOMMENDED to support non-mandatory authentication and the Authentication-Control header defined there, except the "auth-style" parameter. This specification also proposes (however, not mandates) default "auth-style" to be "non-modal". Web applications SHOULD however consider the security impacts of the behaviors of clients that do not support these headers. Authentication-initializing messages with the Optional-WWW-Authenticate header are used where 401-INIT response is valid. Such a message is called a 200-Optional-INIT message in this document. (It will not replace other 401-type messages such as 401-STALE and 401-KEX-S1.) Oiwa, et al. Expires May 3, 2012 [Page 27] Internet-Draft Mutual Authentication Protocol for HTTP October 2011 9. Decision Procedure for Clients To securely implement the protocol, the user client must be careful about accepting the authenticated responses from the server. This also holds true for the reception of "normal responses" (responses which do not contain Mutual-related headers) from HTTP servers. Clients SHOULD implement a decision procedure equivalent to the one shown below. (Unless implementers understand what is required for the security, they should not alter this.) In particular, clients SHOULD NOT accept "normal responses" unless explicitly allowed below. The labels on the steps are for informational purposes only. Action entries within each step are checked in top-to-bottom order, and the first clause satisfied SHOULD be taken. Step 1 (step_new_request): If the client software needs to access a new Web resource, check whether the resource is expected to be inside some authentication realm for which the user has already been authenticated by the Mutual authentication scheme. If yes, go to Step 2. Otherwise, go to Step 5. Step 2: Check whether there is an available sid for the authentication realm you expect. If there is one, go to Step 3. Otherwise, go to Step 4. Step 3 (step_send_vfy_1): Send a req-VFY-C request. * If you receive a 401-INIT message with a different authentication realm than expected, go to Step 6. * If you receive a 200-Optional-INIT message with a different authentication realm than expected, go to Step 6. * If you receive a 401-STALE message, go to Step 9. * If you receive a 401-INIT message, go to Step 13. * If you receive a 200-VFY-S message, go to Step 14. * If you receive a normal response, go to Step 11. Oiwa, et al. Expires May 3, 2012 [Page 28] Internet-Draft Mutual Authentication Protocol for HTTP October 2011 Step 4 (step_send_kex1_1): Send a req-KEX-C1 request. * If you receive a 401-INIT message with a different authentication realm than expected, go to Step 6. * If you receive a 200-Optional-INIT message with a different authentication realm than expected, go to Step 6. * If you receive a 401-KEX-S1 message, go to Step 10. * If you receive a 401-INIT message with the same authentication realm, go to Step 13 (see Note 1). * If you receive a normal response, go to Step 11. Step 5 (step_send_normal_1): Send a request without any Mutual authentication headers. * If you receive a 401-INIT message, go to Step 6. * If you receive a 200-Optional-INIT message, go to Step 6. * If you receive a normal response, go to Step 11. Step 6 (step_rcvd_init): Check whether you know the user's password for the requested authentication realm. If yes, go to Step 7. Otherwise, go to Step 12. Step 7: Check whether there is an available sid for the authentication realm you expect. If there is one, go to Step 8. Otherwise, go to Step 9. Step 8 (step_send_vfy): Send a req-VFY-C request. * If you receive a 401-STALE message, go to Step 9. * If you receive a 401-INIT message, go to Step 13. * If you receive a 200-VFY-S message, go to Step 14. Oiwa, et al. Expires May 3, 2012 [Page 29] Internet-Draft Mutual Authentication Protocol for HTTP October 2011 Step 9 (step_send_kex1): Send a req-KEX-C1 request. * If you receive a 401-KEX-S1 message, go to Step 10. * If you receive a 401-INIT message, go to Step 13 (See Note 1). Step 10 (step_rcvd_kex1): Send a req-VFY-C request. * If you receive a 401-INIT message, go to Step 13. * If you receive a 200-VFY-S message, go to Step 14. Step 11 (step_rcvd_normal): The requested resource is out of the authenticated area. The client will be in the "UNAUTHENTICATED" status. If the response contains a request for authentications other than Mutual, it MAY be handled normally. Step 12 (step_rcvd_init_unknown): The requested resource requires a Mutual authentication, and the user is not yet authenticated. The client will be in the "AUTH- REQUESTED" status, and is RECOMMENDED to process the content sent from the server, and to ask user for a user name and a password. When those are supplied from the user, proceed to Step 9. Step 13 (step_rcvd_init_failed): For some reason the authentication failed: possibly the password or the username is invalid for the authenticated resource. Forget the password for the authentication realm and go to Step 12. Step 14 (step_rcvd_vfy): Check the validity of the received VK_s value. If it is equal to the expected value, it means that the mutual authentication has succeeded. The client will be in the "AUTH-SUCCEEDED" status. If the value is unexpected, it is a fatal communication error. If a user explicitly requests to log out (via user interfaces), the client MUST forget the user's password, go to step 5 and reload the current resource without an authentication header. Note 1: These transitions MAY be accepted by clients, but NOT RECOMMENDED for servers to initiate. Any kind of response (including a normal response) other than those Oiwa, et al. Expires May 3, 2012 [Page 30] Internet-Draft Mutual Authentication Protocol for HTTP October 2011 shown in the above procedure SHOULD be interpreted as a fatal communication error, and in such cases the clients MUST NOT process any data (response body and other content-related headers) sent from the server. However, to handle exceptional error cases, clients MAY accept a message without an Authentication-Info header, if it is a Server-Error (5xx) status. The client will be in the "UNAUTHENTICATED" status in these cases. The client software SHOULD display the three client status to the end-user. For an interactive client, however, if a request is a sub- request for a resource included in another page (e.g., embedded images, style sheets, frames etc.), its status MAY be omitted from being shown, and any "AUTH-REQUESTED" statuses MAY be treated in the same way as an "UNAUTHENTICATED" status. Figure 9 shows a diagram of the client-side state. Oiwa, et al. Expires May 3, 2012 [Page 31] Internet-Draft Mutual Authentication Protocol for HTTP October 2011 =========== -(11)------------ NEW REQUEST ( UNAUTHENTICATED ) =========== ----------------- | ^ normal v | response +(1)-------------------+ NO +(5)----------+ | The requested URI |--------------------------->| send normal | | known to be auth'ed? | | request | +----------------------+ +-------------+ YES | 401-INIT, 200-Optional-INIT 401-INIT| | with a different realm 200-Optional-INIT| | -----------------------------------. | | / v v | | -(12)------------ NO +(6)--------+ | | ( AUTH-REQUESTED )<------| user/pass | | | ----------------- | known? | | | +-----------+ | | |YES v | v +(2)--------+ | +(7)--------+ | session | | | session | NO NO /| available?| | | available?|\ / +-----------+ | +-----------+ | / |YES | |YES | | | /| | | | v / | 401- 401- v | | +(3)--------+ | INIT --(13)---------- INIT +(8)--------+ | | | send |--+----->/ AUTH-REQUESTED \<-------| send | | | /| req-VFY-C | | \forget password / | req-VFY-C | | \/ +-----------+ / ---------------- /+-----------+ | /\ \ \/ ^ 401-INIT | |401- | | ------ \/\ 401-STALE | | | STALE / | \ /\ -----------------+--------------+---. | / | | / \ | | | | / | v / | 401- | 401- | v v v | +(4)--------+ | KEX-S1 +(10)-------+ KEX-S1 | +(9)--------+ | | send |-|--------->| send |<-------+-| send | | --| req-KEX-C1| | | req-VFY-C | | | req-KEX-C1| |/ +-----------+ | +-----------+ | +-----------+ | |200-VFY-S | 200-VFY-S| ^ |normal | |200-VFY-S / | |response | v / ================== v \ -(14)--------- / USER/PASS INPUTTED -(11)------------ ------->( AUTH-SUCCEED )<-- ================== ( UNAUTHENTICATED ) -------------- ----------------- Figure 9: State diagram for clients Oiwa, et al. Expires May 3, 2012 [Page 32] Internet-Draft Mutual Authentication Protocol for HTTP October 2011 10. Decision Procedure for Servers Each server SHOULD have a table of session states. This table need not be persistent over a long term; it MAY be cleared upon server restart, reboot, or others. Each entry in the table SHOULD contain at least the following information: o The session identifier, the value of the sid parameter. o The algorithm used. o The authentication realm. o The state of the protocol: one of "key exchanging", "authenticated", "rejected", or "inactive". o The user name received from the client o The boolean flag noting whether or not the session is fake. o When the state is "key exchanging", the values of K_c1 and S_s1. o When the state is "authenticated", the following information: * The value of the session secret z * The largest nc received from the client (largest-nc) * For each possible nc values between (largest-nc - nc- window + 1) and max_nc, a flag whether or not a request with the corresponding nc has been received. The table MAY contain other information. Servers SHOULD respond to the client requests according to the following procedure: o When the server receives a normal request: * If the requested resource is not protected by the Mutual Authentication, send a normal response. * If the resource is protected by the Mutual Authentication, send a 401-INIT response. * If the resource is protected by the optional Mutual Authentication, send a 200-Optional-INIT response. Oiwa, et al. Expires May 3, 2012 [Page 33] Internet-Draft Mutual Authentication Protocol for HTTP October 2011 o When the server receives a req-KEX-C1 request: * If the requested resource is not protected by the Mutual Authentication, send a normal response. * If the authentication realm specified in the req-KEX-C1 request is not the expected one, send either a 401-INIT or a 200-Optional-INIT response. * If the server cannot validate the parameter kc1, send a 401-INIT response. * If the received user name is either invalid, unknown or unacceptable, create a new session, mark it a "fake" session, compute a random value as K_s1, and send a fake 401-KEX-S1 response. (Note: the server SHOULD NOT send a 401-INIT response in this case, because it will leak the information to the client that the specified user will not be accepted. Instead, postpone it to the response for the next req-VFY-C request.) * Otherwise, create a new session, compute K_s1 and send a 401-KEX-S1 response. The created session has the "key exchanging" state. o When the server receives a req-VFY-C request: * If the requested resource is not protected by the Mutual Authentication, send a normal response. * If the authentication realm specified in the req-VFY-C request is not the expected one, send either a 401-INIT or a 200-Optional-INIT response. If none of above holds true, the server will lookup the session corresponding to the received sid and the authentication realm. * If the session corresponding to the received sid could not be found, or it is in the "inactive" state, send a 401-STALE response. * If the session is in the "rejected" state, send either a 401-INIT or a 401-STALE message. * If the session is in the "authenticated" state, and the request has an nc value that was previously received from the client, send a 401-STALE message. The session SHOULD be changed to the Oiwa, et al. Expires May 3, 2012 [Page 34] Internet-Draft Mutual Authentication Protocol for HTTP October 2011 "inactive" status. * If the nc value in the request is larger than the nc-max parameter sent from the server, or if it is not larger then (largest-nc - nc-window) (when in "authenticated" status), the server MAY (but not REQUIRED to) send a 401-STALE message. The session SHOULD be changed to the "inactive" status if so. * If the session is a "fake" session, or if the received vkc is incorrect, then send a 401-INIT response. If the session is in the "key exchanging" state, it SHOULD be changed to the "rejected" state; otherwise, it MAY either be changed to the "rejected" status or kept in the previous state. * Otherwise, send a 200-VFY-S response. If the session was in the "key exchanging" state, the session SHOULD be changed to an "authenticated" state. The maximum nc and nc flags of the state SHOULD be updated properly. At any time, the server MAY change any state entries with both the "rejected" and "authenticated" statuses to the "inactive" status, and MAY discard any "inactive" states from the table. The entries with the "key exchanging" status SHOULD be kept unless there is an emergency situation such as a server reboot or a table capacity overflow. 11. Authentication Algorithms Cryptographic authentication algorithms which are used with this protocol will be defined separately. The algorithm definition MUST at least provide a definitions for the following functions: o The server-side authentication credential J, derived from user- side authentication credential pi. o Key exchange values K_c1, K_s1 (exchanged on wire) and S_c1, S_s1 (kept secret in each peer). o Shared secret z, to be computed in both server-side and client side. o A hash function H to be used with the protocol. All algorithm used with this protocol SHOULD provide secure mutual authentication between client and servers, and generate a cryptographically strong shared secret value z, equivalently strong to or stronger than the hash function H. If any passwords (or pass- Oiwa, et al. Expires May 3, 2012 [Page 35] Internet-Draft Mutual Authentication Protocol for HTTP October 2011 phrases or any equivalents, i.e. weak secrets) are involved, these SHOULD NOT be guessable from any data transmitted in the protocol, even if an attacker (either an eavesdropper or an active server) knows the possible thoroughly-searchable candidate list of the passwords. Furthermore, if possible, the function for deriving server-side authentication credential J is RECOMMENDED to be one-way so that pi should not be easily computed from J(pi). 11.1. Support Functions and Notations In this section we define several support functions and notations to be shared by several algorithm definitions: The integers in the specification are in decimal, or in hexadecimal when prefixed with "0x". The function octet(c) generates a single octet string whose code value is equal to c. The operator |, when applied to octet strings, denotes the concatenation of two operands. The function VI encodes natural numbers into octet strings in the following manner: numbers are represented in big-endian radix-128 string, where each digit is represented by a octet within 0x80-0xff except the last digit represented by a octet within 0x00-0x7f. The first octet MUST NOT be 0x80. For example, VI(i) = octet(i) for i < 128, and VI(i) = octet(0x80 + (i >> 7)) | octet(i & 127) for 128 <= i < 16384. This encoding is the same as the one used for the subcomponents of object identifiers in the ASN.1 encoding [ITU.X690.1994], and available as a "w" conversion in the pack function of several scripting languages. The function VS encodes a variable-length octet string into a uniquely-decoded, self-delimited octet string, as in the following manner: VS(s) = VI(length(s)) | s where length(s) is a number of octets (not characters) in s. Some examples: VI(0) = "\000" (in C string notation) VI(100) = "d" VI(10000) = "\316\020" Oiwa, et al. Expires May 3, 2012 [Page 36] Internet-Draft Mutual Authentication Protocol for HTTP October 2011 VI(1000000) = "\275\204@" VS("") = "\000" VS("Tea") = "\003Tea" VS("Caf" [in UTF-8]) = "\005Caf\303\251" VS([10000 "a"s]) = "\316\020aaaaa..." (10002 octets) [Editorial note: Unlike the colon-separated notion used in the Basic/ Digest HTTP authentication scheme, the string generated by a concatenation of the VS-encoded strings will be unique, regardless of the characters included in the strings to be encoded.] The function OCTETS converts an integer into the corresponding radix- 256 big-endian octet string having its natural length: See Section 3.2 for the definition of "natural length". 11.2. Default Functions for Algorithms The functions defined in this section are common default functions among authentication algorithms. The client-side password-based string pi used by this authentication is derived in the following manner: pi = H(VS(algorithm) | VS(auth-domain) | VS(realm) | VS(username) | VS(ph(password))). The values of algorithm, realm, and auth-domain are taken from the values contained in the 401-INIT (or 200-Optional-INIT, hereafter implied) message. When pi is used in the context of an octet string, it SHALL have the natural length derived from the size of the output of function H (e.g. 32 octets for SHA-256). The function ph is determined by the value of the pwd-hash parameter given in a 401-INIT message. If the password comes from a user input, it SHOULD first be prepared using SASLprep [RFC4013]. Then, the password SHALL be encoded as a UTF-8 string before passed to ph. The values VK_c and VK_s are derived by the following equation. VK_c = H(octet(4) | OCTETS(K_c1) | OCTETS(K_s1) | OCTETS(z) | VI(nc) | VS(v)) VK_s = H(octet(3) | OCTETS(K_c1) | OCTETS(K_s1) | OCTETS(z) | VI(nc) | VS(v)) Oiwa, et al. Expires May 3, 2012 [Page 37] Internet-Draft Mutual Authentication Protocol for HTTP October 2011 Specifications for cryptographic algorithms used with this framework MAY override the functions pi, VK_c, and VK_s defined above. In such cases implementations MUST use the ones defined with such algorithm specifications. 12. Application Channel Binding Applications and upper-layer communication protocols may need authentication binding to the HTTP-layer authenticated user. Such applications MAY use the following values as a standard shared secret. These values are keyed with an optional octet string (t) which may be arbitrary chosen by each applications or protocols. If there is no appropriate value to be specified, use a null string for t. For applications requiring binding to either an authenticated user or a shared-key session (to ensure that the requesting client is certainly authenticated), the following value b_1 MAY be used. b_1 = OCTETS(H(OCTETS(H(octet(6) | OCTETS(K_c1) | OCTETS(K_s1) | OCTETS(z) | VI(0) | VS(v))) | VS(t))). For applications requiring binding to a specific request (to ensure that the payload data is generated for the exact HTTP request), the following value b_2 MAY be used. b_2 = OCTETS(H(OCTETS(H(octet(7) | OCTETS(K_c1) | OCTETS(K_s1) | OCTETS(z) | VI(nc) | VS(v))) | VS(t))). Note: Channel bindings to lower-layer transports (TCP and TLS) are defined in Section 7. 13. Application for Proxy Authentication The authentication scheme defined by the previous sections can be applied m.m. for proxy authentications. In such cases, the following alterations MUST be applied: o The 407 status is to be sent and recognized for places where the 401 status is used, o Proxy-Authenticate: header is to be used for places where WWW- Authenticate: is used, Oiwa, et al. Expires May 3, 2012 [Page 38] Internet-Draft Mutual Authentication Protocol for HTTP October 2011 o Proxy-Authorization: header is to be used for places where Authorization: is used, o Proxy-Authentication-Info: header is to be used for places where Authentication-Info: is used, o The auth-domain parameter is fixed to the host-name of the proxy, which means to cover all requests processed through the specific proxy, o The limitation for the paths contained in the path parameter of 401-KEX-S1 messages is disregarded, o The omission of the path parameter of 401-KEX-S1 messages means that the authentication realm will potentially cover all requests processed by the proxy, o The scheme, host name and the port of the proxy is used for validation tokens, and o Authentication extension in [I-D.oiwa-http-auth-extension] is not applicable. The requirements for client software to display the authentication status to the end-user is also not applicable for proxy authentication. If the client software supports both end-to-end and proxy authentication using this protocol, it SHOULD be careful that the authentication status of the proxy communication will never be confused by users with authentication statuses of the end-to-end resource authentications. 14. Methods to Extend This Protocol If a non-standard extension to this protocol is implemented, it MUST use the extension-tokens defined in Section 3 to avoid conflicts with this protocol and other extensions. Specifications defining authentication algorithms MAY use other representations for the parameters "kc1", "ks1", "vkc", and "vks", replace those keys, and/or add parameters to the messages containing those parameters in supplemental specifications, provided that syntactic and semantic requirements in Section 3, [I-D.ietf-httpbis-p1-messaging] and [I-D.ietf-httpbis-p7-auth] are satisfied. Any parameters starting with "kc", "ks", "vkc" or "vks" and followed by decimal natural numbers (e.g. kc2, ks0, vkc1, vks3 etc.) are reserved for this purpose. If those specifications use keys other than those mentioned above, it is RECOMMENDED to use Oiwa, et al. Expires May 3, 2012 [Page 39] Internet-Draft Mutual Authentication Protocol for HTTP October 2011 extension-tokens to avoid any key-name conflict with the future extension of this protocol (standardized or being-standardizing extensions MAY use extension-tokens.) Extension-tokens MAY be freely used for any non-standard, private, and/or experimental uses for those parameters provided that the domain part in the token is appropriately used. 15. IANA Considerations When bare-tokens are used for the authentication-algorithm, pwd-hash, and validation parameters MUST be allocated by IANA. To acquire registered tokens, a specification for the use of such tokens MUST be available as an RFC, as outlined in [RFC5226]. Note: More formal declarations will be added in the future drafts to meet the RFC 5226 requirements. 16. Security Considerations 16.1. Security Properties o The protocol is secure against passive eavesdropping and replay attacks. However, the protocol relies on transport security including DNS integrity for data secrecy and integrity. HTTP/TLS SHOULD be used where transport security is not assured and/or data secrecy is important. o When used with HTTP/TLS, if TLS server certificates are reliably verified, the protocol provides true protection against active man-in-the-middle attacks. o Even if the server certificate is not used or is unreliable, the protocol provides protection against active man-in-the-middle attacks for each HTTP request/response pair. However, in such cases, JavaScript or similar scripting facilities can be used to affect the Mutually-authenticated contents from other contents not protected by this authentication mechanism. This is the reason why this protocol requires that valid TLS server certificates MUST be presented (Section 7). 16.2. Denial-of-service Attacks to Servers The protocol requires a server-side table of active sessions, which may become a critical point of the server resource consumptions. For proper operation, the protocol requires that at least one key Oiwa, et al. Expires May 3, 2012 [Page 40] Internet-Draft Mutual Authentication Protocol for HTTP October 2011 verification request is processed for each session identifier. After that, servers MAY discard sessions internally at any time, without causing any operational problems to clients. Clients will silently reestablishes a new session then. However, if a malicious client sends too many requests of key exchanges (req-KEX-C1 messages) only, resource starvation might occur. In such critical situations, servers MAY discard any kind of existing sessions regardless of these statuses. One way to mitigate such attacks are that servers MAY have a number and a time limits for unverified pending key exchange requests (in the "wa received" status). This is a common weakness of authentication protocols with almost any kind of negotiations or states, including Digest authentication method and most Cookie-based authentication implementations. However, regarding the resource consumption, a situation of the mutual authentication method is a slightly better than the Digest, because HTTP requests without any kind of authentication requests will not generate any kind of sessions. Session identifiers are only generated after a client starts a key negotiation. It means that simple clients such as web crawlers will not accidentally consume server-side resources for session managements. 16.3. Implementation Considerations o To securely implement the protocol, the Authentication-Info headers in the 200-VFY-S messages MUST always be validated by the client. If the validation fails, the client MUST NOT process any content sent with the message, including other headers and the body part. Non-compliance to this requirement will allow phishing attacks. o The authentication status on the client-side SHOULD be visible to the users of the client. In addition, the method for asking for the user's name and passwords SHOULD be carefully designed so that (1) the user can easily distinguish the request from this authentication method from any other authentication methods such as Basic and Digest methods, and (2) the Web contents cannot imitate the user-interfaces for this protocol. An informational memo regarding user-interface considerations and recommendations for implementing this protocol will be separately published. o For HTTP/TLS communications, when a web form is submitted from Mutually-authenticated pages with the "tls-cert" validation method to a URI that is protected by the same realm (so indicated by the Oiwa, et al. Expires May 3, 2012 [Page 41] Internet-Draft Mutual Authentication Protocol for HTTP October 2011 path parameter), if the server certificate has been changed since the pages were received, the peer is RECOMMENDED to be revalidated using a req-KEX-C1 message with an "Expect: 100-continue" header. The same applies when the page is received with the "tls-key" validation method, and when the TLS session has expired. o Server-side storages of user passwords are advised to contain the values encrypted by one-way function J(pi), instead of the real passwords, those hashed by ph, or pi. 16.4. Usage Considerations o The user-names inputted by a user may be sent automatically to any servers sharing the same auth-domain. This means that when host- type auth-domain is used for authentication on an HTTPS site, and when an HTTP server on the same host requests Mutual authentication within the same realm, the client will send the user-name in a clear text. If user-names have to be kept secret against eavesdropping, the server must use full-scheme-type auth- domain parameter. Contrarily, passwords are not exposed to eavesdroppers even on HTTP requests. o The "pwd-hash" parameter is only provided for backward compatibility of password databases. The use of "none" function is the most secure choice and is RECOMMENDED. If values other than "none" are used, you MUST ensure that the hash values of the passwords were not exposed to the public. Note that hashed password databases for plain-text authentications are usually not considered secret. o If the server provides several ways for storing server-side password secrets into the password database, it is advised to store the values encrypted by using the one-way function J(pi), instead of the real passwords, those hashed by ph, or pi. 17. Notice on Intellectual Properties The National Institute of Advanced Industrial Science and Technology (AIST) and Yahoo! Japan, Inc. has jointly submitted a patent application on the protocol proposed in this documentation to the Patent Office of Japan. The patent is intended to be open to any implementors of this protocol and its variants under non-exclusive royalty-free manner. For the details of the patent application and its status, please contact the author of this document. The elliptic-curve based authentication algorithms might involve several existing third-party patents. The authors of the document Oiwa, et al. Expires May 3, 2012 [Page 42] Internet-Draft Mutual Authentication Protocol for HTTP October 2011 take no position regarding the validity or scope of such patents, and other patents as well. 18. References 18.1. Normative References [I-D.ietf-httpbis-p1-messaging] Fielding, R., Gettys, J., Mogul, J., Nielsen, H., Masinter, L., Leach, P., Berners-Lee, T., Reschke, J., and Y. Lafon, "HTTP/1.1, part 1: URIs, Connections, and Message Parsing", draft-ietf-httpbis-p1-messaging-16 (work in progress), August 2011. [I-D.ietf-httpbis-p7-auth] Fielding, R., Gettys, J., Mogul, J., Nielsen, H., Masinter, L., Leach, P., Berners-Lee, T., Reschke, J., and Y. Lafon, "HTTP/1.1, part 7: Authentication", draft-ietf-httpbis-p7-auth-16 (work in progress), August 2011. [I-D.oiwa-http-auth-extension] Oiwa, Y., Watanabe, H., Takagi, H., Kihara, B., Hayashi, T., and Y. Ioku, "HTTP Authentication Extensions for Interactive Clients", draft-oiwa-http-auth-extension-00 (work in progress), October 2011. [I-D.oiwa-http-mutualauth-algo] Oiwa, Y., Watanabe, H., Takagi, H., Kihara, B., Hayashi, T., and Y. Ioku, "Mutual Authentication Protocol for HTTP: Cryptographic Algorithms", draft-oiwa-http-mutualauth-algo-01 (work in progress), October 2011. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO 10646", STD 63, RFC 3629, November 2003. [RFC4013] Zeilenga, K., "SASLprep: Stringprep Profile for User Names and Passwords", RFC 4013, February 2005. [RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data Encodings", RFC 4648, October 2006. [RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax Oiwa, et al. Expires May 3, 2012 [Page 43] Internet-Draft Mutual Authentication Protocol for HTTP October 2011 Specifications: ABNF", STD 68, RFC 5234, January 2008. [RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security (TLS) Protocol Version 1.2", RFC 5246, August 2008. 18.2. Informative References [I-D.blanchet-precis-framework] Blanchet, M. and P. Saint-Andre, "PRECIS Framework: Handling Internationalized Strings in Protocols", draft-blanchet-precis-framework-03 (work in progress), August 2011. [ISO.10646-1.1993] International Organization for Standardization, "Information Technology - Universal Multiple-octet coded Character Set (UCS) - Part 1: Architecture and Basic Multilingual Plane", ISO Standard 10646-1, May 1993. [ITU.X690.1994] International Telecommunications Union, "Information Technology - ASN.1 encoding rules: Specification of Basic Encoding Rules (BER), Canonical Encoding Rules (CER) and Distinguished Encoding Rules (DER)", ITU-T Recommendation X.690, 1994. [RFC2617] Franks, J., Hallam-Baker, P., Hostetler, J., Lawrence, S., Leach, P., Luotonen, A., and L. Stewart, "HTTP Authentication: Basic and Digest Access Authentication", RFC 2617, June 1999. [RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000. [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 5226, May 2008. [RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S., Housley, R., and W. Polk, "Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile", RFC 5280, May 2008. [RFC5890] Klensin, J., "Internationalized Domain Names for Applications (IDNA): Definitions and Document Framework", RFC 5890, August 2010. [RFC5929] Altman, J., Williams, N., and L. Zhu, "Channel Bindings for TLS", RFC 5929, July 2010. Oiwa, et al. Expires May 3, 2012 [Page 44] Internet-Draft Mutual Authentication Protocol for HTTP October 2011 [RFC6265] Barth, A., "HTTP State Management Mechanism", RFC 6265, April 2011. Appendix A. (Informative) Generic Syntax of Headers Several headers (e.g. WWW-Authenticate: headers in 401-INIT, 401-STALE, and 401-KEX-S1 messages) shares common header names. To parse values of these headers, one MAY use the following general syntax definition of the message syntax: Mutual-auth-scheme = "Mutual" challenge-Mutual = Mutual-auth-scheme 1*SP 1#param credentials-Mutual = Mutual-auth-scheme 1*SP 1#param auth-info-Mutual = Mutual-auth-scheme 1*SP 1#param ; for WWW-Authenticate, Authorization, Authentication-Info resp. param = key EQ value ; either a specific or ; an extension parameter key = token value = token / integer ; parse to token/string first / hex-fixed-number / base64-fixed-number / string integer = "0" / (%x31-39 *%x30-39) ; no leading zeros hex-fixed-number = 1*(%x30-39 / %x41-46 / %x61-66) base64-fixed-number = quoted-string string = quoted-string Figure 10: Common BNF syntax for header values in the protocol In this way of parsing, messages will be distinguished by the parameters contained in a header corresponding to the authentication. The procedure below determines the kind of each HTTP request/ response. o If the message is a response with a "401" status: * If it does not contain any WWW-Authenticate header, it is an error. * If the WWW-Authenticate header specifies a scheme other than "Mutual", it is a normal response within this draft's scope. * Otherwise, the response contains a "WWW-Authenticate: Mutual" header. If the header contains both sid and stale parameters, it is an error. Oiwa, et al. Expires May 3, 2012 [Page 45] Internet-Draft Mutual Authentication Protocol for HTTP October 2011 * If the header contains a stale parameter with a value of 0, it is a 401-INIT message. * If the header contains a stale parameter with a value of 1, it is a 401-STALE message. * If the header contains an sid parameter, it is a 401-KEX-S1 message. o If the message is a response other than a "401" status: * If it contains both Authentication-Info and Optional-WWW-Authenticate headers, it is an error. * If it contains a Authentication-Info header with the "Mutual" scheme, it is a 200-VFY-S message. * If it contains a Optional-WWW-Authenticate header with the "Mutual" scheme, it is a 200-Optional-INIT message. * Otherwise, it is a normal response. o If the message is a request: * If it does not contain an Authorization header, or it contains an Authorization header with a scheme other than Mutual, it is a normal request. * Otherwise, the request contains a "Authorization: Mutual" header. If the header contains an sid parameter, it is a req-VFY-C message. * If the header do not contain an sid parameter, it is a req-KEX-C1 message. Implementations MAY perform checks stricter than the procedure above, according to the definitions in Section 3. Appendix B. (Informative) Draft Remarks from Authors The following items are currently under consideration for future revisions by the authors. o Whether to keep TLS-key validation or not. o When keeping tls-key validation, whether to use "TLS channel binding" [RFC5929] for "tls-key" verification (Section 7). Note Oiwa, et al. Expires May 3, 2012 [Page 46] Internet-Draft Mutual Authentication Protocol for HTTP October 2011 that existing TLS implementations should be considered to determine this. o Adopt [I-D.blanchet-precis-framework] for replacing SASLprep reference. Especially, use NFC canonicalization instead of NFKC. o Adding test vectors for ensuring implementation correctness. o Possibly adding a method for servers to detect availability of Mutual authentication on client-side. o Possible support for optional key renewal and cross-site federated authentication. Appendix C. (Informative) Draft Change Log C.1. Changes in Revision 10 o The authentication extension parts (non-mandatory authentication and authentication controls) are separated to yet another draft. o The default auth-domain parameter is changed to the full scheme- host-port syntax, which is consistent with usual HTTP authentication framework behavior. o Provision for application channel binding is added. o Provision for proxy access authentication is added. o Bug fix: syntax specification of sid parameter was wrong: it was inconsistent with the type specified in the main text (the bug introduced in -07 draft). o Terminologies for headers are changed to be in harmony with httpbis drafts (e.g. field to parameter). o Syntax definitions are changed to use HTTP-extended ABNF syntax, and only the header values are shown for header syntax, in harmony with httpbis drafts. o Names of parameters and corresponding mathematical values are now renamed to more informative ones. The following list shows correspondence between the new and the old names. Oiwa, et al. Expires May 3, 2012 [Page 47] Internet-Draft Mutual Authentication Protocol for HTTP October 2011 +------------+----------+-------------------------------------------+ | new name | old name | description | +------------+----------+-------------------------------------------+ | S_c1, S_s1 | s_a, s_b | client/server-side secret randoms | | K_c1, K_s1 | w_a, w_b | client/server-side exchanged key | | | | components | | kc1, ks1 | wa, wb | parameter names for those | | VK_c, VK_s | o_a, o_b | client/server-side key verifiers | | vkc, vks | oa, ob | parameter names for those | | z | z | session secrets | +------------+----------+-------------------------------------------+ C.2. Changes in Revision 09 o The (default) cryptographic algorithms are separated to another draft. o Names of the messages are changed to more informative ones than before. The following is the correspondence table of those names: +-------------------+-----------------+-----------------------------+ | new name | old name | description | +-------------------+-----------------+-----------------------------+ | 401-INIT | 401-B0 | initial response | | 401-STALE | 401-B0-stale | session key expired | | req-KEX-C1 | req-A1 | client->server key exchange | | 401-KEX-S1 | 401-B1 | server->client key exchange | | req-VFY-C | req-A3 | client->server auth. | | | | verification | | 200-VFY-S | 200-B4 | server->client auth. | | | | verification | | 200-Optional-INIT | 200-Optional-B0 | initial with non-mandatory | | | | authentication | +-------------------+-----------------+-----------------------------+ C.3. Changes in Revision 08 o The English text has been revised. C.4. Changes in Revision 07 o Adapt to httpbis HTTP/1.1 drafts: * Changed definition of extensive-token. * LWSP continuation-line (%0D.0A.20) deprecated. Oiwa, et al. Expires May 3, 2012 [Page 48] Internet-Draft Mutual Authentication Protocol for HTTP October 2011 o To simplify the whole spec, the type of nonce-counter related parameters are change from hex-integer to integer. o Algorithm tokens are renamed to include names of hash algorithms. o Clarified the session management, added details of server-side protocol decisions. o The whole draft was reorganized; introduction and overview has been rewritten. C.5. Changes in Revision 06 o Integrated Optional Mutual Authentication to the main part. o Clarified the decision procedure for message recognitions. o Clarified that a new authentication request for any sub-requests in interactive clients may be silently discarded. o Typos and confusing phrases are fixed. o Several "future considerations" are added. C.6. Changes in Revision 05 o A new parameter called "version" is added for supporting future incompatible changes with a single implementation. In the (first) final specification its value will be changed to 1. o A new header "Authentication-Control" is added for precise control of application-level authentication behavior. C.7. Changes in Revision 04 o Changed text of patent licenses: the phrase "once the protocol is accepted as an Internet standard" is removed so that the sentence also covers the draft versions of this protocol. o The "tls-key" verification is now OPTIONAL. o Several description fixes and clarifications. C.8. Changes in Revision 03 o Wildcard domain specifications (e.g. "*.example.com") are allowed for auth-domain parameters (Section 4.1). Oiwa, et al. Expires May 3, 2012 [Page 49] Internet-Draft Mutual Authentication Protocol for HTTP October 2011 o Specification of the "tls-cert" verification is updated (incompatible change). o State transitions fixed. o Requirements for servers concerning w_a values are clarified. o RFC references are updated. C.9. Changes in Revision 02 o Auth-realm is extended to allow full-scheme type. o A decision diagram for clients and decision procedures for servers are added. o 401-B1 and req-A3 messages are changed to contain authentication realm information. o Bugs on equations for o_A and o_B are fixed. o Detailed equations for the entire algorithm are included. o Elliptic-curve algorithms are updated. o Several clarifications and other minor updates. C.10. Changes in Revision 01 o Several texts are rewritten for clarification. o Added several security consideration clauses. Authors' Addresses Yutaka Oiwa National Institute of Advanced Industrial Science and Technology Research Center for Information Security Tsukuba Central 2 1-1-1 Umezono Tsukuba-shi, Ibaraki JP Email: mutual-auth-contact@m.aist.go.jp Oiwa, et al. Expires May 3, 2012 [Page 50] Internet-Draft Mutual Authentication Protocol for HTTP October 2011 Hajime Watanabe National Institute of Advanced Industrial Science and Technology Hiromitsu Takagi National Institute of Advanced Industrial Science and Technology Boku Kihara Lepidum Co. Ltd. #602, Village Sasazuka 3 1-30-3 Sasazuka Shibuya-ku, Tokyo JP Tatsuya Hayashi Lepidum Co. Ltd. Yuichi Ioku Yahoo! Japan, Inc. Midtown Tower 9-7-1 Akasaka Minato-ku, Tokyo JP Oiwa, et al. Expires May 3, 2012 [Page 51]