Network Working Group M. Wasserman Internet-Draft S. Hartman Intended status: Experimental Painless Security Expires: April 05, 2014 D. Zhang Huawei October 02, 2013 Port Control Protocol (PCP) Authentication Mechanism draft-ietf-pcp-authentication-02 Abstract An IPv4 or IPv6 host can use the Port Control Protocol (PCP) to flexibly manage the IP address and port mapping information on Network Address Translators (NATs) or firewalls, to facilitate communications with remote hosts. However, the un-controlled generation or deletion of IP address mappings on such network devices may cause security risks and should be avoided. In some cases the client may need to prove that it is authorized to modify, create or delete PCP mappings. This document proposes an in-band authentication mechanism for PCP that can be used in those cases. The Extensible Authentication Protocol (EAP) is used to perform authentication between PCP devices. 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." This Internet-Draft will expire on April 05, 2014. Copyright Notice Copyright (c) 2013 IETF Trust and the persons identified as the document authors. All rights reserved. Wasserman, et al. Expires April 05, 2014 [Page 1] Internet-Draft PCP Authentication October 2013 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. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Protocol Details . . . . . . . . . . . . . . . . . . . . . . 5 3.1. Session Initiation . . . . . . . . . . . . . . . . . . . 5 3.2. Session Termination . . . . . . . . . . . . . . . . . . . 7 3.3. Session Re-Authentication . . . . . . . . . . . . . . . . 7 4. PA Security Association . . . . . . . . . . . . . . . . . . . 8 5. Result Code . . . . . . . . . . . . . . . . . . . . . . . . . 9 6. Packet Format . . . . . . . . . . . . . . . . . . . . . . . . 10 6.1. Packet Format of PCP Auth Messages . . . . . . . . . . . 10 6.2. Authentication OpCode Format . . . . . . . . . . . . . . 11 6.3. Nonce Option . . . . . . . . . . . . . . . . . . . . . . 12 6.4. Authentication Tag Option . . . . . . . . . . . . . . . . 12 6.5. EAP Payload Option . . . . . . . . . . . . . . . . . . . 13 6.6. PRF Option . . . . . . . . . . . . . . . . . . . . . . . 13 6.7. MAC Algorithm Option . . . . . . . . . . . . . . . . . . 14 6.8. Session Lifetime Option . . . . . . . . . . . . . . . . . 14 6.9. Received Packet Option . . . . . . . . . . . . . . . . . 14 7. Processing Rules . . . . . . . . . . . . . . . . . . . . . . 15 7.1. Authentication Data Generation . . . . . . . . . . . . . 15 7.2. Authentication Data Validation . . . . . . . . . . . . . 15 7.3. Retransmission Policies . . . . . . . . . . . . . . . . . 16 7.4. Sequence Number . . . . . . . . . . . . . . . . . . . . . 16 7.5. MTU Considerations . . . . . . . . . . . . . . . . . . . 17 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17 9. Security Considerations . . . . . . . . . . . . . . . . . . . 17 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 18 11. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . 18 11.1. Changes from wasserman-pcp-authentication-02 to ietf- pcp-authentication-00 . . . . . . . . . . . . . . . . . 18 11.2. Changes from wasserman-pcp-authentication-01 to -02 . . 18 11.3. Changes from ietf-pcp-authentication-00 to -01 . . . . . 18 11.4. Changes from ietf-pcp-authentication-01 to -02 . . . . . 18 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 19 12.1. Normative References . . . . . . . . . . . . . . . . . . 19 12.2. Informative References . . . . . . . . . . . . . . . . . 19 Wasserman, et al. Expires April 05, 2014 [Page 2] Internet-Draft PCP Authentication October 2013 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 19 1. Introduction Using the Port Control Protocol (PCP) [RFC6887], an IPv4 or IPv6 host can flexibly manage the IP address mapping information on its network address translators (NATs) and firewalls, and control their policies in processing incoming and outgoing IP packets. Because NATs and firewalls both play important roles in network security architectures, there are many situations in which authentication and access control are required to prevent un-authorized users from accessing such devices. This document proposes a PCP security extension which enables PCP servers to authenticate their clients with Extensible Authentication Protocol (EAP). The EAP messages are encapsulated within PCP packets during transportation. The following issues are considered in the design of this extension: o Loss of EAP messages during transportation o Disordered delivery of EAP messages o Generation of transport keys o Integrity protection and data origin authentication for PCP messages o Algorithm agility The mechanism described in this document meets the security requirements to address the Advanced Threat Model described in the base PCP specification [RFC6887]. This mechanism can be used to secure PCP in the following situations:: o On security infrastructure equipment, such as corporate firewalls, that does not create implicit mappings. o On equipment (such as CGNs or service provider firewalls) that serve multiple administrative domains and do not have a mechanism to securely partition traffic from those domains. o For any implementation that wants to be more permissive in authorizing explicit mappings than it is in authorizing implicit mappings. o For implementations that support the THIRD_PARTY Option (unless they can meet the constraints outlined in Section 14.1.2.2). Wasserman, et al. Expires April 05, 2014 [Page 3] Internet-Draft PCP Authentication October 2013 o For implementations that wish to support any deployment scenario that does not meet the constraints described in Section 14.1. 2. Terminology The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [RFC2119]. Most of the terms used in this document are introduced in [RFC6887]. PCP Client: A PCP device (e.g., a host) which is responsible for issuing PCP requests to a PCP server. In this document, a PCP client is also a EAP peer [RFC3748], and it is the responsibility of a PCP client to provide the credentials when authentication is required. PCP Server: A PCP device (e.g., a NAT or a firewall) that implements the server-side of the PCP protocol, via which PCP clients request and manage explicit mappings. In this document, a PCP server is integrated with an EAP authenticator [RFC3748]. Therefore, when necessary, a PCP server can verify the credentials provided by a PCP client and make an access control decision based on the authentication result. PCP Authentication (PCP Auth) Session: A series of PCP message exchanges transferred between a PCP client and a PCP server. The PCP message involved within a session includes the PCP Auth messages used to perform authentication, key distribution and session management, and the common PCP messages secured with the distributed keys. Each PCP Auth session is assigned a distinctive Session ID. Session Partner: A PCP device involved within a PCP Auth session. Each PCP Auth session has two session partners (a PCP server and a PCP client). Session Lifetime: The life period associated with a PCP Auth session, which decides the lifetime of the current authorization given to the PCP client. PCP Security Association (PCP SA): A PCP security association is formed between a PCP client and a PCP server by sharing cryptographic keying material and associated context. The formed duplex security association is used to protect the bidirectional PCP signaling traffic between the PCP client and PCP server. Master Session Key (MSK): A key derived by the partners of a PCP Auth session, using an EAP key generating method (e.g., the one defined in [RFC5448]). Wasserman, et al. Expires April 05, 2014 [Page 4] Internet-Draft PCP Authentication October 2013 PCP Authentication (PCP Auth) message: A PCP message containing an Authentication OpCode. Particularly, a PCP Auth message sent from a PCP server to a PCP client is referred to as a PCP-Auth-Request, while PCP Auth message sent from a PCP client to a PCP server is referred to as a PCP-Auth-Answer. Therefore, a PCP-Auth-Request is actually a PCP response message specified [RFC6887], and a PCP-Auth- Answer is a PCP request message. Common PCP message: A PCP message which does not contain an Authentication OpCode. This document specifies an authentication option to provide integrity protection and message origin authentication for the common PCP messages. 3. Protocol Details 3.1. Session Initiation At be beginning of a PCP Auth Session, a set of PCP Auth messages need to be exchanged between two PCP devices in order to carry out an EAP authentication process. Each PCP Auth message is attached with an Authentication OpCode and may optionally contain the Options for various purposes (e.g., transporting authentication messages and session managements). The Authentication OpCode consists of two fields: Session ID, and Sequence Number. The Session ID field is used to identify the session to which the message belongs. The sequence number field is used to detect the disorder or the duplication occurred during packet delivery. When a PCP client intends to proactively initiate a PCP Auth session with a PCP server, it sends a PCP-Auth-Initiation message (a PCP- Auth-Answer message with the result code "INITIATION") to the PCP server. In the message, the Session ID and Sequence Number fields of the Authentication OpCode are set as 0. The PCP client MAY also append a nonce option which consists of a random nonce with PCP-Auth- Initiation message. After receiving the PCP-Auth-Initiation, if the PCP server would like to initiate a PCP Auth session, it will reply with a PCP-Auth-Request which contains an EAP Identity Request. The Sequence Number field in the PCP-Auth-Request is set as 0, and the Session ID field MUST be filled with the session identifier assigned by the PCP server for this session. If there is a nonce option in the received PCP-Auth-Initiation message, the PCP-Auth-Request MUST be attached with a nonce option which contains the nonce value learned from the PCP client. The nonce will then be used by the PCP client to check the freshness of the PCP-Auth-Request from the PCP server. From now on, every PCP Auth message within this session will use this session identifier to distinguish itself from the messages not belonging to the session. When receiving a PCP Auth message from an unknown session, a PCP device MUST discard the message silently. Wasserman, et al. Expires April 05, 2014 [Page 5] Internet-Draft PCP Authentication October 2013 If the PCP client intends to simplify the authentication process, it can append an EAP Identity Response message within the PCP-Auth- Initiation message so as to inform the PCP server that it would like to perform EAP authentication and skip the step of waiting for the EAP Identity Request. In the scenario where a PCP server receives a common PCP request message from a PCP client which needs to be authenticated, the PCP server can reply with a PCP-Auth-Request to initiate a PCP Auth session; the result code field of the PCP-Auth-Request is set as AUTHENTICATION-REQUIRED. In addition, the PCP server MUST assign a session ID for the session and transfer it within the PCP-Auth- Request. The Sequence Number field in the PCP-Auth-Request is set as 0. In the PCP Auth messages exchanged afterwards in this session, the session ID MUST be used in order to help session partners distinguish the messages within this session from those not within. When the PCP client receives this initial PCP-Auth-Request message from the PCP server, it can reply with a PCP-Auth-Answer message or silently discard the request message according to its local policies. In the PCP-Auth-Answer message, the PCP client MAY append a nonce option which consists of a random nonce with PCP-Auth-Initiation message. If so, in the next PCP-Auth-Request message, the PCP sever MUST forward the nonce back within a nonce option. In a PCP Auth session, PCP-Auth-Request messages are sent from PCP servers to PCP clients while PCP-Auth-Answer messages are only sent from PCP clients to PCP servers. Correspondently, an EAP request message MUST be transported within a PCP-Auth-Request message, and an EAP answer message MUST be transported within a PCP-Auth-Answer message. When a PCP device receives a PCP-Auth message from its partner and cannot generate a response within a pre-specified period due to certain reasons (e.g., waiting for human input to construct a EAP message), the PCP device MAY reply with a PCP-Auth-Acknowledge message (a PCP-Auth message with the result code "PACKET-RECEIVED- ACK") to notify the packet has been received, and thus un-necessarily retransmission of the PCP Auth message can be avoided. In this approach, it is mandated for a PCP client and a PCP server to perform a key-generating EAP method in authentication. Therefore, after a successful authentication procedure, a Master Session Key (MSK) will be generated. If the PCP client and the PCP server want to generate a traffic key using the MSK, they need to agree upon a Pseudo-Random Function (PRF) for the transport key derivation and a MAC algorithm to provide data origin authentication for subsequent PCP packets. On this occasion, the PCP server needs to append the initial PCP-Auth-Request message with a set of PRF Options and MAC Algorithm Options. Each PRF Option contains a PRF that the PCP server supports, and each MAC Algorithm Option contains a MAC Wasserman, et al. Expires April 05, 2014 [Page 6] Internet-Draft PCP Authentication October 2013 (Message Authentication Code) algorithm that the PCP server supports. After receiving the request, the PCP client selects a PRF and a MAC algorithm which it would like to use, and sends back a PCP-Auth- Answer with a PRF Option and a MAC Algorithm Option for the selected algorithm. The last PCP-Auth-Request message transported within a PCP Auth session carries the EAP authentication and PCP authorization results. If the EAP authentication succeeds, the result code of the last PCP- Auth-Request is AUTHENTICATION-SUCCEED. In this case, before sending out the PCP-Auth-Request, the PCP server must derive a transport key and use it to generate digests to protect the integrity and authenticity of the PCP-Auth-Request. Such digests are transported within Authentication Tag Options. In addition, the PCP-Auth-Request may need to be appended with a Session Lifetime Option which includes the life-time of the PCP Auth session (i.e., the life-time of the MSK). If the PCP client also authenticate the PCP server, the PCP client then generates the PCP SA and uses the derived traffic key to secure the packet receiving acknowledgement. From then on, all the PCP messages within the session are secured with the traffic key and the MAC algorithm sepcified in the PCP SA, unless re-authentication is performed. If the EAP authentication fails, the result code of the last PCP-Auth-Request is AUTHENTICATION-FAILED. If the EAP authentication succeeds but Authorization fails, the result code of the last PCP-Auth-Request is AUTHORIZATION-FAILED. In the latter two cases, the PCP Auth session MUST be terminated immediately after the last PCP authentication message exchange. 3.2. Session Termination A PCP Auth session can be explicitly terminated by sending a termination-indicating PCP Auth message (a PCP Auth message with a result code "SESSION-TERMINATION" ) from either session partner. After receiving a termination-indicating message from the session partner, a PCP device MUST respond with a termination-indicating PCP Auth message and remove the PCP Auth SA immediately. When the session partner initiating the termination process receives the acknowledge message, it will remove the associated PCP Auth SA immediately. 3.3. Session Re-Authentication A session partner may select to perform EAP re-authentication if it would like to update the PCP SA (e.g., update the MSK, or extend the session life period) instead of initiating a new PCP Auth session. When the PCP server initiates re-authentication, it sends a PCP-Auth- Request message containing the EAP message for re-authentication to Wasserman, et al. Expires April 05, 2014 [Page 7] Internet-Draft PCP Authentication October 2013 the PCP client. The result code of the PCP-Auth-Request message is set to "RE-AUTHENTICATION", which indicates the message is for an re- authentication process. If the PCP client would like to start the re-authentication, it will send an PCP-Auth-Answer message containing the EAP message for re-authentication to the PCP server, The result code of the PCP-Auth-Answer message is set to "RE-AUTHENTICATION". Then, the session partners exchange PCP Auth messages to transfer EAP messages for the re-authentication. During the re-authentication procedure, the session partners protect the integrity of PCP Auth messages with the key and MAC algorithm specified in the current PCP SA; the sequence numbers associated with the packet will never be rolled back and keep increasing according to Section 6.3. If the EAP re-authentication succeeds, the result code of the last PCP-Auth-Request is "AUTHENTICATION-SUCCEED". In this case, before sending out the PCP-Auth-Request, the PCP server must update the SA and use the new key to generate digests to protect the integrity and authenticity of the PCP-Auth-Request and any subsequent PCP message. In addition, the PCP-Auth-Request MAY be appended with a Session Lifetime Option which indicates the new life-time of the PCP Auth session. If the EAP authentication fails, the result code of the last PCP- Auth-Request is "AUTHENTICATION-FAILED". If the EAP authentication succeeds but Authorization fails, the result code of the last PCP- Auth-Request is "AUTHORIZATION-FAILED". In the latter two cases, the PCP Auth session MUST be terminated immediately after the last PCP authentication message exchange. 4. PA Security Association At the beginning of a PCP Auth session, a session SHOULD generate a PCP Auth SA to maintain its state information during the session. The parameters of a PCP Auth SA are listed as follows: o IP address and UDP port number of the PCP client o IP address and UDP port number of the PCP server o Session Identifier o Sequence number for the next outgoing PCP message o Sequence number for the next incoming PCP message o Last outgoing message payload o Retransmission interval Wasserman, et al. Expires April 05, 2014 [Page 8] Internet-Draft PCP Authentication October 2013 o MSK: The master session key generated by the EAP method. o MAC algorithm: The algorithm that the transport key should use to generate digests for PCP messages. o Pseudo-random function: The pseudo random function negotiated in the initial PCP-Auth-Request and PCP-Auth-Answer exchange for the transport key derivation o Transport key: the key derived from the MSK to provide integrity protection and data origin authentication for the messages in the PCP Auth session. The life-time of the transport key SHOULD be identical to the life-time of the session. o The nonce selected by the PCP client at the initiation of the session. o Key ID: the ID associated with Transport key. Particularly, the transport key is computed in the following way: Transport key = prf(MSK, "IETF PCP"| Session_ID| Nonce| key ID), where: o The prf: The pseudo-random function assigned in the Pseudo-random function parameter. o MSK: The master session key generated by the EAP method. o "IETF PCP": The ASCII code representation of the non-NULL terminated string (excluding the double quotes around it). o Session_ID: The ID of the session which the MSK is derived from. o Nonce: The nonce selected by the client and transported in the Initial PCP-Auth-Answer packet. If the PCP client does not select one, this value is set as 0. o Key ID: The ID assigned for the traffic key. 5. Result Code This message use the result code field specified in the PCP headers to transport the information for authentication and session management. Particularly, the values of following result codes are specified. TBD INITIATION Wasserman, et al. Expires April 05, 2014 [Page 9] Internet-Draft PCP Authentication October 2013 TBD PACKET-RECEIVED-ACK TBD AUTHENTICATION-REQUIRED TBD AUTHENTICATION-FAILED TBD AUTHENTICATION-SUCCEED TBD AUTHORIZATION-FAILED TBD SESSION-TERMINATION 6. Packet Format 6.1. Packet Format of PCP Auth Messages The format of PCP-Auth-request messages is identical to the response packet format specified in Section 7.2 of [RFC6887]. As illustrated in Figure 1, the PCP-Auth-Answer messages use the requester header specified in Section 7.1 of [RFC6887]. The only difference is that eight reserved bits are used to transfer the result codes (e.g., "INITIATION"). Other fields in Figure 1 are described in Section 7.1 of [RFC6887]. Wasserman, et al. Expires April 05, 2014 [Page 10] Internet-Draft PCP Authentication October 2013 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Version = 2 |R| Opcode | Reserved | Result Code | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Requested Lifetime (32 bits) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | PCP Client's IP Address (128 bits) | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ : : : (optional) Opcode-specific information : : : +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ : : : (optional) PCP Options : : : +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 1. PCP-Auth-Answer message Format 6.2. Authentication OpCode Format The following figure illustrates the format of an authentication OpCode: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Session ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Sequence Number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Session ID: This field contains a 32-bit PCP Auth session identifier. Sequence Number: This field contains a 32-bit sequence number. In this solution, a sequence number needs to be incremented on every new (non-retransmission) outgoing packet in order to provide ordering guarantee for PCP. Wasserman, et al. Expires April 05, 2014 [Page 11] Internet-Draft PCP Authentication October 2013 6.3. Nonce Option Because the session identifier of PCP Auth session is determined by the PCP server, a PCP client does not know the session identifier which will be used when it sends out a PCP-Auth-Initiation message. In order to prevent an attacker from interrupting the authentication process by sending off-line generated PCP-Auth-Request messages, the PCP client needs to generate a random number as nonce in the PCP- Auth-Initiation message. The PCP server will append the nonce within the initial PCP-Auth-Request message. If the PCP-Auth-Request message does not carry the correct nonce, the message will be discarded silently. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Option Code | Reserved | Option-Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Nonce | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Option-Length: The length of the Nonce Option (in octet), including the 4 octet fixed header and the variable length of the authentication data. Nonce: A random 32 bits number which is transported within a PCC- Initiate message and the corresponding reply message from the PCP server. 6.4. Authentication Tag Option 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Option Code | Reserved | Option-Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Session ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Key ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | Authentication Data (Variable) | ~ ~ | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Wasserman, et al. Expires April 05, 2014 [Page 12] Internet-Draft PCP Authentication October 2013 Option-Length: The length of the Authentication Tag Option (in octet), including the 12 octet fixed header and the variable length of the authentication data. Session ID: A 32-bit field used to indicates the identifier of the session that the message belongs to and identifies the secret key used to create the message digest appended to the PCP message. Key ID: The ID associated with the traffic key used to generate authentication data. This field is filled with zero if MSK is directly used to secure the message. Authentication Data: A variable-length field that carries the Message Authentication Code for the PCP packet. The generation of the digest can be various according to the algorithms specified in different PCP SAs. This field MUST end on a 32-bit boundary, padded with 0's when necessary. 6.5. EAP Payload Option 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Option Code | Reserved | Option-Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | EAP Message | ~ ~ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Option-Length: The length of the EAP Payload Option (in octet), including the 4 octet fixed header and the variable length of the EAP message. EAP Message: The EAP message transferred. Note this field MUST end on a 32-bit boundary, padded with 0's when necessary. 6.6. PRF Option Wasserman, et al. Expires April 05, 2014 [Page 13] Internet-Draft PCP Authentication October 2013 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Option Code | Reserved | Option-Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | PRF | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ PRF: The Pseudo-Random Function which the sender supports to generate an MSK. This field contains an IKEv2 Transform ID of Transform Type 2 [RFC4306]. 6.7. MAC Algorithm Option 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Option Code | Reserved | Option-Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | MAC Algorithm ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ MAC Algorithm ID: Indicate the MAC algorithm which the sender supports to generate authentication data. The MAC Algorithm ID field contains an IKEv2 Transform ID of Transform Type 3 [RFC4306]. 6.8. Session Lifetime Option 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Option Code | Reserved | Option-Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Session Lifetime | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Session Lifetime: The life time of the PCP Auth Session, which is decided by the authorization result. 6.9. Received Packet Option This option is used in a PCP-Auth-Acknowledgement message to indicate a packet with the contained sequence number has been received. Wasserman, et al. Expires April 05, 2014 [Page 14] Internet-Draft PCP Authentication October 2013 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Option Code | Reserved | Option-Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Received Sequence Number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Received Sequence Number: The sequence number of the last received PCP packet. 7. Processing Rules 7.1. Authentication Data Generation If a PCP SA is generated as the result of a successful EAP authentication process, every subsequent PCP message within the session MUST carry an Authentication Tag Option which contains the digest of the PCP message for data origin authentication and integrity protection. Before generating a digest for a PCP message, a device needs to first select a traffic key in the session and append the Authentication Tag Option at the end of the PCP message being protected. The length of the Authentication Data field is decided by the MAC algorithm adopted in the session. The device then fills the Session ID field and the PCP SA ID field, and sets the Authentication Data field to 0. After this, the device generates a digest for the entire PCP message (including the PCP header and Authentication Tag Option) with the MAC algorithm and the selected traffic key, and input the generated digest into the Authentication Data field. 7.2. Authentication Data Validation When a device receives a PCP packet with an Authentication Tag Option, it needs to use the session ID transported in the option to locate the proper SA, and then find the associated transport key (using key ID) and the MAC algorithm. If no proper SA is found, the PCP packet MUST be discarded silently. After storing the value of the Authentication field of the Authentication Tag Option, the device fills the Authentication field with zeros. Then, the device generates a digest for the packet (including the PCP header and Authentication Tag Option) with the transport key and the MAC algorithm found in the first step. If the value of the newly generated digest is identical to the stored one, the device can ensure that the packet has not been tampered with, and the validation succeeds. Otherwise, the packet MUST be discarded. Wasserman, et al. Expires April 05, 2014 [Page 15] Internet-Draft PCP Authentication October 2013 7.3. Retransmission Policies In order to provide reliable transmission over PCP messages, the retransmission poclies needs to be considered. In the base PCP protocol, only PCP clients are responsible for reliable delivery of PCP request messages according to policies specified in Section 8.1.1 of [RFC6887], However, in this document, both PCP clients and PCP servers need to provide reliable delivery of PCP Auth messages. Therefore, such retransmission policy can be also applied by the PCP servers. 7.4. Sequence Number PCP adopts UDP to transport signaling messages. As an un-reliable transport protocol, UDP does not guarantee ordered packet delivery and does not provide any protection from packet loss. In order to ensure the EAP messages are exchanged in a reliable way, every PCP packet exchanged during EAP authentication must carry an monotonically increasing sequence number. During a PCP Auth session, a PCP device needs to maintain two sequence numbers, one for incoming packets and one for outgoing packets. When generating an outgoing PCP packet, the device attaches the outgoing sequence number to the packet and increments the sequence number maintained in the SA by 1. When receiving a PCP packet from its session partner, the device will not accept it if the sequence number carried in the packet does not match the incoming sequence number the device maintains. After confirming that the received packet is valid, the device increments the incoming sequence number maintained in the SA by 1. The above rules are not applied to PCP-Auth-Acknowledgement messages whose result code fields are set as PACKET-RECEIVED-ACK. This type of message is optionally used to avoid un-necessary packet retransmission and the reliable transmission does not have to be guaranteed. Therefore, when receiving or sending out a PCP-Auth- Acknowledgement message, the device MUST not increase the corresponding sequence number stored in the SA. Otherwise, the lost of a PCP-Auth-Acknowledgement message during transportation will cause the mismatching issues with the sequence numbers. Another exception is message retransmission. When a device does not receive any response from its session partner in a certain period, it needs to retransmit the last outgoing PCP Auth message with a limited rate. The duplicate messages and the original message MUST use the identical sequence number. When the device receives such duplicate PCP Auth messages from its session partner, it MUST try to answer them by sending the last outgoing PCP Auth message with a limited rate unless it has received another valid message with a larger Wasserman, et al. Expires April 05, 2014 [Page 16] Internet-Draft PCP Authentication October 2013 sequence number from its session. In such cases, the maintained incoming and outgoing sequence numbers will not be affected by the message retransmission. 7.5. MTU Considerations EAP methods are responsible for MTU handling, so no special facilities are required in this protocol to deal with MTU issues. 8. IANA Considerations TBD 9. Security Considerations This section applies only to the in-band key management mechanism. It will need to be updated if the WG choose to pursue the out-of-band key management mechanism discussed above. In this work, after a successful EAP authentication process performed between two PCP devices, a MSK will be exported. The MSK can be used to derive the transport keys to generate MAC digests for subsequent PCP message exchanges. This work does not exclude the possibility of using the MSK to generate keys for different security protocols to enable per-packet cryptographic protection. The methods of deriving the transport key for the security protocols is out of scope of this document. However, before a transport key has been generated, the PCP Auth messages exchanged within a PCP Auth session have little cryptographic protection, and if there is no already established security channel between two session partners, these messages are subject to man-in-the-middle attacks and DOS attacks. For instance, the initial PCP-Auth-Request and PCP-Auth-Answer exchange is vulnerable to spoofing attacks as these messages are not authenticated and integrity protected. In addition, because the PRF and MAC algorithms are transported at this stage, an attacker may try to remove the PRF and MAC options containing strong algorithms from the initial PCP-Auth-Request message and force the client choose the weakest algorithms. Therefore, the server needs to guarantee that all the PRF and MAC algorithms it provids support are strong enough. Wasserman, et al. Expires April 05, 2014 [Page 17] Internet-Draft PCP Authentication October 2013 In order to prevent very basic DOS attacks, a PCP device SHOULD generate state information as little as possible in the initial PCP- Auth-Request and PCP-Auth-Answer exchanges. The choice of EAP method is also very important. The selected EAP method must be resilient to the attacks possibly in an insecure network environment, and the user-identity confidentiality, protection against dictionary attacks, and session-key establishment must be supported. 10. Acknowledgements 11. Change Log 11.1. Changes from wasserman-pcp-authentication-02 to ietf-pcp- authentication-00 o Added discussion of in-band and out-of-band key management options, leaving choice open for later WG decision. o Removed support for fragmenting EAP messages, as that is handled by EAP methods. 11.2. Changes from wasserman-pcp-authentication-01 to -02 o Add a nonce into the first two exchanged PCP Auth message between the PCP client and PCP server. When a PCP client initiate the session, it can use the nonce to detect offline attacks. o Add the key ID field into the authentication tag option so that a MSK can generate multiple traffic keys. o Specify that when a PCP device receives a PCP-Auth-Request or a PCP-Auth-Answer message from its partner the PCP device needs to reply with a PCP-Auth-Acknowledge message to indicate that the message has been received. o Add the support of fragmenting EAP messages. 11.3. Changes from ietf-pcp-authentication-00 to -01 o Editorial changes, added use cases to introduction. 11.4. Changes from ietf-pcp-authentication-01 to -02 o Add the support of re-authentication initiated by PCP server. Wasserman, et al. Expires April 05, 2014 [Page 18] Internet-Draft PCP Authentication October 2013 o Specify that when a PCP device receives a PCP-Auth-Request or a PCP-Auth-Answer message from its partner the PCP device MAY reply with a PCP-Auth-Acknowledge message to indicate that the message has been received. o Discuss the format of the PCP-Auth-Acknowledge message. o Remove the redundant information from the Auth OpCode, and specify new result codes transported in PCP packet headers 12. References 12.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. 12.2. Informative References [RFC3748] Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and H. Levkowetz, "Extensible Authentication Protocol (EAP)", RFC 3748, June 2004. [RFC4306] Kaufman, C., "Internet Key Exchange (IKEv2) Protocol", RFC 4306, December 2005. [RFC5191] Forsberg, D., Ohba, Y., Patil, B., Tschofenig, H., and A. Yegin, "Protocol for Carrying Authentication for Network Access (PANA)", RFC 5191, May 2008. [RFC5448] Arkko, J., Lehtovirta, V., and P. Eronen, "Improved Extensible Authentication Protocol Method for 3rd Generation Authentication and Key Agreement (EAP-AKA')", RFC 5448, May 2009. [RFC6887] Wing, D., Cheshire, S., Boucadair, M., Penno, R., and P. Selkirk, "Port Control Protocol (PCP)", RFC 6887, April 2013. Authors' Addresses Wasserman, et al. Expires April 05, 2014 [Page 19] Internet-Draft PCP Authentication October 2013 Margaret Wasserman Painless Security 356 Abbott Street North Andover, MA 01845 USA Phone: +1 781 405 7464 Email: mrw@painless-security.com URI: http://www.painless-security.com Sam Hartman Painless Security 356 Abbott Street North Andover, MA 01845 USA Email: hartmans@painless-security.com URI: http://www.painless-security.com Dacheng Zhang Huawei Beijing China Email: zhangdacheng@huawei.com Wasserman, et al. Expires April 05, 2014 [Page 20]