Internet DRAFT - draft-ahrens-httpbis-digest-auth-update
draft-ahrens-httpbis-digest-auth-update
INTERNET-DRAFT David Ahrens
Intended Status: Standards Track Rifaat Shekh-Yusef
Expires: January 31, 2013 Avaya
July 30, 2012
HTTP Digest Access Authentication Algorithm Update
draft-ahrens-httpbis-digest-auth-update-00
Abstract
This document specifies extensions to the HTTP Digest Authentication
mechanism to add support for the SHA1 and SHA2 digest algorithms to
the HTTP Digest access authentication scheme.
Status of this Memo
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Copyright (c) 2012 IETF Trust and the persons identified as the
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carefully, as they describe your rights and restrictions with respect
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Table of Contents
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1 Terminology . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Digest Access Authentication Scheme Update . . . . . . . . . . 3
2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1.1 Representation of digest values . . . . . . . . . . . . 3
2.1.2 Limitations . . . . . . . . . . . . . . . . . . . . . . 4
2.2 Specification of Digest Headers . . . . . . . . . . . . . . 4
2.2.1 The WWW-Authenticate Response Header . . . . . . . . . . 4
2.2.2 The Authorization Request Header . . . . . . . . . . . . 5
2.3 Digest Operation . . . . . . . . . . . . . . . . . . . . . . 6
2.4 Security Protocol Operation . . . . . . . . . . . . . . . . 6
2.5 Example . . . . . . . . . . . . . . . . . . . . . . . . . . 6
3 Security Considerations . . . . . . . . . . . . . . . . . . . . 7
4 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 7
5 References . . . . . . . . . . . . . . . . . . . . . . . . . . 8
5.1 Normative References . . . . . . . . . . . . . . . . . . . 8
5.2 Informative References . . . . . . . . . . . . . . . . . . 8
6 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 9
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1 Introduction
This document specifies extensions to the HTTP Digest Access
Authentication scheme by adding support for the SHA1 and SHA2 suite
of hash algorithms. RFC 2617 specifies the MD5 algorithm as the
default hash algorithm used in the digest access authentication
scheme. Since RFC 2617 was first proposed, the MD5 algorithm has
been broken. In 2008 the US-CERT issued a note that MD5 "should be
considered cryptographically broken and unsuitable for further use."
1.1 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].
2. Digest Access Authentication Scheme Update
The Digest Access Authentication scheme is based on a simple
challenge-response paradigm. The Digest scheme challenges using a
nonce value. A valid response contains a checksum of the username,
the password, the given nonce value and the requested URI. In this
way the password is never sent in the clear.
2.1 Introduction
2.1.1 Representation of digest values
An optional header allows the server to specify the algorithm used to
create the checksum or digest. By default and to maintain backwards
compatibility, the MD5 algorithm is used.
The size of the digest depends on the algorithm used. The bits in
the digest are converted from the most significant to the least
significant bit, four bits at a time to the ASCII representation as
follows. Each four bits is represented by its familiar hexadecimal
notation from the characters 0123456789abcdef, that is binary 0000 is
represented by the character '0', 0001 by '1' and so on up to the
representation of 1111 as 'f'. If the MD5 algorithm is used to
calculate the digest, then the digest will be represented as 32
hexadecimal characters, SHA1 by 40 hexadecimal characters, SHA2-224
by 56 hexadecimal characters, SHA2-256 by 64 hexadecimal characters,
SHA2-384 by 96 hexadecimal characters, and SHA2-512 by 128
hexadecimal characters.
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2.1.2 Limitations
The Digest authentication scheme specified in RFC 2617 suffers from
many known limitations. The update proposed in this draft does not
address those limitations.
2.2 Specification of Digest Headers
The modifications to the formats of the WWW-Authenticate Header line
and the Authorization header line are specified below.
2.2.1 The WWW-Authenticate Response Header
If a server receives a request for an access protected object, and an
acceptable Authorization header is not sent, the server responds with
a "401 Unauthorized" status code, and a WWW-Authenticate header. The
server MAY include multiple WWW-Authenticate headers to allow the
server to utilize the best available algorithm supported by the
client.
The algorithm directive is extended as follows:
algorithm = "algorithm" "=" ("MD5" | "MD5-sess" |
"SHA1" | "SHA1-sess" |
"SHA224" | "SHA224-sess" |
"SHA256" | "SHA256-sess" |
"SHA384" | "SHA384-sess" |
"SHA512" | "SHA512-sess" |
token)
Algorithm
A string indicating a pair of algorithms used to produce the
digest and a checksum. If the algorithm parameter is not present
it is assumed to be "MD5" to maintain backwards compatibility
with existing implementations. If the algorithm is not
understood, the challenge should be ignored and a different
challenge used if there is more than one.
The string obtained by applying the digest algorithm to the data
"data" with "secret" will be denoted KD(secret, data) and the
string obtained by applying the checksum algorithm to the data
"data" will be denoted H(data). The notation unq(x) means the
value of the quoted string X without the surrounding quotes.
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For the "MD5 and "MD5-sess" algorithms
H(data) = MD5(data)
For the "SHA1" and "SHA1-sess" algorithms
H(data) = SHA1(data)
For the "SHA224" and "SHA224-sess" algorithms
H(data) = SHA224(data)
For the "SHA256" and "SHA256-sess" algorithms
H(data) = SHA256(data)
For the "SHA384" and "SHA384-sess" algorithms
H(data) = SHA384(data)
For the "SHA512" and "SHA512-sess" algorithms
H(data) = SHA512(data)
and
KD(secret, data) = H(concat(secret, ":", data))
i.e the digest is the hash of the secret concatenated with a
colon concatenated with the data. The " -sess" algorithm is
intended to allow efficient 3rd party authentication servers;
for the difference in usage see the description in section
RFC2617, Section 3.2.2.2.
2.2.2 The Authorization Request Header
The client is expected to retry the request, passing an Authorization
Request Header line. The Authorization Request Header line is
modified as follows:
request-digest = <"> digest-size LHEX <">
digest-size = "32" | "40" | "56" | "64" | "96" | "128"
The values of the opaque and algorithm fields must match those
supplied in the WWW-Authenticate response header for the entity being
requested.
response
A string of hex digits as defined in RFC2617 which proves
that the user knows a password.
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2.3 Digest Operation
The modifications specified in this document does not introduce any
change to the digest operation specified in RFC2617.
2.4 Security Protocol Operation
When a server receives a request to access a resource, the server
might challenge the client by responding with "401 Unauthorized"
status code, and include one or more WWW-Authenticate headers. If the
server challenges with multiple Digest headers, then each one of
these headers MUST use a different digest algorithm. The server MUST
add these Digest headers to the response in order of preference,
starting with the most preferred header, followed by the less
preferred headers.
When the client receives the response it SHOULD use the topmost
header that it supports, unless a local policy dictates otherwise.
The client should ignore any challenge it does not understand.
2.5 Example
The following example is borrowed from RFC 2617 and assumes that an
access protected document is being requested from the server via a
GET request. The URI of the document is
http://www.nowhere.org/dir/index.html". Both client and server know
that the username for this document is "Mufasa" and the password is
"Circle of Life" ( with one space between each of the three words).
The first time the client requests the document, no Authorization
header is sent, so the server responds with:
HTTP/1.1 401 Unauthorized
WWW-Authenticate: Digest
realm = "testrealm@host.com",
qop="auth, auth-int",
algorithm="SHA1",
nonce=dcd98b7102dd2f0e8b11d0f600bfb0c093",
opaque=5ccc069c403ebaf9f0171e9517f40e41"
WWW-Authenticate: Digest
realm="testrealm@host.com",
qop="auth, auth-int",
algorithm="MD5",
nonce="dcd98b7102dd2f0e8b11d0f600bfb0c093",
opaque="5ccc069c403ebaf9f0171e9517f40ef41"
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The client may prompt the user for their username and password, after
which it will respond with a new request, including the following
Authorization header:
Authorization:Digest username="Mufasa",
realm="testrealm@host.com"
nonce="dcd98b7102dd2f0e8b11d0f600bfb0c093",
uri="/dir/index.html",
qop=auth,
algorithm="MD5"
nc=00000001,
cnonce="0a4f113b",
response="6629fae49393a05397450978507c4ef1",
opaque="5ccc069c403ebaf9f0171e9517f40e41"
3 Security Considerations
This specification updates the Digest Access Authentication scheme
specified in RFC 2617 to add support for the SHA1 and SHA2 algorithm
suites. Support for these additional hash algorithms does not alter
the security properties of the Digest Access Authentication scheme.
4 Acknowledgments
The authors would like to thank Geoff Baskwill and Eric Cooper for
their careful review and comments.
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5 References
5.1 Normative References
[KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[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.
5.2 Informative References
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6 Authors' Addresses
David Ahrens
Avaya, Inc.
4655 Great America Parkway
Santa Clara, CA 95054
Phone: (408) 562-5502
EMail: davidahrens@avaya.com
Rifaat Shekh-Yusef
Avaya, Inc.
250 Sydney Street
Belleville, Ontario
Canada
Phone: +1-613-967-5267
Email: rifatyu@avaya.com
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