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| author | Zhang zhengguang <zhengguang.zhang@intel.com> | 2014-11-04 11:12:11 +0800 |
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| committer | Zhang zhengguang <zhengguang.zhang@intel.com> | 2014-11-04 11:12:11 +0800 |
| commit | 9f52ffa8b526e717e324fe0835ab794478650f11 (patch) | |
| tree | 4c1ec36d951519b39e0e1e7acd90bccfcd6fc2ff /docs/specs/rfc2617.txt | |
| parent | 39e527cdc1af04afdf13207f5503afa7b772043e (diff) | |
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diff --git a/docs/specs/rfc2617.txt b/docs/specs/rfc2617.txt deleted file mode 100644 index b8fdf59f..00000000 --- a/docs/specs/rfc2617.txt +++ /dev/null @@ -1,1909 +0,0 @@ - -[[ Text in double brackets is from the unofficial errata at ]] -[[ http://skrb.org/ietf/http_errata.html ]] - -Network Working Group J. Franks -Request for Comments: 2617 Northwestern University -Obsoletes: 2069 P. Hallam-Baker -Category: Standards Track Verisign, Inc. - J. Hostetler - AbiSource, Inc. - S. Lawrence - Agranat Systems, Inc. - P. Leach - Microsoft Corporation - A. Luotonen - Netscape Communications Corporation - L. Stewart - Open Market, Inc. - June 1999 - - - HTTP Authentication: Basic and Digest Access Authentication - -Status of this Memo - - This document specifies an Internet standards track protocol for the - Internet community, and requests discussion and suggestions for - improvements. Please refer to the current edition of the "Internet - Official Protocol Standards" (STD 1) for the standardization state - and status of this protocol. Distribution of this memo is unlimited. - -Copyright Notice - - Copyright (C) The Internet Society (1999). All Rights Reserved. - -Abstract - - "HTTP/1.0", includes the specification for a Basic Access - Authentication scheme. This scheme is not considered to be a secure - method of user authentication (unless used in conjunction with some - external secure system such as SSL [5]), as the user name and - password are passed over the network as cleartext. - - This document also provides the specification for HTTP's - authentication framework, the original Basic authentication scheme - and a scheme based on cryptographic hashes, referred to as "Digest - Access Authentication". It is therefore also intended to serve as a - replacement for RFC 2069 [6]. Some optional elements specified by - RFC 2069 have been removed from this specification due to problems - found since its publication; other new elements have been added for - compatibility, those new elements have been made optional, but are - strongly recommended. - - - -Franks, et al. Standards Track [Page 1] - -RFC 2617 HTTP Authentication June 1999 - - - Like Basic, Digest access authentication verifies that both parties - to a communication know a shared secret (a password); unlike Basic, - this verification can be done without sending the password in the - clear, which is Basic's biggest weakness. As with most other - authentication protocols, the greatest sources of risks are usually - found not in the core protocol itself but in policies and procedures - surrounding its use. - -Table of Contents - - 1 Access Authentication................................ 3 - 1.1 Reliance on the HTTP/1.1 Specification............ 3 - 1.2 Access Authentication Framework................... 3 - 2 Basic Authentication Scheme.......................... 5 - 3 Digest Access Authentication Scheme.................. 6 - 3.1 Introduction...................................... 6 - 3.1.1 Purpose......................................... 6 - 3.1.2 Overall Operation............................... 6 - 3.1.3 Representation of digest values................. 7 - 3.1.4 Limitations..................................... 7 - 3.2 Specification of Digest Headers................... 7 - 3.2.1 The WWW-Authenticate Response Header............ 8 - 3.2.2 The Authorization Request Header................ 11 - 3.2.3 The Authentication-Info Header.................. 15 - 3.3 Digest Operation.................................. 17 - 3.4 Security Protocol Negotiation..................... 18 - 3.5 Example........................................... 18 - 3.6 Proxy-Authentication and Proxy-Authorization...... 19 - 4 Security Considerations.............................. 19 - 4.1 Authentication of Clients using Basic - Authentication.................................... 19 - 4.2 Authentication of Clients using Digest - Authentication.................................... 20 - 4.3 Limited Use Nonce Values.......................... 21 - 4.4 Comparison of Digest with Basic Authentication.... 22 - 4.5 Replay Attacks.................................... 22 - 4.6 Weakness Created by Multiple Authentication - Schemes........................................... 23 - 4.7 Online dictionary attacks......................... 23 - 4.8 Man in the Middle................................. 24 - 4.9 Chosen plaintext attacks.......................... 24 - 4.10 Precomputed dictionary attacks.................... 25 - 4.11 Batch brute force attacks......................... 25 - 4.12 Spoofing by Counterfeit Servers................... 25 - 4.13 Storing passwords................................. 26 - 4.14 Summary........................................... 26 - 5 Sample implementation................................ 27 - 6 Acknowledgments...................................... 31 - - - -Franks, et al. Standards Track [Page 2] - -RFC 2617 HTTP Authentication June 1999 - - - 7 References........................................... 31 - 8 Authors' Addresses................................... 32 - 9 Full Copyright Statement............................. 34 - -1 Access Authentication - -1.1 Reliance on the HTTP/1.1 Specification - - This specification is a companion to the HTTP/1.1 specification [2]. - It uses the augmented BNF section 2.1 of that document, and relies on - both the non-terminals defined in that document and other aspects of - the HTTP/1.1 specification. - -1.2 Access Authentication Framework - - HTTP provides a simple challenge-response authentication mechanism - that MAY be used by a server to challenge a client request and by a - client to provide authentication information. It uses an extensible, - case-insensitive token to identify the authentication scheme, - followed by a comma-separated list of attribute-value pairs which - carry the parameters necessary for achieving authentication via that - scheme. - - auth-scheme = token - auth-param = token "=" ( token | quoted-string ) - - The 401 (Unauthorized) response message is used by an origin server - to challenge the authorization of a user agent. This response MUST - include a WWW-Authenticate header field containing at least one - challenge applicable to the requested resource. The 407 (Proxy - Authentication Required) response message is used by a proxy to - challenge the authorization of a client and MUST include a Proxy- - Authenticate header field containing at least one challenge - applicable to the proxy for the requested resource. - - challenge = auth-scheme 1*SP 1#auth-param - - Note: User agents will need to take special care in parsing the WWW- - Authenticate or Proxy-Authenticate header field value if it contains - more than one challenge, or if more than one WWW-Authenticate header - field is provided, since the contents of a challenge may itself - contain a comma-separated list of authentication parameters. - - The authentication parameter realm is defined for all authentication - schemes: - - realm = "realm" "=" realm-value - realm-value = quoted-string - - - -Franks, et al. Standards Track [Page 3] - -RFC 2617 HTTP Authentication June 1999 - - - The realm directive (case-insensitive) is required for all - authentication schemes that issue a challenge. The realm value - (case-sensitive), in combination with the canonical root URL (the - absoluteURI for the server whose abs_path is empty; see section 5.1.2 - of [2]) of the server being accessed, defines the protection space. - These realms allow the protected resources on a server to be - partitioned into a set of protection spaces, each with its own - authentication scheme and/or authorization database. The realm value - is a string, generally assigned by the origin server, which may have - additional semantics specific to the authentication scheme. Note that - there may be multiple challenges with the same auth-scheme but - different realms. - - A user agent that wishes to authenticate itself with an origin - server--usually, but not necessarily, after receiving a 401 - (Unauthorized)--MAY do so by including an Authorization header field - with the request. A client that wishes to authenticate itself with a - proxy--usually, but not necessarily, after receiving a 407 (Proxy - Authentication Required)--MAY do so by including a Proxy- - Authorization header field with the request. Both the Authorization - field value and the Proxy-Authorization field value consist of - credentials containing the authentication information of the client - for the realm of the resource being requested. The user agent MUST - choose to use one of the challenges with the strongest auth-scheme it - understands and request credentials from the user based upon that - challenge. - - credentials = auth-scheme #auth-param - - Note that many browsers will only recognize Basic and will require - that it be the first auth-scheme presented. Servers should only - include Basic if it is minimally acceptable. - - The protection space determines the domain over which credentials can - be automatically applied. If a prior request has been authorized, the - same credentials MAY be reused for all other requests within that - protection space for a period of time determined by the - authentication scheme, parameters, and/or user preference. Unless - otherwise defined by the authentication scheme, a single protection - space cannot extend outside the scope of its server. - - If the origin server does not wish to accept the credentials sent - with a request, it SHOULD return a 401 (Unauthorized) response. The - response MUST include a WWW-Authenticate header field containing at - least one (possibly new) challenge applicable to the requested - resource. If a proxy does not accept the credentials sent with a - request, it SHOULD return a 407 (Proxy Authentication Required). The - response MUST include a Proxy-Authenticate header field containing a - - - -Franks, et al. Standards Track [Page 4] - -RFC 2617 HTTP Authentication June 1999 - - - (possibly new) challenge applicable to the proxy for the requested - resource. - - The HTTP protocol does not restrict applications to this simple - challenge-response mechanism for access authentication. Additional - mechanisms MAY be used, such as encryption at the transport level or - via message encapsulation, and with additional header fields - specifying authentication information. However, these additional - mechanisms are not defined by this specification. - - Proxies MUST be completely transparent regarding user agent - authentication by origin servers. That is, they must forward the - WWW-Authenticate and Authorization headers untouched, and follow the - rules found in section 14.8 of [2]. Both the Proxy-Authenticate and - the Proxy-Authorization header fields are hop-by-hop headers (see - section 13.5.1 of [2]). - -2 Basic Authentication Scheme - - The "basic" authentication scheme is based on the model that the - client must authenticate itself with a user-ID and a password for - each realm. The realm value should be considered an opaque string - which can only be compared for equality with other realms on that - server. The server will service the request only if it can validate - the user-ID and password for the protection space of the Request-URI. - There are no optional authentication parameters. - - For Basic, the framework above is utilized as follows: - - challenge = "Basic" realm - credentials = "Basic" basic-credentials - - Upon receipt of an unauthorized request for a URI within the - protection space, the origin server MAY respond with a challenge like - the following: - - WWW-Authenticate: Basic realm="WallyWorld" - - where "WallyWorld" is the string assigned by the server to identify - the protection space of the Request-URI. A proxy may respond with the - same challenge using the Proxy-Authenticate header field. - - To receive authorization, the client sends the userid and password, - separated by a single colon (":") character, within a base64 [7] - encoded string in the credentials. - - basic-credentials = base64-user-pass - base64-user-pass = <base64 [4] encoding of user-pass, - - - -Franks, et al. Standards Track [Page 5] - -RFC 2617 HTTP Authentication June 1999 - - - except not limited to 76 char/line> - user-pass = userid ":" password - userid = *<TEXT excluding ":"> - password = *TEXT - - Userids might be case sensitive. - - If the user agent wishes to send the userid "Aladdin" and password - "open sesame", it would use the following header field: - - Authorization: Basic QWxhZGRpbjpvcGVuIHNlc2FtZQ== - - A client SHOULD assume that all paths at or deeper than the depth of - the last symbolic element in the path field of the Request-URI also - are within the protection space specified by the Basic realm value of - the current challenge. A client MAY preemptively send the - corresponding Authorization header with requests for resources in - that space without receipt of another challenge from the server. - Similarly, when a client sends a request to a proxy, it may reuse a - userid and password in the Proxy-Authorization header field without - receiving another challenge from the proxy server. See section 4 for - security considerations associated with Basic authentication. - -3 Digest Access Authentication Scheme - -3.1 Introduction - -3.1.1 Purpose - - The protocol referred to as "HTTP/1.0" includes the specification for - a Basic Access Authentication scheme[1]. That scheme is not - considered to be a secure method of user authentication, as the user - name and password are passed over the network in an unencrypted form. - This section provides the specification for a scheme that does not - send the password in cleartext, referred to as "Digest Access - Authentication". - - The Digest Access Authentication scheme is not intended to be a - complete answer to the need for security in the World Wide Web. This - scheme provides no encryption of message content. The intent is - simply to create an access authentication method that avoids the most - serious flaws of Basic authentication. - -3.1.2 Overall Operation - - Like Basic Access Authentication, the Digest scheme is based on a - simple challenge-response paradigm. The Digest scheme challenges - using a nonce value. A valid response contains a checksum (by - - - -Franks, et al. Standards Track [Page 6] - -RFC 2617 HTTP Authentication June 1999 - - - default, the MD5 checksum) of the username, the password, the given - nonce value, the HTTP method, and the requested URI. In this way, the - password is never sent in the clear. Just as with the Basic scheme, - the username and password must be prearranged in some fashion not - addressed by this document. - -3.1.3 Representation of digest values - - An optional header allows the server to specify the algorithm used to - create the checksum or digest. By default the MD5 algorithm is used - and that is the only algorithm described in this document. - - For the purposes of this document, an MD5 digest of 128 bits is - represented as 32 ASCII printable characters. The bits in the 128 bit - digest are converted from most significant to least significant bit, - four bits at a time to their ASCII presentation as follows. Each four - bits is represented by its familiar hexadecimal notation from the - characters 0123456789abcdef. That is, binary 0000 gets represented by - the character '0', 0001, by '1', and so on up to the representation - of 1111 as 'f'. - -3.1.4 Limitations - - The Digest authentication scheme described in this document suffers - from many known limitations. It is intended as a replacement for - Basic authentication and nothing more. It is a password-based system - and (on the server side) suffers from all the same problems of any - password system. In particular, no provision is made in this protocol - for the initial secure arrangement between user and server to - establish the user's password. - - Users and implementors should be aware that this protocol is not as - secure as Kerberos, and not as secure as any client-side private-key - scheme. Nevertheless it is better than nothing, better than what is - commonly used with telnet and ftp, and better than Basic - authentication. - -3.2 Specification of Digest Headers - - The Digest Access Authentication scheme is conceptually similar to - the Basic scheme. The formats of the modified WWW-Authenticate header - line and the Authorization header line are specified below. In - addition, a new header, Authentication-Info, is specified. - - - - - - - - -Franks, et al. Standards Track [Page 7] - -RFC 2617 HTTP Authentication June 1999 - - -3.2.1 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 as - per the framework defined above, which for the digest scheme is - utilized as follows: - - challenge = "Digest" digest-challenge - - digest-challenge = 1#( realm | [ domain ] | nonce | - [ opaque ] |[ stale ] | [ algorithm ] | - [ qop-options ] | [auth-param] ) - - - domain = "domain" "=" <"> URI ( 1*SP URI ) <"> - [[ Should be: ]] - [[ domain = "domain" "=" <"> URI *( 1*SP URI ) <"> ]] - URI = absoluteURI | abs_path - nonce = "nonce" "=" nonce-value - nonce-value = quoted-string - opaque = "opaque" "=" quoted-string - stale = "stale" "=" ( "true" | "false" ) - algorithm = "algorithm" "=" ( "MD5" | "MD5-sess" | - token ) - qop-options = "qop" "=" <"> 1#qop-value <"> - qop-value = "auth" | "auth-int" | token - - The meanings of the values of the directives used above are as - follows: - - realm - A string to be displayed to users so they know which username and - password to use. This string should contain at least the name of - the host performing the authentication and might additionally - indicate the collection of users who might have access. An example - might be "registered_users@gotham.news.com". - - domain - A quoted, space-separated list of URIs, as specified in RFC XURI - [7], that define the protection space. If a URI is an abs_path, it - is relative to the canonical root URL (see section 1.2 above) of - the server being accessed. An absoluteURI in this list may refer to - a different server than the one being accessed. The client can use - this list to determine the set of URIs for which the same - authentication information may be sent: any URI that has a URI in - this list as a prefix (after both have been made absolute) may be - assumed to be in the same protection space. If this directive is - omitted or its value is empty, the client should assume that the - protection space consists of all URIs on the responding server. - - - -Franks, et al. Standards Track [Page 8] - -RFC 2617 HTTP Authentication June 1999 - - - This directive is not meaningful in Proxy-Authenticate headers, for - which the protection space is always the entire proxy; if present - it should be ignored. - - nonce - A server-specified data string which should be uniquely generated - each time a 401 response is made. It is recommended that this - string be base64 or hexadecimal data. Specifically, since the - string is passed in the header lines as a quoted string, the - double-quote character is not allowed. - - The contents of the nonce are implementation dependent. The quality - of the implementation depends on a good choice. A nonce might, for - example, be constructed as the base 64 encoding of - - time-stamp H(time-stamp ":" ETag ":" private-key) - - where time-stamp is a server-generated time or other non-repeating - value, ETag is the value of the HTTP ETag header associated with - the requested entity, and private-key is data known only to the - server. With a nonce of this form a server would recalculate the - hash portion after receiving the client authentication header and - reject the request if it did not match the nonce from that header - or if the time-stamp value is not recent enough. In this way the - server can limit the time of the nonce's validity. The inclusion of - the ETag prevents a replay request for an updated version of the - resource. (Note: including the IP address of the client in the - nonce would appear to offer the server the ability to limit the - reuse of the nonce to the same client that originally got it. - However, that would break proxy farms, where requests from a single - user often go through different proxies in the farm. Also, IP - address spoofing is not that hard.) - - An implementation might choose not to accept a previously used - nonce or a previously used digest, in order to protect against a - replay attack. Or, an implementation might choose to use one-time - nonces or digests for POST or PUT requests and a time-stamp for GET - requests. For more details on the issues involved see section 4. - of this document. - - The nonce is opaque to the client. - - opaque - A string of data, specified by the server, which should be returned - by the client unchanged in the Authorization header of subsequent - requests with URIs in the same protection space. It is recommended - that this string be base64 or hexadecimal data. - - - - -Franks, et al. Standards Track [Page 9] - -RFC 2617 HTTP Authentication June 1999 - - - stale - A flag, indicating that the previous request from the client was - rejected because the nonce value was stale. If stale is TRUE - (case-insensitive), the client may wish to simply retry the request - with a new encrypted response, without reprompting the user for a - new username and password. The server should only set stale to TRUE - if it receives a request for which the nonce is invalid but with a - valid digest for that nonce (indicating that the client knows the - correct username/password). If stale is FALSE, or anything other - than TRUE, or the stale directive is not present, the username - and/or password are invalid, and new values must be obtained. - - algorithm - A string indicating a pair of algorithms used to produce the digest - and a checksum. If this is not present it is assumed to be "MD5". - If the algorithm is not understood, the challenge should be ignored - (and a different one used, if there is more than one). - - In this document the string obtained by applying the digest - algorithm to the data "data" with secret "secret" will be denoted - by 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. - - For the "MD5" and "MD5-sess" algorithms - - H(data) = MD5(data) - - and - - KD(secret, data) = H(concat(secret, ":", data)) - - i.e., the digest is the MD5 of the secret concatenated with a colon - concatenated with the data. The "MD5-sess" algorithm is intended to - allow efficient 3rd party authentication servers; for the - difference in usage, see the description in section 3.2.2.2. - - qop-options - This directive is optional, but is made so only for backward - compatibility with RFC 2069 [6]; it SHOULD be used by all - implementations compliant with this version of the Digest scheme. - If present, it is a quoted string of one or more tokens indicating - the "quality of protection" values supported by the server. The - value "auth" indicates authentication; the value "auth-int" - indicates authentication with integrity protection; see the - - - - - -Franks, et al. Standards Track [Page 10] - -RFC 2617 HTTP Authentication June 1999 - - - descriptions below for calculating the response directive value for - the application of this choice. Unrecognized options MUST be - ignored. - - auth-param - This directive allows for future extensions. Any unrecognized - directive MUST be ignored. - -3.2.2 The Authorization Request Header - - The client is expected to retry the request, passing an Authorization - header line, which is defined according to the framework above, - utilized as follows. - - credentials = "Digest" digest-response - digest-response = 1#( username | realm | nonce | digest-uri - | response | [ algorithm ] | [cnonce] | - [opaque] | [message-qop] | - [nonce-count] | [auth-param] ) - - username = "username" "=" username-value - username-value = quoted-string - digest-uri = "uri" "=" digest-uri-value - digest-uri-value = request-uri ; As specified by HTTP/1.1 - message-qop = "qop" "=" qop-value - cnonce = "cnonce" "=" cnonce-value - cnonce-value = nonce-value - nonce-count = "nc" "=" nc-value - nc-value = 8LHEX - response = "response" "=" request-digest - request-digest = <"> 32LHEX <"> - LHEX = "0" | "1" | "2" | "3" | - "4" | "5" | "6" | "7" | - "8" | "9" | "a" | "b" | - "c" | "d" | "e" | "f" - - The values of the opaque and algorithm fields must be those supplied - in the WWW-Authenticate response header for the entity being - requested. - - response - A string of 32 hex digits computed as defined below, which proves - that the user knows a password - - username - The user's name in the specified realm. - - - - - -Franks, et al. Standards Track [Page 11] - -RFC 2617 HTTP Authentication June 1999 - - - digest-uri - The URI from Request-URI of the Request-Line; duplicated here - because proxies are allowed to change the Request-Line in transit. - - qop - Indicates what "quality of protection" the client has applied to - the message. If present, its value MUST be one of the alternatives - the server indicated it supports in the WWW-Authenticate header. - These values affect the computation of the request-digest. Note - that this is a single token, not a quoted list of alternatives as - in WWW- Authenticate. This directive is optional in order to - preserve backward compatibility with a minimal implementation of - RFC 2069 [6], but SHOULD be used if the server indicated that qop - is supported by providing a qop directive in the WWW-Authenticate - header field. - - cnonce - This MUST be specified if a qop directive is sent (see above), and - MUST NOT be specified if the server did not send a qop directive in - the WWW-Authenticate header field. The cnonce-value is an opaque - quoted string value provided by the client and used by both client - and server to avoid chosen plaintext attacks, to provide mutual - authentication, and to provide some message integrity protection. - See the descriptions below of the calculation of the response- - digest and request-digest values. - - nonce-count - This MUST be specified if a qop directive is sent (see above), and - MUST NOT be specified if the server did not send a qop directive in - the WWW-Authenticate header field. The nc-value is the hexadecimal - count of the number of requests (including the current request) - that the client has sent with the nonce value in this request. For - example, in the first request sent in response to a given nonce - value, the client sends "nc=00000001". The purpose of this - directive is to allow the server to detect request replays by - maintaining its own copy of this count - if the same nc-value is - seen twice, then the request is a replay. See the description - below of the construction of the request-digest value. - - auth-param - This directive allows for future extensions. Any unrecognized - directive MUST be ignored. - - If a directive or its value is improper, or required directives are - missing, the proper response is 400 Bad Request. If the request- - digest is invalid, then a login failure should be logged, since - repeated login failures from a single client may indicate an attacker - attempting to guess passwords. - - - -Franks, et al. Standards Track [Page 12] - -RFC 2617 HTTP Authentication June 1999 - - - The definition of request-digest above indicates the encoding for its - value. The following definitions show how the value is computed. - -3.2.2.1 Request-Digest - - If the "qop" value is "auth" or "auth-int": - - request-digest = <"> < KD ( H(A1), unq(nonce-value) - ":" nc-value - ":" unq(cnonce-value) - ":" unq(qop-value) - ":" H(A2) - ) <"> - - If the "qop" directive is not present (this construction is for - compatibility with RFC 2069): - - request-digest = - <"> < KD ( H(A1), unq(nonce-value) ":" H(A2) ) > - <"> - - See below for the definitions for A1 and A2. - -3.2.2.2 A1 - - If the "algorithm" directive's value is "MD5" or is unspecified, then - A1 is: - - A1 = unq(username-value) ":" unq(realm-value) ":" passwd - - where - - passwd = < user's password > - - If the "algorithm" directive's value is "MD5-sess", then A1 is - calculated only once - on the first request by the client following - receipt of a WWW-Authenticate challenge from the server. It uses the - server nonce from that challenge, and the first client nonce value to - construct A1 as follows: - - A1 = H( unq(username-value) ":" unq(realm-value) - ":" passwd ) - ":" unq(nonce-value) ":" unq(cnonce-value) - - This creates a 'session key' for the authentication of subsequent - requests and responses which is different for each "authentication - session", thus limiting the amount of material hashed with any one - key. (Note: see further discussion of the authentication session in - - - -Franks, et al. Standards Track [Page 13] - -RFC 2617 HTTP Authentication June 1999 - - - section 3.3.) Because the server need only use the hash of the user - credentials in order to create the A1 value, this construction could - be used in conjunction with a third party authentication service so - that the web server would not need the actual password value. The - specification of such a protocol is beyond the scope of this - specification. - -3.2.2.3 A2 - - If the "qop" directive's value is "auth" or is unspecified, then A2 - is: - - A2 = Method ":" digest-uri-value - - If the "qop" value is "auth-int", then A2 is: - - A2 = Method ":" digest-uri-value ":" H(entity-body) - -3.2.2.4 Directive values and quoted-string - - Note that the value of many of the directives, such as "username- - value", are defined as a "quoted-string". However, the "unq" notation - indicates that surrounding quotation marks are removed in forming the - string A1. Thus if the Authorization header includes the fields - - username="Mufasa", realm=myhost@testrealm.com - - and the user Mufasa has password "Circle Of Life" then H(A1) would be - H(Mufasa:myhost@testrealm.com:Circle Of Life) with no quotation marks - in the digested string. - - No white space is allowed in any of the strings to which the digest - function H() is applied unless that white space exists in the quoted - strings or entity body whose contents make up the string to be - digested. For example, the string A1 illustrated above must be - - Mufasa:myhost@testrealm.com:Circle Of Life - - with no white space on either side of the colons, but with the white - space between the words used in the password value. Likewise, the - other strings digested by H() must not have white space on either - side of the colons which delimit their fields unless that white space - was in the quoted strings or entity body being digested. - - Also note that if integrity protection is applied (qop=auth-int), the - H(entity-body) is the hash of the entity body, not the message body - - it is computed before any transfer encoding is applied by the sender - - - - -Franks, et al. Standards Track [Page 14] - -RFC 2617 HTTP Authentication June 1999 - - - and after it has been removed by the recipient. Note that this - includes multipart boundaries and embedded headers in each part of - any multipart content-type. - -3.2.2.5 Various considerations - - The "Method" value is the HTTP request method as specified in section - 5.1.1 of [2]. The "request-uri" value is the Request-URI from the - request line as specified in section 5.1.2 of [2]. This may be "*", - an "absoluteURL" or an "abs_path" as specified in section 5.1.2 of - [2], but it MUST agree with the Request-URI. In particular, it MUST - be an "absoluteURL" if the Request-URI is an "absoluteURL". The - "cnonce-value" is an optional client-chosen value whose purpose is - to foil chosen plaintext attacks. - - The authenticating server must assure that the resource designated by - the "uri" directive is the same as the resource specified in the - Request-Line; if they are not, the server SHOULD return a 400 Bad - Request error. (Since this may be a symptom of an attack, server - implementers may want to consider logging such errors.) The purpose - of duplicating information from the request URL in this field is to - deal with the possibility that an intermediate proxy may alter the - client's Request-Line. This altered (but presumably semantically - equivalent) request would not result in the same digest as that - calculated by the client. - - Implementers should be aware of how authenticated transactions - interact with shared caches. The HTTP/1.1 protocol specifies that - when a shared cache (see section 13.7 of [2]) has received a request - containing an Authorization header and a response from relaying that - request, it MUST NOT return that response as a reply to any other - request, unless one of two Cache-Control (see section 14.9 of [2]) - directives was present in the response. If the original response - included the "must-revalidate" Cache-Control directive, the cache MAY - use the entity of that response in replying to a subsequent request, - but MUST first revalidate it with the origin server, using the - request headers from the new request to allow the origin server to - authenticate the new request. Alternatively, if the original response - included the "public" Cache-Control directive, the response entity - MAY be returned in reply to any subsequent request. - -3.2.3 The Authentication-Info Header - - The Authentication-Info header is used by the server to communicate - some information regarding the successful authentication in the - response. - - - - - -Franks, et al. Standards Track [Page 15] - -RFC 2617 HTTP Authentication June 1999 - - - AuthenticationInfo = "Authentication-Info" ":" auth-info - auth-info = 1#(nextnonce | [ message-qop ] - | [ response-auth ] | [ cnonce ] - | [nonce-count] ) - nextnonce = "nextnonce" "=" nonce-value - response-auth = "rspauth" "=" response-digest - response-digest = <"> *LHEX <"> - - The value of the nextnonce directive is the nonce the server wishes - the client to use for a future authentication response. The server - may send the Authentication-Info header with a nextnonce field as a - means of implementing one-time or otherwise changing nonces. If the - nextnonce field is present the client SHOULD use it when constructing - the Authorization header for its next request. Failure of the client - to do so may result in a request to re-authenticate from the server - with the "stale=TRUE". - - Server implementations should carefully consider the performance - implications of the use of this mechanism; pipelined requests will - not be possible if every response includes a nextnonce directive - that must be used on the next request received by the server. - Consideration should be given to the performance vs. security - tradeoffs of allowing an old nonce value to be used for a limited - time to permit request pipelining. Use of the nonce-count can - retain most of the security advantages of a new server nonce - without the deleterious affects on pipelining. - - message-qop - Indicates the "quality of protection" options applied to the - response by the server. The value "auth" indicates authentication; - the value "auth-int" indicates authentication with integrity - protection. The server SHOULD use the same value for the message- - qop directive in the response as was sent by the client in the - corresponding request. - - The optional response digest in the "response-auth" directive - supports mutual authentication -- the server proves that it knows the - user's secret, and with qop=auth-int also provides limited integrity - protection of the response. The "response-digest" value is calculated - as for the "request-digest" in the Authorization header, except that - if "qop=auth" or is not specified in the Authorization header for the - request, A2 is - - A2 = ":" digest-uri-value - - and if "qop=auth-int", then A2 is - - A2 = ":" digest-uri-value ":" H(entity-body) - - - -Franks, et al. Standards Track [Page 16] - -RFC 2617 HTTP Authentication June 1999 - - - where "digest-uri-value" is the value of the "uri" directive on the - Authorization header in the request. The "cnonce-value" and "nc- - value" MUST be the ones for the client request to which this message - is the response. The "response-auth", "cnonce", and "nonce-count" - directives MUST BE present if "qop=auth" or "qop=auth-int" is - specified. - - The Authentication-Info header is allowed in the trailer of an HTTP - message transferred via chunked transfer-coding. - -3.3 Digest Operation - - Upon receiving the Authorization header, the server may check its - validity by looking up the password that corresponds to the submitted - username. Then, the server must perform the same digest operation - (e.g., MD5) performed by the client, and compare the result to the - given request-digest value. - - Note that the HTTP server does not actually need to know the user's - cleartext password. As long as H(A1) is available to the server, the - validity of an Authorization header may be verified. - - The client response to a WWW-Authenticate challenge for a protection - space starts an authentication session with that protection space. - The authentication session lasts until the client receives another - WWW-Authenticate challenge from any server in the protection space. A - client should remember the username, password, nonce, nonce count and - opaque values associated with an authentication session to use to - construct the Authorization header in future requests within that - protection space. The Authorization header may be included - preemptively; doing so improves server efficiency and avoids extra - round trips for authentication challenges. The server may choose to - accept the old Authorization header information, even though the - nonce value included might not be fresh. Alternatively, the server - may return a 401 response with a new nonce value, causing the client - to retry the request; by specifying stale=TRUE with this response, - the server tells the client to retry with the new nonce, but without - prompting for a new username and password. - - Because the client is required to return the value of the opaque - directive given to it by the server for the duration of a session, - the opaque data may be used to transport authentication session state - information. (Note that any such use can also be accomplished more - easily and safely by including the state in the nonce.) For example, - a server could be responsible for authenticating content that - actually sits on another server. It would achieve this by having the - first 401 response include a domain directive whose value includes a - URI on the second server, and an opaque directive whose value - - - -Franks, et al. Standards Track [Page 17] - -RFC 2617 HTTP Authentication June 1999 - - - contains the state information. The client will retry the request, at - which time the server might respond with a 301/302 redirection, - pointing to the URI on the second server. The client will follow the - redirection, and pass an Authorization header , including the - <opaque> data. - - As with the basic scheme, proxies must be completely transparent in - the Digest access authentication scheme. That is, they must forward - the WWW-Authenticate, Authentication-Info and Authorization headers - untouched. If a proxy wants to authenticate a client before a request - is forwarded to the server, it can be done using the Proxy- - Authenticate and Proxy-Authorization headers described in section 3.6 - below. - -3.4 Security Protocol Negotiation - - It is useful for a server to be able to know which security schemes a - client is capable of handling. - - It is possible that a server may want to require Digest as its - authentication method, even if the server does not know that the - client supports it. A client is encouraged to fail gracefully if the - server specifies only authentication schemes it cannot handle. - -3.5 Example - - The following example 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", - nonce="dcd98b7102dd2f0e8b11d0f600bfb0c093", - opaque="5ccc069c403ebaf9f0171e9517f40e41" - - The client may prompt the user for the username and password, after - which it will respond with a new request, including the following - Authorization header: - - - - - -Franks, et al. Standards Track [Page 18] - -RFC 2617 HTTP Authentication June 1999 - - - Authorization: Digest username="Mufasa", - realm="testrealm@host.com", - nonce="dcd98b7102dd2f0e8b11d0f600bfb0c093", - uri="/dir/index.html", - qop=auth, - nc=00000001, - cnonce="0a4f113b", - response="6629fae49393a05397450978507c4ef1", - opaque="5ccc069c403ebaf9f0171e9517f40e41" - -3.6 Proxy-Authentication and Proxy-Authorization - - The digest authentication scheme may also be used for authenticating - users to proxies, proxies to proxies, or proxies to origin servers by - use of the Proxy-Authenticate and Proxy-Authorization headers. These - headers are instances of the Proxy-Authenticate and Proxy- - Authorization headers specified in sections 10.33 and 10.34 of the - HTTP/1.1 specification [2] and their behavior is subject to - restrictions described there. The transactions for proxy - authentication are very similar to those already described. Upon - receiving a request which requires authentication, the proxy/server - must issue the "407 Proxy Authentication Required" response with a - "Proxy-Authenticate" header. The digest-challenge used in the - Proxy-Authenticate header is the same as that for the WWW- - Authenticate header as defined above in section 3.2.1. - - The client/proxy must then re-issue the request with a Proxy- - Authorization header, with directives as specified for the - Authorization header in section 3.2.2 above. - - On subsequent responses, the server sends Proxy-Authentication-Info - with directives the same as those for the Authentication-Info header - field. - - Note that in principle a client could be asked to authenticate itself - to both a proxy and an end-server, but never in the same response. - -4 Security Considerations - -4.1 Authentication of Clients using Basic Authentication - - The Basic authentication scheme is not a secure method of user - authentication, nor does it in any way protect the entity, which is - transmitted in cleartext across the physical network used as the - carrier. HTTP does not prevent additional authentication schemes and - encryption mechanisms from being employed to increase security or the - addition of enhancements (such as schemes to use one-time passwords) - to Basic authentication. - - - -Franks, et al. Standards Track [Page 19] - -RFC 2617 HTTP Authentication June 1999 - - - The most serious flaw in Basic authentication is that it results in - the essentially cleartext transmission of the user's password over - the physical network. It is this problem which Digest Authentication - attempts to address. - - Because Basic authentication involves the cleartext transmission of - passwords it SHOULD NOT be used (without enhancements) to protect - sensitive or valuable information. - - A common use of Basic authentication is for identification purposes - -- requiring the user to provide a user name and password as a means - of identification, for example, for purposes of gathering accurate - usage statistics on a server. When used in this way it is tempting to - think that there is no danger in its use if illicit access to the - protected documents is not a major concern. This is only correct if - the server issues both user name and password to the users and in - particular does not allow the user to choose his or her own password. - The danger arises because naive users frequently reuse a single - password to avoid the task of maintaining multiple passwords. - - If a server permits users to select their own passwords, then the - threat is not only unauthorized access to documents on the server but - also unauthorized access to any other resources on other systems that - the user protects with the same password. Furthermore, in the - server's password database, many of the passwords may also be users' - passwords for other sites. The owner or administrator of such a - system could therefore expose all users of the system to the risk of - unauthorized access to all those sites if this information is not - maintained in a secure fashion. - - Basic Authentication is also vulnerable to spoofing by counterfeit - servers. If a user can be led to believe that he is connecting to a - host containing information protected by Basic authentication when, - in fact, he is connecting to a hostile server or gateway, then the - attacker can request a password, store it for later use, and feign an - error. This type of attack is not possible with Digest - Authentication. Server implementers SHOULD guard against the - possibility of this sort of counterfeiting by gateways or CGI - scripts. In particular it is very dangerous for a server to simply - turn over a connection to a gateway. That gateway can then use the - persistent connection mechanism to engage in multiple transactions - with the client while impersonating the original server in a way that - is not detectable by the client. - -4.2 Authentication of Clients using Digest Authentication - - Digest Authentication does not provide a strong authentication - mechanism, when compared to public key based mechanisms, for example. - - - -Franks, et al. Standards Track [Page 20] - -RFC 2617 HTTP Authentication June 1999 - - - However, it is significantly stronger than (e.g.) CRAM-MD5, which has - been proposed for use with LDAP [10], POP and IMAP (see RFC 2195 - [9]). It is intended to replace the much weaker and even more - dangerous Basic mechanism. - - Digest Authentication offers no confidentiality protection beyond - protecting the actual password. All of the rest of the request and - response are available to an eavesdropper. - - Digest Authentication offers only limited integrity protection for - the messages in either direction. If qop=auth-int mechanism is used, - those parts of the message used in the calculation of the WWW- - Authenticate and Authorization header field response directive values - (see section 3.2 above) are protected. Most header fields and their - values could be modified as a part of a man-in-the-middle attack. - - Many needs for secure HTTP transactions cannot be met by Digest - Authentication. For those needs TLS or SHTTP are more appropriate - protocols. In particular Digest authentication cannot be used for any - transaction requiring confidentiality protection. Nevertheless many - functions remain for which Digest authentication is both useful and - appropriate. Any service in present use that uses Basic should be - switched to Digest as soon as practical. - -4.3 Limited Use Nonce Values - - The Digest scheme uses a server-specified nonce to seed the - generation of the request-digest value (as specified in section - 3.2.2.1 above). As shown in the example nonce in section 3.2.1, the - server is free to construct the nonce such that it may only be used - from a particular client, for a particular resource, for a limited - period of time or number of uses, or any other restrictions. Doing - so strengthens the protection provided against, for example, replay - attacks (see 4.5). However, it should be noted that the method - chosen for generating and checking the nonce also has performance and - resource implications. For example, a server may choose to allow - each nonce value to be used only once by maintaining a record of - whether or not each recently issued nonce has been returned and - sending a next-nonce directive in the Authentication-Info header - field of every response. This protects against even an immediate - replay attack, but has a high cost checking nonce values, and perhaps - more important will cause authentication failures for any pipelined - requests (presumably returning a stale nonce indication). Similarly, - incorporating a request-specific element such as the Etag value for a - resource limits the use of the nonce to that version of the resource - and also defeats pipelining. Thus it may be useful to do so for - methods with side effects but have unacceptable performance for those - that do not. - - - -Franks, et al. Standards Track [Page 21] - -RFC 2617 HTTP Authentication June 1999 - - -4.4 Comparison of Digest with Basic Authentication - - Both Digest and Basic Authentication are very much on the weak end of - the security strength spectrum. But a comparison between the two - points out the utility, even necessity, of replacing Basic by Digest. - - The greatest threat to the type of transactions for which these - protocols are used is network snooping. This kind of transaction - might involve, for example, online access to a database whose use is - restricted to paying subscribers. With Basic authentication an - eavesdropper can obtain the password of the user. This not only - permits him to access anything in the database, but, often worse, - will permit access to anything else the user protects with the same - password. - - By contrast, with Digest Authentication the eavesdropper only gets - access to the transaction in question and not to the user's password. - The information gained by the eavesdropper would permit a replay - attack, but only with a request for the same document, and even that - may be limited by the server's choice of nonce. - -4.5 Replay Attacks - - A replay attack against Digest authentication would usually be - pointless for a simple GET request since an eavesdropper would - already have seen the only document he could obtain with a replay. - This is because the URI of the requested document is digested in the - client request and the server will only deliver that document. By - contrast under Basic Authentication once the eavesdropper has the - user's password, any document protected by that password is open to - him. - - Thus, for some purposes, it is necessary to protect against replay - attacks. A good Digest implementation can do this in various ways. - The server created "nonce" value is implementation dependent, but if - it contains a digest of the client IP, a time-stamp, the resource - ETag, and a private server key (as recommended above) then a replay - attack is not simple. An attacker must convince the server that the - request is coming from a false IP address and must cause the server - to deliver the document to an IP address different from the address - to which it believes it is sending the document. An attack can only - succeed in the period before the time-stamp expires. Digesting the - client IP and time-stamp in the nonce permits an implementation which - does not maintain state between transactions. - - For applications where no possibility of replay attack can be - tolerated the server can use one-time nonce values which will not be - honored for a second use. This requires the overhead of the server - - - -Franks, et al. Standards Track [Page 22] - -RFC 2617 HTTP Authentication June 1999 - - - remembering which nonce values have been used until the nonce time- - stamp (and hence the digest built with it) has expired, but it - effectively protects against replay attacks. - - An implementation must give special attention to the possibility of - replay attacks with POST and PUT requests. Unless the server employs - one-time or otherwise limited-use nonces and/or insists on the use of - the integrity protection of qop=auth-int, an attacker could replay - valid credentials from a successful request with counterfeit form - data or other message body. Even with the use of integrity protection - most metadata in header fields is not protected. Proper nonce - generation and checking provides some protection against replay of - previously used valid credentials, but see 4.8. - -4.6 Weakness Created by Multiple Authentication Schemes - - An HTTP/1.1 server may return multiple challenges with a 401 - (Authenticate) response, and each challenge may use a different - auth-scheme. A user agent MUST choose to use the strongest auth- - scheme it understands and request credentials from the user based - upon that challenge. - - Note that many browsers will only recognize Basic and will require - that it be the first auth-scheme presented. Servers should only - include Basic if it is minimally acceptable. - - When the server offers choices of authentication schemes using the - WWW-Authenticate header, the strength of the resulting authentication - is only as good as that of the of the weakest of the authentication - schemes. See section 4.8 below for discussion of particular attack - scenarios that exploit multiple authentication schemes. - -4.7 Online dictionary attacks - - If the attacker can eavesdrop, then it can test any overheard - nonce/response pairs against a list of common words. Such a list is - usually much smaller than the total number of possible passwords. The - cost of computing the response for each password on the list is paid - once for each challenge. - - The server can mitigate this attack by not allowing users to select - passwords that are in a dictionary. - - - - - - - - - -Franks, et al. Standards Track [Page 23] - -RFC 2617 HTTP Authentication June 1999 - - -4.8 Man in the Middle - - Both Basic and Digest authentication are vulnerable to "man in the - middle" (MITM) attacks, for example, from a hostile or compromised - proxy. Clearly, this would present all the problems of eavesdropping. - But it also offers some additional opportunities to the attacker. - - A possible man-in-the-middle attack would be to add a weak - authentication scheme to the set of choices, hoping that the client - will use one that exposes the user's credentials (e.g. password). For - this reason, the client should always use the strongest scheme that - it understands from the choices offered. - - An even better MITM attack would be to remove all offered choices, - replacing them with a challenge that requests only Basic - authentication, then uses the cleartext credentials from the Basic - authentication to authenticate to the origin server using the - stronger scheme it requested. A particularly insidious way to mount - such a MITM attack would be to offer a "free" proxy caching service - to gullible users. - - User agents should consider measures such as presenting a visual - indication at the time of the credentials request of what - authentication scheme is to be used, or remembering the strongest - authentication scheme ever requested by a server and produce a - warning message before using a weaker one. It might also be a good - idea for the user agent to be configured to demand Digest - authentication in general, or from specific sites. - - Or, a hostile proxy might spoof the client into making a request the - attacker wanted rather than one the client wanted. Of course, this is - still much harder than a comparable attack against Basic - Authentication. - -4.9 Chosen plaintext attacks - - With Digest authentication, a MITM or a malicious server can - arbitrarily choose the nonce that the client will use to compute the - response. This is called a "chosen plaintext" attack. The ability to - choose the nonce is known to make cryptanalysis much easier [8]. - - However, no way to analyze the MD5 one-way function used by Digest - using chosen plaintext is currently known. - - The countermeasure against this attack is for clients to be - configured to require the use of the optional "cnonce" directive; - this allows the client to vary the input to the hash in a way not - chosen by the attacker. - - - -Franks, et al. Standards Track [Page 24] - -RFC 2617 HTTP Authentication June 1999 - - -4.10 Precomputed dictionary attacks - - With Digest authentication, if the attacker can execute a chosen - plaintext attack, the attacker can precompute the response for many - common words to a nonce of its choice, and store a dictionary of - (response, password) pairs. Such precomputation can often be done in - parallel on many machines. It can then use the chosen plaintext - attack to acquire a response corresponding to that challenge, and - just look up the password in the dictionary. Even if most passwords - are not in the dictionary, some might be. Since the attacker gets to - pick the challenge, the cost of computing the response for each - password on the list can be amortized over finding many passwords. A - dictionary with 100 million password/response pairs would take about - 3.2 gigabytes of disk storage. - - The countermeasure against this attack is to for clients to be - configured to require the use of the optional "cnonce" directive. - -4.11 Batch brute force attacks - - With Digest authentication, a MITM can execute a chosen plaintext - attack, and can gather responses from many users to the same nonce. - It can then find all the passwords within any subset of password - space that would generate one of the nonce/response pairs in a single - pass over that space. It also reduces the time to find the first - password by a factor equal to the number of nonce/response pairs - gathered. This search of the password space can often be done in - parallel on many machines, and even a single machine can search large - subsets of the password space very quickly -- reports exist of - searching all passwords with six or fewer letters in a few hours. - - The countermeasure against this attack is to for clients to be - configured to require the use of the optional "cnonce" directive. - -4.12 Spoofing by Counterfeit Servers - - Basic Authentication is vulnerable to spoofing by counterfeit - servers. If a user can be led to believe that she is connecting to a - host containing information protected by a password she knows, when - in fact she is connecting to a hostile server, then the hostile - server can request a password, store it away for later use, and feign - an error. This type of attack is more difficult with Digest - Authentication -- but the client must know to demand that Digest - authentication be used, perhaps using some of the techniques - described above to counter "man-in-the-middle" attacks. Again, the - user can be helped in detecting this attack by a visual indication of - the authentication mechanism in use with appropriate guidance in - interpreting the implications of each scheme. - - - -Franks, et al. Standards Track [Page 25] - -RFC 2617 HTTP Authentication June 1999 - - -4.13 Storing passwords - - Digest authentication requires that the authenticating agent (usually - the server) store some data derived from the user's name and password - in a "password file" associated with a given realm. Normally this - might contain pairs consisting of username and H(A1), where H(A1) is - the digested value of the username, realm, and password as described - above. - - The security implications of this are that if this password file is - compromised, then an attacker gains immediate access to documents on - the server using this realm. Unlike, say a standard UNIX password - file, this information need not be decrypted in order to access - documents in the server realm associated with this file. On the other - hand, decryption, or more likely a brute force attack, would be - necessary to obtain the user's password. This is the reason that the - realm is part of the digested data stored in the password file. It - means that if one Digest authentication password file is compromised, - it does not automatically compromise others with the same username - and password (though it does expose them to brute force attack). - - There are two important security consequences of this. First the - password file must be protected as if it contained unencrypted - passwords, because for the purpose of accessing documents in its - realm, it effectively does. - - A second consequence of this is that the realm string should be - unique among all realms which any single user is likely to use. In - particular a realm string should include the name of the host doing - the authentication. The inability of the client to authenticate the - server is a weakness of Digest Authentication. - -4.14 Summary - - By modern cryptographic standards Digest Authentication is weak. But - for a large range of purposes it is valuable as a replacement for - Basic Authentication. It remedies some, but not all, weaknesses of - Basic Authentication. Its strength may vary depending on the - implementation. In particular the structure of the nonce (which is - dependent on the server implementation) may affect the ease of - mounting a replay attack. A range of server options is appropriate - since, for example, some implementations may be willing to accept the - server overhead of one-time nonces or digests to eliminate the - possibility of replay. Others may satisfied with a nonce like the one - recommended above restricted to a single IP address and a single ETag - or with a limited lifetime. - - - - - -Franks, et al. Standards Track [Page 26] - -RFC 2617 HTTP Authentication June 1999 - - - The bottom line is that *any* compliant implementation will be - relatively weak by cryptographic standards, but *any* compliant - implementation will be far superior to Basic Authentication. - -5 Sample implementation - - [[ WARNING: DigestCalcHA1 IS WRONG ]] - - The following code implements the calculations of H(A1), H(A2), - request-digest and response-digest, and a test program which computes - the values used in the example of section 3.5. It uses the MD5 - implementation from RFC 1321. - - File "digcalc.h": - -#define HASHLEN 16 -typedef char HASH[HASHLEN]; -#define HASHHEXLEN 32 -typedef char HASHHEX[HASHHEXLEN+1]; -#define IN -#define OUT - -/* calculate H(A1) as per HTTP Digest spec */ -void DigestCalcHA1( - IN char * pszAlg, - IN char * pszUserName, - IN char * pszRealm, - IN char * pszPassword, - IN char * pszNonce, - IN char * pszCNonce, - OUT HASHHEX SessionKey - ); - -/* calculate request-digest/response-digest as per HTTP Digest spec */ -void DigestCalcResponse( - IN HASHHEX HA1, /* H(A1) */ - IN char * pszNonce, /* nonce from server */ - IN char * pszNonceCount, /* 8 hex digits */ - IN char * pszCNonce, /* client nonce */ - IN char * pszQop, /* qop-value: "", "auth", "auth-int" */ - IN char * pszMethod, /* method from the request */ - IN char * pszDigestUri, /* requested URL */ - IN HASHHEX HEntity, /* H(entity body) if qop="auth-int" */ - OUT HASHHEX Response /* request-digest or response-digest */ - ); - -File "digcalc.c": - -#include <global.h> -#include <md5.h> - - - -Franks, et al. Standards Track [Page 27] - -RFC 2617 HTTP Authentication June 1999 - - -#include <string.h> -#include "digcalc.h" - -void CvtHex( - IN HASH Bin, - OUT HASHHEX Hex - ) -{ - unsigned short i; - unsigned char j; - - for (i = 0; i < HASHLEN; i++) { - j = (Bin[i] >> 4) & 0xf; - if (j <= 9) - Hex[i*2] = (j + '0'); - else - Hex[i*2] = (j + 'a' - 10); - j = Bin[i] & 0xf; - if (j <= 9) - Hex[i*2+1] = (j + '0'); - else - Hex[i*2+1] = (j + 'a' - 10); - }; - Hex[HASHHEXLEN] = '\0'; -}; - -/* calculate H(A1) as per spec */ -void DigestCalcHA1( - IN char * pszAlg, - IN char * pszUserName, - IN char * pszRealm, - IN char * pszPassword, - IN char * pszNonce, - IN char * pszCNonce, - OUT HASHHEX SessionKey - ) -{ - MD5_CTX Md5Ctx; - HASH HA1; - - MD5Init(&Md5Ctx); - MD5Update(&Md5Ctx, pszUserName, strlen(pszUserName)); - MD5Update(&Md5Ctx, ":", 1); - MD5Update(&Md5Ctx, pszRealm, strlen(pszRealm)); - MD5Update(&Md5Ctx, ":", 1); - MD5Update(&Md5Ctx, pszPassword, strlen(pszPassword)); - MD5Final(HA1, &Md5Ctx); - if (stricmp(pszAlg, "md5-sess") == 0) { - - - -Franks, et al. Standards Track [Page 28] - -RFC 2617 HTTP Authentication June 1999 - - - MD5Init(&Md5Ctx); - MD5Update(&Md5Ctx, HA1, HASHLEN); - MD5Update(&Md5Ctx, ":", 1); - MD5Update(&Md5Ctx, pszNonce, strlen(pszNonce)); - MD5Update(&Md5Ctx, ":", 1); - MD5Update(&Md5Ctx, pszCNonce, strlen(pszCNonce)); - MD5Final(HA1, &Md5Ctx); - }; - CvtHex(HA1, SessionKey); -}; - -/* calculate request-digest/response-digest as per HTTP Digest spec */ -void DigestCalcResponse( - IN HASHHEX HA1, /* H(A1) */ - IN char * pszNonce, /* nonce from server */ - IN char * pszNonceCount, /* 8 hex digits */ - IN char * pszCNonce, /* client nonce */ - IN char * pszQop, /* qop-value: "", "auth", "auth-int" */ - IN char * pszMethod, /* method from the request */ - IN char * pszDigestUri, /* requested URL */ - IN HASHHEX HEntity, /* H(entity body) if qop="auth-int" */ - OUT HASHHEX Response /* request-digest or response-digest */ - ) -{ - MD5_CTX Md5Ctx; - HASH HA2; - HASH RespHash; - HASHHEX HA2Hex; - - // calculate H(A2) - MD5Init(&Md5Ctx); - MD5Update(&Md5Ctx, pszMethod, strlen(pszMethod)); - MD5Update(&Md5Ctx, ":", 1); - MD5Update(&Md5Ctx, pszDigestUri, strlen(pszDigestUri)); - if (stricmp(pszQop, "auth-int") == 0) { - MD5Update(&Md5Ctx, ":", 1); - MD5Update(&Md5Ctx, HEntity, HASHHEXLEN); - }; - MD5Final(HA2, &Md5Ctx); - CvtHex(HA2, HA2Hex); - - // calculate response - MD5Init(&Md5Ctx); - MD5Update(&Md5Ctx, HA1, HASHHEXLEN); - MD5Update(&Md5Ctx, ":", 1); - MD5Update(&Md5Ctx, pszNonce, strlen(pszNonce)); - MD5Update(&Md5Ctx, ":", 1); - if (*pszQop) { - - - -Franks, et al. Standards Track [Page 29] - -RFC 2617 HTTP Authentication June 1999 - - - MD5Update(&Md5Ctx, pszNonceCount, strlen(pszNonceCount)); - MD5Update(&Md5Ctx, ":", 1); - MD5Update(&Md5Ctx, pszCNonce, strlen(pszCNonce)); - MD5Update(&Md5Ctx, ":", 1); - MD5Update(&Md5Ctx, pszQop, strlen(pszQop)); - MD5Update(&Md5Ctx, ":", 1); - }; - MD5Update(&Md5Ctx, HA2Hex, HASHHEXLEN); - MD5Final(RespHash, &Md5Ctx); - CvtHex(RespHash, Response); -}; - -File "digtest.c": - - -#include <stdio.h> -#include "digcalc.h" - -void main(int argc, char ** argv) { - - char * pszNonce = "dcd98b7102dd2f0e8b11d0f600bfb0c093"; - char * pszCNonce = "0a4f113b"; - char * pszUser = "Mufasa"; - char * pszRealm = "testrealm@host.com"; - char * pszPass = "Circle Of Life"; - char * pszAlg = "md5"; - char szNonceCount[9] = "00000001"; - char * pszMethod = "GET"; - char * pszQop = "auth"; - char * pszURI = "/dir/index.html"; - HASHHEX HA1; - HASHHEX HA2 = ""; - HASHHEX Response; - - DigestCalcHA1(pszAlg, pszUser, pszRealm, pszPass, pszNonce, -pszCNonce, HA1); - DigestCalcResponse(HA1, pszNonce, szNonceCount, pszCNonce, pszQop, - pszMethod, pszURI, HA2, Response); - printf("Response = %s\n", Response); -}; - - - - - - - - - - - -Franks, et al. Standards Track [Page 30] - -RFC 2617 HTTP Authentication June 1999 - - -6 Acknowledgments - - Eric W. Sink, of AbiSource, Inc., was one of the original authors - before the specification underwent substantial revision. - - In addition to the authors, valuable discussion instrumental in - creating this document has come from Peter J. Churchyard, Ned Freed, - and David M. Kristol. - - Jim Gettys and Larry Masinter edited this document for update. - -7 References - - [1] Berners-Lee, T., Fielding, R. and H. Frystyk, "Hypertext - Transfer Protocol -- HTTP/1.0", RFC 1945, May 1996. - - [2] Fielding, R., Gettys, J., Mogul, J., Frysyk, H., Masinter, L., - Leach, P. and T. Berners-Lee, "Hypertext Transfer Protocol -- - HTTP/1.1", RFC 2616, June 1999. - - [3] Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321, April - 1992. - - [4] Freed, N. and N. Borenstein. "Multipurpose Internet Mail - Extensions (MIME) Part One: Format of Internet Message Bodies", - RFC 2045, November 1996. - - [5] Dierks, T. and C. Allen "The TLS Protocol, Version 1.0", RFC - 2246, January 1999. - - [6] Franks, J., Hallam-Baker, P., Hostetler, J., Leach, P., - Luotonen, A., Sink, E. and L. Stewart, "An Extension to HTTP : - Digest Access Authentication", RFC 2069, January 1997. - - [7] Berners Lee, T, Fielding, R. and L. Masinter, "Uniform Resource - Identifiers (URI): Generic Syntax", RFC 2396, August 1998. - - [8] Kaliski, B.,Robshaw, M., "Message Authentication with MD5", - CryptoBytes, Sping 1995, RSA Inc, - (http://www.rsa.com/rsalabs/pubs/cryptobytes/spring95/md5.htm) - - [9] Klensin, J., Catoe, R. and P. Krumviede, "IMAP/POP AUTHorize - Extension for Simple Challenge/Response", RFC 2195, September - 1997. - - [10] Morgan, B., Alvestrand, H., Hodges, J., Wahl, M., - "Authentication Methods for LDAP", Work in Progress. - - - - -Franks, et al. Standards Track [Page 31] - -RFC 2617 HTTP Authentication June 1999 - - -8 Authors' Addresses - - John Franks - Professor of Mathematics - Department of Mathematics - Northwestern University - Evanston, IL 60208-2730, USA - - EMail: john@math.nwu.edu - - - Phillip M. Hallam-Baker - Principal Consultant - Verisign Inc. - 301 Edgewater Place - Suite 210 - Wakefield MA 01880, USA - - EMail: pbaker@verisign.com - - - Jeffery L. Hostetler - Software Craftsman - AbiSource, Inc. - 6 Dunlap Court - Savoy, IL 61874 - - EMail: jeff@AbiSource.com - - - Scott D. Lawrence - Agranat Systems, Inc. - 5 Clocktower Place, Suite 400 - Maynard, MA 01754, USA - - EMail: lawrence@agranat.com - - - Paul J. Leach - Microsoft Corporation - 1 Microsoft Way - Redmond, WA 98052, USA - - EMail: paulle@microsoft.com - - - - - - - -Franks, et al. Standards Track [Page 32] - -RFC 2617 HTTP Authentication June 1999 - - - Ari Luotonen - Member of Technical Staff - Netscape Communications Corporation - 501 East Middlefield Road - Mountain View, CA 94043, USA - - - Lawrence C. Stewart - Open Market, Inc. - 215 First Street - Cambridge, MA 02142, USA - - EMail: stewart@OpenMarket.com - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -Franks, et al. Standards Track [Page 33] - -RFC 2617 HTTP Authentication June 1999 - - -9. Full Copyright Statement - - Copyright (C) The Internet Society (1999). All Rights Reserved. - - This document and translations of it may be copied and furnished to - others, and derivative works that comment on or otherwise explain it - or assist in its implementation may be prepared, copied, published - and distributed, in whole or in part, without restriction of any - kind, provided that the above copyright notice and this paragraph are - included on all such copies and derivative works. However, this - document itself may not be modified in any way, such as by removing - the copyright notice or references to the Internet Society or other - Internet organizations, except as needed for the purpose of - developing Internet standards in which case the procedures for - copyrights defined in the Internet Standards process must be - followed, or as required to translate it into languages other than - English. - - The limited permissions granted above are perpetual and will not be - revoked by the Internet Society or its successors or assigns. - - This document and the information contained herein is provided on an - "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING - TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING - BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION - HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF - MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. - -Acknowledgement - - Funding for the RFC Editor function is currently provided by the - Internet Society. - - - - - - - - - - - - - - - - - - - -Franks, et al. Standards Track [Page 34] - |