Internet Engineering Task Force Y. Oiwa
Internet-Draft H. Watanabe
Intended status: Standards Track H. Takagi
Expires: January 6, 2012 RCIS, AIST
Y. Ioku
Yahoo! Japan
T. Hayashi
Lepidum
July 5, 2011
Mutual Authentication Protocol for HTTP
draft-oiwa-http-mutualauth-09
Abstract
This document specifies a mutual authentication method for the Hyper-
text Transport Protocol (HTTP). This method provides a true mutual
authentication between an HTTP client and an HTTP server using
password-based authentication. Unlike the Basic and Digest
authentication methods, the Mutual authentication method specified in
this document assures the user that the server truly knows the user's
encrypted password. This prevents common phishing attacks: a
phishing attacker controlling a fake website cannot convince a user
that he authenticated to the genuine website. Furthermore, even when
a user authenticates to an illegitimate server, the server cannot
gain any information about the user's password. The Mutual
authentication method is designed as an extension to the HTTP
protocol, and is intended to replace the existing authentication
methods used in HTTP (the Basic method, Digest method, and
authentication using HTML forms).
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on January 6, 2012.
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Copyright Notice
Copyright (c) 2011 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 5
1.2. Document Structure Overview . . . . . . . . . . . . . . . 6
2. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 6
2.1. Messages . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.2. Typical Flows of the protocol . . . . . . . . . . . . . . 7
2.3. Alternative flows . . . . . . . . . . . . . . . . . . . . 10
3. Message Syntax . . . . . . . . . . . . . . . . . . . . . . . . 11
3.1. Tokens and Extensive-tokens . . . . . . . . . . . . . . . 12
3.2. Numbers . . . . . . . . . . . . . . . . . . . . . . . . . 12
3.3. Strings . . . . . . . . . . . . . . . . . . . . . . . . . 13
4. Messages . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
4.1. 401-INIT . . . . . . . . . . . . . . . . . . . . . . . . . 14
4.2. 401-STALE . . . . . . . . . . . . . . . . . . . . . . . . 16
4.3. req-KEX-C1 . . . . . . . . . . . . . . . . . . . . . . . . 16
4.4. 401-KEX-S1 . . . . . . . . . . . . . . . . . . . . . . . . 17
4.5. req-VFY-C . . . . . . . . . . . . . . . . . . . . . . . . 18
4.6. 200-VFY-S . . . . . . . . . . . . . . . . . . . . . . . . 19
4.7. 200-Optional-INIT . . . . . . . . . . . . . . . . . . . . 20
5. Authentication Realms . . . . . . . . . . . . . . . . . . . . 21
5.1. Resolving ambiguities . . . . . . . . . . . . . . . . . . 23
6. Session Management . . . . . . . . . . . . . . . . . . . . . . 23
7. Validation Methods . . . . . . . . . . . . . . . . . . . . . . 25
8. Decision procedure for client . . . . . . . . . . . . . . . . 27
9. Decision procedure for the server . . . . . . . . . . . . . . 32
10. Authentication-Control header . . . . . . . . . . . . . . . . 34
10.1. Location-when-unauthenticated field . . . . . . . . . . . 35
10.2. Location-when-logout field . . . . . . . . . . . . . . . . 35
10.3. Logout-timeout . . . . . . . . . . . . . . . . . . . . . . 36
11. Authentication Algorithms . . . . . . . . . . . . . . . . . . 36
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11.1. Support functions and notations . . . . . . . . . . . . . 37
11.2. Default functions for algorithms . . . . . . . . . . . . . 38
12. Methods to extend this protocol . . . . . . . . . . . . . . . 38
13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 39
14. Security Considerations . . . . . . . . . . . . . . . . . . . 39
14.1. Security Properties . . . . . . . . . . . . . . . . . . . 39
14.2. Denial-of-service attacks to servers . . . . . . . . . . . 39
14.3. Implementation Considerations . . . . . . . . . . . . . . 40
14.4. Usage Considerations . . . . . . . . . . . . . . . . . . . 41
15. Notice on intellectual properties . . . . . . . . . . . . . . 41
16. References . . . . . . . . . . . . . . . . . . . . . . . . . . 42
16.1. Normative References . . . . . . . . . . . . . . . . . . . 42
16.2. Informative References . . . . . . . . . . . . . . . . . . 42
Appendix A. (Informative) Generic syntax of headers . . . . . . . 43
Appendix B. (Informative) Draft Remarks from Authors . . . . . . 45
Appendix C. (Informative) Draft Change Log . . . . . . . . . . . 46
C.1. Changes in revision 09 . . . . . . . . . . . . . . . . . . 46
C.2. Changes in revision 08 . . . . . . . . . . . . . . . . . . 46
C.3. Changes in revision 07 . . . . . . . . . . . . . . . . . . 46
C.4. Changes in revision 06 . . . . . . . . . . . . . . . . . . 47
C.5. Changes in revision 05 . . . . . . . . . . . . . . . . . . 47
C.6. Changes in revision 04 . . . . . . . . . . . . . . . . . . 47
C.7. Changes in revision 03 . . . . . . . . . . . . . . . . . . 47
C.8. Changes in revision 02 . . . . . . . . . . . . . . . . . . 48
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 48
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1. Introduction
This document specifies a mutual authentication method for Hyper-Text
Transport Protocol (HTTP). The method, called "Mutual Authentication
Protocol" in this document, provides a true mutual authentication
between an HTTP client and an HTTP server, using just a simple
password as a credential.
The currently available methods for authentication in HTTP and Web
systems have several deficiencies. The Basic authentication method
[RFC2617] sends a plaintext password to a server without any
protection; the Digest method uses a hash function that suffers from
simple dictionary-based off-line attacks, and people have begun to
think it is obsolete.
The authentication method proposed in this document solves these
problems, substitutes for these existing methods, and serves as a
long-term solution to Web authentication security. It has the
following main characteristics:
o It provides "true" mutual authentication: in addition to assuring
the server that the user knows the password, it also assures the
user that the server truly knows the user's encrypted password at
the same time. It makes it impossible for fake website owners to
persuade users that thee authenticated with the original websites.
o It uses only passwords as the user's credential: unlike public-
key-based security algorithms, the method does not rely on secret
keys or other cryptographic data that have to be stored inside the
users' computers. The proposed method can be used as a drop-in
replacement to the current authentication methods like Basic or
Digest, while ensuring a much stronger level of security.
o It is secure: when the server fails to authenticate with a user,
the protocol will not reveal any bit of the user's password.
Users can discriminate between true and fake Web servers using their
own passwords by using the proposed method. Even when a user inputs
his/her password to a fake website owned by illegitimate phishers,
the user will certainly notice that the authentication has failed.
Phishers will not be successful in their authentication attempts,
even if they forward the received data from a user to a legitimate
server or vice versa. Users can input sensitive data to the web
forms after confirming that the mutual authentication has succeeded,
without fear of phishing attacks.
The document also proposes several extensions to the current HTTP
authentication framework, to replace current widely-used form-based
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Web authentication. A majority of the recent Web-sites on the
Internet use custom application-layer authentication implementations
using Web forms. The reasons for these may vary, but many people
believe that the current HTTP Basic (and Digest, too) authentication
method does not have enough functionality (including a good-feeling
user interfaces) to support most of realistic Web-based applications.
However, the method is very weak against phishing attacks, because
the whole behavior of the authentication is controlled from the
server side. To overcome this problem, we need to "modernize" the
HTTP authentication framework so that better client-controlled secure
methods can be used with Web applications. The extensions proposed
in this document include:
o Multi-host single authentication within an Internet domain
(Section 5),
o non-mandatory, optional authentication on HTTP (Section 4.7),
o log out from both server and client side (Section 10), and
o finer control for redirection depending on authentication status
(Section 10).
1.1. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
[RFC2119].
The terms "encouraged" and "advised" are used for suggestions that do
not constitute "SHOULD"-level requirements. People MAY freely choose
not to include the suggested items regarding [RFC2119], but complying
with those suggestions would be a best practice; it will improve the
security, interoperability, and/or operational performance.
This document distinguishes the terms "client" and "user" in the
following way: A "client" is an entity understanding and talking HTTP
and the specified authentication protocol, usually computer software;
a "user" is a (usually natural) person who wants to access data
resources using "a client".
The term "natural numbers" refers to the non-negative integers
(including zero) throughout this document.
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1.2. Document Structure Overview
The entire document is organized as follows:
o Section 2 presents an overview of the protocol design.
o Sections 3 to 9 define a general framework of the Mutual
authentication protocol. This framework is independent of
specific cryptographic primitives.
o Section 10 defines an optional extension to the generic HTTP
authentication framework, which is mostly useful for controlling
the behavior of the Web browser for the authentication.
o Section 11 describes properties needed for cryptographic
algorithms used with this protocol framework, and defines a few
functions which will be shared among such cryptographic
algorithms.
o The sections after that contain general normative and informative
information about the protocol.
o The appendices contain some information that may help developers
to implement the protocol.
2. Protocol Overview
The protocol, as a whole, is designed as a natural extension to the
HTTP protocol [RFC2616] using a framework defined in [RFC2617].
Internally, the server and the client will first perform a
cryptographic key exchange, using the secret password as a "tweak" to
the exchange. The key-exchange will only succeed when the secrets
used by the both peers are correctly related (i.e. generated from the
same password). Then, both peers will verify the authentication
results by confirming the sharing of the exchanged key. This section
describes a brief image of the protocol and the exchanged messages.
2.1. Messages
The authentication protocol uses seven kinds of messages to perform
mutual authentication. These messages have specific names within
this specification.
o Authentication request messages: used by the servers to request
clients to start mutual authentication.
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* 401-INIT message: a general message to start the authentication
protocol. It is also used as a message indicating an
authentication failure.
* 200-Optional-INIT message: a variant of the 401-INIT message
indicating that an authentication is not mandatory.
* 401-STALE message: a message indicating that it has to start a
new authentication trial.
o Authenticated key exchange messages: used by both peers to perform
authentication and the sharing of a cryptographic secret.
* req-KEX-C1 message: a message sent from the client.
* 401-KEX-S1 message: a message sent from the server as a
response to a req-KEX-C1 message.
o Authentication verification messages: used by both peers to verify
the authentication results.
* req-VFY-C message: a message used by the client, requesting
that the server authenticates and authorizes the client.
* 200-VFY-S message: a successful response used by the server,
and also asserting that the server is authentic to the client
simultaneously.
In addition to the above, either a request or a response without any
HTTP headers related to this specification will be hereafter called a
"normal request" or a "normal response", respectively.
2.2. Typical Flows of the protocol
In typical cases, the client access to a resource protected by the
Mutual authentication will follow the following protocol sequence.
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Client Server
| |
| ---- (1) normal request ---------> |
GET / HTTP/1.1 |
| |
| <---------------- (2) 401-INIT --- |
| 401 Authentication Required
| WWW-Authenticate: Mutual realm="a realm"
| |
[user, | |
pass]-->| |
| ---- (3) req-KEX-C1 -------------> |
GET / HTTP/1.1 |
Authorization: Mutual user="john", |--> [user DB]
wa="...", ... |<-- [user info]
| |
| <-------------- (4) 401-KEX-S1 --- |
| 401 Authentication Required
| WWW-Authenticate: Mutual sid=..., wb="...", ...
| |
[compute] (5) compute session secret [compute]
| |
| |
| ---- (6) req-VFY-C --------------> |
GET / HTTP/1.1 |--> [verify (6)]
Authorization: Mutual sid=..., |<-- OK
oa="...", ... |
| |
| <--------------- (7) 200-VFY-S --- |
[verify | 200 OK |
(7)]<--| Authentication-Info: Mutual ob="..."
| |
v v
Figure 1: Typical communication flow for first access to resource
o As usual in general HTTP protocol designs, a client will at first
request a resource without any authentication attempt (1). If the
requested resource is protected by the Mutual authentication, the
server will respond with a message requesting authentication
(401-INIT) (2).
o The client processes the body of the message, and waits for the
user to input the user name and a password. If the user name and
the password are available, the client will send a message with
the authenticated key exchange (req-KEX-C1) to start the
authentication (3).
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o If the server has received a req-KEX-C1 message, the server looks
up the user's authentication information within its user database.
Then the server creates a new session identifier (sid) that will
be used to identify sets of the messages that follow it, and
responds back with a message containing a server-side
authenticated key exchange value (401-KEX-S1) (4).
o At this point (5), both peers calculate a shared "session secret"
using the exchanged values in the key exchange messages. Only
when both the server and the client have used secret credentials
generated from the same password will the session secret values
match. This session secret will be used for the actual access
authentication after this point.
o The client will send a request with a client-side authentication
verification value (req-VFY-C) (6), generated from the client-
owned session secret. The server will check the validity of the
verification value using its own session secret.
o If the authentication verification value from the client was
correct, it means that the client definitely owns the credential
based on the expected password (i.e. the client authentication
succeeded.) The server will respond with a successful message
(200-VFY-S) (7). Contrary to the usual one-way authentication
(e.g. HTTP Basic authentication or POP APOP authentication), this
message also contains a server-side authentication verification
value.
When the client's verification value is incorrect (e.g. because
the user-supplied password was incorrect), the server will respond
with the 401-INIT message (the same one as used in (2)) instead.
o The client MUST first check the validity of the server-side
authentication verification value contained in the message (7).
If the value was equal to the expected one, the server
authentication succeeded.
If it is not the value expected, or if the message does not
contain the authentication verification value, it means that the
mutual authentication has been broken for some unexpected reason.
The client MUST NOT process any body or header values contained in
this case. (Note: This case should not happen between a
correctly-implemented server and a client.)
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2.3. Alternative flows
As shown above, the typical flow for a first authenticated request
requires three request-response pairs. To reduce the protocol
overhead, the protocol enables several short-cut flows which require
fewer messages.
o (case A) If the client knows that the resource is likely to
require the authentication, the client MAY omit the first
unauthenticated request (1) and immediately send a key exchange
(req-KEX-C1 message). This will reduce one round-trip of
messages.
o (case B) If both the client and the server previously shared a
session secret associated with a valid session identifier (sid),
the client MAY directly send a req-VFY-C message using the
existing session identifier and corresponding session secret.
This will further reduce one round-trip of messages.
In such cases, the server MAY have thrown out the corresponding
sessions from the session table. In this case, the server will
respond with a 401-STALE message, indicating a new key exchange is
required. The client SHOULD retry constructing a req-KEX-C1
message in this case.
Figure 2 depicts the shortcut flows described above. Under the
appropriate settings and implementations, most of the requests to
resources are expected to meet both the criteria, and thus only one
round-trip of request/responses will be required in most cases.
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(A) omit first request
(2 round trips)
Client Server
| |
| --- req-KEX-C1 ----> |
| |
| <---- 401-KEX-S1 --- |
| |
| ---- req-VFY-C ----> |
| |
| <----- 200-VFY-S --- |
| |
(B) reusing session secret
(B-1) key available (B-2) key expired
(1 round trip) (3 round trips)
Client Server Client Server
| | | |
| ---- req-VFY-C ----> | | --- req-VFY-C -------> |
| | | |
| <----- 200-VFY-S --- | | <------- 401-STALE --- |
| | | |
| --- req-KEX-C1 ------> |
| |
| <------ 401-KEX-S1 --- |
| |
| --- req-VFY-C -------> |
| |
| <------- 200-VFY-S --- |
| |
Figure 2: Several alternative flows on protocol
For more details, see Sections 8 and 9.
3. Message Syntax
The Mutual authentication protocol uses five headers:
WWW-Authenticate (in responses with status code 401),
Optional-WWW-Authenticate (in responses with non-401 status codes),
Authentication-Control (in responses), Authorization (in requests),
and Authentication-Info (in responses other than 401 status). These
headers follow a common framework described in [RFC2617] [Editorial
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Note: to be httpbis-p7]. The detailed syntax definitions for these
headers are contained in Section 4.
These headers use some common syntax elements described in Figure 3.
The syntax is denoted in the augmented BNF syntax defined in
[RFC5234].
auth-scheme = "Mutual" ; see HTTP for other values
extension-field = extension-token "=" value
token = 1*(%x30-39 / %x41-5A / %x61-7A / "-" / "_")
extensive-token = token / extension-token
extension-token = "-" token 1*("." token)
value = extensive-token / integer
/ hex-fixed-number
/ base64-fixed-number / string
integer = "0" / (%x31-39 *%x30-39) ; no leading zeros
hex-fixed-number = 1*(%x30-39 / %x41-46 / %x61-66)
base64-fixed-number = string
string = %x22 *(%x20-21 / %x23-5B / %x5D-FF
/ %x5C.22 / "\\") %x22
spaces = 1*(" " / %x09)
Figure 3: BNF syntax for common elements used in protocol
3.1. Tokens and Extensive-tokens
The tokens are case insensitive; Senders SHOULD send these in lower-
case, and receivers MUST accept both upper- and lower-cases. When
tokens are used as the (partial) inputs to any hash or other
mathematical functions, it MUST always be used in lower-case. All
hexadecimal numbers are also case-insensitive, and SHOULD be sent in
lower-case.
Extensive-tokens are used in this protocol where the set of
acceptable tokens may include non-standard extensions. Any non-
standard extensions of this protocol MUST use the extension-tokens
with format "-<token>.<domain-name>", where <domain-name> is a
validly registered (sub-)domain name on the Internet owned by the
party who defines the extensions.
3.2. Numbers
The syntax definition of the integers only allows representations
that do not contain extra leading zeros.
The numbers represented as a hex-fixed-number MUST include an even
number of characters (i.e. multiples of eight bits). When these are
generated from any cryptographic values, they SHOULD have their
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"natural length": if these are generated from a hash function, these
lengths SHOULD correspond to the hash size; if these are representing
elements of a mathematical set (or group), its lengths SHOULD be the
shortest for representing all the elements in the set. For example,
any results of SHA-256 hash function will be represented by 64
characters, and any elements in 2048-bit prime field (modulo a 2048-
bit integer) will be represented by 512 characters, regardless of how
much 0's will be appear in front of such representations. Session-
identifiers and other non-cryptographically generated values are
represented in any (even) length determined by the side who generates
it first, and the same length SHALL be used throughout the all
communications by both peers.
The numbers represented as base64-fixed-number SHALL be generated as
follows: first, the number is converted to a big-endian octet-string
representation. The length of the representation is determined in
the same way as mentioned above. Then, the string is encoded using
the Base 64 encoding [RFC4648] without any spaces and newlines, and
then enclosed by two double-quotations.
3.3. Strings
All the strings outside ASCII character sets MUST be encoded using
the UTF-8 encoding [RFC3629] for the ISO 10646-1 character set
[ISO.10646-1.1993]. Both peers are RECOMMENDED to reject any invalid
UTF-8 sequences that might cause decoding ambiguities (e.g.,
containing <"> in the second or later byte of the UTF-8 encoded
characters).
To encode character strings to header values, they will first be
encoded according to UTF-8 without a leading BOM, then all
occurrences of the characters <"> and "\" will be escaped by
prepending "\", and two <">s will be put around the string. These
escaping backslashes and enclosing quotes SHALL be removed before any
processing other than when using them in a header field.
If strings are representing a domain name or URI that contains non-
ASCII characters, the host parts SHOULD be encoded as it is used in
the HTTP protocol layer (e.g. in a Host: header); under current
standards it will be the one defined in [RFC5890]. It SHOULD use
lower-case ASCII characters.
For base64-fixed-numbers, which use the string syntax, see the
previous section.
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4. Messages
In this section we define the seven kinds of messages used in the
authentication protocol along with the formats and requirements of
the headers for each message.
To determine which message are expected to be sent, see Sections 8
and 9.
In the descriptions below, the type of allowable values for each
header field is shown in parenthesis after the key names. The
"algorithm-determined" type means that the acceptable value for the
field is one of the types defined in Section 3, and is determined by
the value of the "algorithm" field. The fields marked "mandatory"
SHALL be contained in the message. The fields marked "non-mandatory"
MAY either be contained or omitted in the message. Each field SHALL
appear in each headers exactly once at most.
4.1. 401-INIT
Every 401-INIT message SHALL be a valid HTTP 401 (Authentication
Required) message containing one (and only one: hereafter not
explicitly noticed) "WWW-Authenticate" header of the following
format.
WWW-Authenticate: Mutual algorithm=xxxx, validation=xxxx,
realm="xxxx", stale=0, version=-draft07
header-401-INIT = "WWW-Authenticate" ":" [spaces]
auth-scheme spaces fields-401-INIT
fields-401-INIT = field-401-INIT *([spaces] "," spaces field-401-INIT)
field-401-INIT = version / algorithm / validation
/ auth-domain / realm / pwd-hash / stale
/ extension-field
version = "version" "=" extensive-token
algorithm = "algorithm" "=" extensive-token
validation = "validation" "=" extensive-token
auth-domain = "auth-domain" "=" string
realm = "realm" "=" string
pwd-hash = "pwd-hash" "=" extensive-token
stale = token
Figure 4: BNF syntax for header in 401-INIT header
The header SHALL contain all of the fields marked "mandatory" below,
and MAY contain those marked "non-mandatory".
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version: (mandatory extensive-token) should be the token
"-draft07" in this specification. The behavior is
undefined when other values are specified.
algorithm: (mandatory extensive-token) specifies the
authentication algorithm to be used. The value MUST
be one of the tokens specified in &algo_draft; or
other supplemental specification documentation.
validation: (mandatory extensive-token) specifies the method of
host validation. The value MUST be one of the tokens
described in Section 7, or the tokens specified in
other supplemental specification documentation.
auth-domain: (non-mandatory string) specifies the authentication
domain, the set of hosts for which the authentication
credentials are valid. It MUST be one of the strings
described in Section 5. If the value is omitted, it
is assumed to be the host part of the requested URI.
realm: (mandatory string) is a UTF-8 encoded string
representing the name of the authentication realm
inside the authentication domain.
pwd-hash: (non-mandatory extensive-token) specifies the hash
algorithm (hereafter referred to by ph) used for
additionally hashing the password. The valid tokens
are
* none: ph(p) = p
* md5: ph(p) = MD5(p)
* digest-md5: ph(p) = MD5(username | ":" | realm |
":" | p), the same value as MD5(A1) for "MD5"
algorithm in [RFC2617].
* sha1: ph(p) = SHA1(p)
If omitted, the value "none" is assumed. The use of
"none" is recommended.
stale: (mandatory token) MUST be "0".
The algorithm specified in this header will determine the types and
the values for w_A, w_B, o_A and o_B.
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4.2. 401-STALE
A 401-STALE message is a variant of the 401-INIT message, which means
that the client has sent a request message that is not for any active
session.
WWW-Authenticate: Mutual algorithm=xxxx, validation=xxxx,
realm="xxxx", stale=1, version=-draft07
The header MUST contain the same fields as in 401-INIT, except that
the stale field contains token 1.
4.3. req-KEX-C1
Every req-KEX-C1 message SHALL be a valid HTTP request message
containing an "Authorization" header of the following format.
Authorization: Mutual algorithm=xxxx, validation=xxxx, realm="xxxx",
user="xxxx", wa=xxxx, version=-draft07
header-req-KEX-C1 = "Authorization" ":" [spaces]
auth-scheme spaces fields-req-KEX-C1
fields-req-KEX-C1 = field-req-KEX-C1
*([spaces] "," spaces field-req-KEX-C1)
field-req-KEX-C1 = version / algorithm / validation
/ auth-domain / realm / user / wa
/ extension-field
user = "user" "=" string
wa = "wa" "=" value
Figure 5: the BNF syntax for the header in req-KEX-C1 message
The header SHALL contain the fields with the following keys:
version: (mandatory, extensive-token) should be the token
"-draft07" in this specification. The behavior is
undefined when other values are specified.
algorithm, validation, auth-domain, realm: MUST be the same value as
it is when received from the server.
user: (mandatory, string) is the UTF-8 encoded name of the
user. If this name comes from a user input, client
software SHOULD prepare the string using SASLprep
[RFC4013] before encoding it to UTF-8.
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wa: (mandatory, algorithm-determined) is the client-side
key exchange value w_A, which is specified by the
algorithm that is used.
4.4. 401-KEX-S1
Every 401-KEX-S1 message SHALL be a valid HTTP 401 (Authentication
Required) message containing a "WWW-Authenticate" header of the
following format.
WWW-Authenticate: Mutual algorithm=xxxx, validation=xxxx,
realm="xxxx", sid=xxxx, wb=xxxx, nc-max=x, nc-window=x, time=x,
path="xxxx", version=-draft07
header-401-KEX-S1 = "WWW-Authenticate" ":" [spaces]
auth-scheme spaces fields-401-KEX-S1
fields-401-KEX-S1 = field-401-KEX-S1
*([spaces] "," spaces field-401-KEX-S1)
field-401-KEX-S1 = version / algorithm / validation
/ auth-domain / realm / sid / wb
/ nc-max / nc-window / time / path
/ extension-field
sid = "sid" "=" string
wb = "wb" "=" value
nc-max = "nc-max" "=" integer
nc-window = "nc-window" "=" integer
time = "time" "=" integer
path = "path" "=" string
Figure 6: the BNF syntax for the header in 401-KEX-S1 message
The header SHALL contain the fields with the following keys:
version: (mandatory, extensive-token) should be the token
"-draft07" in this specification. The behavior is
undefined when other values are specified.
algorithm, validation, auth-domain, realm: MUST be the same value as
it is when received from the client.
sid: (mandatory, hex-fixed-number) MUST be a session
identifier, which is a random integer. The sid SHOULD
have uniqueness of at least 80 bits or the square of
the maximal estimated transactions concurrently
available in the session table, whichever is larger.
Session identifiers are local to each concerned
authentication realm: the same sids for different
authentication realms SHOULD be treated as independent
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ones.
wb: (mandatory, algorithm-determined) is the server-side
key exchange value w_B, which is specified by the
algorithm.
nc-max: (mandatory, integer) is the maximal value of nonce
counts that the server accepts.
nc-window: (mandatory, integer) the number of available nonce
slots that the server will accept. The value of the
nc-window field is RECOMMENDED to be 32 or more.
time: (mandatory, integer) represents the suggested time (in
seconds) that the client can reuse the session
represented by the sid. It is RECOMMENDED to be at
least 60. The value of this field is not directly
linked to the duration that the server keeps track of
the session represented by the sid.
path: (non-mandatory, string) specifies which path in the
URI space the same authentication is expected to be
applied. The value is a space-separated list of URIs,
in the same format as it was specified in domain
parameter [RFC2617] for the Digest authentications,
and clients are RECOMMENDED to recognize it. The all
path elements contained in the field MUST be inside
the specified auth-domain: if not, clients SHOULD
ignore such elements.
4.5. req-VFY-C
Every req-VFY-C message SHALL be a valid HTTP request message
containing an "Authorization" header of the following format.
Authorization: Mutual algorithm=xxxx, validation=xxxx, realm="xxxx",
sid=xxxx, nc=x, oa=xxxx, version=-draft07
header-req-VFY-C = "Authorization" ":" [spaces]
auth-scheme spaces fields-req-VFY-C
fields-req-VFY-C = field-req-VFY-C
*([spaces] "," spaces field-req-VFY-C)
field-req-VFY-C = version / algorithm / validation
/ auth-domain / realm / sid / nc / oa
/ extension-field
nc = "nc" "=" integer
oa = "oa" "=" value
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Figure 7: the BNF syntax for the header in req-VFY-C message
The fields contained in the header are as follows:
version: (mandatory, extensive-token) should be the token
"-draft07" in this specification. The behavior is
undefined when other values are specified.
algorithm, validation, auth-domain, realm: MUST be the same value as
it is when received from the server for the session.
sid: (mandatory, hex-fixed-number) MUST be one of the sid
values that was received from the server for the same
authentication realm.
nc: (mandatory, integer) is a nonce value that is unique
among the requests sharing the same sid. The values
of the nonces SHOULD satisfy the properties outlined
in Section 6.
oa: (mandatory, algorithm-determined) is the client-side
authentication verification value o_A, which is
specified by the algorithm.
4.6. 200-VFY-S
Every 200-VFY-S message SHALL be a valid HTTP message that is not of
the 401 (Authentication Required) type, containing an
"Authentication-Info" header of the following format.
Authentication-Info: Mutual sid=xxxx, ob=xxxx, version=-draft07
header-200-VFY-S = "Authentication-Info" ":" [spaces]
auth-scheme spaces fields-200-VFY-S
fields-200-VFY-S = field-200-VFY-S
*([spaces] "," spaces field-200-VFY-S)
field-200-VFY-S = version / sid / ob / logout-timeout
ob = "ob" "=" value
logout-timeout = "logout-timeout" "=" integer
Figure 8: BNF syntax for header in 200-VFY-S message
The fields contained in the header are as follows:
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version: (mandatory, extensive-token) should be the token
"-draft07" in this specification. The behavior is
undefined when other values are specified.
sid: (mandatory, hex-fixed-number) MUST be the value
received from the client.
ob: (mandatory, algorithm-determined) is the server-side
authentication verification value o_B, which is
specified by the algorithm.
logout-timeout: (non-mandatory, integer) is the number of seconds
after which the client should re-validate the user's
password for the current authentication realm. The
value 0 means that the client SHOULD automatically
forget the user-inputted password for the current
authentication realm and revert to the unauthenticated
state (i.e. server-initiated logout). This does not,
however, mean that the long-term memories for the
passwords (such as the password reminders and auto
fill-ins) should be removed. If a new timeout value
is received for the same authentication realm, it
overrides the previous timeout.
The header MUST be sent before the content body: it MUST NOT be sent
in the trailer of a chunked-encoded response. If a "100 Continue"
response is sent from the server, the Authentication-Info header
SHOULD be included in that response, instead of the final response.
4.7. 200-Optional-INIT
The 200-Optional-INIT messages enable a non-mandatory authentication,
which is not possible under the current HTTP authentication
mechanism. In several Web applications, users can access the same
contents as both a guest user and an authenticated user. In most Web
applications, it is implemented using HTTP cookies [RFC6265] and
custom form-based authentications. The new authentication method
using this message will provide a replacement for these
authentication systems. Support for this message is RECOMMENDED,
unless the protocol is used for some specific applications in which
the authentication is always mandatory.
Servers MAY send HTTP successful responses (response code 200, 206
and others) containing the Optional-WWW-Authenticate header, when it
is allowed to send 401-INIT responses (with one exception described
below). Such responses are hereafter called 200-Optional-INIT
responses.
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HTTP/1.1 200 OK
Optional-WWW-Authenticate: Mutual version=-draft07, algorithm=xxxx,
validation=xxxx, realm="xxxx", stale=0
header-200-Optional-INIT = "Optional-WWW-Authenticate" ":"
[spaces] auth-scheme
spaces fields-401-INIT
Figure 9: BNF syntax for header in 200-Optional-INIT header
The fields contained in the Optional-WWW-Authenticate header are the
same as those for the 401-INIT message described in Section 4.1. For
authentication-related matters, a 200-Optional-INIT message will have
the same meaning as a 401-INIT message with a corresponding
WWW-Authenticate header. (The behavior for other matters, such as
caching, MAY be different between the 200-Optional-INIT and 401-INIT
messages.)
The 200-Optional-INIT message is the only place where an
Optional-WWW-Authenticate header is allowed. If a server is supposed
to send a 401-KEX-S1 or a 401-STALE response, it SHALL NOT replace it
with 200-Optional-INIT or similar responses. Furthermore, if a
server is going to send a 401-INIT message as a response to a
req-VFY-C message with a correct realm, the server MUST send a
401-INIT message, not a 200-Optional-INIT message.
Servers requesting non-mandatory authentication SHOULD send the path
field in the 401-KEX-S1 messages with an appropriate value. Clients
supporting non-mandatory authentication MUST recognize the field, and
MUST send either a req-KEX-C1 or a req-VFY-C request for the URI
space inside the specified paths, instead of a normal request without
an Authorization header.
5. Authentication Realms
In this protocol, an "authentication realm" is defined as a set of
resources (URIs) for which the same set of user names and passwords
is valid for. If the server requests authentication for an
authentication realm that the client is already authenticated for,
the client will automatically perform the authentication using the
already-known secrets. However, for the different authentication
realms, the clients SHOULD NOT automatically reuse the usernames and
passwords for another realm.
Just like in Basic and Digest access authentication protocols, Mutual
authentication protocol supports multiple, separate authentication
realms to be set up inside each host. Furthermore, the protocol
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supports that a single authentication realm spans over several hosts
within the same Internet domain.
Each authentication realm is defined and distinguished by the triple
of an "authentication algorithm", an "authentication domain", and a
"realm" parameter. However, server operators are NOT RECOMMENDED to
use the same pair of an authentication domain and a realm for
different authentication algorithms.
The realm parameter is a string as defined in Section 4.
Authentication domains are described in the remainder of this
section.
An authentication domain specifies the range of hosts that the
authentication realm spans over. In this protocol, it MUST be one of
the following strings.
o The string in format "<scheme>://<host>:<port>", where <scheme>,
<host>, and <port> are the URI parts of the requested URI. Even
if the request-URI does not have a port part, the string will
include one (i.e. 80 for http and 443 for https). Use this when
authentication is only valid for specific protocol (such as
https).
o The "host" part of the requested URI. This is the default value.
Authentication realms within this kind of authentication domain
will span over several protocols (i.e. http and https) and ports,
but not over different hosts.
o The string in format "*.<domain-postfix>", where <domain-postfix>
is either the host part of the requested URI or any domain in
which the requested host is included (this means that the
specification "*.example.com" is valid for all of hosts
"www.example.com", "web.example.com", "www.sales.example.com" and
"example.com"). The domain-postfix sent from the servers MUST be
equal to or included in a valid Internet domain assigned to a
specific organization: if clients know, by some means such as a
blacklist for HTTP cookies, that the specified domain is not to be
assigned to any specific organization (e.g. "*.com" or "*.jp"),
the clients are RECOMMENDED to reject the authentication request.
In the above specifications, every "scheme", "host", and "domain"
MUST be in lower-case, and any internationalized domain names beyond
the ASCII character set SHALL be represented in the way they are sent
in the underlying HTTP protocol, represented in lower-case
characters; i.e.  these SHALL be in the form of the LDH labels in
IDNA [RFC5890]. All "port"s MUST be in the shortest, unsigned,
decimal number notation. Not obeying these requirements will cause
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failure of valid authentication attempts.
5.1. Resolving ambiguities
In the above definitions of authentication domains, several domains
will overlap each other. Depending on the "path" parameters given in
the "401-KEX-S1" message (see Section 4), there may be several
candidates when the client is going to send a request including an
authentication credential (Steps 3 and 4 of the decision procedure
presented in Section 8).
If such choices are required, the following procedure SHOULD be
followed.
o If the client has previously sent a request to the same URI, and
it remembers the authentication realm requested by 401-INIT
messages at that time, use that realm.
o In other cases, use one of authentication realms representing the
most-specific authentication domains. From the list of possible
domain specifications shown above, each one has priority over ones
described after that.
If there are several choices with different domain-postfix
specifications, the one that has the longest domain-postfix has
priority over ones with a shorter domain-postfix.
o If there are realms with the same authentication domain, there is
no defined priority: the client MAY choose any one of the possible
choices.
If possible, server operators are encouraged to avoid such
ambiguities by properly setting the "path" parameters.
6. Session Management
In the Mutual authentication protocol, a session represented by an
sid is set up using first four messages (first request, 401-INIT,
req-KEX-C1 and 401-KEX-S1), and a "session secret" (z) associated
with the session is established. After sharing a session secret,
this session, along with the secret, can be used for one or more
requests for resources protected by the same realm in the same
server. Note that session management is only an inside detail of the
protocol and usually not visible to normal users. If a session
expires, the client and server SHOULD automatically reestablish
another session without informing the users.
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The sessions are local to each port of the host inside an
authentication domain; the clients MUST establish separate sessions
for each port of a host to be accessed.
The server SHOULD accept at least one req-VFY-C request for each
session, given that the request reaches the server in a time window
specified by the timeout field in the 401-KEX-S1 message, and that
there are no emergent reasons (such as flooding attacks) to forget
the sessions. After that, the server MAY discard any session at any
time and MAY send 401-STALE messages for any req-VFY-C requests.
The client MAY send two or more requests using a single session
specified by the sid. However, for all such requests, each value of
the nonce (in the nc field) MUST satisfy the following conditions:
o It is a natural number.
o The same nonce was not sent within the same session.
o It is not larger than the nc-max value that was sent from the
server in the session represented by the sid.
o It is larger than (largest-nc - nc-window), where largest-nc is
the maximal value of nc which was previously sent in the session,
and nc-window is the value of the nc-window field which was
received from the server in the session.
The last condition allows servers to reject any nonce values that are
"significantly" smaller than the "current" value (defined by the
value of nc-window) of the nonce used in the session involved. In
other words, servers MAY treat such nonces as "already received".
This restriction enables servers to implement duplicated nonce
detection in a constant amount of memory (for each session).
Servers MUST check for duplication of the received nonces, and if any
duplication is detected, the server MUST discard the session and
respond with a 401-STALE message, as outlined in Section 9. The
server MAY also reject other invalid nonce values (such as ones above
the nc-max limit) by sending a 401-STALE message.
For example, assume the nc-window value of the current session is 32,
nc-max is 100, and that the client has already used the following
nonce values: {1-20, 22, 24, 30-38, 45-60, 63-72}. Then the nonce
values that can be used for next request is one of the following set:
{41-44, 61-62, 73-100}. The values {0, 21, 23, 25-29, 39-40} MAY be
rejected by the server because they are not above the current "window
limit" (40 = 72 - 32).
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Typically, clients can ensure the above property by using a
monotonically-increasing integer counter that counts from zero upto
the value of nc-max.
The values of the nonces and any nonce-related values MUST always be
treated as natural numbers within an infinite range. Implementations
using fixed-width integers or fixed-precision floating numbers MUST
correctly and carefully handle integer overflows. Such
implementations are RECOMMENDED to accept any larger values that
cannot be represented in the fixed-width integer representations, as
long as other limits such as internal header-length restrictions are
not involved. The protocol is designed carefully so that both the
clients and servers can implement the protocol using only fixed-width
integers, by rounding any overflowed values to the maximum possible
value.
7. Validation Methods
The "validation method" specifies a method to "relate" the mutual
authentication processed by this protocol with other authentications
already performed in the underlying layers and to prevent man-in-the-
middle attacks. It decides the value v that is an input to the
authentication protocols.
The valid tokens for the validation field and corresponding values of
v are as follows:
host: hostname validation: The value v will be the ASCII
string in the following format:
"<scheme>://<host>:<port>", where <scheme>, <host>,
and <port> are the URI components corresponding to the
currently accessing resource. The scheme and host are
in lower-case, and the port is in a shortest decimal
representation. Even if the request-URI does not have
a port part, v will include one.
tls-cert: TLS certificate validation: The value v will be the
octet string of the hash value of the public key
certificate used in the underlying TLS [RFC5246] (or
SSL) connection. The hash value is defined as the
value of the entire signed certificate (specified as
"Certificate" in [RFC5280]), hashed by the hash
algorithm specified by the authentication algorithm
used.
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tls-key: TLS shared-key validation: The value v will be the
octet string of the shared master secret negotiated in
the underlying TLS (or SSL) connection.
If the HTTP protocol is used on a non-encrypted channel (TCP and
SCTP, for example), the validation type MUST be "host". If HTTP/TLS
[RFC2818] (https) protocol is used with the server certificates, the
validation type MUST be either "tls-cert" or "tls-key". If HTTP/TLS
protocol is used with an anonymous Diffie-Hellman key exchange, the
validation type MUST be "tls-key" (see the note below).
If the validation type "tls-cert" is used, the server certificate
provided on TLS connection MUST be verified to make sure that the
server actually owns the corresponding secret key.
Clients MUST validate this field upon reception of the 401-INIT
messages.
However, when the client is a Web browser with any scripting
capabilities, the underlying TLS channel used with HTTP/TLS MUST
provide server identity verification. This means (1) the anonymous
Diffie-Hellman key exchange ciphersuite MUST NOT be used, and (2) the
verification of the server certificate provided from the server MUST
be performed.
For other systems, when the underlying TLS channel used with HTTP/TLS
does not perform server identity verification, the client SHOULD
ensure that all the responses are validated using the Mutual
authentication protocol, regardless of the existence of the 401-INIT
responses.
Note: The protocol defines two variants for validation on the TLS
connections. The "tls-key" method is more secure. However, there
are some situations where tls-cert is more preferable.
o When TLS accelerating proxies are used, it is difficult for the
authenticating server to acquire the TLS key information that is
used between the client and the proxy. This is not the case for
client-side "tunneling" proxies using a CONNECT method extension
of HTTP.
o When a black-box implementation of the TLS protocol is used on
either peer.
Implementations supporting a Mutual authentication over the HTTPS
protocol SHOULD support the "tls-cert" validation. Support for
"tls-key" validation is OPTIONAL for both the servers and clients.
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8. Decision procedure for client
To securely implement the protocol, the user client must be careful
about accepting the authenticated responses from the server. This
also holds true for the reception of "normal responses" (responses
which do not contain Mutual-related headers) from HTTP servers.
Clients SHOULD implement a decision procedure equivalent to the one
shown below. (Unless implementers understand what is required for
the security, they should not alter this.) In particular, clients
SHOULD NOT accept "normal responses" unless explicitly allowed below.
The labels on the steps are for informational purposes only. Action
entries within each step are checked in top-to-bottom order, and the
first clause satisfied SHOULD be taken.
Step 1 (step_new_request):
If the client software needs to access a new Web resource, check
whether the resource is expected to be inside some authentication
realm for which the user has already been authenticated by the
Mutual authentication scheme. If yes, go to Step 2. Otherwise,
go to Step 5.
Step 2:
Check whether there is an available sid for the authentication
realm you expect. If there is one, go to Step 3. Otherwise, go
to Step 4.
Step 3 (step_send_vfy_1):
Send a req-VFY-C request.
* If you receive a 401-INIT message with a different
authentication realm than expected, go to Step 6.
* If you receive a 200-Optional-INIT message with a different
authentication realm than expected, go to Step 6.
* If you receive a 401-STALE message, go to Step 9.
* If you receive a 401-INIT message, go to Step 13.
* If you receive a 200-VFY-S message, go to Step 14.
* If you receive a normal response, go to Step 11.
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Step 4 (step_send_kex1_1):
Send a req-KEX-C1 request.
* If you receive a 401-INIT message with a different
authentication realm than expected, go to Step 6.
* If you receive a 200-Optional-INIT message with a different
authentication realm than expected, go to Step 6.
* If you receive a 401-KEX-S1 message, go to Step 10.
* If you receive a 401-INIT message with the same authentication
realm, go to Step 13 (see Note 1).
* If you receive a normal response, go to Step 11.
Step 5 (step_send_normal_1):
Send a request without any Mutual authentication headers.
* If you receive a 401-INIT message, go to Step 6.
* If you receive a 200-Optional-INIT message, go to Step 6.
* If you receive a normal response, go to Step 11.
Step 6 (step_rcvd_init):
Check whether you know the user's password for the requested
authentication realm. If yes, go to Step 7. Otherwise, go to
Step 12.
Step 7:
Check whether there is an available sid for the authentication
realm you expect. If there is one, go to Step 8. Otherwise, go
to Step 9.
Step 8 (step_send_vfy):
Send a req-VFY-C request.
* If you receive a 401-STALE message, go to Step 9.
* If you receive a 401-INIT message, go to Step 13.
* If you receive a 200-VFY-S message, go to Step 14.
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Step 9 (step_send_kex1):
Send a req-KEX-C1 request.
* If you receive a 401-KEX-S1 message, go to Step 10.
* If you receive a 401-INIT message, go to Step 13 (See Note 1).
Step 10 (step_rcvd_kex1):
Send a req-VFY-C request.
* If you receive a 401-INIT message, go to Step 13.
* If you receive a 200-VFY-S message, go to Step 14.
Step 11 (step_rcvd_normal):
The requested resource is out of the authenticated area. The
client will be in the "UNAUTHENTICATED" status. If the response
contains a request for authentications other than Mutual, it MAY
be handled normally.
Step 12 (step_rcvd_init_unknown):
The requested resource requires a Mutual authentication, and the
user is not yet authenticated. The client will be in the
"AUTH_REQUESTED" status, and is RECOMMENDED to process the
content sent from the server, and to ask user for a user name and
a password. When those are supplied from the user, proceed to
Step 9.
Step 13 (step_rcvd_init_failed):
For some reason the authentication failed: possibly the password
or the username is invalid for the authenticated resource.
Forget the password for the authentication realm and go to Step
12.
Step 14 (step_rcvd_vfy):
Check the validity of the received o_b value. If it is equal to
the expected value, it means that the mutual authentication has
succeeded. The client will be in the "AUTH_SUCCEEDED" status.
If the value is unexpected, it is a fatal communication error.
If a user explicitly requests to log out (via user interfaces),
the client MUST forget the user's password, go to step 5 and
reload the current resource without an authentication header.
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Note 1: These transitions are valid for clients, but not recommended
for servers to initiate.
Any kind of response (including a normal response) other than those
shown in the above procedure SHOULD be interpreted as a fatal
communication error, and in such cases the clients MUST NOT process
any data (response body and other content-related headers) sent from
the server. However, to handle exceptional error cases, clients MAY
accept a message without an Authentication-Info header, if it is a
Server-Error (5xx) status. The client will be in the
"UNAUTHENTICATED" status in these cases.
The client software SHOULD display the three client status to the
end-user. For an interactive client, however, if a request is a sub-
request for a resource included in another page (e.g., embedded
images, style sheets, frames etc.), its status MAY be omitted from
being shown, and any "AUTH_REQUESTED" statuses MAY be treated in the
same way as an "UNAUTHENTICATED" status.
Figure 10 shows a diagram of the client-side state.
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=========== -(11)------------
NEW REQUEST ( UNAUTHENTICATED )
=========== -----------------
| ^ normal
v | response
+(1)-------------------+ NO +(5)----------+
| The requested URI |--------------------------->| send normal |
| known to be auth'ed? | | request |
+----------------------+ +-------------+
YES | 401-INIT, 200-Optional-INIT 401-INIT|
| with a different realm 200-Optional-INIT|
| -----------------------------------. |
| / v v
| | -(12)------------ NO +(6)--------+
| | ( AUTH_REQUESTED )<------| user/pass |
| | ----------------- | known? |
| | +-----------+
| | |YES
v | v
+(2)--------+ | +(7)--------+
| session | | | session | NO
NO /| available?| | | available?|\
/ +-----------+ | +-----------+ |
/ |YES | |YES |
| | /| | |
| v / | 401- 401- v |
| +(3)--------+ | INIT --(13)---------- INIT +(8)--------+ |
| | send |--+----->/ AUTH_REQUESTED \<-------| send | |
| /| req-VFY-C | | \forget password / | req-VFY-C | |
\/ +-----------+ / ---------------- /+-----------+ |
/\ \ \/ ^ 401-INIT | |401- |
| ------ \/\ 401-STALE | | | STALE /
| \ /\ -----------------+--------------+---. | /
| | / \ | | | | /
| v / | 401- | 401- | v v v
| +(4)--------+ | KEX-S1 +(10)-------+ KEX-S1 | +(9)--------+
| | send |-|--------->| send |<-------+-| send |
| --| req-KEX-C1| | | req-VFY-C | | | req-KEX-C1|
|/ +-----------+ | +-----------+ | +-----------+
| |200-VFY-S | 200-VFY-S| ^
|normal | |200-VFY-S / |
|response | v / ==================
v \ -(14)--------- / USER/PASS INPUTTED
-(11)------------ ------->( AUTH-SUCCEED )<-- ==================
( UNAUTHENTICATED ) --------------
-----------------
Figure 10: State diagram for clients
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9. Decision procedure for the server
Each server SHOULD have a table of session states. This table need
not be persistent over a long term; it MAY be cleared upon server
restart, reboot, or others. Each entry in the table SHOULD contain
at least the following information:
o The session identifier, the value of the sid field.
o The algorithm used.
o The authentication realm.
o The state of the protocol: one of "wa received", "authenticated",
"rejected", or "inactive".
o The user name received from the client
o The boolean flag noting whether or not the session is fake.
o When the state is "wa received", the values of wa and sb.
o When the state is "authenticated", the following information:
* The value of the session secret z
* The largest nc received from the client (largest-nc)
* For each possible nc values between (largest-nc - nc-
window + 1) and max_nc, a flag whether or not a request with
the corresponding nc has been received.
The table MAY contain other information.
Servers SHOULD respond to the client requests according to the
following procedure:
o When the server receives a normal request:
* If the requested resource is not protected by the Mutual
Authentication, send a normal response.
* If the resource is protected by the Mutual Authentication, send
a 401-INIT response.
* If the resource is protected by the optional Mutual
Authentication, send a 200-Optional-INIT response.
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o When the server receives a req-KEX-C1 request:
* If the requested resource is not protected by the Mutual
Authentication, send a normal response.
* If the authentication realm specified in the req-KEX-C1 request
is not the expected one, send either a 401-INIT or a
200-Optional-INIT response.
* If the server cannot validate the field wa, send a 401-INIT
response.
* If the received user name is either invalid, unknown or
unacceptable, create a new session, mark it a "fake" session,
compute a random value as wb, and send a fake 401-KEX-S1
response. (Note: the server SHOULD NOT send a 401-INIT
response in this case, because it will leak the information to
the client that the specified user will not be accepted.
Instead, postpone it to the response for the next req-VFY-C
request.)
* Otherwise, create a new session, compute wb and send a
401-KEX-S1 response.
The created session has the "wa received" state.
o When the server receives a req-VFY-C request:
* If the requested resource is not protected by the Mutual
Authentication, send a normal response.
* If the authentication realm specified in the req-VFY-C request
is not the expected one, send either a 401-INIT or a
200-Optional-INIT response.
If none of above holds true, the server will lookup the session
corresponding to the received sid and the authentication realm.
* If the session corresponding to the received sid could not be
found, or it is inactive, send a 401-STALE response.
* If the session is in the "rejected" state, send either a
401-INIT or a 401-STALE message.
* If the session is a "fake" session, or if the received oa is
incorrect, then send a 401-INIT response. If the session is in
the "wa received" state, it SHOULD be changed to the "rejected"
state; otherwise, it MAY either be changed to the "rejected"
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status or kept in the previous state.
* If the session is in the "active" state, and the request has an
nc value that was previously received from the client, send a
401-STALE message. The session SHOULD be changed to the
"inactive" status.
* If the nc value in the request is larger than the nc-max field
sent from the server, or if it is not larger then (largest-nc -
nc-window) (when in "authenticated" status), the server MAY
(not REQUIRED to) send a 401-STALE message. The session SHOULD
be changed to the "inactive" status if so.
* Otherwise, send a 200-VFY-S response. If the session was in
the "wa received" state, the session SHOULD be changed to an
"authenticated" state. The maximum nc and nc flags of the
state SHOULD be updated properly.
At any time, the server MAY change any state entries with both the
"rejected" and "authenticated" statuses to the "inactive" status, and
MAY discard any "inactive" states from the table. The entries with
the "wa received" status SHOULD be kept unless there is an emergency
situation such as a server reboot or a table capacity overflow.
10. Authentication-Control header
Authentication-Control-header
= "Authentication-Control" ":" [spaces]
auth-scheme spaces Auth-Ctrl-fields
Auth-Ctrl-fields = Auth-Ctrl-field
*([spaces] "," spaces Auth-Ctrl-field)
Auth-Ctrl-field = loc-when-unauthed / loc-when-logout
/ logout-timeout
/ extension-field
loc-when-unauthed = "location-when-unauthenticated" "=" string
loc-when-logout = "location-when-logout" "=" string
Figure 11: the BNF syntax for the Authentication-Control header
The Authentication-Control header provides a more precise control of
the client behavior for Web applications using the Mutual
authentication protocol. This header will usually be generated in
the application layer, as opposed to WWW-Authenticate headers which
will be generated by the Web servers.
Support of this header is RECOMMENDED for interactive clients and not
required for non-interactive clients. Web applications SHOULD
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consider the security impacts of the behaviors of clients that do not
support this header.
The "auth-scheme" of this header and other authentication-related
headers within the same message MUST be equal. This document does
not define any behavior associated with this header, when the
"auth-scheme" of this header is not "Mutual".
10.1. Location-when-unauthenticated field
Authentication-Control: Mutual
location-when-unauthenticated="http://www.example.com/login.html"
The field "location-when-unauthenticated" specifies a location where
any unauthenticated clients should be redirected to. This header may
be used, for example, when there is a central login page for the
entire Web application. The value of this field MUST be a string
that contains an absolute URL location. If a given URL is not
absolute, the clients MAY consider it a relative URL from the current
location.
This field MAY be used with a 401-INIT and 200-Optional-INIT message;
however, use of this field with 200-Optional-INIT messages is not
recommended. If there is a 200-VFY-S, 401-STALE or 401-KEX-S1
message with this field, the clients MUST ignore this field.
When a client receives a message with this field, if and only if the
client's state after processing the response is either Step 12 or 13
(i.e., a state in which the client will process the response body and
ask for the user's password), the client will treat the entire
response as if it were a 303 "See Other" response with a Location
header that contains the value of this field (i.e., client will be
redirected to the specified location with a GET request). Unlike a
normal 303 response, if the client can process authentication without
the user's interaction (like Steps 3, 4, 8, 9 and 10), this field is
ignored.
The specified location SHOULD be included in a set of locations
specified in the "auth-domain" field of the corresponding 401-INIT
message. If this is not satisfied, the clients MAY ignore this
field.
10.2. Location-when-logout field
Authentication-Control: Mutual
location-when-logout="http://www.example.com/byebye.html"
The field "location-when-logout" specifies a location where the
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client is to be redirected when the user explicitly request a logout.
The value of this field MUST be a string that contains an absolute
URL location. If a given URL is not absolute, the clients MAY
consider it a relative URL from the current location.
This field MAY be used with 200-VFY-S messages. If there is a
401-INIT, 401-KEX-S1, 401-STALE, 200-Optional-INIT or normal 200
message with this field, the clients MUST ignore this field.
When the user of a client request to terminate an authentication
session, and if the client currently displays a page supplied by a
response with this field, the client will be redirected to the
specified location by a new GET request (as if it received a 303
response), instead of reloading the page without the authentication
credential. Web applications are encouraged to send this field with
an appropriate value for any responses (except those with redirection
(3XX) statuses) for non-GET requests.
10.3. Logout-timeout
Authentication-Control: Mutual logout-timeout=300
The field "logout-timeout" has the same meaning as the field of the
same name in the "Authentication-Info" header. This field will be
used with 200-VFY-S messages. If both are specified, clients are
RECOMMENDED to use the one with the smaller value.
11. Authentication Algorithms
Cryptographic authentication algorithms which are used with this
protocol will be defined separately. The algorithm definition MUST
at least provide a definitions for the following functions:
o The server-side authentication credential J, derived from user-
side authentication credential pi.
o Key exchange values w_A and w_B.
o Shared secret z, to be computed in both server-side and client
side.
o A hash function H to be used with the protocol.
All algorithm used with this protocol SHOULD provide secure mutual
authentication between client and servers, and generate a
cryptographically strong shared secret value z, equivalently strong
to or stronger than the hash function H. If any passwords (or pass-
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phrases or any equivalents, i.e. weak secrets) are involved, these
SHOULD NOT be guessable from any data transmitted in the protocol,
even if an attacker (either an eavesdropper or an active server)
knows the possible thoroughly-searchable candidate list of the
passwords. Furthermore, if possible, the function for deriving
server-side authentication credential J is RECOMMENDED to be one-way
so that pi should not be easily computed from J(pi).
11.1. Support functions and notations
In this section we define several support functions and notations to
be shared by several algorithm definitions:
The integers in the specification are in decimal, or in hexadecimal
when prefixed with "0x".
The function octet(c) generates a single octet string whose code
value is equal to c. The operator |, when applied to octet strings,
denotes the concatenation of two operands.
The function VI encodes natural numbers into octet strings in the
following manner: numbers are represented in big-endian radix-128
string, where each digit is represented by a octet within 0x80-0xff
except the last digit represented by a octet within 0x00-0x7f. The
first octet MUST NOT be 0x80. For example, VI(i) = octet(i) for i <
128, and VI(i) = octet(0x80 + (i >> 7)) | octet(i & 127) for 128 <= i
< 16384. This encoding is the same as the one used for the
subcomponents of object identifiers in the ASN.1 encoding
[ITU.X690.1994], and available as a "w" conversion in the pack
function of several scripting languages.
The function VS encodes a variable-length octet string into a
uniquely-decoded, self-delimited octet string, as in the following
manner:
VS(s) = VI(length(s)) | s
where length(s) is a number of octets (not characters) in s.
[Editorial note: Unlike the colon-separated notion used in the Basic/
Digest HTTP authentication scheme, the string generated by a
concatenation of the VS-encoded strings will be unique, regardless of
the characters included in the strings to be encoded.]
The function OCTETS converts an integer into the corresponding radix-
256 big-endian octet string having its natural length: See
Section 3.2 for the definition of "natural length".
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11.2. Default functions for algorithms
The functions defined in this section are common default functions
among authentication algorithms.
The client-side password-based string pi used by this authentication
is derived in the following manner:
pi = H(VS(algorithm) | VS(auth-domain) | VS(realm) | VS(username) |
VS(ph(password)).
The values of algorithm, realm, and auth-domain are taken from the
values contained in the 401-INIT (or 200-Optional-INIT, hereafter
implied) message. When pi is used in the context of an octet string,
it SHALL have the natural length derived from the size of the output
of function H (e.g. 32 octets for SHA-256). The function ph is
determined by the value of the pwd-hash field given in a 401-INIT
message. If the password comes from a user input, it SHOULD first be
prepared using SASLprep [RFC4013]. Then, the password SHALL be
encoded as a UTF-8 string before passed to ph.
The values o_A and o_B are derived by the following equation.
o_A = H(octet(4) | OCTETS(w_A) | OCTETS(w_B) | OCTETS(z) | VI(nc) |
VS(v))
o_B = H(octet(3) | OCTETS(w_A) | OCTETS(w_B) | OCTETS(z) | VI(nc) |
VS(v))
Specifications for cryptographic algorithms used with this framework
MAY override the functions pi, o_A, and o_B defined above. In such
cases implementations MUST use the ones defined with such algorithm
specifications.
12. Methods to extend this protocol
If a non-standard extension to this protocol is implemented, it MUST
use the extension-tokens defined in Section 3 to avoid conflicts with
this protocol and other extensions.
Authentication algorithms other than those defined in this document
MAY use other representations for the fields "wa", "wb", "oa", and
"ob", replace those keys, and/or add fields to the messages
containing those fields in supplemental specifications. Two-octet
keys from "wc" to "wz" and from "oc" to "oz" are reserved for this
purpose. If those specifications use keys other than those mentioned
above, it is RECOMMENDED to use extension-tokens to avoid any key-
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name conflict with the future extension of this protocol.
Extension-tokens MAY be freely used for any non-standard, private,
and/or experimental uses for those fields provided that the domain
part in the token is appropriately used.
13. IANA Considerations
The tokens used for the authentication-algorithm, pwd-hash, and
validation fields MUST be allocated by IANA. To acquire registered
tokens, a specification for the use of such tokens MUST be available
as an RFC, as outlined in [RFC5226].
Note: More formal declarations will be added in the future drafts to
meet the RFC 5226 requirements.
14. Security Considerations
14.1. Security Properties
o The protocol is secure against passive eavesdropping and replay
attacks. However, the protocol relies on transport security
including DNS integrity for data secrecy and integrity. HTTP/TLS
SHOULD be used where transport security is not assured and/or data
secrecy is important.
o When used with HTTP/TLS, if TLS server certificates are reliably
verified, the protocol provides true protection against active
man-in-the-middle attacks.
o Even if the server certificate is not used or is unreliable, the
protocol provides protection against active man-in-the-middle
attacks for each HTTP request/response pair. However, in such
cases, JavaScript or similar scripting facilities can be used to
affect the Mutually-authenticated contents from other contents not
protected by this authentication mechanism. This is the reason
why this protocol requires that valid TLS server certificates MUST
be presented (Section 7).
14.2. Denial-of-service attacks to servers
The protocol requires a server-side table of active sessions, which
may become a critical point of the server resource consumptions. For
proper operation, the protocol requires that at least one key
verification request is processed for each session identifier. After
that, servers MAY discard sessions internally at any time, without
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causing any operational problems to clients. Clients will silently
reestablishes a new session then.
However, if a malicious client sends too many requests of key
exchanges (req-KEX-C1 messages) only, resource starvation might
occur. In such critical situations, servers MAY discard any kind of
existing sessions regardless of these statuses. One way to mitigate
such attacks are that servers MAY have a number and a time limits for
unverified pending key exchange requests (in the "wa received"
status).
This is a common weakness of authentication protocols with almost any
kind of negotiations or states, including Digest authentication
method and most Cookie-based authentication implementations.
However, regarding the resource consumption, a situation of the
mutual authentication method is a slightly better than the Digest,
because HTTP requests without any kind of authentication requests
will not generate any kind of sessions. Session identifiers are only
generated after a client starts a key negotiation. It means that
simple clients such as web crawlers will not accidentally consume
server-side resources for session managements.
14.3. Implementation Considerations
o To securely implement the protocol, the Authentication-Info
headers in the 200-VFY-S messages MUST always be validated by the
client. If the validation fails, the client MUST NOT process any
content sent with the message, including other headers and the
body part. Non-compliance to this requirement will allow phishing
attacks.
o The authentication status on the client-side SHOULD be visible to
the users of the client. In addition, the method for asking for
the user's name and passwords SHOULD be carefully designed so that
(1) the user can easily distinguish the request from this
authentication method from any other authentication methods such
as Basic and Digest methods, and (2) the Web contents cannot
imitate the user-interfaces for this protocol.
An informational memo regarding user-interface considerations and
recommendations for implementing this protocol will be separately
published.
o For HTTP/TLS communications, when a web form is submitted from
Mutually-authenticated pages with the "tls-cert" validation method
to a URI that is protected by the same realm (so indicated by the
path field), if the server certificate has been changed since the
pages were received, the peer is RECOMMENDED to be revalidated
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using a req-KEX-C1 message with an "Expect: 100-continue" header.
The same applies when the page is received with the "tls-key"
validation method, and when the TLS session has expired.
o Server-side storages of user passwords are advised to contain the
values encrypted by one-way function J(pi), instead of the real
passwords, those hashed by ph, or pi.
14.4. Usage Considerations
o The user-names inputted by a user may be sent automatically to any
servers sharing the same auth-domain. This means that when host-
type auth-domain is used for authentication on an HTTPS site, and
when an HTTP server on the same host requests Mutual
authentication within the same realm, the client will send the
user-name in a clear text. If user-names have to be kept secret
against eavesdropping, the server must use full-scheme-type auth-
domain parameter. Contrarily, passwords are not exposed to
eavesdroppers even on HTTP requests.
o The "Pwd_hash" field is only provided for backward compatibility
of password databases. The use of "none" function is the most
secure choice and is RECOMMENDED. If values other than "none" are
used, you MUST ensure that the hash values of the passwords were
not exposed to the public. Note that hashed password databases
for plain-text authentications are usually not considered secret.
o If the server provides several ways for storing server-side
password secrets into the password database, it is advised to
store the values encrypted by using the one-way function J(pi),
instead of the real passwords, those hashed by ph, or pi.
15. Notice on intellectual properties
The National Institute of Advanced Industrial Science and Technology
(AIST) and Yahoo! Japan, Inc. has jointly submitted a patent
application on the protocol proposed in this documentation to the
Patent Office of Japan. The patent is intended to be open to any
implementors of this protocol and its variants under non-exclusive
royalty-free manner. For the details of the patent application and
its status, please contact the author of this document.
The elliptic-curve based authentication algorithms might involve
several existing third-party patents. The authors of the document
take no position regarding the validity or scope of such patents, and
other patents as well.
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16. References
16.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO
10646", STD 63, RFC 3629, November 2003.
[RFC4013] Zeilenga, K., "SASLprep: Stringprep Profile for User Names
and Passwords", RFC 4013, February 2005.
[RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data
Encodings", RFC 4648, October 2006.
[RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234, January 2008.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246, August 2008.
16.2. Informative References
[ISO.10646-1.1993]
International Organization for Standardization,
"Information Technology - Universal Multiple-octet coded
Character Set (UCS) - Part 1: Architecture and Basic
Multilingual Plane", ISO Standard 10646-1, May 1993.
[ITU.X690.1994]
International Telecommunications Union, "Information
Technology - ASN.1 encoding rules: Specification of Basic
Encoding Rules (BER), Canonical Encoding Rules (CER) and
Distinguished Encoding Rules (DER)", ITU-T Recommendation
X.690, 1994.
[RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.
[RFC2617] Franks, J., Hallam-Baker, P., Hostetler, J., Lawrence, S.,
Leach, P., Luotonen, A., and L. Stewart, "HTTP
Authentication: Basic and Digest Access Authentication",
RFC 2617, June 1999.
[RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000.
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[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, May 2008.
[RFC5890] Klensin, J., "Internationalized Domain Names for
Applications (IDNA): Definitions and Document Framework",
RFC 5890, August 2010.
[RFC5929] Altman, J., Williams, N., and L. Zhu, "Channel Bindings
for TLS", RFC 5929, July 2010.
[RFC6265] Barth, A., "HTTP State Management Mechanism", RFC 6265,
April 2011.
Appendix A. (Informative) Generic syntax of headers
Several headers (e.g. WWW-Authenticate: headers in 401-INIT,
401-STALE, and 401-KEX-S1 messages) shares common header names. To
parse these headers, one MAY use the following general syntax
definition of the message syntax:
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header = header-name ":" [spaces] auth-scheme
spaces fields
header-name = "WWW-Authenticate" / "Optional-WWW-Authenticate"
/ "Authorization" / "Authentication-info"
/ "Authentication-Control"
auth-scheme = "Mutual" ; see HTTP for other values
fields = field *([spaces] "," spaces field)
field = key "=" value ; either a specific or
; an extension field
key = extensive-token
token = 1*(%x30-39 / %x41-5A / %x61-7A / "-" / "_")
extensive-token = token / extension-token
extension-token = "-" token 1*("." token)
value = extensive-token / integer
/ hex-fixed-number
/ base64-fixed-number / string
integer = "0" / (%x31-39 *%x30-39) ; no leading zeros
hex-fixed-number = 1*(%x30-39 / %x41-46 / %x61-66)
base64-fixed-number = string
string = %x22 *(%x20-21 / %x23-5B / %x5D-FF
/ %x5C.22 / "\\") %x22
spaces = 1*(" " / %x09)
Figure 12: Common BNF syntax for headers in the protocol
In this way of parsing, messages will be distinguished by the fields
contained in a header corresponding to the authentication. The
procedure below determines the kind of each HTTP request/response.
o If the message is a response with a "401" status:
* If it does not contain any WWW-Authenticate header, it is an
error.
* If the WWW-Authenticate header specifies a scheme other than
"Mutual", it is a normal response within this draft's scope.
* Otherwise, the response contains a "WWW-Authenticate: Mutual"
header. If the header contains both sid and stale fields, it
is an error.
* If the header contains a stale field with a value of 0, it is a
401-INIT message.
* If the header contains a stale field with a value of 1, it is a
401-STALE message.
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* If the header contains an sid field, it is a 401-KEX-S1
message.
o If the message is a response other than a "401" status:
* If it contains both Authentication-Info and
Optional-WWW-Authenticate headers, it is an error.
* If it contains a Authentication-Info header with the "Mutual"
scheme, it is a 200-VFY-S message.
* If it contains a Optional-WWW-Authenticate header with the
"Mutual" scheme, it is a 200-Optional-INIT message.
* If it contains a Optional-WWW-Authenticate header with a scheme
other than "Mutual", it is either an error or a normal
response, and the behavior is not defined in this
specification.
* Otherwise, it is a normal response.
o If the message is a request:
* If it does not contain an Authorization header, or it contains
an Authorization header with a scheme other than Mutual, it is
a normal request.
* Otherwise, the request contains a "Authorization: Mutual"
header. If the header contains an sid field, it is a req-VFY-C
message.
* If the header do not contain an sid field, it is a req-KEX-C1
message.
Implementations MAY perform checks stricter than the procedure above,
according to the definitions in Section 3.
Appendix B. (Informative) Draft Remarks from Authors
The following items are currently under consideration for future
revisions by the authors.
o Restructuring of the draft, further separating the HTTP extensions
part from this document.
o Format of the "Authentication-Control" header and other header
fields extending the general HTTP authentication scheme, and
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harmonization of those with other draft proposals.
o Whether to keep TLS-key validation or not.
o When keeping tls-key validation, whether to use "TLS channel
binding" [RFC5929] for "tls-key" verification (Section 7). Note
that existing TLS implementations should be considered to
determine this.
o Adding test vectors for ensuring implementation correctness.
o Possibly adding a method for servers to detect availability of
Mutual authentication on client-side.
o Applying the protocol for proxy authentication/authorization.
o Possible support for optional key renewal and cross-site federated
authentication.
Appendix C. (Informative) Draft Change Log
C.1. Changes in revision 09
Note: the token for the header field "version" is NOT changed from
draft-07, because the protocol semantics has not been changed in this
revision.
o The (default) cryptographic algorithms are separated to another
draft.
o Names of the messages are changed to more informative one (like
KEX-C for client key-exchange) than before.
C.2. Changes in revision 08
o The English text has been revised.
C.3. Changes in revision 07
o Adapt to httpbis HTTP/1.1 drafts:
* Changed definition of extensive-token.
* LWSP continuation-line (%0D.0A.20) deprecated.
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o To simplify the whole spec, the type of nonce-counter related
fields are change from hex-integer to integer.
o Algorithm tokens are renamed to include names of hash algorithms.
o Clarified the session management, added details of server-side
protocol decisions.
o The whole draft was reorganized; introduction and overview has
been rewritten.
C.4. Changes in revision 06
o Integrated Optional Mutual Authentication to the main part.
o Clarified the decision procedure for message recognitions.
o Clarified that a new authentication request for any sub-requests
in interactive clients may be silently discarded.
o Typos and confusing phrases are fixed.
o Several "future considerations" are added.
C.5. Changes in revision 05
o A new field called "version" is added for supporting future
incompatible changes with a single implementation. In the (first)
final specification its value will be changed to 1.
o A new header "Authentication-Control" is added for precise control
of application-level authentication behavior.
C.6. Changes in revision 04
o Changed text of patent licenses: the phrase "once the protocol is
accepted as an Internet standard" is removed so that the sentence
also covers the draft versions of this protocol.
o The "tls-key" verification is now OPTIONAL.
o Several description fixes and clarifications.
C.7. Changes in revision 03
o Wildcard domain specifications (e.g. "*.example.com") are allowed
for auth-domain parameters (Section 4.1).
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o Specification of the "tls-cert" verification is updated
(incompatible change).
o State transitions fixed.
o Requirements for servers concerning w_a values are clarified.
o RFC references are updated.
C.8. Changes in revision 02
o Auth-realm is extended to allow full-scheme type.
o A decision diagram for clients and decision procedures for servers
are added.
o 401-KEX-S1 and req-VFY-C messages are changed to contain
authentication realm information.
o Bugs on equations for o_A and o_B are fixed.
o Detailed equations for the entire algorithm are included.
o Elliptic-curve algorithms are updated.
o Several clarifications and other minor updates.
Authors' Addresses
Yutaka Oiwa
National Institute of Advanced Industrial Science and Technology
Research Center for Information Security
Room #1003, Akihabara Daibiru
1-18-13 Sotokanda
Chiyoda-ku, Tokyo
JP
Phone: +81 3-5298-4722
Email: mutual-auth-contact@m.aist.go.jp
Hajime Watanabe
National Institute of Advanced Industrial Science and Technology
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Hiromitsu Takagi
National Institute of Advanced Industrial Science and Technology
Yuichi Ioku
Yahoo! Japan, Inc.
Midtown Tower
9-7-1 Akasaka
Minato-ku, Tokyo
JP
Tatsuya Hayashi
Lepidum Co. Ltd.
#602, Village Sasazuka 3
1-30-3 Sasazuka
Shibuya-ku, Tokyo
JP
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