HTTPAUTH Working Group Y. Oiwa
Internet-Draft H. Watanabe
Intended status: Experimental H. Takagi
Expires: April 24, 2014 RISEC, AIST
T. Hayashi
Lepidum
Y. Ioku
Individual
October 21, 2013
Mutual Authentication Protocol for HTTP
draft-ietf-httpauth-mutual-01
Abstract
This document specifies a mutual authentication method for the Hyper-
text Transfer 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.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on April 24, 2014.
Copyright Notice
Copyright (c) 2013 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
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(http://trustee.ietf.org/license-info) in effect on the date of
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
1.2. Document Structure and Related Documents . . . . . . . . . 5
2. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 5
2.1. Messages Overview . . . . . . . . . . . . . . . . . . . . 6
2.2. Typical Flows of the Protocol . . . . . . . . . . . . . . 6
2.3. Alternative Flows . . . . . . . . . . . . . . . . . . . . 9
3. Message Syntax . . . . . . . . . . . . . . . . . . . . . . . . 10
3.1. Values . . . . . . . . . . . . . . . . . . . . . . . . . . 11
3.1.1. Tokens . . . . . . . . . . . . . . . . . . . . . . . . 11
3.1.2. Strings . . . . . . . . . . . . . . . . . . . . . . . 12
3.1.3. Numbers . . . . . . . . . . . . . . . . . . . . . . . 12
4. Messages . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
4.1. 401-INIT and 401-STALE . . . . . . . . . . . . . . . . . . 14
4.2. req-KEX-C1 . . . . . . . . . . . . . . . . . . . . . . . . 17
4.3. 401-KEX-S1 . . . . . . . . . . . . . . . . . . . . . . . . 17
4.4. req-VFY-C . . . . . . . . . . . . . . . . . . . . . . . . 18
4.5. 200-VFY-S . . . . . . . . . . . . . . . . . . . . . . . . 19
5. Authentication Realms . . . . . . . . . . . . . . . . . . . . 19
5.1. Resolving Ambiguities . . . . . . . . . . . . . . . . . . 21
6. Session Management . . . . . . . . . . . . . . . . . . . . . . 22
7. Host Validation Methods . . . . . . . . . . . . . . . . . . . 23
7.1. Applicability notes . . . . . . . . . . . . . . . . . . . 25
7.2. Interoperability notes on tls-unique . . . . . . . . . . . 25
8. Authentication Extensions . . . . . . . . . . . . . . . . . . 26
9. Decision Procedure for Clients . . . . . . . . . . . . . . . . 26
10. Decision Procedure for Servers . . . . . . . . . . . . . . . . 31
11. Authentication Algorithms . . . . . . . . . . . . . . . . . . 33
11.1. Support Functions and Notations . . . . . . . . . . . . . 34
11.2. Default Functions for Algorithms . . . . . . . . . . . . . 35
12. Application Channel Binding . . . . . . . . . . . . . . . . . 36
13. Application for Proxy Authentication . . . . . . . . . . . . . 36
14. Methods to Extend This Protocol . . . . . . . . . . . . . . . 37
15. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 38
16. Security Considerations . . . . . . . . . . . . . . . . . . . 38
16.1. Security Properties . . . . . . . . . . . . . . . . . . . 38
16.2. Denial-of-service Attacks to Servers . . . . . . . . . . . 39
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16.2.1. On-line Active Password Attacks . . . . . . . . . . . 39
16.3. Communicating the status of mutual authentication with
users . . . . . . . . . . . . . . . . . . . . . . . . . . 39
16.4. Implementation Considerations . . . . . . . . . . . . . . 40
16.5. Usage Considerations . . . . . . . . . . . . . . . . . . . 41
17. Notice on Intellectual Properties . . . . . . . . . . . . . . 41
18. References . . . . . . . . . . . . . . . . . . . . . . . . . . 42
18.1. Normative References . . . . . . . . . . . . . . . . . . . 42
18.2. Informative References . . . . . . . . . . . . . . . . . . 42
Appendix A. (Informative) Draft Remarks from Authors . . . . . . 44
Appendix B. (Informative) Draft Change Log . . . . . . . . . . . 44
B.1. Changes in Httpauth WG Revision 01 . . . . . . . . . . . . 44
B.2. Changes in Httpauth Revision 00 . . . . . . . . . . . . . 44
B.3. Changes in HttpBis Revision 00 . . . . . . . . . . . . . . 45
B.4. Changes in Revision 12 . . . . . . . . . . . . . . . . . . 45
B.5. Changes in Revision 11 . . . . . . . . . . . . . . . . . . 45
B.6. Changes in Revision 10 . . . . . . . . . . . . . . . . . . 45
B.7. Changes in Revision 09 . . . . . . . . . . . . . . . . . . 46
B.8. Changes in Revision 08 . . . . . . . . . . . . . . . . . . 46
B.9. Changes in Revision 07 . . . . . . . . . . . . . . . . . . 46
B.10. Changes in Revision 06 . . . . . . . . . . . . . . . . . . 47
B.11. Changes in Revision 05 . . . . . . . . . . . . . . . . . . 47
B.12. Changes in Revision 04 . . . . . . . . . . . . . . . . . . 47
B.13. Changes in Revision 03 . . . . . . . . . . . . . . . . . . 48
B.14. Changes in Revision 02 . . . . . . . . . . . . . . . . . . 48
B.15. Changes in Revision 01 . . . . . . . . . . . . . . . . . . 48
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 48
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1. Introduction
This document specifies a mutual authentication method for Hyper-Text
Transfer 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 authentication method proposed in this document has the following
main characteristics:
o It provides "true" mutual authentication: in addition to assuring
the server that the user knows the password, it also assures the
user that the server truly knows the user's encrypted password at
the same time. This makes it impossible for fake website owners
to persuade users that they have authenticated with the original
websites.
o It uses only passwords as the user's credential: unlike public-
key-based security algorithms, the method does not rely on secret
keys or other cryptographic data that have to be stored inside the
users' computers. The proposed method can be used as a drop-in
replacement to the current authentication methods like Basic or
Digest, while ensuring a much stronger level of security.
o It is secure: when the server fails to authenticate with a user,
the protocol will not reveal any tiny bit of information about the
user's password.
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].
This document distinguishes the terms "client" and "user" in the
following way: A "client" is an entity understanding and talking HTTP
and the specified authentication protocol, usually computer software;
a "user" is a (usually natural) person who wants to access data
resources using "a client".
The term "natural numbers" refers to the non-negative integers
(including zero) throughout this document.
This document treats target (codomain) of hash functions to be octet
strings. The notation INT(H(s)) gives a numerical (natural-number)
output of hash function H applied to string s.
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1.2. Document Structure and Related Documents
The entire document is organized as follows:
o Section 2 presents an overview of the protocol design.
o Sections 3 to 10 define a general framework of the Mutual
authentication protocol. This framework is independent of
specific cryptographic primitives.
o Section 11 describes properties needed for cryptographic
algorithms used with this protocol framework, and defines a few
functions which will be shared among such cryptographic
algorithms.
o The sections after that contain general normative and informative
information about the protocol.
o The appendices contain some information that may help developers
to implement the protocol.
In addition, there are two companion documents which are referred
from/related to this specification:
o [I-D.oiwa-httpauth-mutual-algo]: defines a cryptographic
primitives which can be used with this protocol framework. [draft
note: it is separated from this document so that it may be
replaced with another crypto in future.]
o [I-D.ietf-httpauth-extension]: defines a small but useful
extensions to the current HTTP authentication framework so that it
can support application-level semantics of existing Web systems.
2. Protocol Overview
The protocol, as a whole, is designed as a natural extension to the
HTTP protocol [I-D.ietf-httpbis-p1-messaging] using a framework
defined in [I-D.ietf-httpbis-p7-auth]. Internally, the server and
the client will first perform a cryptographic key exchange, using the
secret password as a "tweak" to the exchange. The key-exchange will
only succeed when the secrets used by the both peers are correctly
related (i.e. generated from the same password). Then, both peers
will verify the authentication results by confirming the sharing of
the exchanged key. This section describes a brief image of the
protocol and the exchanged messages.
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2.1. Messages Overview
The authentication protocol uses seven kinds of messages to perform
mutual authentication. These messages have specific names within
this specification.
o Authentication request messages: used by the servers to request
clients to start mutual authentication.
* 401-INIT message: a general message to start the authentication
protocol. It is also used as a message indicating an
authentication failure.
* 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]
kc1="...", ... |<-- [user info]
| |
| <-------------- (4) 401-KEX-S1 --- |
| 401 Authentication Required
| WWW-Authenticate: Mutual sid=..., ks1="...", ...
| |
[compute] (5) compute session secret [compute]
| |
| |
| ---- (6) req-VFY-C --------------> |
GET / HTTP/1.1 |--> [verify (6)]
Authorization: Mutual sid=..., |<-- OK
vkc="...", ... |
| |
| <--------------- (7) 200-VFY-S --- |
[verify | 200 OK |
(7)]<--| Authentication-Info: Mutual vks="..."
| |
v v
Figure 1: Typical communication flow for first access to resource
o As usual in general HTTP protocol designs, a client will at first
request a resource without any authentication attempt (1). If the
requested resource is protected by the Mutual authentication, the
server will respond with a message requesting authentication
(401-INIT) (2).
o The client processes the body of the message, and waits for the
user to input the user name and a password. If the user name and
the password are available, the client will send a message with
the authenticated key exchange (req-KEX-C1) to start the
authentication (3).
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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,the session secret values will
match. This session secret will be used for access authentication
of every individual request 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
[RFC1939]), 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 without any
interventions. Possible cause of such cases might be either a
man-in-the-middle attack or a mis-implementation.)
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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 (re-authentication)
(B-1) key available (B-2) key expired
(1 round trip) (3 round trips)
Client Server Client Server
| | | |
| ---- req-VFY-C ----> | | --- req-VFY-C -------> |
| | | |
| <----- 200-VFY-S --- | | <------- 401-STALE --- |
| | | |
| --- req-KEX-C1 ------> |
| |
| <------ 401-KEX-S1 --- |
| |
| --- req-VFY-C -------> |
| |
| <------- 200-VFY-S --- |
| |
Figure 2: Several alternative flows on protocol
For more details, see Sections 9 and 10.
3. Message Syntax
Throughout this specification, The syntax is denoted in the extended
augmented BNF syntax defined in [I-D.ietf-httpbis-p1-messaging] and
[RFC5234]. The following elements are quoted from [RFC5234],
[I-D.ietf-httpbis-p1-messaging] and [I-D.ietf-httpbis-p7-auth]:
DIGIT, ALPHA, SP, auth-scheme, quoted-string, auth-param, header-
field, token, challenge, and credential.
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The Mutual authentication protocol uses three headers:
WWW-Authenticate (in responses with status code 401), Authorization
(in requests), and Authentication-Info (in responses other than 401
status). These headers follow a common framework described in
[I-D.ietf-httpbis-p7-auth]. The detailed meanings for these headers
are contained in Section 4.
The framework in [I-D.ietf-httpbis-p7-auth] defines the syntax for
the headers WWW-Authenticate and Authorization as the syntax elements
"challenge" and "credentials", respectively. The "auth-scheme"
contained in those headers MUST be "Mutual" throughout this protocol
specification. The syntax for "challenge" and "credentials" to be
used with the "Mutual" auth-scheme SHALL be name-value pairs (#auth-
param), not the "b64token" defined in [I-D.ietf-httpbis-p7-auth].
The Authentication-Info: header used in this protocol SHALL contain
the value in same syntax as those the "WWW-Authenticate" header, i.e.
the "challenge" syntax element.
In HTTP, the WWW-Authenticate header may contain more than one
challenges. Client implementations SHOULD be aware of and be capable
of handle those cases correctly.
3.1. Values
The parameter values contained in challenge/credentials MUST be
parsed strictly conforming to the HTTP semantics (especially un-
quoting of the string parameter values). In this protocol, those
values are further categorized into the following value types: tokens
(bare-token and extensive-token), string, integer, hex-fixed-number,
and base64-fixed-number.
For clarity, implementations are RECOMMENDED to use the canonical
representations specified in the following subsections for sending
values. Recipients SHOULD accept both quoted and unquoted
representations interchangeably as specified in HTTP.
3.1.1. Tokens
For sustaining both security and extensibility at the same time, this
protocol defines a stricter sub-syntax for the "token" to be used.
The extensive-token values SHOULD follow the following syntax (after
HTTP value parsing):
bare-token = 1*(DIGIT / ALPHA / "-" / "_")
extension-token = "-" bare-token 1*("." bare-token)
extensive-token = bare-token / extension-token
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Figure 3: BNF syntax for token values
The tokens (bare-token and extension-token) are case insensitive;
Senders SHOULD send these in lower-case, and receivers MUST accept
both upper- and lower-cases. When tokens are used as (partial)
inputs to any hash or other mathematical functions, it MUST always be
used 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 SHOULD use the extension-tokens
with format "-<bare-token>.<domain-name>", where <domain-name> is a
validly registered (sub-)domain name on the Internet owned by the
party who defines the extensions.
Bare-tokens and extensive-tokens are also used for parameter names
(of course in the unquoted form). Requirements for using the
extension-token for the parameter names are the same as the above.
The canonical format for bare-tokens and tokens are unquoted tokens.
3.1.2. Strings
All character strings MUST be encoded to octet strings using the
UTF-8 encoding [RFC3629] for the ISO 10646-1 character set
[ISO.10646-1.1993]. Such strings MUST NOT contain any leading BOM
characters (ZERO WIDTH NO-BREAK SPACE, U+FEFF or EF BB BF). Both
peers are RECOMMENDED to reject any invalid UTF-8 sequences that
might cause decoding ambiguities (e.g., containing <"> in the second
or later bytes of the UTF-8 encoded characters).
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.
The canonical format for strings are quoted-string (as it may contain
equal signs, plus signs and slashes).
3.1.3. Numbers
The following syntax definitions gives a syntax for number-type
values:
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integer = "0" / (%x31-39 *DIGIT) ; no leading zeros
hex-fixed-number = 1*(2(DIGIT / %x41-46 / %x61-66))
base64-fixed-number = 1*( ALPHA / DIGIT / "+" / "/" ) 0*2"="
Figure 4: BNF syntax for number types
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). Those values
are case-insensitive, and SHOULD be sent in lower-case. When these
values are generated from any cryptographic values, they SHOULD have
their "natural length": if these are generated from a hash function,
these lengths SHOULD correspond to the hash size; if these are
representing elements of a mathematical set (or group), its lengths
SHOULD be the shortest for representing all the elements in the set.
For example, any results of SHA-256 hash function will be represented
by 64 characters, and any elements in 2048-bit prime field (modulo a
2048-bit integer) will be represented by 512 characters, regardless
of how much 0's will be appear in front of such representations.
Session-identifiers and other non-cryptographically generated values
are represented in any (even) length determined by the side who
generates it first, and the same length SHALL be used throughout the
all communications by both peers.
The numbers represented as base64-fixed-number SHALL be generated as
follows: first, the number is converted to a big-endian radix-256
binary representation as an octet string. The length of the
representation is determined in the same way as mentioned above.
Then, the string is encoded using the Base 64 encoding [RFC4648]
without any spaces and newlines. Implementations decoding base64-
fixed-number SHOULD reject any input data with invalid characters,
excess/insufficient paddings, or non-canonical pad bits (See Sections
3.1 to 3.5 of [RFC4648]).
The canonical format for integer and hex-fixed-number are unquoted
tokens, and that for base64-fixed-number is quoted-string.
4. Messages
In this section we define the seven kinds of messages used in the
authentication protocol along with the formats and requirements of
the headers for each message.
To determine which message are expected to be sent, see Sections 9
and 10.
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In the descriptions below, the type of allowable values for each
header parameter is shown in parenthesis after each parameter name.
The "algorithm-determined" type means that the acceptable value for
the parameter is one of the types defined in Section 3, and is
determined by the value of the "algorithm" parameter. The parameters
marked "mandatory" SHALL be contained in the message. The parameters
marked "non-mandatory" MAY either be contained or omitted in the
message. Each parameter SHALL appear in each headers exactly once at
most.
All credentials and challenges MAY contain any parameters not
explicitly specified in the following sections. Recipients who do
not understand such parameters MUST silently ignore those. However,
all credentials and challenges MUST meet the following criteria:
o For responses, the parameters "reason", any "ks*" (where * stands
for any decimal integers), and "vks" are mutually exclusive: any
challenge MUST NOT contain two or more parameters among them.
They MUST NOT contain any "kc*" and "vkc" parameters.
o For requests, the parameters "kc*" (where * stands for any decimal
integers), and "vkc" are mutually exclusive and any challenge
MUST NOT contain two or more parameters among them. They MUST NOT
contain any "ks*" and "vks" parameters.
Every message in this section contains a "version" field, to detect
future incompatible revisions of the protocol. Implementations of
the protocol described in this specification MUST always send a token
"-wg-draft01", and recipients MUST reject messages which contain any
other value as a version, unless another specification defines a
behavior for that version. [[Editorial Note: This token is updated
on every draft revisions which will affect the wire protocol. It
will (shall) be updated to "1" in the final published RFC.]]
4.1. 401-INIT and 401-STALE
Every 401-INIT or 401-STALE message SHALL be a valid HTTP 401-status
(Authentication Required) message containing one (and only one:
hereafter not explicitly noticed) "WWW-Authenticate" header
containing a "reason" parameter in the challenge. The challenge
SHALL contain all of the parameters marked "mandatory" below, and MAY
contain those marked "non-mandatory".
version: (mandatory extensive-token) should be the token "-wg-
draft01".
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algorithm: (mandatory extensive-token) specifies the
authentication algorithm to be used. The value MUST
be one of the tokens specified in
[I-D.oiwa-httpauth-mutual-algo] or other supplemental
specification documentation.
validation: (mandatory extensive-token) specifies the method of
host validation. The value MUST be one of the tokens
described in Section 7, or the tokens specified in
other supplemental specification documentation.
auth-domain: (non-mandatory string) specifies the authentication
domain, the set of hosts for which the authentication
credentials are valid. It MUST be one of the strings
described in Section 5. If the value is omitted, it
is assumed to be the "single-server" type domain in
Section 5.
realm: (mandatory string) is a UTF-8 encoded string
representing the name of the authentication realm
inside the authentication domain. As specified in
[I-D.ietf-httpbis-p7-auth], this value MUST always be
sent in the quoted-string form.
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 desirable.
reason: (mandatory extensive-token) SHALL be an extensive-
token which describes the possible reason of the
failed authentication/authorization. Both servers and
clients SHALL understand and support the following
three tokens:
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* initial: authentication was not tried because there
was no Authorization header in the corresponding
request.
* stale-session: the provided sid; in the request was
either unknown to or expired in the server.
* auth-failed: authentication trial was failed by
some reasons, possibly with a bad authentication
credentials.
Implementations MAY support the following tokens or
any extensive-tokens defined outside this
specification. If clients has received any unknown
tokens, these SHOULD treat these as if it were "auth-
failed" or "initial".
* reauth-needed: server-side application requires a
new authentication trial, regardless of the current
status.
* invalid-parameters: authentication was not even
tried in the server-side because some parameters
are not acceptable.
* internal-error: authentication was not even tried
in the server-side because there is some troubles
on the server-side.
* user-unknown: a special case of auth-failed,
suggesting that the provided user-name is invalid.
The use of this parameter is NOT RECOMMENDED for
security implications, except for special-purpose
applications which makes this value sense.
* invalid-credential: ditto, suggesting that the
provided user-name was valid but authentication was
failed. The use of this parameter is
NOT RECOMMENDED as the same as the above.
* authz-failed: authentication was successful, but
access to the specified resource is not authorized
to the specific authenticated user. (It is
different from 403 responses which suggest that the
reason of inaccessibility is other that
authentication.)
The algorithm specified in this header will determine the types
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(among those defined in Section 3) and the values for K_c1, K_s1,
VK_c and VK_s.
Among these messages, those with the reason parameter of value
"stale-session" will be called "401-STALE" messages hereafter,
because these have a special meaning in the protocol flow. Messages
with any other reason parameters will be called "401-INIT" messages.
4.2. req-KEX-C1
Every req-KEX-C1 message SHALL be a valid HTTP request message
containing an "Authorization" header with a credential containing a
"kc1" parameter.
The credential SHALL contain the parameters with the following names:
version: (mandatory, extensive-token) should be the token "-wg-
draft01".
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 HTTPAUTHprep
[I-D.oiwa-precis-httpauthprep] before encoding it to
UTF-8. [[Editorial: merger with new SASLprep is being
considered and discussed in precis WG. Replace the
reference once it is done.]]
kc1: (mandatory, algorithm-determined) is the client-side
key exchange value K_c1, which is specified by the
algorithm that is used.
4.3. 401-KEX-S1
Every 401-KEX-S1 message SHALL be a valid HTTP 401-status
(Authentication Required) response message containing a
"WWW-Authenticate" header with a challenge containing a "ks1"
parameter.
The challenge SHALL contain the parameters with the following names:
version: (mandatory, extensive-token) should be the token "-wg-
draft01".
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algorithm, validation, auth-domain, realm: MUST be the same value as
it is when received from the client.
sid: (mandatory, hex-fixed-number) MUST be a session
identifier, which is a random integer. The sid SHOULD
have uniqueness of at least 80 bits or the square of
the maximal estimated transactions concurrently
available in the session table, whichever is larger.
See Section 6 for more details.
ks1: (mandatory, algorithm-determined) is the server-side
key exchange value K_s1, which is specified by the
algorithm.
nc-max: (mandatory, integer) is the maximal value of nonce
counts that the server accepts.
nc-window: (mandatory, integer) the number of available nonce
slots that the server will accept. The value of the
nc-window parameter is RECOMMENDED to be 32 or more.
time: (mandatory, integer) represents the suggested time (in
seconds) that the client can reuse the session
represented by the sid. It is RECOMMENDED to be at
least 60. The value of this parameter is not directly
linked to the duration that the server keeps track of
the session represented by the sid.
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.
The all path elements contained in the parameter MUST
be inside the specified auth-domain; if not, clients
SHOULD ignore such elements. For better performance,
recognition of this parameter by clients are
significantly important.
4.4. req-VFY-C
Every req-VFY-C message SHALL be a valid HTTP request message
containing an "Authorization" header with a credential containing a
"vkc" parameter.
The parameters contained in the header are as follows:
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version: (mandatory, extensive-token) should be the token "-wg-
draft01".
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.
vkc: (mandatory, algorithm-determined) is the client-side
authentication verification value VK_c, which is
specified by the algorithm.
4.5. 200-VFY-S
Every 200-VFY-S message SHALL be a valid HTTP message that is not of
the 401 (Authentication Required) status, containing an
"Authentication-Info" header with a "vks" parameter.
The parameters contained in the header are as follows:
version: (mandatory, extensive-token) should be the token "-wg-
draft01".
sid: (mandatory, hex-fixed-number) MUST be the value
received from the client.
vks: (mandatory, algorithm-determined) is the server-side
authentication verification value VK_s, which is
specified by the algorithm.
The header MUST be sent before the content body: it MUST NOT be sent
in the trailer of a chunked-encoded response. If a "100 Continue"
response is sent from the server, the Authentication-Info header
SHOULD be included in that response, instead of the final response.
5. Authentication Realms
In this protocol, an "authentication realm" is defined as a set of
resources (URIs) for which the same set of user names and passwords
is valid for. If the server requests authentication for an
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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 MUST NOT automatically reuse the user names and
passwords for another realm.
Just like in Basic and Digest access authentication protocols, Mutual
authentication protocol supports multiple, separate protection spaces
to be set up inside each host. Furthermore, the protocol supports
that a single authentication realm spans over several hosts within
the same Internet domain.
Each authentication realm is defined and distinguished by the triple
of an "authentication algorithm", an "authentication domain", and a
"realm" parameter. However, server operators are NOT RECOMMENDED to
use the same pair of an authentication domain and a realm for
different authentication algorithms.
The realm parameter is a string as defined in Section 4.
Authentication domains are described in the remainder of this
section.
An authentication domain specifies the range of hosts that the
authentication realm spans over. In this protocol, it MUST be one of
the following strings.
o Single-server type: The string in format
"<scheme>://<host>:<port>", where <scheme>, <host>, and <port> are
the corresponding URI parts of the request URI. Even if the
request-URI does not have a port part, the string will include one
(i.e. 80 for http and 443 for https). The port part MUST NOT
contain leading zeros. Use this when authentication is only valid
for specific protocol (such as https).
o Single-host type: The "host" part of the requested URI. This is
the default value. Authentication realms within this kind of
authentication domain will span over several protocols (i.e. http
and https) and ports, but not over different hosts.
o Wildcard-domain type: The string in format "*.<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
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[RFC6265], that the specified domain is not to be assigned to any
specific organization (e.g. "*.com" or "*.jp"), the clients are
RECOMMENDED to reject the authentication request.
In the above specifications, every "scheme", "host", and "domain"
MUST be in lower-case, and any internationalized domain names beyond
the ASCII character set SHALL be represented in the way they are sent
in the underlying HTTP protocol, represented in lower-case
characters; i.e. these SHALL be in the form of the LDH labels in IDNA
[RFC5890]. All "port"s MUST be in the shortest, unsigned, decimal
number notation. Not obeying these requirements will cause failure
of valid authentication attempts.
5.1. Resolving Ambiguities
In the above definitions of authentication domains, several domains
will overlap each other. If a client has already been authenticated
to several realms applicable to the same server, the client may have
a multiple list of the "path" parameters received with the
"401-KEX-S1" message (see Section 4). If these path lists have any
overlap, a single URI may belong to multiple possible candidate of
realms to be authenticated to. In such cases, clients faces an
ambiguity on deciding which credentials to be sent for a new request
(in steps 3 and 4 of the decision procedure presented in Section 9).
In such cases, clients MAY send requests which belongs to any of
these candidate realms freely, or it MAY simply send an
unauthenticated request and see for which realm the server request an
authentication. Server operators are RECOMMENDED to provide
properly-configured "path" parameters (more precisely, disjoint path
sets for each realms) for clients so that such ambiguities will not
occur.
The following procedure are one of the possible tactics for resolving
ambiguity in such cases.
o If the client has previously sent a request to the same URI, and
if it remembers the authentication realm requested by 401-INIT
messages at that time, use that realm.
o In other cases, use one of authentication realms representing the
most-specific authentication domains. From the list of possible
domain specifications shown above, each one earlier has priority
over ones described after that.
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.
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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.
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 re-establish
another session without informing the users.
Sessions and session identifiers are local to each server (defined by
scheme, host and port), even if an authentication domain covers
multiple servers; the clients MUST establish separate sessions for
each port of a host to be accessed. Furthermore, sessions and
identifiers are also local to each authentication realm, even if
these are provided from the same server. The same session
identifiers provided either from different servers or for different
realms MUST be treated as independent ones.
The server SHOULD accept at least one req-VFY-C request for each
session, given that the request reaches the server in a time window
specified by the timeout parameter in the 401-KEX-S1 message, and
that there are no emergent reasons (such as flooding attacks) to
forget the sessions. After that, the server MAY discard any session
at any time and MAY send 401-STALE messages for any req-VFY-C
requests.
The client MAY send two or more requests using a single session
specified by the sid. However, for all such requests, each value of
the nonce (in the nc parameter) MUST satisfy the following
conditions:
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.
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o It is larger than (largest-nc - nc-window), where largest-nc is
the maximal value of nc which was previously sent in the session,
and nc-window is the value of the nc-window parameter which was
received from the server in the session.
The last condition allows servers to reject any nonce values that are
"significantly" smaller than the "current" value (defined by the
value of nc-window) of the nonce used in the session involved. In
other words, servers MAY treat such nonces as "already received".
This restriction enables servers to implement duplicated nonce
detection in a constant amount of memory (for each session).
Servers MUST check for duplication of the received nonces, and if any
duplication is detected, the server MUST discard the session and
respond with a 401-STALE message, as outlined in Section 10. The
server MAY also reject other invalid nonce values (such as ones above
the nc-max limit) by sending a 401-STALE message.
For example, assume the nc-window value of the current session is 32,
nc-max is 100, and that the client has already used the following
nonce values: {1-20, 22, 24, 30-38, 45-60, 63-72}. Then the nonce
values that can be used for next request is one of the following set:
{41-44, 61-62, 73-100}. The values {0, 21, 23, 25-29, 39-40} MAY be
rejected by the server because they are not above the current "window
limit" (40 = 72 - 32).
Typically, clients can ensure the above property by using a
monotonically-increasing integer counter that counts from zero upto
the value of nc-max.
The values of the nonces and any nonce-related values MUST always be
treated as natural numbers within an infinite range. Implementations
which uses fixed-width integer representations, fixed-precision
floating numbers or similar representations SHOULD NOT reject any
larger values which overflow such representative limits, and MUST NOT
silently truncate it using any modulus-like rounding operation (e.g.
by mod 2^32). Instead, the whole protocol is carefully designed so
that recipients MAY replace any such overflowed values (e.g. 2^80)
with some reasonably-large maximal representative integer (e.g. 2^31
- 1 or others).
7. Host Validation Methods
The "validation method" specifies a method to "relate" (or "bind")
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 vh that is
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an input to the authentication protocols.
When HTTPS or other possible secure transport is used, this
corresponds to the idea of "channel binding" described in [RFC5929].
Even when HTTP is used, similar, but somewhat limited, "binding" is
performed to prevent a malicious server from trying to authenticate
themselves to another server as a valid user by forwarding the
received credentials.
The valid tokens for the validation parameter and corresponding
values of vh are as follows:
host: host-name validation: The value vh 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 the default port number.
tls-server-end-point: TLS endpoint (certificate) validation: The
value vh will be the octet string of the hash value of
the server's public key certificate used in the
underlying TLS [RFC5246] (or SSL) connection,
processed as specified in Section 4.1 of [RFC5929].
[[Pending editorial issue: a small security issue is
pending around here, awaiting analysis and WG
discussions for final adoption.]]
tls-unique: TLS shared-key validation: The value v will be the
channel binding material derived from the Finished
messages, as defined in Section 3.1 of [RFC5929].
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 "tls-server-end-point". If HTTP/TLS protocol
is used with an anonymous Diffie-Hellman key exchange, the validation
type MUST be "tls-unique" (see the note below).
Implementations supporting a Mutual authentication over the HTTPS
protocol SHOULD support the "tls-server-end-point" validation.
Support for "tls-unique" validation is OPTIONAL for both the servers
and clients.
If the validation type "tls-server-end-point" is used, the server
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certificate provided on TLS connection MUST be verified at least to
make sure that the server actually owns the corresponding secret key.
(Note: this verification is automatic in some RSA-based key exchanges
but NOT automatic in Diffie-Hellman-based key exchanges with separate
exchange for server verifications.)
Clients MUST validate this parameter upon reception of the 401-INIT
messages.
Note: The protocol defines two variants for validation on the TLS
connections. The "tls-unique" method is more secure. However, there
are some situations where tls-server-end-point 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.
7.1. Applicability notes
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 cipher-suite 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.
7.2. Interoperability notes on tls-unique
As described in the interoperability note in the above channel
binding specification, the tls-unique verification value will be
changed by possible TLS renegotiation, causing an interoperability
problem. TLS re-negotiations are used in several HTTPS server
implementations for enforcing some security properties (such as
cryptographic strength) for some specific responses.
If an implementation supports "tls-unique" verification method, the
following caution SHOULD be taken:
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o Both peers must be aware that the values vh used for vkc (in
req-VFY-C) and for vks (in 200-VFY-S) may be different. These
values MUST be retrieved from underlying TLS libraries each time
it is used.
o After calculating value vh and vkc to send a req-VFY-C request,
Clients SHOULD NOT initiate TLS renegotiation until the end of the
corresponding response header is received. Exceptionally, Clients
can and SHOULD perform TLS re-negotiation as a response to
server's request for TLS renegotiation, occurring before the top
of response header.
8. Authentication Extensions
Interactive clients (e.g. Web browsers) supporting this protocol are
RECOMMENDED to support non-mandatory authentication and the
Authentication-Control header defined in
[I-D.ietf-httpauth-extension], except the "auth-style" parameter.
This specification also proposes (however, not mandates) default
"auth-style" to be "non-modal". Web applications SHOULD however
consider the security impacts of the behaviors of clients that do not
support these headers.
Authentication-initializing messages with the
Optional-WWW-Authenticate header are used only where 401-INIT
response is valid. It will not replace other 401-type messages such
as 401-STALE and 401-KEX-S1.
9. Decision Procedure for Clients
To securely implement the protocol, the user client must be careful
about accepting the authenticated responses from the server. This
also holds true for the reception of "normal responses" (responses
which do not contain Mutual-related headers) from HTTP servers.
Clients SHOULD implement a decision procedure equivalent to the one
shown below. (Unless implementers understand what is required for
the security, they should not alter this.) In particular, clients
SHOULD NOT accept "normal responses" unless explicitly allowed below.
The labels on the steps are for informational purposes only. Action
entries within each step are checked in top-to-bottom order, and the
first clause satisfied SHOULD be taken.
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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 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.
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 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 normal response, go to Step 11.
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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.
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.
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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):
The received message is the 200-VFY-S message, which SHALL always
contain a vks field. Check the validity of the received VK_s
value. If it is equal to the expected value, it means that the
mutual authentication has succeeded. The client will be in the
"AUTH-SUCCEEDED" status.
If the value is unexpected, it is a fatal communication error.
If a user explicitly requests to log out (via user interfaces),
the client MUST forget the user's password, go to step 5 and
reload the current resource without an authentication header.
Note 1: These transitions MAY be accepted by clients, but
NOT RECOMMENDED for servers to initiate.
Any kind of response (including a normal response) other than those
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. In such cases, they SHOULD be careful
about processing the body of the content (ignoring it is still
RECOMMENDED), and the client will be in the "UNAUTHENTICATED" status
then.
If a request is a sub-request for a resource included in another
resources (e.g., embedded images, style sheets, frames etc.), clients
MAY treat an AUTH-REQUESTED status as the same as UNAUTHENTICATED
status. In other words, the client MAY ignore server's request to
start authentication with new credentials via sub-requests.
Figure 5 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 401-INIT|
| with a different realm |
| -----------------------------------. |
| / 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 5: State diagram for clients
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10. Decision Procedure for Servers
Each server SHOULD have a table of session states. This table need
not be persistent over a long term; it MAY be cleared upon server
restart, reboot, or others. Each entry in the table SHOULD contain
at least the following information:
o The session identifier, the value of the sid parameter.
o The algorithm used.
o The authentication realm.
o The state of the protocol: one of "key exchanging",
"authenticated", "rejected", or "inactive".
o The user name received from the client
o The boolean flag noting whether or not the session is fake.
o When the state is "key exchanging", the values of K_c1 and S_s1.
o When the state is "authenticated", the following information:
* The value of the session secret z
* The largest nc received from the client (largest-nc)
* For each possible nc values between (largest-nc - nc-
window + 1) and max_nc, a flag whether or not a request with
the corresponding nc has been received.
The table MAY contain other information.
Servers SHOULD respond to the client requests according to the
following procedure: (See Note 1 below for 401-INIT message with *
marks)
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.
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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 a 401-INIT response.
* If the server cannot validate the parameter kc1, send a
401-INIT (*) response.
* If the received user name is either invalid, unknown or
unacceptable, create a new session, mark it a "fake" session,
compute a random value as K_s1, and send a fake 401-KEX-S1
response. (Note 2)
* Otherwise, create a new session, compute K_s1 and send a
401-KEX-S1 response.
The created session has the "key exchanging" state.
o When the server receives a req-VFY-C request:
* If the requested resource is not protected by the Mutual
Authentication, send a normal response.
* If the authentication realm specified in the req-VFY-C request
is not the expected one, send a 401-INIT response.
If none of above holds true, the server will lookup the session
corresponding to the received sid and the authentication realm.
* If the session corresponding to the received sid could not be
found, or it is in the "inactive" state, send a 401-STALE
response.
* If the session is in the "rejected" state, send either a
401-INIT (*) or a 401-STALE message.
* If the session is in the "authenticated" state, and the request
has an nc value that was previously received from the client,
send a 401-STALE message. The session SHOULD be changed to the
"inactive" status.
* If the nc value in the request is larger than the nc-max
parameter sent from the server, or if it is not larger then
(largest-nc - nc-window) (when in "authenticated" status), the
server MAY (but not REQUIRED to) send a 401-STALE message. The
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session SHOULD be changed to the "inactive" status if so.
* If the session is a "fake" session, or if the received vkc is
incorrect, then send a 401-INIT (*) response. If the session
is in the "key exchanging" state, it SHOULD be changed to the
"rejected" state; otherwise, it MAY either be changed to the
"rejected" status or kept in the previous state.
* Otherwise, send a 200-VFY-S response. If the session was in
the "key exchanging" state, the session SHOULD be changed to an
"authenticated" state. The maximum nc and nc flags of the
state SHOULD be updated properly.
At any time, the server MAY change any state entries with both the
"rejected" and "authenticated" statuses to the "inactive" status, and
MAY discard any "inactive" states from the table. The entries with
the "key exchanging" status SHOULD be kept unless there is an
emergency situation such as a server reboot or a table capacity
overflow.
Note 1: In relation with, and following the specification of the
optional authentication defined in [I-D.ietf-httpauth-extension], the
401-INIT messages marked with the asterisks can not be replaced with
a successful responses with an Optional-WWW-Authenticate header.
Every other 401-INIT can be a response with an
Optional-WWW-Authenticate.
Note 2: 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.
11. Authentication Algorithms
Cryptographic authentication algorithms which are used with this
protocol will be defined separately. The algorithm definition MUST
at least provide a definitions for the following functions:
o The server-side authentication credential J, derived from user-
side authentication credential pi.
o Key exchange values K_c1, K_s1 (exchanged on wire) and S_c1, S_s1
(kept secret in each peer).
o Shared secret z, to be computed in both server-side and client
side.
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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-
phrases or any equivalents, i.e. weak secrets) are involved, these
SHOULD NOT be guessable from any data transmitted in the protocol,
even if an attacker (either an eavesdropper or an active server)
knows the possible thoroughly-searchable candidate list of the
passwords. Furthermore, if possible, the function for deriving
server-side authentication credential J is RECOMMENDED to be one-way
so that pi should not be easily computed from J(pi).
11.1. Support Functions and Notations
In this section we define several support functions and notations to
be shared by several algorithm definitions:
The integers in the specification are in decimal, or in hexadecimal
when prefixed with "0x".
The function octet(c) generates a single octet string whose code
value is equal to c. The operator |, when applied to octet strings,
denotes the concatenation of two operands.
The function VI encodes natural numbers into octet strings in the
following manner: numbers are represented in big-endian radix-128
string, where each digit is represented by a octet within 0x80-0xff
except the last digit represented by a octet within 0x00-0x7f. The
first octet MUST NOT be 0x80. For example, VI(i) = octet(i) for i <
128, and VI(i) = octet(0x80 + (i >> 7)) | octet(i & 127) for 128 <= i
< 16384. This encoding is the same as the one used for the
subcomponents of object identifiers in the ASN.1 encoding
[ITU.X690.1994], and available as a "w" conversion in the pack
function of several scripting languages.
The function VS encodes a variable-length octet string into a
uniquely-decoded, self-delimited octet string, as in the following
manner:
VS(s) = VI(length(s)) | s
where length(s) is a number of octets (not characters) in s.
Some examples:
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VI(0) = "\000" (in C string notation)
VI(100) = "d"
VI(10000) = "\316\020"
VI(1000000) = "\275\204@"
VS("") = "\000"
VS("Tea") = "\003Tea"
VS("Caf<e acute>" [in UTF-8]) = "\005Caf\303\251"
VS([10000 "a"s]) = "\316\020aaaaa..." (10002 octets)
(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 3.1.3 for the definition of "natural length".
The function INT converts an octet string into a natural number,
where the input string is treated as a radix-256 big-endian notation.
The identity INT(OCTETS(n)) = n always holds for any natural number
n.
11.2. Default Functions for Algorithms
The functions defined in this section are common default functions
among authentication algorithms.
The client-side password-based (credential) pi used by this
authentication is a natural number derived in the following manner:
pi = INT(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 message. The function ph is
determined by the value of the pwd-hash parameter given in a 401-INIT
message. If the password comes from a user input, it SHOULD first be
prepared using I-D.oiwa-precis-httpauthprep [RFC4013]. Then, the
password SHALL be encoded as a UTF-8 string before passed to ph.
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The values VK_c and VK_s are derived by the following equation.
VK_c = INT(H(octet(4) | OCTETS(K_c1) | OCTETS(K_s1) | OCTETS(z) |
VI(nc) | VS(vh)))
VK_s = INT(H(octet(3) | OCTETS(K_c1) | OCTETS(K_s1) | OCTETS(z) |
VI(nc) | VS(vh)))
Specifications for cryptographic algorithms used with this framework
MAY override the functions pi, VK_c, and VK_s defined above. In such
cases implementations MUST use the ones defined with such algorithm
specifications.
12. Application Channel Binding
Applications and upper-layer communication protocols may need
authentication binding to the HTTP-layer authenticated user. Such
applications MAY use the following values as a standard shared
secret.
These values are parameterized with an optional octet string (t)
which may be arbitrarily chosen by each applications or protocols.
If there is no appropriate value to be specified, use a null string
for t.
For applications requiring binding to either an authenticated user or
a shared-key session (to ensure that the requesting client is
certainly authenticated), the following value b_1 MAY be used.
b_1 = H(H(octet(6) | OCTETS(K_c1) | OCTETS(K_s1) | OCTETS(z) | VI(0)
| VS(vh)) | VS(t)).
For applications requiring binding to a specific request (to ensure
that the payload data is generated for the exact HTTP request), the
following value b_2 MAY be used.
b_2 = H(H(octet(7) | OCTETS(K_c1) | OCTETS(K_s1) | OCTETS(z) | VI(nc)
| VS(vh)) | VS(t)).
Note: Channel bindings to lower-layer transports (TCP and TLS) are
defined in Section 7.
13. Application for Proxy Authentication
The authentication scheme defined by the previous sections can be
applied (with modifications) for proxy authentications. In such
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cases, the following alterations MUST be applied:
o The 407 status is to be sent and recognized for places where the
401 status is used,
o Proxy-Authenticate: header is to be used for places where WWW-
Authenticate: is used,
o Proxy-Authorization: header is to be used for places where
Authorization: is used,
o Proxy-Authentication-Info: header is to be used for places where
Authentication-Info: is used,
o The auth-domain parameter is fixed to the host-name of the proxy,
which means to cover all requests processed through the specific
proxy,
o The limitation for the paths contained in the path parameter of
401-KEX-S1 messages is disregarded,
o The omission of the path parameter of 401-KEX-S1 messages means
that the authentication realm will potentially cover all requests
processed by the proxy,
o The scheme, host name and the port of the proxy is used for host
validation tokens, and
o Authentication extensions in [I-D.ietf-httpauth-extension] are not
applicable.
14. Methods to Extend This Protocol
If a private 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. (standardized or being-
standardizing extensions MAY use either bare-tokens or extension-
tokens.)
Specifications defining authentication algorithms MAY use other
representations for the parameters "kc1", "ks1", "vkc", and "vks",
replace those parameter names, and/or add parameters to the messages
containing those parameters in supplemental specifications, provided
that syntactic and semantic requirements in Section 3,
[I-D.ietf-httpbis-p1-messaging] and [I-D.ietf-httpbis-p7-auth] are
satisfied. Any parameters starting with "kc", "ks", "vkc" or "vks"
and followed by decimal natural numbers (e.g. kc2, ks0, vkc1, vks3
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etc.) are reserved for this purpose. If those specifications use
names other than those mentioned above, it is RECOMMENDED to use
extension-tokens to avoid any parameter 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 parameters provided that the
domain part in the token is appropriately used.
15. IANA Considerations
When bare-tokens are used for the authentication-algorithm, pwd-hash,
and validation parameters MUST be allocated by IANA. To acquire
registered tokens, a specification for the use of such tokens MUST be
available as an RFC, as outlined in [RFC5226].
Note: More formal declarations will be added in the future drafts to
meet the RFC 5226 requirements.
16. Security Considerations
16.1. Security Properties
o The protocol is secure against passive eavesdropping and replay
attacks. However, the protocol relies on transport security
including DNS integrity for data secrecy and integrity. HTTP/TLS
SHOULD be used where transport security is not assured and/or data
confidentiality 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).
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16.2. Denial-of-service Attacks to Servers
The protocol requires a server-side table of active sessions, which
may become a critical point of the server resource consumptions. For
proper operation, the protocol requires that at least one key
verification request is processed for each session identifier. After
that, servers MAY discard sessions internally at any time, without
causing any operational problems to clients. Clients will silently
reestablishes a new session then.
However, if a malicious client sends too many requests of key
exchanges (req-KEX-C1 messages) only, resource starvation might
occur. In such critical situations, servers MAY discard any kind of
existing sessions regardless of these statuses. One way to mitigate
such attacks are that servers MAY have a number and a time limits for
unverified pending key exchange requests (in the "key exchanging"
status).
This is a common weakness of authentication protocols with almost any
kind of negotiations or states, including Digest authentication
method and most Cookie-based authentication implementations.
However, regarding the resource consumption, a situation of the
mutual authentication method is a slightly better than the Digest,
because HTTP requests without any kind of authentication requests
will not generate any kind of sessions. Session identifiers are only
generated after a client starts a key negotiation. It means that
simple clients such as web crawlers will not accidentally consume
server-side resources for session managements.
16.2.1. On-line Active Password Attacks
Although the protocol provides very strong protection against off-
line dictionary attacks from eavesdropped traffics, the protocol, by
its nature, can not prevent an active password attacks which the
attackers sends so many authentication trial requests for every
possible passwords.
Possible countermeasures for preventing such attacks may be rate-
limiting of the password authentication trials, statistics-based
intrusion detection measures or similar protection schemes. If the
server operators assume that the passwords of users are not strong
enough, it may be desirable to introduce such ad-hoc countermeasures.
16.3. Communicating the status of mutual authentication with users
This protocol is designed for two goals. The first goal is just
providing a secure alternative for existing Basic and Digest
authentication. The second goal is to provide users a way to detect
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forged rogue servers imitating user's registered account on server-
side, commonly known as (a part or kind of) Phishing attacks.
For this protocol to effectively work as some countermeasures to such
attacks, it is very important that end users of clients will be
notified of the result of mutual authentication performed by this
protocol, especially the three states "AUTH-SUCCEED",
"UNAUTHENTICATED" and "AUTH-REQUIRED" defined in Section 9. The
design of secure users' interfaces of the HTTP interactive clients
are out of the scope of this document, but if possible, having some
kind of UI indication for the three states above will be desirable
for user's benefits on their security.
Of course, in such cases, the user interfaces for asking passwords
for this authentication shall be clearly identifiable against
imitation by other insecure password input fields (such as forms).
If the passwords are known to malicious attackers outside of the
protocol, the protocol can not work as an effective security
measures.
16.4. 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 For HTTP/TLS communications, when a web form is submitted from
Mutually-authenticated pages with the "tls-server-end-point"
validation method to a URI that is protected by the same realm (so
indicated by the path parameter), if the server certificate has
been changed since the pages were received, the peer is
RECOMMENDED to be revalidated using a req-KEX-C1 message with an
"Expect: 100-continue" header. The same applies when the page is
received with the "tls-unique" validation method, and when the TLS
session has expired.
o For better protection against possible password database steal,
Server-side storages of user passwords are better containing the
values encrypted by one-way function J(pi), instead of the real
passwords, those hashed by ph, or pi.
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16.5. 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 and HTTPS. Contrarily, passwords are not exposed
to eavesdroppers even on HTTP requests.
o The "pwd-hash" parameter is only provided for backward
compatibility of password databases. The use of "none" function
is the most secure choice and is RECOMMENDED. If values other
than "none" are used, you MUST ensure that the hash values of the
passwords were not exposed to the public. Note that hashed
password databases for plain-text authentications are usually not
considered secret.
o If the server provides several ways for storing server-side
password secrets into the password database, it is desirable for
better security to store the values encrypted by using the one-way
function J(pi), instead of the real passwords, those hashed by ph,
or pi.
17. Notice on Intellectual Properties
The National Institute of Advanced Industrial Science and Technology
(AIST) and Yahoo! Japan, Inc. has jointly submitted a patent
application on the protocol proposed in this documentation to the
Patent Office of Japan. The patent is intended to be open to any
implementors of this protocol and its variants under non-exclusive
royalty-free manner. For the details of the patent application and
its status, please contact the author of this document.
The elliptic-curve based authentication algorithms might involve
several existing third-party patents. The authors of the document
take no position regarding the validity or scope of such patents, and
other patents as well.
18. References
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18.1. Normative References
[I-D.ietf-httpauth-extension]
Oiwa, Y., Watanabe, H., Takagi, H., Hayashi, T., and Y.
Ioku, "HTTP Authentication Extensions for Interactive
Clients", draft-ietf-httpauth-extension-01 (work in
progress), October 2013.
[I-D.ietf-httpbis-p1-messaging]
Fielding, R. and J. Reschke, "Hypertext Transfer Protocol
(HTTP/1.1): Message Syntax and Routing",
draft-ietf-httpbis-p1-messaging-24 (work in progress),
September 2013.
[I-D.ietf-httpbis-p7-auth]
Fielding, R. and J. Reschke, "Hypertext Transfer Protocol
(HTTP/1.1): Authentication", draft-ietf-httpbis-p7-auth-24
(work in progress), September 2013.
[I-D.oiwa-precis-httpauthprep]
Oiwa, Y., NEMOTO, T., and B. Kihara, "HTTPAuthPrep: PRECIS
profile for HTTP Authentication",
draft-oiwa-precis-httpauthprep-00 (work in progress),
July 2013.
[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.
18.2. Informative References
[I-D.ietf-precis-framework]
Saint-Andre, P. and M. Blanchet, "PRECIS Framework:
Preparation and Comparison of Internationalized Strings in
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Application Protocols", draft-ietf-precis-framework-11
(work in progress), October 2013.
[I-D.oiwa-httpauth-mutual-algo]
Oiwa, Y., Watanabe, H., Takagi, H., Hayashi, T., and Y.
Ioku, "Mutual Authentication Protocol for HTTP: KAM3-based
Cryptographic Algorithms",
draft-oiwa-httpauth-mutual-algo-01 (work in progress),
October 2013.
[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.
[RFC1939] Myers, J. and M. Rose, "Post Office Protocol - Version 3",
STD 53, RFC 1939, May 1996.
[RFC2617] Franks, J., Hallam-Baker, P., Hostetler, J., Lawrence, S.,
Leach, P., Luotonen, A., and L. Stewart, "HTTP
Authentication: Basic and Digest Access Authentication",
RFC 2617, June 1999.
[RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008.
[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.
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Appendix A. (Informative) Draft Remarks from Authors
The following items are currently under consideration for future
revisions by the authors.
o Whether to keep TLS-unique validation or not.
o Whether to introduce PBKDF2 or similar password strengthening
hashes into the function pi().
o Whether to keep ph() function for legacy migration or not.
o Adding test vectors for ensuring implementation correctness.
o Possibly adding a method for servers to detect availability of
Mutual authentication on client-side.
Appendix B. (Informative) Draft Change Log
B.1. Changes in Httpauth WG Revision 01
o Changed "tls-key" verification to "tls-unique" verification, and
"tls-cert" to "tls-server-end-point", adopting RFC 5929.
o Adopted [I-D.ietf-precis-framework].
o Reverted reservation of "rekey-sid" and "rekey-method" parameters.
o Degraded secure UI requirement to application note level, non-
normative.
o Adjusted levels of several requirements.
o Added warning text for handling of exceptional 5XX responses.
o Dropped several references for optional authentications, except
one "Note".
o Several textual fixes, improvements and revisions.
B.2. Changes in Httpauth Revision 00
o Changed the version token.
o Renamed "verification tokens" to "Host verification tokens" and
variables "v" to "vh" for clarification. (Back-ported from
draft-oiwa-httpauth-multihop-template-00)
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B.3. Changes in HttpBis Revision 00
None.
B.4. Changes in Revision 12
o Added a reason "authz-failed".
B.5. Changes in Revision 11
o Message syntax definition reverted to pre-07 style as httpbis-p1
and p7 now defines a precise rule for parameter value parsing.
o Replaced "stale" parameter with more infomative/extensive "reason"
parameter in 401-INIT and 401-STALE.
o Reserved "rekey-sid" and "rekey-method" parameters for future
extensions.
o Added descriptions for replacing/non-replacing existing
technologies.
B.6. Changes in Revision 10
o The authentication extension parts (non-mandatory authentication
and authentication controls) are separated to yet another draft.
o The default auth-domain parameter is changed to the full scheme-
host-port syntax, which is consistent with usual HTTP
authentication framework behavior.
o Provision for application channel binding is added.
o Provision for proxy access authentication is added.
o Bug fix: syntax specification of sid parameter was wrong: it was
inconsistent with the type specified in the main text (the bug
introduced in -07 draft).
o Terminologies for headers are changed to be in harmony with
httpbis drafts (e.g. field to parameter).
o Syntax definitions are changed to use HTTP-extended ABNF syntax,
and only the header values are shown for header syntax, in harmony
with httpbis drafts.
o Names of parameters and corresponding mathematical values are now
renamed to more informative ones. The following list shows
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correspondence between the new and the old names.
+------------+----------+-------------------------------------------+
| new name | old name | description |
+------------+----------+-------------------------------------------+
| S_c1, S_s1 | s_a, s_b | client/server-side secret randoms |
| K_c1, K_s1 | w_a, w_b | client/server-side exchanged key |
| | | components |
| kc1, ks1 | wa, wb | parameter names for those |
| VK_c, VK_s | o_a, o_b | client/server-side key verifiers |
| vkc, vks | oa, ob | parameter names for those |
| z | z | session secrets |
+------------+----------+-------------------------------------------+
B.7. Changes in Revision 09
o The (default) cryptographic algorithms are separated to another
draft.
o Names of the messages are changed to more informative ones than
before. The following is the correspondence table of those names:
+-------------------+-----------------+-----------------------------+
| new name | old name | description |
+-------------------+-----------------+-----------------------------+
| 401-INIT | 401-B0 | initial response |
| 401-STALE | 401-B0-stale | session key expired |
| req-KEX-C1 | req-A1 | client->server key exchange |
| 401-KEX-S1 | 401-B1 | server->client key exchange |
| req-VFY-C | req-A3 | client->server auth. |
| | | verification |
| 200-VFY-S | 200-B4 | server->client auth. |
| | | verification |
| 200-Optional-INIT | 200-Optional-B0 | initial with non-mandatory |
| | | authentication |
+-------------------+-----------------+-----------------------------+
B.8. Changes in Revision 08
o The English text has been revised.
B.9. Changes in Revision 07
o Adapt to httpbis HTTP/1.1 drafts:
* Changed definition of extensive-token.
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* LWSP continuation-line (%0D.0A.20) deprecated.
o To simplify the whole spec, the type of nonce-counter related
parameters are change from hex-integer to integer.
o Algorithm tokens are renamed to include names of hash algorithms.
o Clarified the session management, added details of server-side
protocol decisions.
o The whole draft was reorganized; introduction and overview has
been rewritten.
B.10. 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.
B.11. Changes in Revision 05
o A new parameter called "version" is added for supporting future
incompatible changes with a single implementation. In the (first)
final specification its value will be changed to 1.
o A new header "Authentication-Control" is added for precise control
of application-level authentication behavior.
B.12. 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.
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B.13. Changes in Revision 03
o Wildcard domain specifications (e.g. "*.example.com") are allowed
for auth-domain parameters (Section 4.1).
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.
B.14. Changes in Revision 02
o Auth-realm is extended to allow full-scheme type.
o A decision diagram for clients and decision procedures for servers
are added.
o 401-B1 and req-A3 messages are changed to contain authentication
realm information.
o Bugs on equations for o_A and o_B are fixed.
o Detailed equations for the entire algorithm are included.
o Elliptic-curve algorithms are updated.
o Several clarifications and other minor updates.
B.15. Changes in Revision 01
o Several texts are rewritten for clarification.
o Added several security consideration clauses.
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Authors' Addresses
Yutaka Oiwa
National Institute of Advanced Industrial Science and Technology
Research Institute for Secure Systems
3-11-46 Nakouji
Amagasaki, Hyogo
JP
Email: mutual-auth-contact-ml@aist.go.jp
Hajime Watanabe
National Institute of Advanced Industrial Science and Technology
Research Institute for Secure Systems
Tsukuba Central 2
1-1-1 Umezono
Tsukuba-shi, Ibaraki
JP
Hiromitsu Takagi
National Institute of Advanced Industrial Science and Technology
Research Institute for Secure Systems
Tsukuba Central 2
1-1-1 Umezono
Tsukuba-shi, Ibaraki
JP
Tatsuya Hayashi
Lepidum Co. Ltd.
#602, Village Sasazuka 3
1-30-3 Sasazuka
Shibuya-ku, Tokyo
JP
Yuichi Ioku
Individual
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