Internet DRAFT - draft-oiwa-httpauth-multihop-template
draft-oiwa-httpauth-multihop-template
Internet Engineering Task Force Y. Oiwa
Internet-Draft H. Watanabe
Intended status: Experimental H. Takagi
Expires: August 22, 2013 RISEC, AIST
B. Kihara
T. Hayashi
Lepidum
Y. Ioku
Yahoo! Japan
February 18, 2013
Common Template for HTTP Message-based Multi-hop Authentication
draft-oiwa-httpauth-multihop-template-00
Abstract
This document specifies a common protocol design template for
authentication on the Hyper-text Transport Protocol (HTTP) involving
multi-hop message exchanges. To facilitate advanced authentication
technologies such as hash-based exchanges, zero-knowledge password
proof, or public-key authentications on HTTP, a kind of state
management and key management facilities are required on the general
HTTP authentication message framework. Also, to optimize performance
of such authentication schemes, a well-designed mechanism for key
caching and re-authentication are needed. The template defined in
this document provides a generic foundation for implementing such
advanced authentication technologies.
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 August 22, 2013.
Copyright Notice
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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
(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.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. How to Use This Document . . . . . . . . . . . . . . . . . 4
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 5
1.3. Document Structure and Related Documents . . . . . . . . . 6
2. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 6
2.1. Messages Overview . . . . . . . . . . . . . . . . . . . . 6
2.2. Typical Flows of the Protocol . . . . . . . . . . . . . . 7
2.3. Alternative Flows . . . . . . . . . . . . . . . . . . . . 9
3. Message Syntax . . . . . . . . . . . . . . . . . . . . . . . . 11
3.1. Values . . . . . . . . . . . . . . . . . . . . . . . . . . 12
3.1.1. Tokens . . . . . . . . . . . . . . . . . . . . . . . . 12
3.1.2. Strings . . . . . . . . . . . . . . . . . . . . . . . 13
3.1.3. Numbers . . . . . . . . . . . . . . . . . . . . . . . 13
4. Messages . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
4.1. 401-INIT and 401-STALE . . . . . . . . . . . . . . . . . . 15
4.2. req-KEX-C1 . . . . . . . . . . . . . . . . . . . . . . . . 16
4.3. 401-KEX-S1 . . . . . . . . . . . . . . . . . . . . . . . . 17
4.4. req-VFY-C . . . . . . . . . . . . . . . . . . . . . . . . 18
4.5. 200-VFY-S . . . . . . . . . . . . . . . . . . . . . . . . 18
5. Session Management . . . . . . . . . . . . . . . . . . . . . . 19
6. Host Validation Methods . . . . . . . . . . . . . . . . . . . 21
7. Decision Procedure for Clients . . . . . . . . . . . . . . . . 22
8. Decision Procedure for Servers . . . . . . . . . . . . . . . . 27
9. Applying for Specific Authentication Schemes . . . . . . . . . 29
9.1. Default Functions for Algorithms . . . . . . . . . . . . . 30
10. Application Channel Binding . . . . . . . . . . . . . . . . . 30
11. String Preparation . . . . . . . . . . . . . . . . . . . . . . 31
12. Application for Proxy Authentication . . . . . . . . . . . . . 31
13. Methods to extend this protocol template . . . . . . . . . . . 32
14. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 33
15. Security Considerations . . . . . . . . . . . . . . . . . . . 33
15.1. Security Properties . . . . . . . . . . . . . . . . . . . 33
15.2. Denial-of-service Attacks to Servers . . . . . . . . . . . 33
16. References . . . . . . . . . . . . . . . . . . . . . . . . . . 34
16.1. Normative References . . . . . . . . . . . . . . . . . . . 34
16.2. Informative References . . . . . . . . . . . . . . . . . . 35
Appendix A. (Normative) Support Functions and Notations . . . . . 35
Appendix B. (Informative) Draft Remarks from Authors . . . . . . 37
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 37
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1. Introduction
This document specifies a common protocol design template for
authentication on the Hyper-text Transport Protocol (HTTP) involving
multi-hop message exchanges.
To facilitate advanced authentication technologies such as hash-based
exchanges, zero-knowledge password proof, or public-key
authentications on HTTP, a kind of state management and key
management facilities are required on the general HTTP authentication
message framework. Also, to optimize performance of such
authentication schemes, a well-designed mechanism for key caching and
re-authentication are needed.
The template defined in this document provides a generic foundation
for implementing such advanced authentication technologies. Such
generic foundations can reduce cumbersomeness of both designers and
implementors of such authentication protocols on HTTP. By using this
template, protocol designers can easily apply any specific
authenticated key exchange (or agreement) mechanisms onto HTTP
protocol and enable authentication session management, shared-key
based optimized re-authentication.
The design template provided on this document is mainly designed for
multi-hop authentication mechanisms which do not use connection-based
session managements. Some of existing authentication technologies
applied on HTTP/1.0 or 1.1 are bound to underlying TCP connection,
which violates strict definition of HTTP stateless semantics and not
directly applicable to forthcoming HTTP/2.0. Retrofitting of such
existing authentication schemes are out-of-scope of this
specification (although, an additional specification for such
retrofitting _may_ be defined on top of this template).
The template is defined using terminology and representation of
existing HTTP/1.1, but it can be also directly applied on forthcoming
HTTP/2.0.
1.1. How to Use This Document
This document is only providing a "template" for actual
implementation of HTTP authentication: by itself only it will be
useless. To use this document, there must be a specific definition
document for each authentication schemes referring to this document.
In other words, this document and such a specific definitions will
compose "layers" of protocol definitions, the latter will exist upon
the former.
However, for implementors' perspective, the definitions in this
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document can be implemented as a "base class" for multi-hop
authentication: such class can be a common bases for "deriving"
implementations of each authentication schemes, which will avoid
duplicated implementation of same features and reduce burdens for
testing such implementations one by one.
For terminology, this document uses the following three terms for
referring each "layers" of protocols:
o "The authentication template" or "this template" will refer to the
common protocol template defined in this document.
o "Authentication scheme(s)" will refer to a scheme which will
realize a specific purpose/method of authentication. Examples of
these schemes (which do not always depend on "this template") are
Basic, Digest and others. Each of them will also correspond to a
specific "auth-scheme" in the HTTP headers.
o "Sub-algorithms" or simply "algorithms" in an authentication
scheme will refer to variations within a single authentication
scheme which will provide a small differences of authentication
properties such as cryptographic strength or others. Examples of
them are "auth" and "auth-int" in Digest. Differences of used
cryptographic primitives and/or parameters which provides the same
functionalities except strengths (e.g. key lengths, hash choices
etc.) will often fall into this category.
1.2. 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
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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This document treats target (codomain) of hash functions to be
natural numbers. The notation OCTETS(H(s)) gives a usual octet-
string output of hash function H applied to string s.
1.3. 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 8 define a general template for the multi-hop
authentication protocol. This template is independent of specific
cryptographic primitives and authentication schemes.
o Section 9 describes requirements for each authentication schemes
used with this protocol template, 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 template, 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, defined for each authentication schemes. The key-exchange
will derive the same session keys only when the clients and servers
are agreed with the authentication credentials used. 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 Overview
The authentication protocol template uses six kinds of messages to
perform multi-hop authentication. These messages have specific names
within this specification.
o Authentication request messages: used by the servers to request
clients to start authentication.
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* 401-INIT message: a general message to start the authentication
exchange. 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 session key (shared 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
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: Example realm="a realm"
| |
[user, | |
cred.]->| |
| ---- (3) req-KEX-C1 -------------> |
GET / HTTP/1.1 |
Authorization: Example user="john", |--> [user DB]
kc1="...", ... |<-- [user info]
| |
| <-------------- (4) 401-KEX-S1 --- |
| 401 Authentication Required
| WWW-Authenticate: Example sid=..., ks1="...", ...
| |
[compute] (5) compute session secret [compute]
| |
| |
| ---- (6) req-VFY-C --------------> |
GET / HTTP/1.1 |--> [verify (6)]
Authorization: Example sid=..., |<-- OK
vkc="...", ... |
| |
| <--------------- (7) 200-VFY-S --- |
[verify | 200 OK |
(7)]<--| Authentication-Info: Example 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 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 authentication credentials (such as a user name
and a password). When the credentials to be used become
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. It is
assumed that underlying authentication protocol will generate the
same "session secret" on both sides only when the user
authentication succeeds. 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 credentials
required for authentication. (i.e. the client authentication
succeeded.) The server will respond with a successful message
(200-VFY-S) (7).
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 response (200-VFY-S) may contain the server-side
authentication verification value (7). When the underlying
authentication mechanism supports bidirectional authentication,
clients can check server's identity using this information.
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.
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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 7 and 8.
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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Authentication schemes using this template 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.
Each authentication scheme using this template SHALL specify a single
token specific to the underlying scheme (like Basic or Digest). All
of the "auth-scheme" contained in all of those headers MUST be that
token.
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 syntax for
"challenge" and "credentials" to be used with this template 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, string, integer, hex-fixed-number, and base64-fixed-number.
For clarity, implementations are encouraged 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
Tokens will have syntax of the "token" defined in HTTP. The
canonical format for tokens are unquoted tokens.
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3.1.2. Strings
All character 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], without any leading BOM characters. 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).
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.
3.1.3. Numbers
The following syntax definitions gives a syntax for number-type
values:
integer = "0" / (%x31-39 *DIGIT) ; no leading zeros
hex-fixed-number = 1*(2(DIGIT / %x41-46 / %x61-66))
base64-fixed-number = 1*( ALPHA / DIGIT /
"-" / "." / "_" / "~" / "+" / "/" ) *"="
Figure 3: 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.
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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 (as it will
contain equal, plus signs and slashs).
4. Messages
In this section we define the six 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 7
and 8.
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 and the auth-
scheme to be used. 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 "vks" are mutually exclusive and any challenge
MUST NOT contain two or more parameters among them. They MUST NOT
contain any "ks*" and "vks" parameters.
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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".
algorithm: (mandatory token) specifies the authentication sub-
algorithm to be used. The set of allowed value for
this field MUST be specified within each specification
for a specific authentication protocol.
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.
validation: (mandatory token) specifies the method of host
validation. The value MUST be one of the tokens
described in Section 6, or the tokens specified in
other supplemental specification documentation.
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:
* 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".
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* 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.)
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:
algorithm, realm: MUST be the same value as it is when received from
the server.
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user: (non-mandatory, string) is the UTF-8 encoded name of
the user. This field MUST be present unless the
authentication scheme defines other means of
identifying the authenticating users other than the
textual user name. If this name comes from a user
input, client software SHOULD prepare the string using
the preparation mechanism defined with each scheme
(see Section 11 for more information) before encoding
it to UTF-8.
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:
algorithm, 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 5 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, however,
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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 parameter MUST be
inside the specified auth-domain: if not, clients
SHOULD ignore such elements.
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:
algorithm, 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 5.
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:
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sid: (mandatory, hex-fixed-number) MUST be the value
received from the client.
algorithm, realm: MUST be the same value as it is when received from
the client.
vks: (mandatory, algorithm-determined) is the server-side
authentication verification value VK_s, which is
specified by the algorithm. If the algorithm
specification do not specify any specific value for
this field, the value SHALL the token "0".
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. Session Management
In this authentication protocol template, a session represented by an
sid is set up using first four messages (first request, 401-INIT,
req-KEX-C1 and 401-KEX-S1). 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); 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 SHOULD 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
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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.
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 8. 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
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
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clients and servers can implement the protocol using only fixed-width
integers, by rounding any overflowed values to the maximum possible
value.
6. Host Validation Methods
The "validation method" specifies a method to "relate" (or "bind")
authentication processed by this template with other authentications
already performed in the underlying layers and to prevent man-in-the-
middle attacks. It decides the value vh that is an input to the
authentication protocols.
The valid tokens for the validation parameter and corresponding
values of vh are as follows:
host: hostname 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, vh will include the default port number.
tls-cert: TLS certificate validation: The value vh 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.
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 "tls-cert". If HTTP/TLS protocol is used
without any kind of server certificates, the validation type MUST be
"tls-key".
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.
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Clients MUST validate this parameter 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.
7. 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" 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
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.
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* 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 authentication headers related to this
specification.
* If you receive a 401-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 authentication credential 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 the specified
scheme, it MAY be handled normally.
Step 12 (step_rcvd_init_unknown):
The requested resource requires a 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 any user's authentication
credentials. 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 used
authentication credentials are invalid for the authenticated
resource. Forget such authentication credentials (or disable,
whichever appropriate for the specific kind of credentials) for
the authentication realm and go to Step 12.
Step 14 (step_rcvd_vfy):
Check the validity of the received VK_s value. If it is equal to
the expected value, it means that the server authentication has
succeeded. The client will be in the "AUTH-SUCCEEDED" status.
If the value is unexpected, it is a fatal communication error.
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 SHOULD NOT process
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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.
Figure 4 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 )<------|credentials|
| | ----------------- | 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 credentials/ | 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 4: State diagram for clients
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8. 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:
o When the server receives a normal request:
* If the requested resource is not protected by the
authentication, send a normal response.
* If the resource is protected by the authentication, send a
401-INIT response.
o When the server receives a req-KEX-C1 request:
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* If the requested resource is not protected by the
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: 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 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
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
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(largest-nc - nc-window) (when in "authenticated" status), the
server MAY (but not REQUIRED to) send a 401-STALE message. The
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.
9. Applying for Specific Authentication Schemes
Each authentication scheme to use this template MUST at least provide
a definitions for the following functions:
o A token for distinguishing the protocol from any others (like
Basic or Digest), to be used as "auth-scheme"s.
o A set of tokens which will be allowed in the "algorithm" field of
401-INIT message.
o * A string preparation algorithm based on
[I-D.ietf-precis-framework]. (see Section 11)
Furthermore, for each sub-algorithm defined by the "algorithm" field,
the following MUST be defined:
o A format for representing fields "kc1", "ks1", "vkc" and "vks".
o An algorithm for computing key exchange values K_c1, K_s1.
o A hash function H to be used with the algorithm.
o * An algorithm for computing authentication confirmation values
VK_c, VK_s. Values derived by these algorithms SHOULD depend on
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the value of "nc" value used for each re-authenticating requests
using the same "sid". It SHOULD also depend on the value of the
host verification value "vh".
o * If possible, an algorithm for computing "application channel
binding keys" (see Section 10).
For items marked with asterisks (*), default template functions are
provided in the following sections.
9.1. Default Functions for Algorithms
If there are no specific (such as compatibility) requirements for
values VK_c, VK_s, schemes MAY use the default functions for
computing VK_c and VK_s, defined in this section. Designers of
specific authentication schemes MAY choose either to use this default
function or not, depending on the nature and the background settings
for each authentication schemes to be defined.
To use this default function, the algorithm specification SHALL
specify the following values.
o Shared secret z, to be computed in both server-side and client
side using exchanged values.
The values VK_c and VK_s are derived by the following equation.
VK_c = H(octet(4) | OCTETS(K_c1) | OCTETS(K_s1) | OCTETS(z) | VI(nc)
| VS(vh))
VK_s = H(octet(3) | OCTETS(K_c1) | OCTETS(K_s1) | OCTETS(z) | VI(nc)
| VS(vh))
The definitions of any support functions in the above definitions are
provided in Appendix A.
10. 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.
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The following definitions are assuming that the authentication scheme
uses the default function shown above for computing VK_c and VK_s.
If not, the specification for the authentication scheme is encouraged
to provide an alternative means for this purpose (e.g., either to
specify the function for z, or to specify functions b_1 and b_2).
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 = OCTETS(H(OCTETS(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 = OCTETS(H(OCTETS(H(octet(7) | OCTETS(K_c1) | OCTETS(K_s1) |
OCTETS(z) | VI(nc) | VS(vh))) | VS(t))).
The definitions of any support functions in the above definitions are
provided in Appendix A.
11. String Preparation
For proper internationalization of the protocol to be designed, each
authentication scheme SHOULD specify algorithms for preparing string
inputs, unless the underlying protocol does not use any kind of
human-readable (i.e., possibly-non-ASCII-capable) identifier or
passwords.
If some algorithm is suitable for each specific authentication scheme
in relation to other existing protocols, that one should be used
(e.g. [RFC4013] or [I-D.melnikov-precis-saslprepbis] for any SASL-
related authentication algorithms).
If there is no specific one to be chosen, schemes may choose the
following default choice: use [I-D.melnikov-precis-saslprepbis] for
user-identifiers and passwords-like strings, except that case mapping
of upper-case and title-case letters will NOT be applied (i.e., the
string will be left case-sensitive, for keeping compatibility with
existing HTTP-based authentication mechanisms).
12. Application for Proxy Authentication
The authentication scheme defined by using the previous sections can
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be applied also for proxy authentications. In such 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 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.
13. Methods to extend this protocol template
The template is designed to have fair amount of flexibility for
implementing several authentication schemes. However, if needed,
specifications defining authentication schemes or authentication
algorithms MAY define its own representations for the parameters
"kc1", "ks1", "vkc", and "vks", 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.
If there is more than two round-trips of messages needed for
performing authentication, messaged named "req-KEX-C2", "401-KEX-S2",
"req-KEX-C3" and so on MAY be used between 401-KEX-S1 and req-VFY-C
messages. These messages MUST have algorithm, realm, and sid fields
as the same as req-KEX-C1 and 401-KEX-S1. and they SHOULD have fields
named "kc2", "ks2", "kc3" and so on, respectively.
It is RECOMMENDED that any parameters starting with "kc", "ks", "vkc"
or "vks" and followed by decimal natural numbers (e.g. kc2, ks0,
vkc1, vks3 etc.) are reserved for this purpose. It is strongly
encouraged that specifications for authentication schemes do not
rename or remove there fields, as they are important for
distinguishing message types.
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14. IANA Considerations
[TBD]
15. Security Considerations
15.1. Security Properties
o The protocol template relies on transport security including DNS
integrity for data secrecy and integrity, regardless of any
underlying authentication algorithm to be used. 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.
15.2. 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 "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 on this
authentication template 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.
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16. References
16.1. Normative References
[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-21 (work in progress),
October 2012.
[I-D.ietf-httpbis-p7-auth]
Fielding, R. and J. Reschke, "Hypertext Transfer Protocol
(HTTP/1.1): Authentication", draft-ietf-httpbis-p7-auth-21
(work in progress), October 2012.
[I-D.ietf-precis-framework]
Saint-Andre, P. and M. Blanchet, "PRECIS Framework:
Preparation and Comparison of Internationalized Strings in
Application Protocols", draft-ietf-precis-framework-06
(work in progress), September 2012.
[I-D.melnikov-precis-saslprepbis]
Saint-Andre, P. and A. Melnikov, "Preparation and
Comparison of Internationalized Strings Representing
Simple User Names and Passwords",
draft-melnikov-precis-saslprepbis-04 (work in progress),
September 2012.
[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.
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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.
[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.
[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.
Appendix A. (Normative) 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
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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:
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)
[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 3.1.3 for the definition of "natural length".
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Appendix B. (Informative) Draft Remarks from Authors
The following items are currently under consideration for future
revisions by the authors.
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 6). Note
that existing TLS implementations should be considered to
determine this.
Authors' Addresses
Yutaka Oiwa
National Institute of Advanced Industrial Science and Technology
Research Institute for Secure Systems
Tsukuba Central 2
1-1-1 Umezono
Tsukuba-shi, Ibaraki
JP
Email: mutual-auth-contact-ml@aist.go.jp
Hajime Watanabe
National Institute of Advanced Industrial Science and Technology
Hiromitsu Takagi
National Institute of Advanced Industrial Science and Technology
Boku Kihara
Lepidum Co. Ltd.
#602, Village Sasazuka 3
1-30-3 Sasazuka
Shibuya-ku, Tokyo
JP
Tatsuya Hayashi
Lepidum Co. Ltd.
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Yuichi Ioku
Yahoo! Japan, Inc.
Midtown Tower
9-7-1 Akasaka
Minato-ku, Tokyo
JP
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