Internet Engineering Task Force Y. Oiwa
Internet-Draft H. Watanabe
Intended status: Standards Track H. Takagi
Expires: August 17, 2009 RCIS, AIST
H. Suzuki
Yahoo! Japan
February 13, 2009
Mutual Authentication Protocol for HTTP
draft-oiwa-http-mutualauth-04
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Abstract
This document specifies the "Mutual authentication protocol for
Hyper-Text Transport Protocol". This protocol provides true mutual
authentication between HTTP clients and servers using simple
password-based authentication. Unlike Basic and Digest HTTP access
authentication protocol, the protocol ensures that server knows the
user's entity (encrypted password) upon successful authentication.
This prevents common phishing attacks: phishing attackers cannot
convince users that the user has been authenticated to the genuine
website. Furthermore, even when a user has been authenticated
against an illegitimate server, the server cannot gain any bit of
information about user's passwords. The protocol is designed as an
extension to the HTTP protocol, and the protocol design intends to
replace existing authentication mechanism such as Basic/Digest access
authentications and form-based authentications.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 5
2. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 5
3. Message Syntax . . . . . . . . . . . . . . . . . . . . . . . . 6
3.1. Tokens and Extensive-tokens . . . . . . . . . . . . . . . 7
3.2. Numbers . . . . . . . . . . . . . . . . . . . . . . . . . 7
3.3. Strings . . . . . . . . . . . . . . . . . . . . . . . . . 8
4. Messages . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
4.1. 401-B0 . . . . . . . . . . . . . . . . . . . . . . . . . . 9
4.2. 401-B0-stale . . . . . . . . . . . . . . . . . . . . . . . 10
4.3. req-A1 . . . . . . . . . . . . . . . . . . . . . . . . . . 10
4.4. 401-B1 . . . . . . . . . . . . . . . . . . . . . . . . . . 11
4.5. req-A3 . . . . . . . . . . . . . . . . . . . . . . . . . . 12
4.6. 200-B4 . . . . . . . . . . . . . . . . . . . . . . . . . . 12
5. Decision procedure for the client . . . . . . . . . . . . . . 13
6. Decision procedure for the server . . . . . . . . . . . . . . 17
7. Authentication Algorithms . . . . . . . . . . . . . . . . . . 18
7.1. Common functions . . . . . . . . . . . . . . . . . . . . . 18
7.2. Functions for discrete-logarithm settings . . . . . . . . 20
7.3. Functions for elliptic-curve settings . . . . . . . . . . 21
8. Authentication Realms . . . . . . . . . . . . . . . . . . . . 22
8.1. Resolving ambiguities . . . . . . . . . . . . . . . . . . 23
9. Validation Methods . . . . . . . . . . . . . . . . . . . . . . 24
10. Session Management . . . . . . . . . . . . . . . . . . . . . . 25
11. Extension 1: Optional Mutual Authentication . . . . . . . . . 26
12. Methods to extend this protocol . . . . . . . . . . . . . . . 27
13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 27
14. Security Considerations . . . . . . . . . . . . . . . . . . . 28
14.1. General Assumptions . . . . . . . . . . . . . . . . . . . 28
14.2. Implementation Considerations . . . . . . . . . . . . . . 28
14.3. Usage Considerations . . . . . . . . . . . . . . . . . . . 29
15. Notice on intellectual properties . . . . . . . . . . . . . . 29
16. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 30
17. References . . . . . . . . . . . . . . . . . . . . . . . . . . 30
17.1. Normative References . . . . . . . . . . . . . . . . . . . 30
17.2. Informative References . . . . . . . . . . . . . . . . . . 30
Appendix A. Group parameters for discrete-logarithm based
algorithms . . . . . . . . . . . . . . . . . . . . . 31
Appendix B. Derived numerical values . . . . . . . . . . . . . . 34
Appendix C. Draft Remarks from the Authors . . . . . . . . . . . 35
Appendix D. Draft Change Log . . . . . . . . . . . . . . . . . . 35
D.1. Changes in revision 04 . . . . . . . . . . . . . . . . . . 35
D.2. Changes in revision 03 . . . . . . . . . . . . . . . . . . 35
D.3. Changes in revision 02 . . . . . . . . . . . . . . . . . . 36
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 36
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1. Introduction
This document specifies the "Mutual authentication protocol for
Hyper-Text Transport Protocol". This protocol provides true mutual
authentication between HTTP clients and servers using simple
password-based authentication. Unlike Basic and Digest HTTP access
authentication protocol [RFC2617], the protocol ensures that server
knows the user's entity (encrypted password) upon successful
authentication. This prevents common phishing attacks: phishing
attackers cannot convince users that the user has been authenticated
to the genuine website. Furthermore, even when a user has been
authenticated against an illegitimate server, the server cannot gain
any bit of information about user's passwords.
Recently, phishing attacks are getting more and more sophisticated.
Phishers not only steal user's password directly, but imitate
successful authentication to steal user's sensitive information,
check the password validity by forwarding the password to the
legitimate server, or employ a man-in-the-middle attack to hijack
user's login session. Existing countermeasures such as one-time
passwords cannot completely solve these problems.
The protocol prevents such attacks by providing users a way to
discriminate between true and fake web servers using their own
passwords. Even when a user inputs his/her password to a fake
website, using this authentication method, any information about the
password does not leak to the phisher, and the user certainly notices
that the mutual authentication has failed. Phishers cannot make such
authentication attempt succeed, even if they forward received data
from a user to the legitimate server or vice versa. Users can safely
input sensitive data to the web forms after confirming that the
mutual authentication has succeeded.
To achieve this goal, this protocol uses a mechanism in ISO/IEC
11770-4 [ISO.11770-4.2006], a kind of PAKE (Password-Authenticated
Key Exchange) authentication algorithms as a basis. The use of PAKE
mechanism allows users to use familiar ID/password based accesses,
without fear of leaking any password information to the communication
peer. The protocol, as a whole, is designed as a natural extension
to the HTTP protocol [RFC2616].
The design also considers to replace current form-based Web
authentication, which is very vulnerable against phishing attacks.
To this purpose, several extensions to current HTTP authentication
mechanism [RFC2617] are introduced.
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1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
2. Protocol Overview
The following sequence is a typical sequence for the first access to
the resource.
o If the server (S) has received a request for mutual-authentication
protected resources from the Client (C) (which is not a req-A1 nor
a req-A3 message), it sends a 401-B0 message to C.
When C has received a 401-B0 message, C SHOULD check validity of
the message. If succeed, C processes the body of the message, and
enables the password entry field.
o If the user has input the username and password as a response to
the 401-B0 message, C creates a value s_A, calculates the value
w_A, and then constructs and sends a req-A1 message.
o If S has received a req-A1 message, S should check validity of
w_A, record the received w_A value, and then look up the username
from the user table. if the user is found, S prepares a new
session id (sid), records it into a session table, and then
constructs s_B, calculates w_B, and sends a 401-B1 message.
If there is no matching user found, the server SHOULD construct a
fake w_B value, and let the protocol going on by sending an 401-B1
message.
o When C has received a 401-B1 message as a response for a req-A1
message, C should check validity of w_B, and compute z and o_A,
and send a req-A3 message.
If C receives any messages other than 401-B1, C MUST NOT process
the message body and treat it as a fatal communication error
condition. This case includes the reception of HTTP OK (200-
status) message.
o If S has received a req-A3 message, S should look up the received
sid from the session table. If there is no matching sid, or if S
has not received the corresponding req-A1 message beforehand, S
SHOULD send a 401-B0-stale message.
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Otherwise, S should compute o_A and check its value. If the
validation has failed, it means that the authentication has been
failed. The server SHOULD send a 401-B0 message.
If the validation has succeeded, the server SHOULD calculate o_B,
and send a 200-B4 message.
o In a response to a req-B1 message, when C has received a 401-B0
message, it means that the authentication has been failed,
possibly due to that the wrong password has been given. C MAY
ignore the body of the 401-B0 message in this case.
When C has received a 200-B4 message, C MUST first compute the
value of o_B and validate the value o_B sent from the server. If
it has not verified successfully, C MUST ignore the body of the
message, and treat the situation as a fatal communication error
condition. If the verification has succeed, C will process the
body of the message.
If C receives any messages other than 401-B0 or valid 200-B4, C
MUST NOT process the message body and other headers and treat it
as a fatal communication error condition. This case includes the
reception of usual HTTP OK (200-status) messages.
For the second or later request to the server, if the client knows
that the resource is likely to require the authentication, the client
MAY omit first unauthenticated request and send req-A1 message
immediately. In this case, the first (and only the first) response
from the server MAY be a normal, unauthenticated message, and client
MAY accept such messages.
Furthermore, if client owns a valid session ID (sid), the client MAY
send a req-A3 message using existing sid. In such cases, the server
MAY have been thrown out the corresponding sessions from the session
table. In this case, the server SHOULD send a 401-B0-stale message
as a response to req-A3 message, and C SHOULD retry from constructing
a req-A1 message.
For more detail, see Section 5.
3. Message Syntax
The Mutual authentication protocol uses four headers:
WWW-Authenticate (in responses with status code 401),
Optional-WWW-Authenticate (in responses with positive status codes),
Authorization (in requests), and Authentication-info (in positive
responses). These four headers share the common syntax described in
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Figure 1. The syntax is denoted in the augmented BNF syntax defined
in [RFC5234]. The syntax is a subset of the one described in
[RFC2617].
header = header-name ":" [spaces] "Mutual" spaces fields
header-name = "WWW-Authenticate" / "Optional-WWW-Authenticate"
/ "Authorization" / "Authentication-info"
spaces = 1*(" " / %x09 / %x0D.0A (" " / %x09)) ; LWSP
fields = field *([spaces] "," spaces field)
field = key "=" value
key = extensive-token
extensive-token = token / extension-token
extension-token = token "@" token
token = 1*(%x30-39 / %x41-5A / %x61-7A / "." / "-" / "_")
value = extensive-token / integer / hex-integer
/ hex-fixed-number
/ base64-fixed-number / string
integer = "0" / (%x31-39 *%x30-39) ; no leading zeros
hex-integer = "0"
/ ((%x31-39 / %x41-46 / %x61-66) ; no leading zeros
*(%x30-39 / %x41-46 / %x61-66))
hex-fixed-number = 1*(%x30-39 / %x41-46 / %x61-66)
base64-fixed-number = string
string = %x22 *(%x20-21 / %x23-5B / %x5D-FF
/ %x5C.22 / "\\" / "\,") %x22
Figure 1: the BNF syntax for the headers used in the protocol
3.1. Tokens and Extensive-tokens
The tokens MUST be interpreted case-insensitively, and SHOULD be sent
in the same case as shown in the specification. When these are used
as (partial) inputs to any hash or other mathematical functions, it
MUST be used in lower-case. All hex-fixed-number or hex-integer
numbers are also case-insensitive, and SHOULD be sent in lower-case.
Extensive-tokens are used where the set of acceptable tokens are
extensible. Any non-standard extensions of this protocol MUST use
the extension-tokens of format "<token>@<domain-name>", where domain-
name is the valid registered (sub-)domain name on the Internet owned
by the party who defines extensions.
3.2. Numbers
The syntax definitions of integer and hex-integer only allow
representations which do not contain extra leading 0s.
The numbers represented as a hex-fixed-number MUST have even
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characters (i.e. multiple of eight bits). When these are generated
from cryptographic values, those SHOULD have the 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 group, its lengths SHOULD be the shortest which can
represent all elements in the group. See Appendix B for information
about the length of the fields used in this specification. Other
values such as session-id are represented in any (even) length
determined by the side who generates it first, and the same length
SHALL be used throughout the whole communications by both peers.
The numbers represented as a base64-fixed-number SHALL be generated
as follows: first, the number is converted to a big-endian octet-
string representation. The length of the representation is
determined in the same way as above. Then, the string is encoded by
the Base 64 encoding [RFC4648], and then enclosed by two double-
quotations.
3.3. Strings
All strings outside ASCII or equivalent character sets SHOULD be
encoded using UTF-8 encoding [RFC3629] of the ISO 10646-1 character
set [ISO.10646-1.1993]. Both peers SHOULD reject any invalid UTF-8
sequences which causes decoding ambiguities (e.g. containing <"> in
the second or later byte of the UTF-8 encoded characters). To encode
character strings, these will first be encoded according to UTF-8
without leading BOM, then all occurrences of characters <"> and "\"
will be escaped by prepending "\", and two <">s will be put around
the string. If the contents of the strings are comma-separated
values, the commas in the values are also quoted by "\".
If strings are representing a domain name or URI which contains non-
ASCII characters, the host parts SHOULD be encoded using puny-code
defined in [RFC3492] instead of UTF-8, and SHOULD use lower-case
ASCII characters.
For Base64-fixed-numbers, which use the string syntax, see the
previous section.
4. Messages
In this section, formats and requirements of the headers for each
message are presented. The allowed type of values for each header
field is shown in parenthesis after the key names. The type
"algorithm-determined" means that the acceptable value type for the
field is one of the types defined in Section 3, and is determined by
the value of the "algorithm" field.
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Note: The term "optional" here means that omitting the field is
allowed and has specific meanings in communications (i.e. it is not
generally "OPTIONAL" defined in [RFC2119]).
4.1. 401-B0
Every 401-B0 message SHALL be a valid HTTP 401 (Authentication
Required) message containing one (and only one: hereafter not
explicitly noticed) "WWW-Authenticate" header of the following
format.
WWW-Authenticate: Mutual algorithm=xxxx, validation=xxxx,
realm="xxxx", stale=0
The header SHALL contain the fields with the following keys:
algorithm: (extensive-token) specifies the authentication
algorithm to be used. The value MUST be one of the
tokens described in Section 7, or the tokens specified
in other supplemental specification documentations.
validation: (extensive-token) specifies the method of host
validation. The value MUST be one of the tokens
described in Section 9, or the tokens specified in
other supplemental specification documentations.
auth-domain: (optional, string) specifies authentication domain,
the set of hosts on which authentication credentials
are valid. It MUST be one of the strings described in
Section 8. If the value is omitted, it is assumed to
be the host part of the requested URI.
realm: (string) is a UTF-8 encoded string representing the
name of the authentication realm inside the
authentication domain.
pwd-hash: (optional, extensive-token) specifies the hash
algorithm (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].
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* sha1: ph(p) = SHA1(p)
If omitted, the value "none" is assumed. The use of
"none" is recommended.
stale: (token) MUST be "0".
Any additional fields SHOULD NOT be contained in the header, except
those explicitly specified in supplement specifications of the
"authentication algorithm".
The algorithm will determine the types and the values for w_A, w_B,
o_A and o_B.
4.2. 401-B0-stale
A 401-B0-stale message is a variant of 401-B0 message, which means
that the client has sent a request message which is not for any
active session.
WWW-Authenticate: Mutual algorithm=xxxx, validation=xxxx,
realm="xxxx", stale=1
The header MUST contain the same fields as in 401-B0, except that
stale field holds the integer 1.
4.3. req-A1
Every req-A1 message SHALL be a valid HTTP request message containing
a "Authorization" header of the following format.
Authorization: Mutual algorithm=xxxx, validation=xxxx, realm="xxxx",
user="xxxx", wa=xxxx
The header SHALL contain the fields with the following keys:
algorithm, validation, auth-domain, realm: MUST be the same value as
it is received from S.
user: (string) is the UTF-8 encoded name of the user.
wa: (algorithm-determined) is the value of w_A specified
by the used algorithm.
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4.4. 401-B1
Every 401-B1 message SHALL be a valid HTTP 401 (Authentication
Required) message containing a "WWW-Authenticate" header of the
following format.
WWW-Authenticate: Mutual algorithm=xxxx, validation=xxxx,
realm="xxxx", sid=xxxx, wb=xxxx, nc-max=x, nc-window=x, time=x,
path="xxxx"
The header SHALL contain the fields with the following keys:
algorithm, validation, auth-domain, realm: MUST be the same value as
it is received from C.
sid: (hex-fixed-number) MUST be a session id, 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. Sids are local to each
authentication realm concerned: the same sids for
different authentication realms SHOULD be treated as
independent ones.
wb: (algorithm-determined) is the value of w_B specified
by the algorithm.
nc-max: (hex-integer) is the maximal value of nonce counts
which S accepts.
nc-window: (hex-integer) the number of available nonce slots
which S will accept. The value of nc-window is
RECOMMENDED to be thirty-two ("20" in hex-integer) or
more.
time: (integer) represents the suggested time (in seconds)
which C can reuse the session represented by sid. It
is RECOMMENDED to be at least 60. The value of this
field is not directly linked to the duration that S
keeps track of the session represented by sid.
path: (optional, string) specifies for which path in the URI
space the same authentication is expected to apply.
The value is in the same format as it is specified in
[RFC2617] for the Digest authentications, and clients
are RECOMMENDED to recognize it. The all path
elements contained in the field MUST be inside the
specified auth-domain: if not, client SHOULD ignore
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such elements.
4.5. req-A3
Every req-A3 message SHALL be a valid HTTP request message containing
a "Authorization" header of the following format.
Authorization: Mutual algorithm=xxxx, validation=xxxx, realm="xxxx",
sid=xxxx, nc=x, oa=xxxx
The fields contained in the header are as follows:
algorithm, validation, auth-domain, realm: MUST be the same value as
it is received from S for the session.
sid: (hex-fixed-number) MUST be one of the sid values which
has been received from S for the same authentication
realm.
nc: (hex-integer) is a nonce value which is unique among
the requests sharing the same sid. The value of nc
SHOULD satisfy the following properties:
* It is not larger than the nc-max value which has
been sent from S in the session represented by the
sid.
* C have not sent the same value in the same session.
* It is not smaller than (largest-nc - nc-window),
where largest-nc is the maximal value of nc which
has previously been sent in the session, and nc-
window is the value of the nc-window field which
has been sent from S in the session.
oa: (algorithm-determined) is the value of o_A specified
by the algorithm.
4.6. 200-B4
Every 200-B1 message SHALL be a valid HTTP message which is not 401
(Authentication Required) type, containing an "Authentication-Info"
header of the following format.
Authentication-Info: Mutual sid=xxxx, ob=xxxx
The fields contained in the header are as follows:
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sid: (hex-fixed-number) MUST be the value received from C.
ob: (algorithm-determined) is the value of o_B specified
by the algorithm.
logout-timeout: (optional, integer) is a number of seconds after
which the client should re-validate the user's
password for the current authentication realm. As a
special case, the value 0 means that the client SHOULD
automatically forget the user-inputed password to the
current authentication realm and revert to the
unauthenticated state (i.e.~server-initiated logout).
This does not, however, mean that the long-term
memories for the passwords (such as password reminders
and auto fill-ins) should be removed. If a new value
of timeout is received for the same authentication
realm, it overrides the previous timeout.
5. Decision procedure for the client
To securely implement the protocol, the user client must be careful
for accepting authenticated responses from the server.
Clients SHOULD implement the decision procedure equivalent to the one
shown below. (Unless implementers understand what is required for
the security, they should not alter this.) The labels on the steps
are for informational purpose only.
Step 1 (step_new_request):
If the client software needs to get a new Web resource, check
whether the resource is expected to be inside some authentication
realm for which the user has already authenticated. 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_a3_1):
Send a req-A3 request.
* If you receive a 401-B0 message with a different
authentication realm than expected, go to Step 6.
* If you receive a 401-B0-stale message, go to Step 9.
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* If you receive a 401-B0 message, go to Step 13.
* If you receive a 200-B4 message, go to Step 14.
* If you receive a normal response (without Mutual-specific
headers), go to Step 11.
Step 4 (step_send_a1_1):
Send a req-A1 request.
* If you receive a 401-B0 message with a different
authentication realm than expected, go to Step 6.
* If you receive a 401-B1 message, go to Step 10.
* If you receive a normal response (without Mutual-specific
headers), go to Step 11.
Step 5 (step_send_normal_1):
Send a request without any authentication headers.
* If you receive a 401-B0 message, go to Step 6.
* If you receive a normal response (without Mutual-specific
headers), go to Step 11.
Step 6 (step_rcvd_b0):
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 expects. If there is one, go to Step 8. Otherwise, go
to Step 9.
Step 8 (step_send_a3):
Send a req-A3 request.
* If you receive a 401-B0-stale message, go to Step 9.
* If you receive a 401-B0 message, go to Step 13.
* If you receive a 200-B4 message, go to Step 14.
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Step 9 (step_send_a1):
Send a req-A1 request.
* If you receive a 401-B1 message, go to Step 10.
Step 10 (step_rcvd_b1):
Send a req-A3 request.
* If you receive a 401-B0 message, go to Step 13.
* If you receive a 200-B4 message, go to Step 14.
Step 11 (step_rcvd_normal):
This case means that the resource requested is out of the
authenticated area. The client will be in the "UNAUTHENTICATED"
status.
Step 12 (step_rcvd_b0_unknown):
This case means that the resource requested requires Mutual
authentication, and the user is not authenticated yet. The
client will be in the "AUTH_REQUESTED" status, is RECOMMENDED to
process the content sent from the server and ask user a username
and password. If the user has input those, go to Step 9.
Step 13 (step_rcvd_b0_failed):
This case means that in 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_b4):
Check the validity of the received o_b value. If it is equal to
the expected value, it means that the mutual authentication has
been succeeded. The client will be in the "AUTH_SUCCEEDED"
status.
If the value is unexpected, it is a fatal communication error.
Any other kind of responses than shown in above procedure SHOULD be
interpreted as fatal communication error, and in such cases user
clients MUST NOT process any data (contents and other content-related
headers) sent from the server.
The client software SHOULD display the three client status to the
end-user.
Figure 2 shows the full client-side state diagram.
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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-B0, 200-Opt-B0 |401-B0
| with different realm |200-Opt-B0
| -----------------------------------. |
| / 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- v |
| +(3)--------+ | B0 --(13)---------- 401-B0 +(8)--------+ |
| | send |--+----->/ AUTH_REQUESTED \<-------| send | |
| /| req-A3 | | \forget user/pass/ | req-A3 | |
\/ +-----------+ / ---------------- /+-----------+ |
/\ \ \/ ^ 401-B0 | |401-B0- |
| -------. \/\ 401-B0-stale | | |stale /
| | /\ -----------------+--------------+----. | /
| v / \ | | v v v
| +(4)--------+ | 401-B1 +(10)-------+ 401-B1 | +(9)--------+
| | send |-|--------->| send |<-------+-| send |
| --| req-A1 | | | req-A3 | | | req-A1 |
|/ +-----------+ | +-----------+ | +-----------+
| |200-B4 | 200-B4| ^
|normal | |200-B4 / |
|response | v / =================
v \ -(14)--------- / USER/PASS INPUTED
-(11)------------ ------->( AUTH-SUCCEED )<-- =================
( UNAUTHENTICATED ) --------------
-----------------
Figure 2: State diagram for clients
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6. Decision procedure for the server
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 Mutual
Authentication, send a normal response.
* If the resource is protected by Mutual Authentication, send a
401-B0 response.
* If the resource is protected by Mutual Authentication with
Optional Mutual Authentication extension (Section 11), send a
200-Optional-B0 response.
o When the server receives a req-A1 request:
* If the requested resource is not protected by Mutual
Authentication, send a normal response.
* If the authentication realm specified in the req-A1 request is
non-expected one, send a 401-B0 (or 200-Optional-B0) response.
* If the server cannot validate field wa, send a 401-B0 response.
* If the received user name is invalid, send a fake 401-B1
response.
* Otherwise, send a 401-B1 response.
o When the server receives a req-A3 request:
* If the requested resource is not protected by Mutual
Authentication, send a normal response.
* If the authentication realm specified in the req-A3 request is
non-expected one, send a 401-B0 (or 200-Optional-B0) response.
* If the received sid is invalid, inactive or unknown, send a
401-B0-stale response.
* If the receive oa is invalid, or the sid correspond to a fake
session generated for an unknown user, send a 401-B0 response.
* If the receive oa is correct, send a 200-B4 response.
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7. Authentication Algorithms
This document specifies only one family of the authentication
algorithm. The family consists of four authentication algorithms,
which only differ in underlying mathematical groups and security
parameters. The algorithms do not add any additional fields. The
tokens for algorithms are
o "iso11770-4-ec-p256" for the 256-bit prime-field elliptic-curve
setting.
o "iso11770-4-ec-p521" for the 521-bit prime-field elliptic-curve
setting.
o "iso11770-4-dl-2048" for the 2048-bit discrete-logarithm setting.
o "iso11770-4-dl-4096" for the 4096-bit discrete-logarithm setting.
For the elliptic-curve settings, the underlying fields and the curves
used for elliptic-curve cryptography are the prime field and the
Curve P-256 and P-521, respectively, specified in the appendix of
FIPS PUB 186-2 [FIPS.186-2.2000] specification. The hash functions H
are SHA-256 for P-256 curve and SHA-512 for P-521 curve,
respectively, defined in FIPS PUB 180-2 [FIPS.180-2.2002]. The
representation of fields wa, wb, oa, and ob is hex-fixed-number.
For discrete-logarithm settings, the underlying groups are 2048-bit
and 4096-bit MODP groups defined in [RFC3526] respectively. See
Appendix A for the exact specification of the group and associated
parameters. The hash functions H are SHA-256 for the 2048-bit field
and SHA-512 for the 4096-bit field, respectively. The representation
of fields wa, wb, oa, and ob is base64-fixed-number.
The clients SHOULD support at least "iso11770-4-dl-2048" algorithm,
and are advised to support all of the above four algorithms whenever
possible. The server software implementations SHOULD support at
least "iso11770-4-dl-2048" algorithm, unless it is known that users
will not use it.
This algorithm uses Key Agreement Mechanism 3 (KAM3) defined in
Section 6.3 of ISO/IEC-11770-4 [ISO.11770-4.2006] as a basis.
7.1. Common functions
The password-based string pi used by this authentication is derived
in the following manner:
pi = H(VS(algorithm) | VS(auth-domain) | VS(realm) | VS(username) |
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VS(ph(password)).
The values of algorithm, realm and auth-domain are taken from the
values contained in the 401-B0 message. When pi is used in the
context of an octet string, it SHALL have the natural length derived
from the size of the output of function H (e.g. 32 octets for SHA-
256). The function ph is defined by the value of the pwd-hash field
given in a 401-B0 message.
The function VI encodes natural numbers into octet strings in the
following manner: integers are represented in big-endian radix-128
string, where each digit is represented by a octet 0x80-0xff except
the last digit represented by 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 subcomponents of object
identifiers in the ASN.1 encoding [ITU.X690.1994].
The function VS encodes variable-length octet string into decodable
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.
The function OCTETS converts an integer to corresponding radix-256
big-endian octet string having its natural length: See Section 3.2
for the definition of the "natural length". Note that this is
different from the function GE2OS_x in [ISO.11770-4.2006], which
takes the shortest representation.
The equations for J, w_A, T, z, and w_B are specified differently for
the discrete-logarithm setting and the elliptic-curve setting based
on [ISO.11770-4.2006]. These equations are defined later in this
section.
The values o_A and o_B are derived by the following equation. Note
that these equations are different from ones specified in
[ISO.11770-4.2006].
o_A = H(octet(04) | OCTETS(w_A) | OCTETS(w_B) | OCTETS(z) | VI(nc) |
VS(v))
o_B = H(octet(03) | OCTETS(w_A) | OCTETS(w_B) | OCTETS(z) | VI(nc) |
VS(v))
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7.2. Functions for discrete-logarithm settings
In this section, the equation (x / y mod z) denotes a natural number
w less than z which satisfies (w * y) mod z = x mod z.
For the discrete-logarithm, we refer some of the domain parameters by
the following symbols:
o q: for "the prime" of the group.
o g: for "the generator" associated with the group.
o r: for the order of the subgroup generated by g.
The function J is defined as
J(pi) = g^(pi) mod q.
The value of w_A is derived as
w_A = g^(s_A) mod q,
where s_A is a random integer within range [1, r-1] and r is the size
of the subgroup generated by g. In addition, s_A MUST be larger than
log(q)/log(g) (so that g^(s_A) > q).
The value of w_A SHALL satisfy 1 < w_A < q-1. The server MUST check
this condition upon reception.
The value of w_B is derived from J(pi) and w_A as:
w_B = (J(pi) * w_A^(H(octet(1) | OCTETS(w_A))))^s_B mod q,
where s_B is a random number within range [1, r-1]. The value of w_B
MUST satisfy 1 < w_B < q-1. If this condition is not hold, the
server MUST retry with another value of s_B. The client MUST check
this condition upon reception.
The value z in the client side is derived by the following equation:
z = w_B^((s_A + H(octet(2) | OCTETS(w_A) | OCTETS(w_B))) / (s_A *
H(octet(1) | w_A) + pi) mod r) mod q.
The value z in the server side is derived by the following equation:
z = (w_A * g^(H(octet(2) | OCTETS(w_A) | OCTETS(w_B))))^s_B mod q.
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7.3. Functions for elliptic-curve settings
For the elliptic-curve setting, we refer some of the domain
parameters by the following symbols:
o q: for the prime used to define the field,
o G: for the defined point called the generator,
o r: for the order of the subfield generated by G.
The function P(p) converts a curve point p to an integer representing
the point p, by computing x * 2 + (y mod 2), where (x, y) are the
coordinates of the point p. P'(z) is the inverse of function P, that
is, it converts an integer z to a point p which satisfies P(p) = z.
If such p is exist, it is uniquely defined. Otherwise, z does not
represent a valid curve point. The operation [x] * p denotes an
integer-multiplication of point p: it calculates p + p + ... (x
times) ... + p. See literatures on elliptic-curve cryptography for
the exact algorithms for those. 0_E represents the infinity point.
The equation (x / y mod z) denotes an natural number w less than z
which satisfies (w * y) mod z = x mod z.
the function J is defined as
J(pi) = [pi] * G.
The value of w_A is derived as
w_A = P(W_A), where W_A = [s_A] x G.
where s_A is a random number within range [1, r-1]. The value of w_A
MUST represent a valid curve point, and W_A SHALL NOT be 0_E. The
server MUST check this condition upon reception.
The value of w_B is derived from J(pi) and W_A = P'(w_A) as:
w_B = P(W_B), where W_B = [s_B] * (J(pi) + [H(octet(1) |
OCTETS(w_A))] * W_A).
where s_B is a random number within range [1, r-1]. The value of w_B
MUST represent a valid curve point and satisfy [4] * P'(w_B) <> 0_E.
If this condition is not hold, the server MUST retry with another
value of s_B. The client MUST check this condition upon reception.
The value z in the client side is derived by the following equation:
z = P([(s_A + H(octet(2) | OCTETS(w_A) | OCTETS(w_B))) / (s_A *
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H(octet(1) | OCTETS(w_A)) + pi) mod r] * W_B), where W_B = P'(w_B).
The value z in the server side is derived by the following equation:
z = P([s_B] * (W_A + [H(octet(2) | OCTETS(w_A) | OCTETS(w_B))] * G)),
where W_A = P'(w_A).
8. 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 the
authentication realm which the client is already authenticated, the
client will automatically perform authentication using the already-
known secrets. On the contrary, for the different authentication
realms, clients SHOULD NOT automatically reuse the usernames and
passwords for another realm.
Just like Basic and Digest access authentication protocol, Mutual
authentication protocol supports multiple, separate authentication
realms to be set up inside each hosts. Furthermore, the protocol
supports that a single authentication realm spans over several hosts
in the same Internet domain.
Each authentication realm is defined and distinguished by the triple
of an "authentication algorithm", an "authentication domain", a
"realm" parameter. Server operators are NOT RECOMMENDED to use the
same pair of an authentication domain and a realm for different
authentication algorithms, however.
Authentication algorithms are defined in Section 4 and Section 7.
Realm parameters are just a string, as defined in Section 4.
Authentication domains are described in the rest of this section.
An authentication domain specifies the range of hosts which the
authentication realm spans over. In the protocol, it MUST currently
be one of the following strings.
o the string in format "<scheme>://<host>:<port>", where scheme,
host and port are the URI parts of the requested URI. Even if the
request-URI does not have a port part, the string will include the
one (i.e. 80 for http and 443 for https). Use this when
authentication is only valid for specific protocol (such as
https).
o The "host" part of the requested URI. This is the default value.
Authentication realms in this kind of authentication domain will
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span over several protocols (i.e. http and https) and ports, but
not over different hosts.
o 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" and "example.com"). The domain-postfix must be
equal to or included in a valid Internet domain assigned to
specific organization: if the clients can know by some way (such
as blacklists for HTTP cookies) that the specified domain is not
to be assigned to any specific organization (e.g. "*.com" or
"*.jp"), the client is RECOMMENDED to reject the authentication
request.
In the above specifications, every "scheme", "host" and "domain" MUST
be in lower-case, and IDNs MUST be represented in puny-code
[RFC3492]. All "port"s MUST be in the shortest, unsigned, decimal
number notation. Not obeying these requirements will cause failure
of valid authentication attempts.
8.1. Resolving ambiguities
In the above definition of authentication domains, several domains
will overwrap each other. Depending on the "path" parameters given
in the "401-B1" message (see Section 4), There may be several
candidate when the client is to send a request with authentication
credentials included (at the Steps 3 and 4 of the decision procedure
shown in Section 5).
If such choices are required, the following procedure SHOULD be
followed.
o If the client has previously sent a request to the same URI, and
it remembers the authentication realm requested by 401-B0 messages
at that time, use that realm.
o In other cases, use one of authentication realms which represents
most-specific authentication domains. In the list of possible
domain specifications shown above, one described earlier has
priority over ones described after that.
If there are several choices with different domain-postfix
specifications, the one which has longer domain possible has
priority over ones with shorter domain-postfix.
o If there are realms with the same specifications of authentication
domain, there is no defined priority: client MAY choose any one of
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possible choices.
If possible, server operators are recommended to avoid such
ambiguities by setting "path" parameters properly.
9. Validation Methods
The "validation method" specifies a method to "relate" the mutual
authentication processed by this protocol with other authentications
already performed in the underlying layers and to prevent man-in-the-
middle attacks. It decides the value of v which is an input to
authentication protocols.
The valid tokens for the validation field and corresponding values of
v are as follows:
host: hostname validation: v will be the ASCII string in the
following format: "scheme://host:port", where scheme,
host and port are the URI parts correspond to the
currently accessing resource. The scheme and host are
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 one.
tls-cert: TLS certificate validation: v will be the octet string
of the hash value of the public key certificate used
in underlying TLS [RFC4346] (or SSL) connection. The
hash value is defined as the value of the whole signed
certificate (specified as "Certificate" in [RFC5280]),
hashed by the hash algorithm specified by the
authentication algorithm used.
tls-key: TLS shared-key validation: v will be the octet string
of the shared master secret negotiated in underlying
TLS (or SSL) connection.
If the HTTP protocol is used on unencrypted channel, the validation
type MUST be "host". If HTTP/TLS [RFC2818] (https) protocol is used
with server certificates, the validation type MUST be either "tls-
cert" or "tls-key". If HTTP/TLS protocol is used with anonymous
Diffie-Hellman key exchange, the validation type MUST be "tls-key"
(but see the note below).
The client MUST validate this field upon reception of 401-B0
messages.
However, when the protocol is used on web browsers with any scripting
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capabilities, the anonymous Diffie-Hellman family of TLS (or SSL)
cipher-suite MUST NOT be used even if "tls-key" validated Mutual
authentication has been employed, and the certificate shown in TLS
(or SSL) negotiation MUST be verified using PKI. For other systems,
if the "tls-key" validation is used on TLS (or SSL) protocol without
certificate verification using PKI, those systems MUST ensure that
all transactions with authenticated peer servers MUST use and be
validated by the Mutual authentication protocol, regardless of the
existence of the 401-B0 responses.
The protocol defines two variants for validation on TLS connections.
The method "tls-key" method is more secure. However, there are some
situations where tls-cert is more preferable.
o When TLS accelerating proxies are used. In this case, it is
difficult for the authenticating server to acquire the TLS key
information which are used between the client and the proxy. It
is not the case for client-side "tunneling" proxies using CONNECT
method extension of HTTP.
o When a black-box implementation of the TLS protocol is used on
either peer.
Implementations supporting Mutual authentication over https protocol
SHOULD support "tls-cert" validation unless it is not applicable.
Support for "tls-key" validation is OPTIONAL for both servers and
clients.
10. Session Management
In the Mutual authentication protocol, a session represented by a sid
is generated By the first 4 messages (first request, 401-B0, req-A1
and 401-B1). This session can be used for one or more requests for
resources protected by the same realm in the same server. Note that
the 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 will automatically reestablish another session
without telling it to the users.
The server SHOULD accept at least one req-A3 request for each
session, given that the request reaches the server in a time window
specified by the timeout field in the 401-B1 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-B0-stale messages for any req-A3 requests.
The client MAY send more than one requests using a single session
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specified by the sid. However, for all such requests, the values of
the nonce-counter (nc field) MUST be different from each other. The
server MUST check for duplication of the received nonces, and if any
duplication is detected, the server MUST discard the session and
respond by a 401-B0-stale message.
In addition, for each sessions, if the client has already sent a
request with nonce value x, it SHOULD NOT send requests with a nonce
value not larger than (x - nc-window). The server MAY reject any
requests with nonces violating this rule with 401-B0-stale responses.
This restriction enables servers to implement duplicated nonce
detection in a constant memory.
Values of nonces and nonce-related values MUST always be treated as
natural numbers within infinite range. Implementations using fixed-
width integers or fixed-precision floating numbers MUST handle
integer overflow correctly and carefully. Such implementations are
RECOMMENDED to accept any larger values which 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 clients and servers can
implement the protocol only with fixed-width integers, by rounding
any overflowed values to the maximum possible value.
11. Extension 1: Optional Mutual Authentication
In several Web applications, users can access the same contents both
as a guest user and as a authenticated users. In usual Web
applications, it is implemented using Cookies and custom form-based
authentications. The extension described in this section provides a
replacement for those authentication systems. The support for this
extension is RECOMMENDED, unless an authentication is mandatory for
some specific applications.
Servers MAY send HTTP successful responses (response code 200, 206
and others) containing the Optional-WWW-Authenticate header, when it
is allowed to send 401-B0 responses and the requests do not contain
Authentication-Info: headers. Such responses are hereafter called
200-Optional-B0 responses.
HTTP/1.1 200 OK
Optional-WWW-Authenticate: Mutual algorithm=xxxx, validation=xxxx,
realm="xxxx", stale=0
The fields contained in the Optional-WWW-Authenticate header is the
same as the 401-B0 message described in Section 4.1. The client
software supporting the mutual authentication protocol receiving a
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200-Optional-B0 message will process the contents of the message and
enables an authentication input field.
When the user input the username and password, the client resends the
request with a req-A1 header. The server MUST respond with a 401-B1
message. In terms of the state management in Section 5, 200-
Optional-B0 responses are treated as if they were 401-B0 responses:
these messages SHOULD NOT be sent as a response to req-A1 and req-A3
messages, unless the authentication realm sent from the client or
indicated by sid is different from the one which the server expects.
Servers requesting optional mutual authentication SHOULD send the
path field in 401-B1 messages with an appropriate value. Client
software supporting optional mutual authentication MUST recognize the
field, and MUST send either req-A1 or req-A3 request for the URI
space inside the specified paths, instead of unauthenticated
requests.
12. Methods to extend this protocol
If a non-standard extension to the this protocol is implemented, it
MUST use the extension-tokens defined in Section 3 to avoid conflicts
with this protocol and other extensions.
Authentication algorithms other than those defined in this document
MAY use other representations for keys "wa", "wb", "oa" and "ob",
replace those keys, and/or add fields to the messages containing
those fields by supplemental specifications. If those specifications
use keys other than shown above, it is RECOMMENDED to use extension-
tokens to avoid any key-name conflict with the future extension of
this protocol.
Extension-tokens MAY be freely used for any non-standard, private
and/or experimental uses for those fields provided that the domain
part in the token is appropriately used.
13. IANA Considerations
The tokens used for authentication-algorithm, pwd-hash, and
validation fields MUST be allocated by IANA. To acquire registered
tokens, a specification for the use of such tokens MUST be available
as an RFC, as outlined in [RFC5226].
Note: More formal declarations will be added in future drafts to meet
RFC 5226 requirements.
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14. Security Considerations
14.1. General Assumptions
o The protocol is secure against passive eavesdropping and replay
attacks. However, the protocol relies on transport security
including DNS security for active attacks. HTTP/TLS SHOULD be
used where transport security is not assured and data secrecy is
important.
o Used with HTTP/TLS, if TLS server certificates are reliably
verified, the protocol gives true protection against active man-
in-the-middle attacks.
o Even if the server certificate is not used or is unreliable, the
protocol gives 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
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 9).
14.2. Implementation Considerations
o To securely implement the protocol, the Authentication-Info
headers in the 200-B4 messages MUST always be validated by the
client. If the validation is failed, the client MUST NOT process
any content sent with the message, including the body part. Non-
compliance to this will enable phishing attacks.
o The authentication status on the client-side SHOULD be visible to
the users of the client. In addition, the method for asking
user's name and passwords SHOULD be carefully designed so that (1)
the user can easily distinguish request of this authentication
methods from other existing authentication methods such as Basic
and Digest methods, and (2) the Web contents cannot imitate the
user-interfaces of this protocol.
An informational memo regarding user-interface considerations and
recommendations for implementing this protocol will be separately
published.
o For HTTP/TLS communications, when a web form is submitted from
Mutually-authenticated pages with the validation methods of "tls-
cert" to a URI which is protected by the same realm (so indicated
by the path field), if server certificate has been changed since
the pages has been received, the peer is RECOMMENDED to be
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revalidated using a req-A1 message with an "Expect: 100-continue"
header. The same applies when the page is received with the
validation methods of "tls-key", and when the TLS session has been
expired.
o Server-side storages of user passwords are advised to have the
values encrypted by one-way function J(pi), instead of the real
passwords, those hashed by ph, or pi.
14.3. Usage Considerations
o The user-names inputted by 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 in HTTPS site, and
when an HTTP server on the same host requests Mutual
authentication with the same realm, the client will send the user-
name in a clear text. If user-names have to kept secret against
eavesdropping, the server must use full-scheme-type auth-domain
parameter. On the contrary, passwords are not exposed to
eavesdroppers even on HTTP requests.
o "Pwd_hash" field is only provided for backward compatibility for
password databases, and using "none" function is the mostly secure
choice and RECOMMENDED. If values other than "none" is 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 of storing server-side
password database, it is advised to store the values encrypted by
one-way function J(pi), instead of the real passwords, those
hashed by ph, or pi.
15. Notice on intellectual properties
The National Institute of Advanced Industrial Science and Technology
(AIST) and Yahoo! Japan, Inc. has jointly submitted a patent
application about 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 detail of the patent application and
its status, please contact the author of this document.
The elliptic-curve based authentication algorithms might involve
several existing patents of third-parties. The authors of the
document take no position regarding the validity or scope of such
patents, and other patents as well.
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16. Acknowledgement
We gratefully acknowledge Lepidum, Co. Ltd. for support on design
and trial implementation of this protocol.
17. References
17.1. Normative References
[FIPS.180-2.2002]
National Institute of Standards and Technology, "Secure
Hash Standard", FIPS PUB 180-2, August 2002, <http://
csrc.nist.gov/publications/fips/fips180-2/fips180-2.pdf>.
[FIPS.186-2.2000]
National Institute of Standards and Technology, "Digital
Signature Standard (DSS)", FIPS PUB 186-2, January 2000, <
http://csrc.nist.gov/publications/fips/fips186-2/
fips186-2-change1.pdf>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000.
[RFC3526] Kivinen, T. and M. Kojo, "More Modular Exponential (MODP)
Diffie-Hellman groups for Internet Key Exchange (IKE)",
RFC 3526, May 2003.
[RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO
10646", STD 63, RFC 3629, November 2003.
[RFC4346] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.1", RFC 4346, April 2006.
[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.
17.2. Informative References
[I-D.altman-tls-channel-bindings]
Altman, J. and N. Williams, "Unique Channel Bindings for
TLS", draft-altman-tls-channel-bindings-03 (work in
progress), November 2007.
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[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.
[ISO.11770-4.2006]
International Organization for Standardization,
"Information technology - Security techniques - Key
management - Part 4: Mechanisms based on weak secrets",
ISO Standard 11770-4, May 2006.
[ITU.X690.1994]
International Telecommunications Union, "Information
Technology - ASN.1 encoding rules: Specification of Basic
Encoding Rules (BER), Canonical Encoding Rules (CER) and
Distinguished Encoding Rules (DER)", ITU-T Recommendation
X.690, 1994.
[RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.
[RFC2617] Franks, J., Hallam-Baker, P., Hostetler, J., Lawrence, S.,
Leach, P., Luotonen, A., and L. Stewart, "HTTP
Authentication: Basic and Digest Access Authentication",
RFC 2617, June 1999.
[RFC3492] Costello, A., "Punycode: A Bootstring encoding of Unicode
for Internationalized Domain Names in Applications
(IDNA)", RFC 3492, March 2003.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, May 2008.
Appendix A. Group parameters for discrete-logarithm based algorithms
The MODP group used for the iso11770-4-dl-2048 algorithm is defined
by the following parameters.
The prime is:
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q = 0xFFFFFFFF FFFFFFFF C90FDAA2 2168C234 C4C6628B 80DC1CD1
29024E08 8A67CC74 020BBEA6 3B139B22 514A0879 8E3404DD
EF9519B3 CD3A431B 302B0A6D F25F1437 4FE1356D 6D51C245
E485B576 625E7EC6 F44C42E9 A637ED6B 0BFF5CB6 F406B7ED
EE386BFB 5A899FA5 AE9F2411 7C4B1FE6 49286651 ECE45B3D
C2007CB8 A163BF05 98DA4836 1C55D39A 69163FA8 FD24CF5F
83655D23 DCA3AD96 1C62F356 208552BB 9ED52907 7096966D
670C354E 4ABC9804 F1746C08 CA18217C 32905E46 2E36CE3B
E39E772C 180E8603 9B2783A2 EC07A28F B5C55DF0 6F4C52C9
DE2BCBF6 95581718 3995497C EA956AE5 15D22618 98FA0510
15728E5A 8AACAA68 FFFFFFFF FFFFFFFF.
The generator is:
g = 2.
The size of the subgroup generated by g is:
r = (q - 1) / 2 =
0x7FFFFFFF FFFFFFFF E487ED51 10B4611A 62633145 C06E0E68
94812704 4533E63A 0105DF53 1D89CD91 28A5043C C71A026E
F7CA8CD9 E69D218D 98158536 F92F8A1B A7F09AB6 B6A8E122
F242DABB 312F3F63 7A262174 D31BF6B5 85FFAE5B 7A035BF6
F71C35FD AD44CFD2 D74F9208 BE258FF3 24943328 F6722D9E
E1003E5C 50B1DF82 CC6D241B 0E2AE9CD 348B1FD4 7E9267AF
C1B2AE91 EE51D6CB 0E3179AB 1042A95D CF6A9483 B84B4B36
B3861AA7 255E4C02 78BA3604 650C10BE 19482F23 171B671D
F1CF3B96 0C074301 CD93C1D1 7603D147 DAE2AEF8 37A62964
EF15E5FB 4AAC0B8C 1CCAA4BE 754AB572 8AE9130C 4C7D0288
0AB9472D 45565534 7FFFFFFF FFFFFFFF.
The MODP group used for the iso11770-4-dl-4096 algorithm is defined
by the following parameters.
The prime is:
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q = 0xFFFFFFFF FFFFFFFF C90FDAA2 2168C234 C4C6628B 80DC1CD1
29024E08 8A67CC74 020BBEA6 3B139B22 514A0879 8E3404DD
EF9519B3 CD3A431B 302B0A6D F25F1437 4FE1356D 6D51C245
E485B576 625E7EC6 F44C42E9 A637ED6B 0BFF5CB6 F406B7ED
EE386BFB 5A899FA5 AE9F2411 7C4B1FE6 49286651 ECE45B3D
C2007CB8 A163BF05 98DA4836 1C55D39A 69163FA8 FD24CF5F
83655D23 DCA3AD96 1C62F356 208552BB 9ED52907 7096966D
670C354E 4ABC9804 F1746C08 CA18217C 32905E46 2E36CE3B
E39E772C 180E8603 9B2783A2 EC07A28F B5C55DF0 6F4C52C9
DE2BCBF6 95581718 3995497C EA956AE5 15D22618 98FA0510
15728E5A 8AAAC42D AD33170D 04507A33 A85521AB DF1CBA64
ECFB8504 58DBEF0A 8AEA7157 5D060C7D B3970F85 A6E1E4C7
ABF5AE8C DB0933D7 1E8C94E0 4A25619D CEE3D226 1AD2EE6B
F12FFA06 D98A0864 D8760273 3EC86A64 521F2B18 177B200C
BBE11757 7A615D6C 770988C0 BAD946E2 08E24FA0 74E5AB31
43DB5BFC E0FD108E 4B82D120 A9210801 1A723C12 A787E6D7
88719A10 BDBA5B26 99C32718 6AF4E23C 1A946834 B6150BDA
2583E9CA 2AD44CE8 DBBBC2DB 04DE8EF9 2E8EFC14 1FBECAA6
287C5947 4E6BC05D 99B2964F A090C3A2 233BA186 515BE7ED
1F612970 CEE2D7AF B81BDD76 2170481C D0069127 D5B05AA9
93B4EA98 8D8FDDC1 86FFB7DC 90A6C08F 4DF435C9 34063199
FFFFFFFF FFFFFFFF.
The generator is:
g = 2.
The size of the subgroup generated by g is:
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r = (q - 1) / 2 =
0x7FFFFFFF FFFFFFFF E487ED51 10B4611A 62633145 C06E0E68
94812704 4533E63A 0105DF53 1D89CD91 28A5043C C71A026E
F7CA8CD9 E69D218D 98158536 F92F8A1B A7F09AB6 B6A8E122
F242DABB 312F3F63 7A262174 D31BF6B5 85FFAE5B 7A035BF6
F71C35FD AD44CFD2 D74F9208 BE258FF3 24943328 F6722D9E
E1003E5C 50B1DF82 CC6D241B 0E2AE9CD 348B1FD4 7E9267AF
C1B2AE91 EE51D6CB 0E3179AB 1042A95D CF6A9483 B84B4B36
B3861AA7 255E4C02 78BA3604 650C10BE 19482F23 171B671D
F1CF3B96 0C074301 CD93C1D1 7603D147 DAE2AEF8 37A62964
EF15E5FB 4AAC0B8C 1CCAA4BE 754AB572 8AE9130C 4C7D0288
0AB9472D 45556216 D6998B86 82283D19 D42A90D5 EF8E5D32
767DC282 2C6DF785 457538AB AE83063E D9CB87C2 D370F263
D5FAD746 6D8499EB 8F464A70 2512B0CE E771E913 0D697735
F897FD03 6CC50432 6C3B0139 9F643532 290F958C 0BBD9006
5DF08BAB BD30AEB6 3B84C460 5D6CA371 047127D0 3A72D598
A1EDADFE 707E8847 25C16890 54908400 8D391E09 53C3F36B
C438CD08 5EDD2D93 4CE1938C 357A711E 0D4A341A 5B0A85ED
12C1F4E5 156A2674 6DDDE16D 826F477C 97477E0A 0FDF6553
143E2CA3 A735E02E CCD94B27 D04861D1 119DD0C3 28ADF3F6
8FB094B8 67716BD7 DC0DEEBB 10B8240E 68034893 EAD82D54
C9DA754C 46C7EEE0 C37FDBEE 48536047 A6FA1AE4 9A0318CC
FFFFFFFF FFFFFFFF.
Appendix B. Derived numerical values
This section gives several numerical values for implementing this
protocol, derived from the above specifications. The values shown in
this section are for informative purpose only.
+----------------+---------+---------+---------+---------+----------+
| | dl-2048 | dl-4096 | ec-p256 | ec-p521 | |
+----------------+---------+---------+---------+---------+----------+
| Size of w_A | 2048 | 4096 | 257 | 522 | (bits) |
| etc. | | | | | |
| Size of H(...) | 256 | 512 | 256 | 512 | (bits) |
| length of | 256 | 512 | 33 | 66 | (octets) |
| OCTETS(w_A) | | | | | |
| etc. | | | | | |
| length of wa, | 346 * | 686 * | 66 | 132 | (octets) |
| wb field | | | | | |
| values. | | | | | |
| length of oa, | 46 * | 90 * | 64 | 128 | (octets) |
| ob field | | | | | |
| values. | | | | | |
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| minimum | 2048 | 4096 | 1 | 1 | |
| allowed s_A | | | | | |
+----------------+---------+---------+---------+---------+----------+
(The numbers marked with * include enclosing quotation marks.)
Appendix C. Draft Remarks from the Authors
The following items are currently under consideration for future
revisions by the authors.
o Whether to use "TLS channel binding"
[I-D.altman-tls-channel-bindings] for "tls-key" verification
(Section 9). Note that existing implementations of TLS should be
considered to determine this.
Appendix D. Draft Change Log
D.1. 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.
D.2. Changes in revision 03
o Wildcard domain specifications (e.g. "*.example.com") is allowed
for auth-domain parameters (Section 4.1).
o Specification of the "tls-host" verification is updated
(incompatible change).
o State transitions fixed.
o Requirements for servers about w_a values clarified.
o RFC references are updated.
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D.3. 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 is changed to have authentication realm
information.
o Bugs on equations for o_A and o_B is fixed.
o Detailed equations for the whole algorithm is included.
o Elliptic-curve algorithms are updated.
o Several clarifications and other minor updates.
Authors' Addresses
Yutaka Oiwa
National Institute of Advanced Industrial Science and Technology
Research Center for Information Security
Akihabara Daibiru #1102
1-18-13 Sotokanda
Chiyoda-ku, Tokyo
JP
Phone: +81 3-5298-4722
Email: mutual-auth-contact@m.aist.go.jp
Hajime Watanabe
National Institute of Advanced Industrial Science and Technology
Hiromitsu Takagi
National Institute of Advanced Industrial Science and Technology
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Hirofumi Suzuki
Yahoo! Japan, Inc.
Roppongi Hills Mori Tower
6-10-1 Roppongi
Minato-ku, Tokyo
JP
Phone: +81 3-6440-6290
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