One document matched: draft-sterman-aaa-sip-04.txt
Differences from draft-sterman-aaa-sip-03.txt
Network Working Group B. Sterman
Internet-Draft Kayote Networks
Expires: November 30, 2004 D. Sadolevsky
SecureOL, Inc.
D. Schwartz
Kayote Networks
D. Williams
Cisco Systems
W. Beck
Deutsche Telekom AG
June 2004
RADIUS Extension for Digest Authentication
draft-sterman-aaa-sip-04.txt
Status of this Memo
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patent or other IPR claims of which I am aware have been disclosed,
or will be disclosed, and any of which I become aware will be
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This Internet-Draft will expire on November 30, 2004.
Copyright Notice
Copyright (C) The Internet Society (2004). All Rights Reserved.
Abstract
Several protocols borrow the authentication mechanisms from the
Hypertext Transfer Protocol, HTTP. This document specifies an
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extension to RADIUS that allows a RADIUS client in an HTTP-style
server, upon reception of a request, retrieve and compute Digest
authentication information from a RADIUS server. Additionally, a
scenario describing the authentication of a user emitting an
HTTP-style request is provided.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1 Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
1.2 Motivation . . . . . . . . . . . . . . . . . . . . . . . . 4
1.3 Overview . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.3.1 Scenario 1, RADIUS client chooses nonces . . . . . . . 6
1.3.2 Scenario 2, RADIUS server chooses nonces . . . . . . . 7
2. New RADIUS attributes . . . . . . . . . . . . . . . . . . . . 9
2.1 Digest-Response attribute . . . . . . . . . . . . . . . . 9
2.2 Digest-Realm attribute . . . . . . . . . . . . . . . . . . 9
2.3 Digest-Nonce attribute . . . . . . . . . . . . . . . . . . 10
2.4 Digest-Response-Auth attribute . . . . . . . . . . . . . . 10
2.5 Digest-Nextnonce attribute . . . . . . . . . . . . . . . . 10
2.6 Digest-Method attribute . . . . . . . . . . . . . . . . . 11
2.7 Digest-URI attribute . . . . . . . . . . . . . . . . . . . 11
2.8 Digest-QoP attribute . . . . . . . . . . . . . . . . . . . 11
2.9 Digest-Algorithm attribute . . . . . . . . . . . . . . . . 12
2.10 Digest-Entity-Body-Hash attribute . . . . . . . . . . . . 12
2.11 Digest-CNonce attribute . . . . . . . . . . . . . . . . . 13
2.12 Digest-Nonce-Count attribute . . . . . . . . . . . . . . . 13
2.13 Digest-Username attribute . . . . . . . . . . . . . . . . 13
2.14 Digest-Opaque attribute . . . . . . . . . . . . . . . . . 14
2.15 Digest-Auth-Param attribute . . . . . . . . . . . . . . . 14
2.16 Digest-AKA-Auts attribute . . . . . . . . . . . . . . . . 14
2.17 Digest-Domain attribute . . . . . . . . . . . . . . . . . 15
2.18 Digest-Stale attribute . . . . . . . . . . . . . . . . . . 15
2.19 Digest-HA1 attribute . . . . . . . . . . . . . . . . . . . 15
3. Detailed Description . . . . . . . . . . . . . . . . . . . . . 17
3.1 RADIUS Client Behaviour . . . . . . . . . . . . . . . . . 17
3.2 RADIUS Server Behaviour . . . . . . . . . . . . . . . . . 19
4. Migration Path to Diameter . . . . . . . . . . . . . . . . . . 21
4.1 Basic operation . . . . . . . . . . . . . . . . . . . . . 22
4.2 Limitations . . . . . . . . . . . . . . . . . . . . . . . 22
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 23
6. Security Considerations . . . . . . . . . . . . . . . . . . . 24
7. Example . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
8. Changes from draft-sterman-aaa-sip-03 . . . . . . . . . . . . 28
9. Changes from draft-sterman-aaa-sip-02 . . . . . . . . . . . . 29
10. Changes from draft-sterman-aaa-sip-01 . . . . . . . . . . . 30
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 31
11.1 Normative References . . . . . . . . . . . . . . . . . . . . 31
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11.2 Informative References . . . . . . . . . . . . . . . . . . . 31
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 32
A. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 34
Intellectual Property and Copyright Statements . . . . . . . . 35
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1. Introduction
1.1 Terminology
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].
1.2 Motivation
Digest authentication is a simple authentication mechanism for HTTP
and SIP. While it was not too successful in HTTP environments, it is
the only SIP authentication mechanism that has been widely adopted.
Due to the limitations and weaknesses of Digest authentication (see
[RFC2617], section 4 />), additional PKI-based authentication and
encryption mechanisms have been introduced into SIP: TLS [RFC2246]
and S/MIME [RFC2633]. The majority of today's SIP clients only
supports HTTP digest.
Current RADIUS-based AAA infrastructures have been built and debugged
over years. Some deficiencies of RADIUS have been mitigated with
proprietary (ie costly) extensions. Operators are therefore
reluctant to replace their RADIUS infrastructure in order to enable a
single new authentication mechanism.
Given the complexity of the alternatives, simple clients will
continue to support HTTP digest authentication only. Its
interoperability with a back-end authentication protocol such as
RADIUS is needed.
Operators that are about to replace their RADIUS-based AAA
infrastructure are strongly recommended to use Diameter.
1.3 Overview
Figure 1 depicts the basic scenario that is relevant for this
document. 'HTTP-style Client' and 'RADIUS Client' are entities using
a protocol with support for HTTP Digest Authentication, like SIP or
HTTP.
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HTTP/SIP RADIUS
+------------+ +--------+ +--------+
| HTTP-style | | RADIUS | | RADIUS |
| Client |<========>| Client |<------->| Server |
| | | | | |
+------------+ +--------+ +--------+
Figure 1: Overview of operation
The approach taken here is to extend RADIUS to support Digest
authentication by mimicking its native support for CHAP
authentication. According to [RFC2865], the RADIUS server
distinguishes between different authentication schemes by looking at
the presence of an attribute specific for that scheme. For the three
natively supported authentication schemes, these attributes are:
User-Password for PAP (or any other clear-text password scheme),
CHAP-Password for CHAP, and State + User- Password for
challenge-response scheme. This document adds another attribute to
be used in this role: Digest-Response. Also according to [RFC2865],
"An Access-Request packet MUST contain either a User-Password or a
CHAP-Password or a State. It MUST NOT contain both a User-Password
and a CHAP-Password. If future extensions allow other kinds of
authentication information to be conveyed, the attribute for that can
be used instead of User-Password or CHAP-Password." The
Digest-Response introduced here therefore can be used instead of
User-Password or CHAP-Password.
The HTTP Authentication parameters found in the Proxy-Authorization
or Authorization request header are mapped into newly defined RADIUS
attributes. These new RADIUS attributes are defined in the document
together with some other information required for calculating the
correct digest response on the RADIUS server with exception of the
password, which the RADIUS server is assumed to be able to retrieve
from a data store given the username.
The nonces required by the digest algorithm are either generated by
the RADIUS client or by the RADIUS server. If at least one
HTTP-style client requires AKA authentication [RFC3310], the RADIUS
server MUST support nonce generation and its RADIUS clients MUST NOT
generate nonces locally.
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1.3.1 Scenario 1, RADIUS client chooses nonces
HTTP/SIP RADIUS
+-----+ (1) +-----+ +-----+
| |==========>| | | |
| | (2) | | | |
| |<==========| | | |
| | (3) | | | |
| |==========>| | | |
| A | | B | (4) | C |
| | | |---------->| |
| | | | (5) | |
| | | |<----------| |
| | (6) | | | |
| |<==========| | | |
+-----+ +-----+ +-----+
====> HTTP/SIP
----> RADIUS
Figure 2: RADIUS client chooses nonces
The roles played by the entities in this scenario are as follows:
A: HTTP client / SIP UA
B: {HTTP server / HTTP proxy server / SIP proxy server / SIP UAS}
acting also as a RADIUS NAS
C: RADIUS server
The relevant order of messages sent in this scenario is as follows:
A sends B an HTTP/SIP request without authorization header (step 1).
B challenges A sending an HTTP/SIP "(Proxy) Authorization required"
response containing a locally generated nonce (step 2). A sends B an
HTTP/SIP request with authorization header (step 3). B sends C a
RADIUS Access-Request with attributes described in this document
(step 4). C responds to B with a RADIUS Access-Accept/Access-Reject
response (step 5). If credentials were accepted B receives an
Access-Accept response and the message sent from A is considered
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authentic. If B receives an Access-Reject response, however, B then
responds to A with a "(Proxy) Authorization required" response (step
6).
1.3.2 Scenario 2, RADIUS server chooses nonces
In most cases, the operation outlined in Section 1.3.1 is sufficient.
It reduces the load on the RADIUS server to a minimum. However, when
using AKA [RFC3310] the nonce is partially derived from a precomputed
authentication vector. These authentication vectors are often stored
centrally.
Figure 3 depicts a scenario, where the RADIUS server chooses nonces.
It shows a generic case where entities A and B communicate in the
front-end using protocols such as HTTP/SIP, while entities B and C
communicate in the back-end using RADIUS.
HTTP/SIP RADIUS
+-----+ (1) +-----+ +-----+
| |==========>| | (2) | |
| | | |---------->| |
| | | | (3) | |
| | (4) | |<----------| |
| |<==========| | | |
| | (5) | | | |
| |==========>| | | |
| A | | B | (6) | C |
| | | |---------->| |
| | | | (7) | |
| | | |<----------| |
| | (8) | | | |
| |<==========| | | |
+-----+ +-----+ +-----+
====> HTTP/SIP
----> RADIUS
Figure 3: RADIUS server chooses nonces
The roles played by the entities in this scenario are as follows:
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A: HTTP client / SIP UA
B: {HTTP server / HTTP proxy server / SIP proxy server / SIP UAS}
acting also as a RADIUS NAS
C: RADIUS server
The relevant order of messages sent in this scenario is as follows:
A sends B an HTTP/SIP request without authorization header (step 1).
B sends an Access-Request message with the newly defined
Digest-Method and Digest-URI attributes but without a Digest-Nonce
attribute to the RADIUS server, C (step 2). C chooses a nonce and
responds with an Access-Challenge (step 3). This Access-Challenge
contains Digest attributes, from which B takes values to construct an
HTTP/SIP "(Proxy) Authorization required" response. The remaining
steps are identical with scenario 1 (Section 1.3.1): B sends this
response to A (step 4). A resends its request with its credentials
(step 5). B sends an Access-Request to C (step 6). C checks the
credentials and replies with Access-Accept or Access-Reject (step 7).
Dependent on the C's result, B processes A's request or rejects it
with a "(Proxy) Authorization required" response (step 8).
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2. New RADIUS attributes
DIG-RES, DIG-REALM, DIG-NONCE, DIG-RSPAUTH, DIG-NEXTNONCE,
DIG-METHOD, DIG-URI, DIG-QOP, DIG-ALG, DIG-BODY, DIG-CNONCE, DIG-NC,
DIG-USER, DIG-OPAQUE, DIG-AUTHP, DIG-AUTS, DIG-DOMAIN, DIG-STALE and
DIG-HA1 are placeholders for values that are taken from the RADIUS
attribute type number space (see Section 5).
The term 'HTTP-style' denotes any protocol that uses HTTP-like
headers and uses HTTP digest authentication as described in
[RFC2617]. Examples are HTTP and SIP.
If not stated otherwise, the attributes have the following format:
0 1 2
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | String...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2.1 Digest-Response attribute
If this attribute is present, the RADIUS server SHOULD view the
Access-Request as a Digest one. When a RADIUS client receives a
(Proxy-)Authorization header, it puts the request-digest value into a
Digest-Response attribute.
Type
DIG-RES for Digest-Response.
Length
34
String
This attribute is only used in Access-Requests. This string
proves the user knows a password. The String field is 32
octets long and contains hexadecimal representation of 16 octet
digest value as it was calculated by the authenticated client.
The String field SHOULD be copied from request-digest of
digest-response ([RFC2617]).
2.2 Digest-Realm attribute
This string attribute describes a protection space of the RADIUS
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server. See [RFC2617] 1.2 for details.
Type
DIG-REALM
Length
>=3
String
In Access-Requests, the RADIUS client takes the value of the
realm directive (realm-value) from the HTTP-style request it
wants to authenticate. In Access-Challenge messages, the
RADIUS server puts the expected realm value into this
attribute.
2.3 Digest-Nonce attribute
This attribute holds a random nonce to be used in the HTTP Digest
calculation.
Type
DIG-NONCE
Length
>=3
String
In Access-Requests, the RADIUS client takes the value of the
nonce directive (nonce-value) from the HTTP-style request it
wants to authenticate. If the Access-Request had a
Digest-Method and a Digest-URI but no Digest-Nonce attribute
and the RADIUS server is configured to choose nonces, it MUST
put a Digest-Nonce attribute into its Access-Challenge message.
2.4 Digest-Response-Auth attribute
Type
DIG-RSPAUTH for Digest-Response-Auth.
Length
34
String
This attribute is only used in Access-Accept messages if the
RADIUS server is configured to choose nonces. This string
proves the RADIUS server knows the password. The RADIUS server
calculates a digest according to section 3.2.3 of [RFC2617] and
copies the result into this string. The RADIUS client puts the
string into the rspauth directive of the Authentication-Info
header.
2.5 Digest-Nextnonce attribute
This attribute holds a random nonce to be used in the HTTP Digest
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calculation.
Type
DIG-NEXTNONCE
Length
>=3
String
If the RADIUS server is configured to choose nonces and to use
Authentication-Info, it puts a Digest-Nextnonce attribute into
its Access-Accept message. It contains the nonce value that
SHOULD be used by the client in the next Access-Request
message. The RADIUS client MUST put the contents of this
attribute into the nextnonce directive of its HTTP-style
response.
2.6 Digest-Method attribute
This attribute holds the method string to be used in the HTTP Digest
calculation.
Type
DIG-METHOD
Length
>=3
String
In Access-Requests, the RADIUS client takes the value of the
request method from the HTTP-style request it wants to
authenticate. This attribute MUST only be used in
Access-Request messages.
2.7 Digest-URI attribute
This attribute holds the URI string to be used in the HTTP Digest
calculation.
Type
DIG-URI
Length
>=3
String
In Access-Requests, the RADIUS client takes the value of the
request URI (digest-uri-value) from the HTTP-style request it
wants to authenticate. The attribute MUST only be used in
Access-Request messages.
2.8 Digest-QoP attribute
This attribute holds the Quality of Protection parameter that
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influences the HTTP Digest calculation.
Type
DIG-QOP
Length
>=3
String
In Access-Requests, the RADIUS client takes the value of the
qop directive (qop-value) from the HTTP-style request it wants
to authenticate. In Access-Challenge messages, the RADIUS
server SHOULD put the desired qop-value into this attribute.
2.9 Digest-Algorithm attribute
This attribute holds the algorithm parameter that influences the HTTP
Digest calculation.
Type
DIG-ALG
Length
>=3
String
In Access-Requests, the RADIUS client takes the value of the
algorithm directive from the HTTP-style request it wants to
authenticate. In Access-Accept messages, the RADIUS server MAY
put the desired algorithm into this attribute.
2.10 Digest-Entity-Body-Hash attribute
When using the qop level 'auth-int', the contents of the message body
are required for digest calculation. Instead of sending the complete
body of the message, only its hash value is sent. This hash value
can be used directly in the digest calculation.
Type
DIG-BODY
Length
34
String
String, hexadecimal representation of a digest calculated over
entity-body of HTTP/SIP request ([RFC2616], [RFC3261]).
Computed by entity B in figure Figure 2. This attribute is not
part of the HTTP Digest response. See [RFC2617] section
3.2.2.3. This attribute MUST only be sent in Access-Request
packets.
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2.11 Digest-CNonce attribute
This attribute holds the client nonce parameter that is used in the
HTTP Digest calculation.
Type
DIG-CNONCE
Length
>=3
String
In Access-Requests, the RADIUS client takes the value of the
cnonce directive (cnonce-value) from the HTTP-style request it
wants to authenticate. The attribute is never used in
Access-Accept, Access-Challenge or Access-Reject messages.
2.12 Digest-Nonce-Count attribute
This attribute holds the nonce count parameter that is used to detect
replay attacks.
Type
DIG-NC
Length
9
String
In Access-Requests, the RADIUS client takes the value of the nc
directive (nc-value) from the HTTP-style request it wants to
authenticate. The attribute MUST only be used in
Access-Request messages.
2.13 Digest-Username attribute
This attribute holds the user name parameter that is used in the HTTP
digest calculation.
Type
DIG-USER
Length
>= 3
String
In Access-Requests, the RADIUS client takes the value of the
username directive (username-value) from the HTTP-style request
it wants to authenticate. The RADIUS server SHOULD NOT use
this value for password finding, but only for digest
calculation purpose. In order to find the user record
containing the password, the RADIUS server SHOULD use the value
of the ([RFC2865] -)User-Name attribute. This attribute MUST
only be sent in Access-Request packets.
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2.14 Digest-Opaque attribute
This attribute holds the opaque parameter that is passed to the
HTTP-style client. Th HTTP-style client passes this value back to
the server (ie the RADIUS client) without modification.
Type
DIG-OPAQUE
Length
>=3
String
This attribute is only used when the RADIUS server chooses
nonces. In Access-Requests, the RADIUS client takes the value
of the opaque directive from the HTTP-style request it wants to
authenticate and puts it into this attribute. In
Access-Challenge messages, the RADIUS server MAY include this
attribute.
2.15 Digest-Auth-Param attribute
This attribute is a placeholder for future extensions.
Type
DIG-AUTHP
Length
>=3
String
This attribute is for future extensions. Any extension
parameter in the digest-response can be put into a
Digest-Auth-Param attribute. The string consists of the whole
parameter, including its name and the equal ('=') sign. RADIUS
servers that do not implement a parameter contained in a
Digest-Auth-Param attribute MUST respond with an Access-Reject
message. RADIUS clients that do not implement a parameter
contained in a Digest-Auth-Param attribute MUST reject the
original HTTP-style request. This attribute MAY be used in
Access-Request and Access-Accept messages.
2.16 Digest-AKA-Auts attribute
This attribute holds the auts parameter that is used in the AKA
Digest ([RFC3310]) calculation.
Type
DIG-AUTS
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Length
>=3
String
In Access-Requests, the RADIUS client takes the value of the
auts directive from the HTTP-style request it wants to
authenticate. It is only used if the algorithm of the
digest-response denotes a version of AKA digest [RFC3310].
RADIUS servers that do not implement AKA digest MUST respond
with an Access-Reject message.
2.17 Digest-Domain attribute
When a RADIUS client has asked for a nonce, the RADIUS server MAY add
one or more Digest-Domain attributes to its Access-Challenge message.
The RADIUS client puts them into the quoted, space-separated list of
URIs of the 'domain' directive of a WWW-Authenticate header. The
URIs in the list define the protection space (see [RFC2617], section
3.2.1).
Type
DIG-DOMAIN
Length
3
String
The string consists of a single URI, that defines a protection
space. RADIUS servers MAY send attributes of this type in
Access-Challenge messages. RADIUS clients MUST NOT put
attributes of this type in Access-Request messages.
2.18 Digest-Stale attribute
If this attribute is present, the RADIUS server did not accept the
nonce value.
Type
DIG-STALE
Length
3
String
The string consists of a single character. If the nonce
presented by the RADIUS client was stale, the character is '1'
and is '0' otherwise. The attribute MUST be used in
Access-Accept messages if the RADIUS server chooses nonces.
2.19 Digest-HA1 attribute
If this attribute is present, the RADIUS server did not accept the
nonce value.
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Type
DIG-HA1
Length
34
String
This string contains the hexadecimal representation of H(A1) as
described in [RFC2617], section 3.2.1 and 3.2.2.2. This
attribute is only used in Access-Accept messages. It is used
by the RADIUS client to calculate the 'rspauth' directive in an
Authentication-Info header when the quality of protection
('qop') is 'auth-int'. Digest-HA1 SHOULD only be sent if the
'algorithm' directive's value is 'MD5-sess' or
'AKAv1-MD5-sess'. This attribute MUST NOT be sent if the qop
parameter was not specified or has value of 'auth'. If the
'algorithm' directive's value is 'MD5' or 'AKAv1-MD5', the
Digest-HA1 attribute MUST NOT be sent by the RADIUS server or
processed by the RADIUS client, unless the authenticity and
integrity of the Access-Accept message was secured by
cryptographic or equivalently secure means.
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3. Detailed Description
3.1 RADIUS Client Behaviour
A RADIUS client without an encrypted or otherwise secured connection
(see Section 6) to its RADIUS server only accepts unsecured
connections from its HTTP-style clients (or else the clients would
have a false sense of security).
The RADIUS client examines the (Proxy-)Authorization header of an
incoming HTTP-style request message. If this header is present and
contains HTTP digest information, the RADIUS client checks the
'nonce' parameter. If the 'nonce' value has not been sent by the
RADIUS client, it responds with a 401 (Unauthorized) or 407 (Proxy
Authentication Required) to the HTTP-style client. In this error
response, the RADIUS client sends a new nonce.
If the RADIUS client recognizes the nonce, it takes the header
parameters and puts them into a RADIUS Access-Request message. It
puts the 'response' parameter into a Digest-Response attribute and
the realm / nonce / qop / algorithm / cnonce / nc / username into the
respective Digest-Realm / Digest-Nonce / Digest-QoP /
Digest-Algorithm / Digest-CNonce / Digest-Nonce-Count /
Digest-Username attributes. The request URI and the request method
are put into the Digest-URI and Digest-Method attributes. Now, the
RADIUS client sends the Access-Request message to the RADIUS server.
The RADIUS server processes the message and responds with an
Access-Accept or an Access-Reject message.
The RADIUS clients constructs an Authentication-Info header:
o If the Access-Accept message contains a Digest-Response-Auth
attribute, the RADIUS client checks the Digest-QoP attribute:
* If the Digest-Qop attribute's value is 'auth' or not specified,
the RADIUS client puts the Digest-Response-Auth attribute's
content into the 'rspauth' directive of the HTTP-style
response.
* If the Digest-Qop attribute's value is 'auth-int', the RADIUS
client ignores the Access-Accept message and behaves like it
had received an Access-Reject message.
o If the Access-Accept message contains a Digest-HA1 attribute, the
RADIUS client checks the Digest-QoP and Digest-Algorithm
attributes:
* If the Digest-Qop attribute is missing or its value is 'auth',
the RADIUS client ignores the Digest-HA1 attribute. It does
not include an Authentication-Info header into its HTTP-style
response.
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* If the Digest-Qop attribute's value is 'auth-int' and the
Digest-Algorithm attribute's value is 'MD5-sess' or
'AKAv1-MD5-sess', the RADIUS client calculates the contents of
the 'rspauth' directive. It creates the HTTP-style response
message and calculates the hash of this message's body. It
uses the result and the Digest-URI attribute's value of the
corresponding Access-Request message to perform the H(A2)
calculation. It takes the Digest-Nonce, Digest-Nonce-Count,
Digest-CNonce and Digest-QoP values of the corresponding
Access-Request and the Digest-HA1 attribute's value to finish
the computation of the 'rspauth' value.
* If the Digest-Qop attribute's value is 'auth-int' and the
Digest-Algorithm attribute's value is 'MD5' or 'AKAv1-MD5', the
RADIUS client MUST NOT use the Digest-HA1 attribute, unless it
knows for sure that the Access-Accept message was encrypted or
otherwise protected against eavesdropping.
The RADIUS server MAY have added a Digest-Nextnonce attribute. If
the RADIUS client discovers this, it puts the contents of this
attribute into a 'nextnonce' directive. Now it can send an
HTTP-style response.
If the RADIUS client did not receive a (Proxy-)Authorization header
from its HTTP-style client, it obtains a new nonce and sends an error
response (401 or 407) containing a (Proxy-)Authenticate header.
If the RADIUS client receives an Access-Reject or no response from
the RADIUS server, it sends an error response to the HTTP-style
request it has received.
The RADIUS client has three ways to obtain nonces: it generates them
locally, it has received one in a Digest-Nonce attribute of a
previously received Access-Accept message, or it asks the RADIUS
server for one. To do the latter, it sends an Access-Request
containing a Digest-Method and a Digest-URI attribute but without a
Digest-Nonce attribute. The RADIUS server chooses a nonce and
responds with an Access-Challenge containing a Digest-Nonce
attribute.
If the RADIUS server responds with an Access-Reject, the RADIUS
client MAY generate a nonce locally. If the RADIUS client does not
generate nonces locally, the authentication has failed. The RADIUS
server can send Digest-QoP, Digest-Algorithm, Digest-Realm,
Digest-Domain and Digest-Opaque attributes in the Access-Challenge
carrying the nonce. If these attributes are present, the client MUST
use them.
If the Digest-Stale attribute is present in the Access-Accept message
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following an Access-Challenge, the RADIUS client sends an error (401
or 407) response containing WWW-/Proxy-Authenticate header with the
directives 'stale' and 'nextnonce'.
3.2 RADIUS Server Behaviour
If the RADIUS server receives an Access-Request message with a
Digest-Method and a Digest-URI attribute but without a Digest-Nonce
attribute, it chooses a nonce. It puts the nonce into a Digest-Nonce
attribute and sends it in an Access-Challenge message to the RADIUS
client. The RADIUS server MUST add Digest-Algorithm, Digest-Realm,
SHOULD add Digest-QoP and MAY add Digest-Domain, Digest-Opaque
attributes to the Access-Challenge message. If the server cannot
choose a nonce, it replies with an Access-Reject message.
If the RADIUS server receives an Access-Request message containing a
Digest-Response attribute, it looks for the following attributes:
Digest-Realm, Digest-Nonce, Digest-Method, Digest-URI, Digest-QoP,
Digest-Algorithm, Digest-Username. Depending on the content of
Digest-Algorithm and Digest-QoP, it looks for
Digest-Entity-Body-Hash, Digest-CNonce and Digest-AKA-Auts, too. See
[RFC2617] and [RFC3310] for details. If it has issued a
Digest-Opaque attribute along with the nonce, the Access-Request MUST
have a matching Digest-Opaque attribute.
If it does not find these attributes, it responds with an
Access-Reject message. If the attributes are present, the RADIUS
server calculates the digest response as described in [RFC2617]. To
look up the password, the RADIUS server uses the RADIUS User-Name
attribute. All other values are taken from the Digest attributes
described in this document. If the calculated digest response equals
the string received in the Digest-Response attribute, the
authentication was successful. If not, the RADIUS server responds
with an Access-Reject.
If the authentication was successful, the RADIUS server adds an
attribute to the Access-Accept message which can be used by the
RADIUS client to construct an Authentication-Info header:
o If the Digest-QoP attribute's value is 'auth' or unspecified, the
RADIUS server puts a Digest-Response-Auth attribute into the
Access-Accept message
o If the Digest-QoP attribute's value is 'auth-int' and the
Digest-Algorithm attribute's value is 'MD5-sess' or
'AKAv1-MD5-sess', the RADIUS server puts a Digest-HA1 attribute
into the Access-Accept message.
o If the Digest-QoP attribute's value is 'auth-int' and the
Digest-Algorithm attribute's value is 'MD5' or 'AKAv1-MD5', the
RADIUS server MUST NOT send a Digest-HA1 attribute unless the
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connection between RADIUS server and client is encrypted or
otherwise protected against eavesdropping.
RADIUS servers issuing nonces MAY construct a Digest-Nextnonce
attribute. This is useful to limit the lifetime of a nonce and to
save a round-trip in future requests (see nextnonce discussion in
[RFC2617], section 3.2.3). The Digest-Response attribute and the
optional Digest-Nextnonce attribute are send to the RADIUS client in
an Access-Accept message.
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4. Migration Path to Diameter
The following table gives an overview of the mapping between RADIUS
attributes defined here and the corresponding Diameter AVPs described
in [I-D.ietf-aaa-diameter-sip-app]:
+-------------------------+-----------------------------------------+
| RADIUS | Diameter |
+-------------------------+-----------------------------------------+
| Digest-Realm | Digest-Realm |
| | |
| Digest-Nonce | Digest-Nonce |
| | |
| Digest-URI | Digest-URI |
| | |
| Digest-Domain | Digest-Domain |
| | |
| Digest-QoP | Digest-Qop |
| | |
| Digest-Algorithm | Digest-Algorithm |
| | |
| Digest-CNonce | Digest-Cnonce |
| | |
| Digest-Nonce-Count | Digest-Nonce-Count |
| | |
| Digest-Method | SIP-Method AVP |
| | |
| Digest-Username | Digest-Username AVP |
| | |
| Digest-Entity-Body-Hash | SIP-Entity-Body-Hash AVP |
| | |
| Digest-Response | SIP-Authorization Digest-Response |
| | |
| Digest-Response-Auth | SIP-Authentication-Info Digest-Response |
| | |
| Digest-Opaque | Digest-Opaque AVP |
| | |
| Digest-Auth-Param | Digest-Auth-Param |
| | |
| Digest-AKA-Auts | Digest-AKA-Auts |
| | |
| Digest-Stale | Digest-Stale AVP |
+-------------------------+-----------------------------------------+
Table 1
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4.1 Basic operation
If an Access-Request message contains a Digest-Method and a
Digest-URI attribute but no Digest-Nonce attribute, the gateway maps
the RADIUS attributes to Diameter according to Table 2. The gateway
construct a MAR message and sends it to the Diameter server.
+---------------+------------+
| RADIUS | Diameter |
+---------------+------------+
| Digest-URI | SIP-AOR |
| | |
| Digest-Method | SIP-Method |
+---------------+------------+
Table 2
The Diameter Server responds with a MAA message. This message
contains a Result-Code AVP set to the value DIAMETER_MULTI_ROUND_AUTH
and challenge parameters. The gateway translates the AVPs and puts
the resulting RADIUS attributes into an Access-Challenge message. It
sends the Access-Challenge message to the RADIUS client.
The gateway maps an Access-Request message containing a
Digest-Response attribute to a MAR message with a Diameter
SIP-Authorization AVP. All RADIUS attributes of the Access-Request
message are mapped to the corresponding Diameter AVPs. The gateway
sends the MAR message to the Diameter server.
If the authentication was successful, the Diameter server replies
with a MAA containing a SIP-Authentication-Info and a Digest-Response
AVP. The gateway converts these to the corresponding RADIUS
attributes and constructs a RADIUS message. If the Result-Code AVP
is Diameter_SUCCESS or a Digest-Stale AVP is present, an
Access-Accept is sent. In all other cases, an Access-Reject is sent.
4.2 Limitations
This document covers not all functionality found in
[I-D.ietf-aaa-diameter-sip-app].
o There is no equivalent to Diameter's UAR/UAA, SAR/SAA, LIR/LIA,
RTR/RTA and PPR/PPA messages
o The operational mode where the Diameter server sends the expected
digest response to the client is not possible.
The operational mode where the RADIUS client chooses nonces is not
possible with [I-D.ietf-aaa-diameter-sip-app].
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5. IANA Considerations
This document serves as IANA registration request for a number of
values from the RADIUS attribute type number space:
+---------------+------------------------+
| placeholder | value assigned by IANA |
+---------------+------------------------+
| DIG-RES | TBD |
| | |
| DIG-REALM | TBD |
| | |
| DIG-NONCE | TBD |
| | |
| DIG-NEXTNONCE | TBD |
| | |
| DIG-RSPAUTH | TBD |
| | |
| DIG-METHOD | TBD |
| | |
| DIG-URI | TBD |
| | |
| DIG-QOP | TBD |
| | |
| DIG-ALG | TBD |
| | |
| DIG-BODY | TBD |
| | |
| DIG-CNONCE | TBD |
| | |
| DIG-NC | TBD |
| | |
| DIG-USER | TBD |
| | |
| DIG-OPAQUE | TBD |
| | |
| DIG-AUTHP | TBD |
| | |
| DIG-AUTS | TBD |
| | |
| DIG-DOMAIN | TBD |
| | |
| DIG-STALE | TBD |
| | |
| DIG-HA1 | TBD |
+---------------+------------------------+
Table 3
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6. Security Considerations
The RADIUS extensions described in this document make RADIUS a
transport protocol for the data that is required to perform a digest
calculation. It adds the vulnerabilities of HTTP Digest (see
[RFC2617], section 4) to those of RADIUS (see [RFC2865], section 8 or
<http://www.untruth.org/~josh/security/radius/radius-auth.html>)).
If an attacker gets access to a RADIUS client or RADIUS proxy, it can
perform man-in-the-middle attacks even if the connections between A,
B and B, C (Figure 2) have been secured with TLS or IPSec.
SIP or HTTP requests occur much more frequently than dial-in
requests. RADIUS servers implementing this specification must meet
that additional performance requirements. An attacker could try to
overload the RADIUS infrastructure by excessively sending SIP or HTTP
requests. This kind of attack was more difficult when RADIUS was
just used for dial-in authentication: the attacker could be
identified by the DSL / Cable interface or with some help of the PSTN
provider.
To make simple denial of service attacks more difficult, RADIUS
clients MUST check if nonces received from a client have been issued
by them. This SHOULD be done statelessly. For example, a nonce
could consist of a cryptographically random part and some kind of
signature of the RADIUS client, as described in [RFC2617], section
3.2.1.
RADIUS servers MAY include Digest-QoP and Digest-Algorithm attributes
in Access-Accept messages. A man in the middle can modify or remove
those attributes in a bidding down attack. In this case, the RADIUS
client would use a weaker authentication scheme than intended.
Informational RfC 3579 [RFC3579], section 3.2 describes a
Message-Authenticator attribute which MAY be used to protect the
integrity of RADIUS messages.
The Digest-HA1 attribute contains no random components if the
algorithm is 'MD5' or 'AKAv1-MD5'. This makes offline dictionary
attacks easier and can be used for replay attacks.
HTTP-style clients can use TLS with server side certificates together
with HTTP-Digest authentication. Instead of TLS, IPSec can be used,
too. TLS or IPSec secure the connection while Digest Authentication
authenticates the user. If a RADIUS client accepts such connections,
it MUST have an equally secure connection to the RADIUS server.
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7. Example
This is an example sniffed from the traffic between a softphone (A),
a Proxy Server (B) and examplecom RADIUS server (C). The
communication between the Proxy Server and a SIP PSTN gateway is
omitted for brevity. The SIP messages are not shown completely.
A->B
INVITE sip:97226491335@10.0.69.38 SIP/2.0
B->A
SIP/2.0 100 Trying
B->A
SIP/2.0 407 Proxy Authentication Required
Proxy-Authenticate: Digest realm="examplecom"
,nonce="3bada1a0", algorithm="md5"
Content-Length: 0
A->B
ACK sip:97226491335@10.0.69.38 SIP/2.0
A->B
INVITE sip:97226491335@10.0.69.38 SIP/2.0
Proxy-Authorization: Digest algorithm="md5",nonce="3bada1a0"
,opaque="",realm="examplecom"
,response="2ae133421cda65d67dc50d13ba0eb9bc"
,uri="sip:97226491335@10.0.69.38",username="12345678"
B->C
Code = 1 (Access-Request)
Attributes:
NAS-IP-Address = a 0 45 26 (10.0.69.38)
NAS-Port-Type = 5 (Virtual)
User-Name = "12345678"
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Digest-Response (DIG-RES) = "2ae133421cda65d67dc50d13ba0eb9bc"
Digest-Realm (DIG-REALM) = "examplecom"
Digest-Nonce (DIG-NONCE) = "3bada1a0"
Digest-Method (DIG-METHOD) = "INVITE"
Digest-URI (DIG-URI) = "sip:97226491335@10.0.69.38"
Digest-Algorithm (DIG-ALG) = "md5"
Digest-Username (DIG-USER) = "12345678"
C->B
Code = 2 (Access-Accept)
Attributes:
Digest-Response-Auth (DIG-RSPAUTH) =
"6303c41b0e2c3e524e413cafe8cce954"
B->A
SIP/2.0 180 Ringing
B->A
SIP/2.0 200 OK
A->B
ACK sip:97226491335@10.0.69.38:5060 SIP/2.0
A second example shows the traffic between a web browser (A), web
server (B) and a RADIUS server (C).
A->B
GET /index.html HTTP/1.1
B->A
HTTP/1.1 407 Authentication Required
WWW-Authenticate: Digest realm="examplecom", domain="/index.html",
,nonce="a3086ac8", algorithm="md5"
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Content-Length: 0
A->B
GET /index.html HTTP/1.1
Authorization: Digest algorithm="md5",nonce="a3086ac8"
,opaque="",realm="examplecom"
,response="369b593b9a79e001256a2b40afe49f4c"
,uri="/index.html",username="12345678"
B->C
Code = 1 (Access-Request)
Attributes:
NAS-IP-Address = a 0 45 26 (10.0.69.38)
NAS-Port-Type = 5 (Virtual)
User-Name = "12345678"
Digest-Response (DIG-RES) = "369b593b9a79e001256a2b40afe49f4c"
Digest-Realm (DIG-REALM) = "examplecom"
Digest-Nonce (DIG-NONCE) = "a3086ac8"
Digest-Method (DIG-METHOD) = "GET"
Digest-URI (DIG-URI) = "/index.html""
Digest-Algorithm (DIG-ALG) = "md5"
Digest-Username (DIG-USER) = "12345678"
C->B
Code = 2 (Access-Accept)
Attributes:
Digest-Response-Auth (DIG-RSPAUTH) =
"e644aa513effbfe1caff67103ff6433c"
B->A
HTTP/1.1 200 OK
...
<html>
...
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8. Changes from draft-sterman-aaa-sip-03
o addressed 'auth-int' issue
o New Digest-Nextnonce attribute
o revised abstract, motivational section and examples
o Access-Challenge instead of 'Access-Accept carrying a Digest-Nonce
attribute'
o shortened SIP messages in example, removed real-world addresses
and product names
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9. Changes from draft-sterman-aaa-sip-02
o Relaxed restrictions for DIG-DOMAIN, DIG-REALM, DIG-OPAQUE,
DIG-QOP and DIG-ALG
o Additional security considerations for DIG-DOMAIN, DIG-QOP and
DIG-ALG usage in Access-Accept messages
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10. Changes from draft-sterman-aaa-sip-01
o Replaced Sub-attributes with flat attributes
o aligned naming with [I-D.ietf-aaa-diameter-sip-app]
o Added how a server must treat unknown attributes.
o Added a section 'Migration path to Diameter'
o Added an optional attribute for support of the digest scheme
described in informational [RFC3310].
o Added a mode of operation where the RADIUS server chooses the
nonce. This was required for AKA [RFC3310], but can be useful for
ordinary Digest authentication when the qop directive is not used.
This required the addition of several attributes.
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11. References
11.1 Normative References
[I-D.ietf-aaa-diameter-sip-app]
Garcia-Martin, M., Belinchon, M., Pallares-Lopez, M.,
Canales-Valenzuela, C. and K. Tammi, "Diameter Session
Initiation Protocol (SIP) Application",
draft-ietf-aaa-diameter-sip-app-03 (work in progress),
July 2004.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[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.
[RFC2865] Rigney, C., Willens, S., Rubens, A. and W. Simpson,
"Remote Authentication Dial In User Service (RADIUS)", RFC
2865, June 2000.
[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
A., Peterson, J., Sparks, R., Handley, M. and E. Schooler,
"SIP: Session Initiation Protocol", RFC 3261, June 2002.
11.2 Informative References
[RFC1750] Eastlake, D., Crocker, S. and J. Schiller, "Randomness
Recommendations for Security", RFC 1750, December 1994.
[RFC2246] Dierks, T. and C. Allen, "The TLS Protocol Version 1.0",
RFC 2246, January 1999.
[RFC2633] Ramsdell, B., "S/MIME Version 3 Message Specification",
RFC 2633, June 1999.
[RFC3310] Niemi, A., Arkko, J. and V. Torvinen, "Hypertext Transfer
Protocol (HTTP) Digest Authentication Using Authentication
and Key Agreement (AKA)", RFC 3310, September 2002.
[RFC3579] Aboba, B. and P. Calhoun, "RADIUS (Remote Authentication
Dial In User Service) Support For Extensible
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Authentication Protocol (EAP)", RFC 3579, September 2003.
[RFC3588] Calhoun, P., Loughney, J., Guttman, E., Zorn, G. and J.
Arkko, "Diameter Base Protocol", RFC 3588, September 2003.
Authors' Addresses
Baruch Sterman
Kayote Networks
P.O. Box 1373
Efrat 90435
Israel
EMail: baruch@kayote.com
Daniel Sadolevsky
SecureOL, Inc.
Jerusalem Technology Park
P.O. Box 16120
Jerusalem 91160
Israel
EMail: dscreat@dscreat.com
David Schwartz
Kayote Networks
P.O. Box 1373
Efrat 90435
Israel
EMail: david@kayote.com
David Williams
Cisco Systems
7025 Kit Creek Road
P.O. Box 14987
Research Triangle Park NC 27709
USA
EMail: dwilli@cisco.com
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Wolfgang Beck
Deutsche Telekom AG
Am Kavalleriesand 3
Darmstadt 64295
Germany
EMail: beckw@t-systems.com
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Appendix A. Acknowledgements
We would like to acknowledge Kevin Mcdermott (Cisco Systems) /or
providing comments and experimental implementation.
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Sterman, et al. Expires November 30, 2004 [Page 35]
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