Network Working Group B. Sterman

Network Working Group B. Sterman
Request for Comments: 4590 Kayote Networks
Category: Standards Track D. Sadolevsky
SecureOL, Inc.
D. Schwartz
Kayote Networks
D. Williams
Cisco Systems
W. Beck
Deutsche Telekom AG
July 2006

RADIUS Extension for Digest Authentication

Status of This Memo

This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.

Copyright Notice

Copyright (C) The Internet Society (2006).

Abstract

This document defines an extension to the Remote Authentication
Dial-In User Service (RADIUS) protocol to enable support of Digest
Authentication, for use with HTTP-style protocols like the Session
Initiation Protocol (SIP) and HTTP.

Table of Contents

1. Introduction ....................................................2
1.1. Terminology ................................................2
1.2. Motivation .................................................3
1.3. Overview ...................................................4
2. Detailed Description ............................................6
2.1. RADIUS Client Behavior .....................................6
2.1.1. Credential Selection ................................6
2.1.2. Constructing an Access-Request ......................6
2.1.3. Constructing an Authentication-Info Header ..........7
2.1.4. Failed Authentication ...............................8
2.1.5. Obtaining Nonces ....................................9
2.2. RADIUS Server Behavior .....................................9

Sterman, et al. Standards Track [Page 1]

RFC 4590 RADIUS Digest Authentication July 2006

2.2.1. General Attribute Checks ............................9
2.2.2. Authentication .....................................10
2.2.3. Constructing the Reply .............................11
3. New RADIUS Attributes ..........................................12
3.1. Digest-Response attribute .................................12
3.2. Digest-Realm Attribute ....................................13
3.3. Digest-Nonce Attribute ....................................13
3.4. Digest-Response-Auth Attribute ............................14
3.5. Digest-Nextnonce Attribute ................................14
3.6. Digest-Method Attribute ...................................14
3.7. Digest-URI Attribute ......................................15
3.8. Digest-Qop Attribute ......................................15
3.9. Digest-Algorithm Attribute ................................16
3.10. Digest-Entity-Body-Hash Attribute ........................16
3.11. Digest-CNonce Attribute ..................................17
3.12. Digest-Nonce-Count Attribute .............................17
3.13. Digest-Username Attribute ................................17
3.14. Digest-Opaque Attribute ..................................18
3.15. Digest-Auth-Param Attribute ..............................18
3.16. Digest-AKA-Auts Attribute ................................19
3.17. Digest-Domain Attribute ..................................19
3.18. Digest-Stale Attribute ...................................20
3.19. Digest-HA1 Attribute .....................................20
3.20. SIP-AOR Attribute ........................................21
4. Diameter Compatibility .........................................21
5. Table of Attributes ............................................22
6. Examples .......................................................23
7. IANA Considerations ............................................27
8. Security Considerations ........................................27
8.1. Denial of Service .........................................28
8.2. Confidentiality and Data Integrity ........................28
9. Acknowledgements ...............................................29
10. References ....................................................29
10.1. Normative References .....................................29
10.2. Informative References ...................................30

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].

The use of normative requirement key words in this document shall
apply only to RADIUS client and RADIUS server implementations that
include the features described in this document. This document
creates no normative requirements for existing implementations.

Sterman, et al. Standards Track [Page 2]

RFC 4590 RADIUS Digest Authentication July 2006

HTTP-style protocol
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 the Session Initiation
Protocol (SIP).

NAS
Network Access Server, the RADIUS client.

nonce
An unpredictable value used to prevent replay attacks. The
nonce generator may use cryptographic mechanisms to produce
nonces it can recognize without maintaining state.

protection space
HTTP-style protocols differ in their definition of the
protection space. For HTTP, it is defined as the combination
of realm and canonical root URL of the requested resource for
which the use is authorized by the RADIUS server. In the case
of SIP, the realm string alone defines the protection space.

SIP UA
SIP User Agent, an Internet endpoint that uses the Session
Initiation Protocol.

SIP UAS
SIP User Agent Server, a logical entity that generates a
response to a SIP (Session Initiation Protocol) request.

1.2. Motivation

The HTTP Digest Authentication mechanism, defined in [RFC2617], was
subsequently adapted for use with SIP [RFC3261]. Due to the
limitations and weaknesses of Digest Authentication (see [RFC2617],
section 4), additional authentication and encryption mechanisms are
defined in SIP [RFC3261], including Transport Layer Security (TLS)
[RFC4346] and Secure MIME (S/MIME) [RFC3851]. However, Digest
Authentication support is mandatory in SIP implementations, and
Digest Authentication is the preferred way for a SIP UA to
authenticate itself to a proxy server. Digest Authentication is used
in other protocols as well.

To simplify the provisioning of users, there is a need to support
this authentication mechanism within Authentication, Authorization,
and Accounting (AAA) protocols such as RADIUS [RFC2865] and Diameter
[RFC3588].

Sterman, et al. Standards Track [Page 3]

RFC 4590 RADIUS Digest Authentication July 2006

This document defines an extension to the RADIUS protocol to enable
support of Digest Authentication for use with SIP, HTTP, and other
HTTP-style protocols using this authentication method. Support for
Digest mechanisms such as Authentication and Key Agreement (AKA)
[RFC3310] is also supported. A companion document [SIP-APP] defines
support for Digest Authentication within Diameter.

1.3. Overview

HTTP Digest is a challenge-response protocol used to authenticate a
client's request to access some resource on a server. Figure 1 shows
a single HTTP Digest transaction.

HTTP/SIP..
+------------+ (1) +------------+
| |--------->| |
| HTTP-style | (2) | HTTP-style |
| client |<---------| server |
| | (3) | |
| |--------->| |
| | (4) | |
| |<---------| |
+------------+ +------------+

Figure 1: Digest operation without RADIUS

If the client sends a request without any credentials (1), the server
will reply with an error response (2) containing a nonce. The client
creates a cryptographic digest from parts of the request, from the
nonce it received from the server, and from a shared secret. The
client re-transmits the request (3) to the server, but now includes
the digest within the packet. The server does the same digest
calculation as the client and compares the result with the digest it
received in (3). If the digest values are identical, the server
grants access to the resource and sends a positive response to the
client (4). If the digest values differ, the server sends a negative
response to the client (4).

Instead of maintaining a local user database, the server could use
RADIUS to access a centralized user database. However, RADIUS
[RFC2865] does not include support for HTTP Digest Authentication.
The RADIUS client cannot use the User-Password attribute, since it
does not receive a password from the HTTP-style client. The
CHAP-Challenge and CHAP-Password attributes described in [RFC1994]
are also not suitable since the CHAP algorithm is not compatible with
HTTP Digest.

Sterman, et al. Standards Track [Page 4]

RFC 4590 RADIUS Digest Authentication July 2006

This document defines new attributes that enable the RADIUS server to
perform the digest calculation defined in [RFC2617], providing
support for Digest Authentication as a native authentication
mechanism within RADIUS.

The nonces required by the digest algorithm are generated by the
RADIUS server. Generating them in the RADIUS client would save a
round-trip, but introduce security and operational issues. Some
digest algorithms -- e.g., AKA [RFC3310] -- would not work.

Figure 2 depicts a scenario in which the HTTP-style server defers
authentication to a RADIUS server. Entities A and B communicate
using HTTP or SIP, while entities B and C communicate using RADIUS.

HTTP/SIP RADIUS

+-----+ (1) +-----+ +-----+
| |==========>| | (2) | |
| | | |---------->| |
| | | | (3) | |
| | (4) | |<----------| |
| |<==========| | | |
| | (5) | | | |
| |==========>| | | |
| A | | B | (6) | C |
| | | |---------->| |
| | | | (7) | |
| | | |<----------| |
| | (8) | | | |
| |<==========| | | |
+-----+ +-----+ +-----+

====> HTTP/SIP
----> RADIUS

Figure 2: HTTP Digest over RADIUS

The entities have the following roles:

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

Sterman, et al. Standards Track [Page 5]

RFC 4590 RADIUS Digest Authentication July 2006

The following messages are sent in this scenario:

A sends B an HTTP/SIP request without an authorization header (step
1). B sends an Access-Request packet 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. 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).
Depending on C's result, B processes A's request or rejects it with a
"(Proxy) Authorization required" response (step 8).

2. Detailed Description

2.1. RADIUS Client Behavior

The attributes described in this document are sent in cleartext.
Therefore, were a RADIUS client to accept secure connections (HTTPS
or SIPS) from HTTP-style clients, this could result in information
intentionally protected by HTTP-style clients being sent in the clear
during RADIUS exchange.

2.1.1. Credential Selection

On reception of an HTTP-style request message, the RADIUS client
checks whether it is authorized to authenticate the request. Where
an HTTP-style request traverses several proxies and each of the
proxies requests to authenticate the HTTP-style client, the request
at the HTTP-style server may contain multiple credential sets.

The RADIUS client can use the 'realm' directive in HTTP to determine
which credentials are applicable. Where none of the realms are of
interest, the RADIUS client MUST behave as though no relevant
credentials were sent. In all situations, the RADIUS client MUST
send zero or exactly one credential to the RADIUS server. The RADIUS
client MUST choose the credential of the (Proxy-)Authorization header
if the realm directive matches its locally configured realm.

2.1.2. Constructing an Access-Request

If a matching (Proxy-)Authorization header is present and contains
HTTP Digest information, the RADIUS client checks the 'nonce'
parameter.

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RFC 4590 RADIUS Digest Authentication July 2006

If the RADIUS client recognizes the nonce, it takes the header
directives and puts them into a RADIUS Access-Request packet. It
puts the 'response' directive into a Digest-Response attribute and
the realm, nonce, digest-uri, qop, algorithm, cnonce, nc, username,
and opaque directives into the respective Digest-Realm, Digest-Nonce,
Digest-URI, Digest-Qop, Digest-Algorithm, Digest-CNonce,
Digest-Nonce-Count, Digest-Username, and Digest-Opaque attributes.
The RADIUS client puts the request method into the Digest-Method
attribute.

Due to syntactic requirements, HTTP-style protocols have to escape
with backslash all quote and backslash characters in contents of HTTP
Digest directives. When translating directives into RADIUS
attributes, the RADIUS client only removes the surrounding quotes
where present. See Section 3 for an example.

If the Quality of Protection (qop) directive's value is 'auth-int',
the RADIUS client calculates H(entity-body) as described in
[RFC2617], Section 3.2.1, and puts the result in a
Digest-Entity-Body-Hash attribute.

The RADIUS client adds a Message-Authenticator attribute, defined in
[RFC3579], and sends the Access-Request packet to the RADIUS server.

The RADIUS server processes the packet and responds with an
Access-Accept or an Access-Reject.

2.1.3. Constructing an Authentication-Info Header

After having received an Access-Accept from the RADIUS server, the
RADIUS client constructs an Authentication-Info header:

o If the Access-Accept packet 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 Authentication-Info header's 'rspauth'
directive of the HTTP-style response.

* If the Digest-Qop attribute's value is 'auth-int', the RADIUS
client ignores the Access-Accept packet and behaves as if it
had received an Access-Reject packet (Digest-Response-Auth
can't be correct as the RADIUS server does not know the
contents of the HTTP-style response's body).

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RFC 4590 RADIUS Digest Authentication July 2006

o If the Access-Accept packet contains a Digest-HA1 attribute, the
RADIUS client checks the 'qop' and 'algorithm' directives in the
Authorization header of the HTTP-style request it wants to
authorize:

* If the 'qop' directive is missing or its value is 'auth', the
RADIUS client ignores the Digest-HA1 attribute. It does not
include an Authentication-Info header in its HTTP-style
response.

* If the 'qop' directive's value is 'auth-int' and at least one
of the following conditions is true, the RADIUS client
calculates the contents of the HTTP-style response's 'rspauth'
directive:

+ The algorithm directive's value is 'MD5-sess' or
'AKAv1-MD5-sess'.

+ IP Security (IPsec) is configured to protect traffic between
the RADIUS client and RADIUS server with IPsec (see
Section 8).

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 packet 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.

o If the Access-Accept packet contains neither a
Digest-Response-Auth nor a Digest-HA1 attribute, the RADIUS client
will not create an Authentication-Info header for its HTTP-style
response.

When the RADIUS server provides a Digest-Nextnonce attribute in the
Access-Accept packet, the RADIUS client puts the contents of this
attribute into a 'nextnonce' directive. Now it can send an
HTTP-style response.

2.1.4. Failed Authentication

If the RADIUS client did receive an HTTP-style request without a
(Proxy-)Authorization header matching its locally configured realm
value, it obtains a new nonce and sends an error response (401 or
407) containing a (Proxy-)Authenticate header.

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RFC 4590 RADIUS Digest Authentication July 2006

If the RADIUS client receives an Access-Challenge packet in response
to an Access-Request containing a Digest-Nonce attribute, the RADIUS
server did not accept the nonce. If a Digest-Stale attribute is
present in the Access-Challenge and has a value of 'true' (without
surrounding quotes), the RADIUS client sends an error response (401
or 407) containing a WWW-/Proxy-Authenticate header with the
directive 'stale' and the digest directives derived from the Digest-*
attributes.

If the RADIUS client receives an Access-Reject from the RADIUS
server, it sends an error response to the HTTP-style request it has
received. If the RADIUS client does not receive a response, it
retransmits or fails over to another RADIUS server as described in
[RFC2865].

2.1.5. Obtaining Nonces

The RADIUS client has two ways to obtain nonces: it has received one
in a Digest-Nextnonce attribute of a previously received
Access-Accept packet 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. It adds a
Message-Authenticator (see [RFC3579]) attribute to the Access-Request
packet. The RADIUS server chooses a nonce and responds with an
Access-Challenge containing a Digest-Nonce attribute.

The RADIUS client constructs a (Proxy-)Authenticate header using the
received Digest-Nonce and Digest-Realm attributes to fill the nonce
and realm directives. The RADIUS server can send Digest-Qop,
Digest-Algorithm, Digest-Domain, and Digest-Opaque attributes in the
Access-Challenge carrying the nonce. If these attributes are
present, the client MUST use them.

2.2. RADIUS Server Behavior

If the RADIUS server receives an Access-Request packet 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 packet to the RADIUS
client. The RADIUS server MUST add Digest-Realm,
Message-Authenticator (see [RFC3579]), SHOULD add Digest-Algorithm
and one or more Digest-Qop, and MAY add Digest-Domain or
Digest-Opaque attributes to the Access-Challenge packet.

2.2.1. General Attribute Checks

If the RADIUS server receives an Access-Request packet containing a
Digest-Response attribute, it looks for the following attributes:

Sterman, et al. Standards Track [Page 9]

RFC 4590 RADIUS Digest Authentication July 2006

Digest-Realm, Digest-Nonce, Digest-Method, Digest-URI, Digest-Qop,
Digest-Algorithm, and 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 the Digest-Algorithm
attribute is missing, 'MD5' is assumed. If the RADIUS server has
issued a Digest-Opaque attribute along with the nonce, the
Access-Request MUST have a matching Digest-Opaque attribute.

If mandatory attributes are missing, it MUST respond with an
Access-Reject packet.

The RADIUS server removes '\' characters that escape quote and '\'
characters from the text values it has received in the Digest-*
attributes.

If the mandatory attributes are present, the RADIUS server MUST check
if the RADIUS client is authorized to serve users of the realm
mentioned in the Digest-Realm attribute. If the RADIUS client is not
authorized, the RADIUS server MUST send an Access-Reject. The RADIUS
server SHOULD log the event so as to notify the operator, and MAY
take additional action such as sending an Access-Reject in response
to all future requests from this client, until this behavior is reset
by management action.

The RADIUS server determines the age of the nonce in Digest-Nonce by
using an embedded time-stamp or by looking it up in a local table.
The RADIUS server MUST check the integrity of the nonce if it embeds
the time-stamp in the nonce. Section 2.2.2 describes how the server
handles old nonces.

2.2.2. Authentication

If the Access-Request message has passed the checks described above,
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. The RADIUS server MUST check if the user
identified by the User-Name attribute

o is authorized to access the protection space and

o is authorized to use the URI included in the SIP-AOR attribute, if
this attribute is present.

If any of those checks fails, the RADIUS server MUST send an
Access-Reject.

Sterman, et al. Standards Track [Page 10]

RFC 4590 RADIUS Digest Authentication July 2006

Correlation between User-Name and SIP-AOR AVP values is required just
to avoid that any user can register or misuse a SIP-AOR allocated to
a different user.

All values required for the digest calculation are taken from the
Digest attributes described in this document. If the calculated
digest response equals the value received in the Digest-Response
attribute, the authentication was successful.

If the response values match, but the RADIUS server considers the
nonce in the Digest-Nonce attribute as too old, it sends an
Access-Challenge packet containing a new nonce and a Digest-Stale
attribute with a value of 'true' (without surrounding quotes).

If the response values don't match, the RADIUS server responds with
an Access-Reject.

2.2.3. Constructing the Reply

If the authentication was successful, the RADIUS server adds an
attribute to the Access-Accept packet that 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 SHOULD put a Digest-Response-Auth attribute into the
Access-Accept packet.

o If the Digest-Qop attribute's value is 'auth-int' and at least one
of the following conditions is true, the RADIUS server SHOULD put
a Digest-HA1 attribute into the Access-Accept packet:

* The Digest-Algorithm attribute's value is 'MD5-sess' or
'AKAv1-MD5-sess'.

* IPsec is configured to protect traffic between the RADIUS
client and RADIUS server with IPsec (see Section 8).

In all other cases, Digest-Response-Auth or Digest-HA1 MUST NOT be
sent.

RADIUS servers MAY construct a Digest-Nextnonce attribute and add it
to the Access-Accept packet. 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 RADIUS server adds a
Message-Authenticator attribute (see [RFC3579]) and sends the
Access-Accept packet to the RADIUS client.

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RFC 4590 RADIUS Digest Authentication July 2006

If the RADIUS server does not accept the nonce received in an
Access-Request packet but authentication was successful, the RADIUS
server MUST send an Access-Challenge packet containing a Digest-Stale
attribute set to 'true' (without surrounding quotes). The RADIUS
server MUST add Message-Authenticator (see [RFC3579]), Digest-Nonce,
Digest-Realm, SHOULD add Digest-Algorithm and one or more Digest-Qop
and MAY add Digest-Domain, Digest-Opaque attributes to the
Access-Challenge packet.

3. New RADIUS Attributes

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 | Text ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Quote and backslash characters in Digest-* attributes representing
HTTP-style directives with a quoted-string syntax are escaped. The
surrounding quotes are removed. They are syntactical delimiters that
are redundant in RADIUS. For example, the directive

realm="the \"example\" value"

is represented as follows:

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Digest-Realm | 23 | the \"example\" value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

3.1. Digest-Response attribute

Description
If this attribute is present in an Access-Request message, a
RADIUS server implementing this specification MUST treat the
Access-Request as a request for Digest Authentication. When a
RADIUS client receives a (Proxy-)Authorization header, it puts
the request-digest value into a Digest-Response attribute.
This attribute (which enables the user to prove possession of
the password) MUST only be used in Access-Requests.
Type
103 for Digest-Response.
Length
>= 3

Sterman, et al. Standards Track [Page 12]

RFC 4590 RADIUS Digest Authentication July 2006

Text
When using HTTP Digest, the text field is 32 octets long and
contains a hexadecimal representation of a 16-octet digest
value as it was calculated by the authenticated client. Other
digest algorithms MAY define different digest lengths. The
text field MUST be copied from request-digest of
digest-response ([RFC2617]) without surrounding quotes.

3.2. Digest-Realm Attribute

Description
This attribute describes a protection space component of the
RADIUS server. HTTP-style protocols differ in their definition
of the protection space. See [RFC2617], Section 1.2, for
details. It MUST only be used in Access-Request and
Access-Challenge packets.
Type
104 for Digest-Realm
Length
>=3
Text
In Access-Requests, the RADIUS client takes the value of the
realm directive (realm-value according to [RFC2617]) without
surrounding quotes from the HTTP-style request it wants to
authenticate. In Access-Challenge packets, the RADIUS server
puts the expected realm value into this attribute.

3.3. Digest-Nonce Attribute

Description

This attribute holds a nonce to be used in the HTTP Digest
calculation. If the Access-Request had a Digest-Method and a
Digest-URI but no Digest-Nonce attribute, the RADIUS server
MUST put a Digest-Nonce attribute into its Access-Challenge
packet. This attribute MUST only be used in Access-Request and
Access-Challenge packets.
Type
105 for Digest-Nonce
Length
>=3
Text
In Access-Requests, the RADIUS client takes the value of the
nonce directive (nonce-value in [RFC2617]) without surrounding
quotes from the HTTP-style request it wants to authenticate.
In Access-Challenge packets, the attribute contains the nonce
selected by the RADIUS server.

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RFC 4590 RADIUS Digest Authentication July 2006

3.4. Digest-Response-Auth Attribute

Description
This attribute enables the RADIUS server to prove possession of
the password. If the previously received Digest-Qop attribute
was 'auth-int' (without surrounding quotes), the RADIUS server
MUST send a Digest-HA1 attribute instead of a
Digest-Response-Auth attribute. The Digest-Response-Auth
attribute MUST only be used in Access-Accept packets. The
RADIUS client puts the attribute value without surrounding
quotes into the rspauth directive of the Authentication-Info
header.
Type
106 for Digest-Response-Auth.
Length
>= 3
Text
The RADIUS server calculates a digest according to section
3.2.3 of [RFC2617] and copies the result into this attribute.
Digest algorithms other than the one defined in [RFC2617] MAY
define digest lengths other than 32.

3.5. Digest-Nextnonce Attribute

This attribute holds a nonce to be used in the HTTP Digest
calculation.

Description

The RADIUS server MAY put a Digest-Nextnonce attribute into an
Access-Accept packet. If this attribute is present, the RADIUS
client MUST put the contents of this attribute into the
nextnonce directive of an Authentication-Info header in its
HTTP-style response. This attribute MUST only be used in
Access-Accept packets.
Type
107 for Digest-Nextnonce
Length
>=3
Text
It is recommended that this text be base64 or hexadecimal data.

3.6. Digest-Method Attribute

Description
This attribute holds the method value to be used in the HTTP
Digest calculation. This attribute MUST only be used in
Access-Request packets.

Sterman, et al. Standards Track [Page 14]

RFC 4590 RADIUS Digest Authentication July 2006

Type
108 for Digest-Method
Length
>=3
Text
In Access-Requests, the RADIUS client takes the value of the
request method from the HTTP-style request it wants to
authenticate.

3.7. Digest-URI Attribute

Description
This attribute is used to transport the contents of the
digest-uri directive or the URI of the HTTP-style request. It
MUST only be used in Access-Request packets.
Type
109 for Digest-URI
Length
>=3
Text
If the HTTP-style request has an Authorization header, the
RADIUS client puts the value of the "uri" directive found in
the HTTP-style request Authorization header (known as
"digest-uri-value" in section 3.2.2 of [RFC2617]) without
surrounding quotes into this attribute. If there is no
Authorization header, the RADIUS client takes the value of the
request URI from the HTTP-style request it wants to
authenticate.

3.8. Digest-Qop Attribute

Description
This attribute holds the Quality of Protection parameter that
influences the HTTP Digest calculation. This attribute MUST
only be used in Access-Request and Access-Challenge packets. A
RADIUS client SHOULD insert one of the Digest-Qop attributes it
has received in a previous Access-Challenge packet. RADIUS
servers SHOULD insert at least one Digest-Qop attribute in an
Access-Challenge packet. Digest-Qop is optional in order to
preserve backward compatibility with a minimal implementation
of [RFC2069].
Type
110 for Digest-Qop
Length
>=3
Text
In Access-Requests, the RADIUS client takes the value of the
qop directive (qop-value as described in [RFC2617]) from the

Sterman, et al. Standards Track [Page 15]

RFC 4590 RADIUS Digest Authentication July 2006

HTTP-style request it wants to authenticate. In
Access-Challenge packets, the RADIUS server puts a desired
qop-value into this attribute. If the RADIUS server supports
more than one "quality of protection" value, it puts each
qop-value into a separate Digest-Qop attribute.

3.9. Digest-Algorithm Attribute

Description
This attribute holds the algorithm parameter that influences
the HTTP Digest calculation. It MUST only be used in
Access-Request and Access-Challenge packets. If this attribute
is missing, MD5 is assumed.
Type
111 for Digest-Algorithm
Length
>=3
Text
In Access-Requests, the RADIUS client takes the value of the
algorithm directive (as described in [RFC2617], section 3.2.1)
from the HTTP-style request it wants to authenticate. In
Access-Challenge packets, the RADIUS server SHOULD put the
desired algorithm into this attribute.

3.10. Digest-Entity-Body-Hash Attribute

Description
When using the qop-level 'auth-int', a hash of the HTTP-style
message body's contents is 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.

The clarifications described in section 22.4 of [RFC3261] about
the hash of empty entity bodies apply to the
Digest-Entity-Body-Hash attribute. This attribute MUST only be
sent in Access-Request packets.
Type
112 for Digest-Entity-Body-Hash
Length
>=3
Text
The attribute holds the hexadecimal representation of
H(entity-body). This hash is required by certain
authentication mechanisms, such as HTTP Digest with quality of
protection set to "auth-int". RADIUS clients MUST use this
attribute to transport the hash of the entity body when HTTP
Digest is the authentication mechanism and the RADIUS server

Sterman, et al. Standards Track [Page 16]

RFC 4590 RADIUS Digest Authentication July 2006

requires that the integrity of the entity body (e.g., qop
parameter set to "auth-int") be verified. Extensions to this
document may define support for authentication mechanisms other
than HTTP Digest.

3.11. Digest-CNonce Attribute

Description
This attribute holds the client nonce parameter that is used in
the HTTP Digest calculation. It MUST only be used in
Access-Request packets.
Type
113 for Digest-CNonce
Length
>=3
Text
This attribute includes the value of the cnonce-value [RFC2617]
without surrounding quotes, taken from the HTTP-style request.

3.12. Digest-Nonce-Count Attribute

Description
This attribute includes the nonce count parameter that is used
to detect replay attacks. The attribute MUST only be used in
Access-Request packets.

Type
114 for Digest-Nonce-Count
Length
10
Text
In Access-Requests, the RADIUS client takes the value of the nc
directive (nc-value according to [RFC2617]) without surrounding
quotes from the HTTP-style request it wants to authenticate.

3.13. Digest-Username Attribute

Description
This attribute holds the user name used in the HTTP Digest
calculation. The RADIUS server MUST use this attribute only
for the purposes of calculating the digest. In order to
determine the appropriate user credentials, the RADIUS server
MUST use the User-Name (1) attribute, and MUST NOT use the
Digest-Username attribute. This attribute MUST only be used in
Access-Request packets.
Type
115 for Digest-Username

Sterman, et al. Standards Track [Page 17]

RFC 4590 RADIUS Digest Authentication July 2006

Length
>= 3
Text
In Access-Requests, the RADIUS client takes the value of the
username directive (username-value according to [RFC2617])
without surrounding quotes from the HTTP-style request it wants
to authenticate.

3.14. Digest-Opaque Attribute

Description
This attribute holds the opaque parameter that is passed to the
HTTP-style client. The HTTP-style client will pass this value
back to the server (i.e., the RADIUS client) without
modification. This attribute MUST only be used in
Access-Request and Access-Challenge packets.
Type
116 for Digest-Opaque
Length
>=3
Text
In Access-Requests, the RADIUS client takes the value of the
opaque directive (opaque-value according to [RFC2617]) without
surrounding quotes from the HTTP-style request it wants to
authenticate and puts it into this attribute. In
Access-Challenge packets, the RADIUS server MAY include this
attribute.

3.15. Digest-Auth-Param Attribute

Description
This attribute is a placeholder for future extensions and
corresponds to the "auth-param" parameter defined in section
3.2.1 of [RFC2617]. The Digest-Auth-Param is the mechanism
whereby the RADIUS client and RADIUS server can exchange
auth-param extension parameters contained within Digest headers
that are not understood by the RADIUS client and for which
there are no corresponding stand-alone attributes.

Unlike the previously listed Digest-* attributes, the
Digest-Auth-Param contains not only the value but also the
parameter name, since the parameter name is unknown to the
RADIUS client. If the Digest header contains several unknown
parameters, then the RADIUS implementation MUST repeat this
attribute and each instance MUST contain one different unknown
Digest parameter/value combination. This attribute MUST ONLY
be used in Access-Request, Access-Challenge, or Access-Accept
packets.

Sterman, et al. Standards Track [Page 18]

RFC 4590 RADIUS Digest Authentication July 2006

Type
117 for Digest-Auth-Param
Length
>=3
Text
The text consists of the whole parameter, including its name
and the equal sign ('=') and quotes.

3.16. Digest-AKA-Auts Attribute

Description
This attribute holds the auts parameter that is used in the
Digest AKA ([RFC3310]) calculation. It is only used if the
algorithm of the digest-response denotes a version of AKA
Digest [RFC3310]. This attribute MUST only be used in
Access-Request packets.
Type
118 for Digest-AKA-Auts
Length
>=3
Text
In Access-Requests, the RADIUS client takes the value of the
auts directive (auts-param according to section 3.4 of
[RFC3310]) without surrounding quotes from the HTTP-style
request it wants to authenticate.

3.17. Digest-Domain Attribute

Description
When a RADIUS client has asked for a nonce, the RADIUS server
MAY send one or more Digest-Domain attributes in its
Access-Challenge packet. The RADIUS client puts them into the
quoted, space-separated list of URIs of the 'domain' directive
of a WWW-Authenticate header. Together with Digest-Realm, the
URIs in the list define the protection space (see [RFC2617],
section 3.2.1) for some HTTP-style protocols. This attribute
MUST only be used in Access-Challenge packets.
Type
119 for Digest-Domain
Length
3
Text
This attribute consists of a single URI that defines a
protection space component.

Sterman, et al. Standards Track [Page 19]

RFC 4590 RADIUS Digest Authentication July 2006

3.18. Digest-Stale Attribute

Description
This attribute is sent by a RADIUS server in order to notify
the RADIUS client whether it has accepted a nonce. If the
nonce presented by the RADIUS client was stale, the value is
'true' and is 'false' otherwise. The RADIUS client puts the
content of this attribute into a 'stale' directive of the
WWW-Authenticate header in the HTTP-style response to the
request it wants to authenticate. The attribute MUST only be
used in Access-Challenge packets.
Type
120 for Digest-Stale
Length
3
Text
The attribute has either the value 'true' or 'false' (both
values without surrounding quotes).

3.19. Digest-HA1 Attribute

Description
This attribute is used to allow the generation of an
Authentication-Info header, even if the HTTP-style response's
body is required for the calculation of the rspauth value. It
SHOULD be used in Access-Accept packets if the required quality
of protection ('qop') is 'auth-int'.

This attribute MUST NOT be sent if the qop parameter was not
specified or has a value of 'auth' (in this case, use
Digest-Response-Auth instead).

The Digest-HA1 attribute MUST only be sent by the RADIUS server
or processed by the RADIUS client if at least one of the
following conditions is true:

+ The Digest-Algorithm attribute's value is 'MD5-sess' or
'AKAv1-MD5-sess'.

+ IPsec is configured to protect traffic between RADIUS client
and RADIUS server with IPsec (see Section 8).

This attribute MUST only be used in Access-Accept packets.
Type
121 for Digest-HA1
Length
>= 3

Sterman, et al. Standards Track [Page 20]

RFC 4590 RADIUS Digest Authentication July 2006

Text
This attribute contains the hexadecimal representation of H(A1)
as described in [RFC2617], sections 3.1.3, 3.2.1, and 3.2.2.2.

3.20. SIP-AOR Attribute

Description
This attribute is used for the authorization of SIP messages.
The SIP-AOR attribute identifies the URI, the use of which must
be authenticated and authorized. The RADIUS server uses this
attribute to authorize the processing of the SIP request. The
SIP-AOR can be derived from, for example, the To header field
in a SIP REGISTER request (user under registration), or the
From header field in other SIP requests. However, the exact
mapping of this attribute to SIP can change due to new
developments in the protocol. This attribute MUST only be used
when the RADIUS client wants to authorize SIP users and MUST
only be used in Access-Request packets.
Type
122 for SIP-AOR
Length
>=3
Text
The syntax of this attribute corresponds either to a SIP URI
(with the format defined in [RFC3261] or a tel URI (with the
format defined in [RFC3966]).

The SIP-AOR attribute holds the complete URI, including
parameters and other parts. It is up to the RADIUS server what
components of the URI are regarded in the authorization
decision.

4. Diameter Compatibility

This document defines support for Digest Authentication in RADIUS. A
companion document "Diameter Session Initiation Protocol (SIP)
Application" [SIP-APP] defines support for Digest Authentication in
Diameter, and addresses compatibility issues between RADIUS and
Diameter.

Sterman, et al. Standards Track [Page 21]

RFC 4590 RADIUS Digest Authentication July 2006

5. Table of Attributes

The following table provides a guide to which attributes may be found
in which kinds of packets, and in what quantity.

+-----+--------+--------+-----------+-----+-------------------------+
| Req | Accept | Reject | Challenge | # | Attribute |
+-----+--------+--------+-----------+-----+-------------------------+
| 1 | 0 | 0 | 0 | 1 | User-Name |
| 1 | 1 | 1 | 1 | 80 | Message-Authenticator |
| 0-1 | 0 | 0 | 0 | 103 | Digest-Response |
| 0-1 | 0 | 0 | 1 | 104 | Digest-Realm |
| 0-1 | 0 | 0 | 1 | 105 | Digest-Nonce |
| 0 | 0-1 | 0 | 0 | 106 | Digest-Response-Auth |
| | | | | | (see Note 1, 2) |
| 0 | 0-1 | 0 | 0 | 107 | Digest-Nextnonce |
| 0-1 | 0 | 0 | 0 | 108 | Digest-Method |
| 0-1 | 0 | 0 | 0 | 109 | Digest-URI |
| 0-1 | 0 | 0 | 0+ | 110 | Digest-Qop |
| 0-1 | 0 | 0 | 0-1 | 111 | Digest-Algorithm (see |
| | | | | | Note 3) |
| 0-1 | 0 | 0 | 0 | 112 | Digest-Entity-Body-Hash |
| 0-1 | 0 | 0 | 0 | 113 | Digest-CNonce |
| 0-1 | 0 | 0 | 0 | 114 | Digest-Nonce-Count |
| 0-1 | 0 | 0 | 0 | 115 | Digest-Username |
| 0-1 | 0 | 0 | 0-1 | 116 | Digest-Opaque |
| 0+ | 0+ | 0 | 0+ | 117 | Digest-Auth-Param |
| 0-1 | 0 | 0 | 0 | 118 | Digest-AKA-Auts |
| 0 | 0 | 0 | 0+ | 119 | Digest-Domain |
| 0 | 0 | 0 | 0-1 | 120 | Digest-Stale |
| 0 | 0-1 | 0 | 0 | 121 | Digest-HA1 (see Note 1, |
| | | | | | 2) |
| 0-1 | 0 | 0 | 0 | 122 | SIP-AOR |
+-----+--------+--------+-----------+-----+-------------------------+

Table 1

[Note 1] Digest-HA1 MUST be used instead of Digest-Response-Auth if
Digest-Qop is 'auth-int'.

[Note 2] Digest-Response-Auth MUST be used instead of Digest-HA1 if
Digest-Qop is 'auth'.

[Note 3] If Digest-Algorithm is missing, 'MD5' is assumed.

Sterman, et al. Standards Track [Page 22]

RFC 4590 RADIUS Digest Authentication July 2006

6. Examples

This is an example selected from the traffic between a softphone (A),
a Proxy Server (B), and an example.com RADIUS server (C). The
communication between the Proxy Server and a SIP Public Switched
Telephone Network (PSTN) gateway is omitted for brevity. The SIP
messages are not shown completely.

A->B

INVITE sip:[email protected] SIP/2.0
From: <sip:[email protected]>
To: <sip:[email protected]>

B->A

SIP/2.0 100 Trying

B->C

Code = 1 (Access-Request)
Attributes:
NAS-IP-Address = c0 0 2 26 (192.0.2.38)
NAS-Port-Type = 5 (Virtual)
User-Name = 12345678
Digest-Method = INVITE
Digest-URI = sip:[email protected]
Message-Authenticator =
08 af 7e 01 b6 8d 74 c3 a4 3c 33 e1 56 2a 80 43

C->B

Code = 11 (Access-Challenge)
Attributes:
Digest-Nonce = 3bada1a0
Digest-Realm = example.com
Digest-Qop = auth
Digest-Algorithm = MD5
Message-Authenticator =
f8 01 26 9f 70 5e ef 5d 24 ac f5 ca fb 27 da 40

B->A

SIP/2.0 407 Proxy Authentication Required
Proxy-Authenticate: Digest realm="example.com"
,nonce="3bada1a0",qop=auth,algorithm=MD5
Content-Length: 0

Sterman, et al. Standards Track [Page 23]

RFC 4590 RADIUS Digest Authentication July 2006

A->B

ACK sip:[email protected] SIP/2.0

A->B

INVITE sip:[email protected] SIP/2.0
Proxy-Authorization: Digest algorithm="md5",nonce="3bada1a0"
,realm="example.com"
,response="f3ce87e6984557cd0fecc26f3c5e97a4"
,uri="sip:[email protected]",username="12345678"
,qop=auth,algorithm=MD5
From: <sip:[email protected]>
To: <sip:[email protected]>

B->C

Code = 1 (Access-Request)
Attributes:
NAS-IP-Address = c0 0 2 26 (192.0.2.38)
NAS-Port-Type = 5 (Virtual)
User-Name = 12345678
Digest-Response = f3ce87e6984557cd0fecc26f3c5e97a4
Digest-Realm = example.com
Digest-Nonce = 3bada1a0
Digest-Method = INVITE
Digest-URI = sip:[email protected]
Digest-Qop = auth
Digest-Algorithm = md5
Digest-Username = 12345678
SIP-AOR = sip:[email protected]
Message-Authenticator =
ff 67 f4 13 8e b8 59 32 22 f9 37 0f 32 f8 e0 ff

C->B

Code = 2 (Access-Accept)
Attributes:
Digest-Response-Auth =
6303c41b0e2c3e524e413cafe8cce954
Message-Authenticator =
75 8d 44 49 66 1f 7b 47 9d 10 d0 2d 4a 2e aa f1

B->A

SIP/2.0 180 Ringing

Sterman, et al. Standards Track [Page 24]

RFC 4590 RADIUS Digest Authentication July 2006

B->A

SIP/2.0 200 OK

A->B

ACK sip:[email protected] 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->C

Code = 1 (Access-Request)
Attributes:
NAS-IP-Address = c0 0 2 26 (192.0.2.38)
NAS-Port-Type = 5 (Virtual)
Digest-Method = GET
Digest-URI = /index.html
Message-Authenticator =
34 a6 26 46 f3 81 f9 b4 97 c0 dd 9d 11 8f ca c7

C->B

Code = 11 (Access-Challenge)
Attributes:
Digest-Nonce = a3086ac8
Digest-Realm = example.com
Digest-Qop = auth
Digest-Algorithm = MD5
Message-Authenticator =
f8 01 26 9f 70 5e ef 5d 24 ac f5 ca fb 27 da 40

B->A

HTTP/1.1 401 Authentication Required
WWW-Authenticate: Digest realm="example.com",
nonce="a3086ac8",qop=auth,algorithm=MD5
Content-Length: 0

Sterman, et al. Standards Track [Page 25]

RFC 4590 RADIUS Digest Authentication July 2006

A->B

GET /index.html HTTP/1.1
Authorization: Digest algorithm=MD5,nonce="a3086ac8"
,realm="example.com"
,response="f052b68058b2987aba493857ae1ab002"
,uri="/index.html",username="12345678"
,qop=auth,algorithm=MD5

B->C

Code = 1 (Access-Request)
Attributes:
NAS-IP-Address = c0 0 2 26 (192.0.2.38)
NAS-Port-Type = 5 (Virtual)
User-Name = 12345678
Digest-Response = f052b68058b2987aba493857ae1ab002
Digest-Realm = example.com
Digest-Nonce = a3086ac8
Digest-Method = GET
Digest-URI = /index.html
Digest-Username = 12345678
Digest-Qop = auth
Digest-Algorithm = MD5
Message-Authenticator =
06 e1 65 23 57 94 e6 de 87 5a e8 ce a2 7d 43 6b

C->B

Code = 2 (Access-Accept)
Attributes:
Digest-Response-Auth =
e644aa513effbfe1caff67103ff6433c
Message-Authenticator =
7a 66 73 a3 52 44 dd ca 90 e2 f6 10 61 2d 81 d7

B->A

HTTP/1.1 200 OK
...

<html>
...

Sterman, et al. Standards Track [Page 26]

RFC 4590 RADIUS Digest Authentication July 2006

7. IANA Considerations

This document serves as an IANA registration request for a number of
values from the RADIUS attribute type number space. The IANA has
assigned the following:

+-------------------------+------------------------+
| placeholder | value assigned by IANA |
+-------------------------+------------------------+
| Digest-Response | 103 |
| Digest-Realm | 104 |
| Digest-Nonce | 105 |
| Digest-Nextnonce | 106 |
| Digest-Response-Auth | 107 |
| Digest-Method | 108 |
| Digest-URI | 109 |
| Digest-Qop | 110 |
| Digest-Algorithm | 111 |
| Digest-Entity-Body-Hash | 112 |
| Digest-CNonce | 113 |
| Digest-Nonce-Count | 114 |
| Digest-Username | 115 |
| Digest-Opaque | 116 |
| Digest-Auth-Param | 117 |
| Digest-AKA-Auts | 118 |
| Digest-Domain | 119 |
| Digest-Stale | 120 |
| Digest-HA1 | 121 |
| SIP-AOR | 122 |
+-------------------------+------------------------+

Table 2

8. Security Considerations

The RADIUS extensions described in this document enable RADIUS to
transport the data that is required to perform a digest calculation.
As a result, RADIUS inherits the vulnerabilities of HTTP Digest (see
[RFC2617], section 4) in addition to RADIUS security vulnerabilities
described in [RFC2865], section 8, and [RFC3579], section 4.

An attacker compromising a RADIUS client or proxy can carry out
man-in-the-middle attacks even if the paths between A, B and B, C
(Figure 2) have been secured with TLS or IPsec.

The RADIUS server MUST check the Digest-Realm attribute it has
received from a client. If the RADIUS client is not authorized to
serve HTTP-style clients of that realm, it might be compromised.

Sterman, et al. Standards Track [Page 27]

RFC 4590 RADIUS Digest Authentication July 2006

8.1. Denial of Service

RADIUS clients implementing the extension described in this document
may authenticate HTTP-style requests received over the Internet. As
compared with the use of RADIUS to authenticate link-layer network
access, attackers may find it easier to cover their tracks in such a
scenario.

An attacker can attempt a denial-of-service attack on one or more
RADIUS servers by sending a large number of HTTP-style requests. To
make simple denial-of-service attacks more difficult, the RADIUS
server MUST check whether it has generated the nonce received from an
HTTP-style client. This SHOULD be done statelessly. For example, a
nonce could consist of a cryptographically random part and some kind
of signature provided by the RADIUS client, as described in
[RFC2617], section 3.2.1.

8.2. Confidentiality and Data Integrity

The attributes described in this document are sent in cleartext.
RADIUS servers SHOULD include Digest-Qop and Digest-Algorithm
attributes in Access-Challenge messages. A man in the middle can
modify or remove those attributes in a bidding down attack, causing
the RADIUS client to use a weaker authentication scheme than
intended.

The Message-Authenticator attribute, described in [RFC3579], section
3.2 MUST be included in Access-Request, Access-Challenge,
Access-Reject, and Access-Accept messages that contain attributes
described in this specification.

The Digest-HA1 attribute contains no random components if the
algorithm is 'MD5' or 'AKAv1-MD5'. This makes offline dictionary
attacks easier and enables replay attacks.

Some parameter combinations require the protection of RADIUS packets
against eavesdropping and tampering. Implementations SHOULD try to
determine automatically whether IPsec is configured to protect
traffic between the RADIUS client and the RADIUS server. If this is
not possible, the implementation checks a configuration parameter
telling it whether IPsec will protect RADIUS traffic. The default
value of this configuration parameter tells the implementation that
RADIUS packets will not be protected.

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. The RADIUS transaction can be regarded as

Sterman, et al. Standards Track [Page 28]

RFC 4590 RADIUS Digest Authentication July 2006

one leg on the path between the HTTP-style client and the HTTP-style
server. To prevent RADIUS from representing the weak link, a RADIUS
client receiving an HTTP-style request via TLS or IPsec could use an
equally secure connection to the RADIUS server. There are several
ways to achieve this, for example:

o The RADIUS client may reject HTTP-style requests received over TLS
or IPsec.

o The RADIUS client may require that traffic be sent and received
over IPsec.

RADIUS over IPsec, if used, MUST conform to the requirements
described in [RFC3579], section 4.2.

9. Acknowledgements

We would like to acknowledge Kevin McDermott (Cisco Systems) for
providing comments and experimental implementation.

Many thanks to all reviewers, especially to Miguel Garcia, Jari
Arkko, Avi Lior, and Jun Wang.

10. References

10.1. Normative References

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.

[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.

[RFC3579] Aboba, B. and P. Calhoun, "RADIUS (Remote Authentication
Dial In User Service) Support For Extensible
Authentication Protocol (EAP)", RFC 3579, September 2003.

Sterman, et al. Standards Track [Page 29]

RFC 4590 RADIUS Digest Authentication July 2006

[RFC3966] Schulzrinne, H., "The tel URI for Telephone Numbers", RFC
3966, December 2004.

10.2. Informative References

[SIP-APP] Garcia-Martin, M., "Diameter Session Initiation Protocol
(SIP) Application", Work in Progress), April 2006.

[RFC1994] Simpson, W., "PPP Challenge Handshake Authentication
Protocol (CHAP)", RFC 1994, August 1996.

[RFC2069] Franks, J., Hallam-Baker, P., Hostetler, J., Leach, P.,
Luotonen, A., Sink, E., and L. Stewart, "An Extension to
HTTP : Digest Access Authentication", RFC 2069, January
1997.

[RFC4346] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.1", RFC 4346, April 2006.

[RFC3851] Ramsdell, B., "Secure/Multipurpose Internet Mail
Extensions (S/MIME) Version 3.1 Message Specification",
RFC 3851, July 2004.

[RFC3310] Niemi, A., Arkko, J., and V. Torvinen, "Hypertext Transfer
Protocol (HTTP) Digest Authentication Using Authentication
and Key Agreement (AKA)", RFC 3310, September 2002.

[RFC3588] Calhoun, P., Loughney, J., Guttman, E., Zorn, G., and J.
Arkko, "Diameter Base Protocol", RFC 3588, September 2003.

Sterman, et al. Standards Track [Page 30]

RFC 4590 RADIUS Digest Authentication July 2006

Authors' Addresses

Baruch Sterman
Kayote Networks
P.O. Box 1373
Efrat 90435
Israel

EMail: [email protected]

Daniel Sadolevsky
SecureOL, Inc.
Jerusalem Technology Park
P.O. Box 16120
Jerusalem 91160
Israel

EMail: [email protected]

David Schwartz
Kayote Networks
P.O. Box 1373
Efrat 90435
Israel

EMail: [email protected]

David Williams
Cisco Systems
7025 Kit Creek Road
P.O. Box 14987
Research Triangle Park NC 27709
USA

EMail: [email protected]

Wolfgang Beck
Deutsche Telekom AG
Deutsche Telekom Allee 7
Darmstadt 64295
Germany

EMail: [email protected]

Sterman, et al. Standards Track [Page 31]

RFC 4590 RADIUS Digest Authentication July 2006

Full Copyright Statement

Copyright (C) The Internet Society (2006).

This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
retain all their rights.

This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
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Sterman, et al. Standards Track [Page 32]