RFC5090

Network Working Group B. Sterman Request for Comments: 5090 Kayote Networks Obsoletes: 4590 D. Sadolevsky Category: Standards Track SecureOL, Inc.

                                                         D. Schwartz
                                                     Kayote Networks
                                                         D. Williams
                                                       Cisco Systems
                                                             W. Beck
                                                 Deutsche Telekom AG
                                                       February 2008

           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.

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 ....................................................3

  1.1. Motivation .................................................3
  1.2. Terminology ................................................3
  1.3. Overview ...................................................4

2. Detailed Description ............................................6

  2.1. RADIUS Client Behavior .....................................6
  2.2. RADIUS Server Behavior .....................................9

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 ...................................15
  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 ............................................21 6. Examples .......................................................23 7. IANA Considerations ............................................27 8. Security Considerations ........................................28

  8.1. Denial of Service .........................................28
  8.2. Confidentiality and Data Integrity ........................28

9. References .....................................................29

  9.1. Normative References ......................................29
  9.2. Informative References ....................................30

Appendix A - Changes from RFC 4590 ................................31 Acknowledgements ..................................................31

Introduction

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].

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 [RFC4740] defines support for Digest Authentication within Diameter.

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.

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 the 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.

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 retransmits 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 Challenge Handshake Authentication Protocol (CHAP) algorithm is not compatible with HTTP Digest.

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

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).

Detailed Description

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.

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.

Constructing an Access-Request

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

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 HTTP syntactic requirements, quoted strings found in HTTP Digest directives may contain escaped quote and backslash characters. When translating these directives into RADIUS attributes, the RADIUS client only removes the leading and trailing quote characters which surround the directive value, it does not unescape anything within the string. 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.

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).

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).

     The RADIUS client 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.

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.

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 stale directive set to 'true' 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].

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.

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.

General Attribute Checks

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

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

Authentication

If the Access-Request message passes 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.

Correlation between User-Name and SIP-AOR AVP values is required just to avoid any user from registering or misusing a SIP-AOR that has been 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 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.

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.

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- Qops, and MAY add Digest-Domain or Digest-Opaque attributes to the Access-Challenge packet.

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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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-Request packets.

Type

     103 for Digest-Response.

Length

     >= 3

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.

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, Access-
     Challenge, and Accounting-Request 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.

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.

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.

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.

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 and Accounting-Request packets.

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.

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 and Accounting-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.

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, Access-Challenge, and
     Accounting-Request 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
     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.

Digest-Algorithm Attribute

Description

     This attribute holds the algorithm parameter that influences
     the HTTP Digest calculation.  It MUST only be used in Access-
     Request, Access-Challenge and Accounting-Request 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-value '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
     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 and Accounting-Request packets.

Type

     115 for Digest-Username

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, Access-Accept, and
     Accounting-Request packets.

Type

     117 for Digest-Auth-Param

Length

     >= 3

Text

     The text consists of the whole parameter, including its name,
     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 and Accounting-Request packets.

Type

     119 for Digest-Domain

Length

     3

Text

     This attribute consists of a single URI that defines a
     protection space component.

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 the 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

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 as
     to which components of the URI are regarded in the
     authorization decision.

Diameter Compatibility

This document defines support for Digest Authentication in RADIUS. A companion document "Diameter Session Initiation Protocol (SIP) Application" [RFC4740] defines support for Digest Authentication in Diameter, and addresses compatibility issues between RADIUS and Diameter.

Table of Attributes

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

Access- Access- Access- Access-    Acct-
Request Accept  Reject  Challenge  Req   #  Attribute
 0-1      0      0      0          0-1   1  User-Name
 0-1      0      0      1          0    24  State [4]
 1        1      1      1          0-1  80  Message-Authenticator
 0-1      0      0      0          0   103  Digest-Response
 0-1      0      0      1          0-1 104  Digest-Realm
 0-1      0      0      1          0   105  Digest-Nonce
 0        0-1    0      0          0   106  Digest-Response-Auth [1][2]
 0        0-1    0      0          0   107  Digest-Nextnonce
 1        0      0      0          0-1 108  Digest-Method
 0-1      0      0      0          0-1 109  Digest-URI
 0-1      0      0      0+         0-1 110  Digest-Qop
 0-1      0      0      0-1        0-1 111  Digest-Algorithm [3]
 0-1      0      0      0          0   112  Digest-Entity-Body-Hash
 0-1      0      0      0          0   113  Digest-CNonce
 0-1      0      0      0          0   114  Digest-Nonce-Count
 0-1      0      0      0          0-1 115  Digest-Username
 0-1      0      0      0-1        0   116  Digest-Opaque
 0+       0+     0      0+         0+  117  Digest-Auth-Param
 0-1      0      0      0          0   118  Digest-AKA-Auts
 0        0      0      0+         0+  119  Digest-Domain
 0        0      0      0-1        0   120  Digest-Stale
 0        0-1    0      0          0   121  Digest-HA1 [1][2]
 0-1      0      0      0          0   122  SIP-AOR

The following table defines the meaning of the above table entries.

  0     This attribute MUST NOT be present in the packet.
  0+    Zero or more instances of this attribute MAY be
        present in the packet.
  0-1   Zero or one instance of this attribute MAY be
        present in the packet.

[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.

[Note 4] An Access-Challenge MUST contain a State attribute, which is

        copied to the subsequent Access-Request.  A server receiving
        an Access-Request that contains a State attribute MUST
        respond with either an Access-Accept or an Access-Reject;
        the server MUST NOT respond with an Access-Challenge.

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.

The password of user '12345678' is 'secret'. The shared secret between the RADIUS client and server is 'secret'. To ease testing, only the last byte of the RADIUS authenticator changes between requests. In a real implementation, this would be a serious flaw.

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 = Access-Request (1)
  Packet identifier = 0x7c (124)
  Length = 97
  Authenticator = F5E55840E324AA49D216D9DBD069807C
  NAS-IP-Address = 192.0.2.38
  NAS-Port = 5
  User-Name = 12345678
  Digest-Method = INVITE
  Digest-URI = sip:[email protected]
  Message-Authenticator = 7600D5B0BDC33987A60D5C6167B28B3B

C->B

  Code = Access-challenge (11)
  Packet identifier = 0x7c (124)
  Length = 72
  Authenticator = EBE20199C26EFEAD69BF8AB0E786CA4D
  Digest-Nonce = 3bada1a0
  Digest-Realm = example.com
  Digest-Qop = auth
  Digest-Algorithm = MD5
  Message-Authenticator = 5DA18ED3BBC9513DCBDE0A37F51B7DE3

B->A

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

A->B

  ACK sip:[email protected] SIP/2.0

A->B

  INVITE sip:[email protected] SIP/2.0
  Proxy-Authorization: Digest nonce="3bada1a0"
       ,realm="example.com"
       ,response="756933f735fcd93f90a4bbdd5467f263"
       ,uri="sip:[email protected]",username="12345678"
       ,qop=auth,algorithm=MD5
       ,cnonce="56593a80,nc="00000001"

  From: <sip:[email protected]>
  To: <sip:[email protected]>

B->C

  Code = Access-Request (1)
  Packet identifier = 0x7d (125)
  Length = 221
  Authenticator = F5E55840E324AA49D216D9DBD069807D
  NAS-IP-Address = 192.0.2.38
  NAS-Port = 5
  User-Name = 12345678
  Digest-Method = INVITE
  Digest-URI = sip:[email protected]
  Digest-Realm = example.com
  Digest-Qop = auth
  Digest-Algorithm = MD5
  Digest-CNonce = 56593a80
  Digest-Nonce = 3bada1a0
  Digest-Nonce-Count = 00000001
  Digest-Response = 756933f735fcd93f90a4bbdd5467f263
  Digest-Username = 12345678
  SIP-AOR = sip:[email protected]
  Message-Authenticator = B6C7F7F8D11EF261A26933D234561A60

C->B

  Code = Access-Accept (2)
  Packet identifier = 0x7d (125)
  Length = 72
  Authenticator = FFDD74D6470D21CB6FC4D6056BE245D2
  Digest-Response-Auth = f847de948d12285f8f4199e366f1af21
  Message-Authenticator = 7B76E2F10A7067AF601938BF13B0A62E

B->A

  SIP/2.0 180 Ringing

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), a web server (B), and a RADIUS server (C).

A->B

  GET /index.html HTTP/1.1

B->C

  Code = Access-Request (1)
  Packet identifier = 0x7e (126)
  Length = 68
  Authenticator = F5E55840E324AA49D216D9DBD069807E
  NAS-IP-Address = 192.0.2.38
  NAS-Port = 5
  Digest-Method = GET
  Digest-URI = /index.html
  Message-Authenticator = 690BFC95E88DF3B185F15CD78E469992

C->B

  Code = Access-challenge (11)
  Packet identifier = 0x7e (126)
  Length = 72
  Authenticator = 2EE5EB01C02C773B6C6EC8515F565E8E
  Digest-Nonce = a3086ac8
  Digest-Realm = example.com
  Digest-Qop = auth
  Digest-Algorithm = MD5
  Message-Authenticator = 646DB2B0AF9E72FFF2CF7FEB33C4952A

B->A

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

A->B

  GET /index.html HTTP/1.1
  Authorization: Digest = algorithm=MD5,qop=auth,nonce="a3086ac8"
       ,nc="00000001",cnonce="56593a80"
       ,realm="example.com"
       ,response="a4fac45c27a30f4f244c54a2e99fa117"
       ,uri="/index.html",username="12345678"

B->C

  Code = Access-Request (1)
  Packet identifier = 0x7f (127)
  Length = 176
  Authenticator = F5E55840E324AA49D216D9DBD069807F
  NAS-IP-Address = 192.0.2.38
  NAS-Port = 5
  User-Name = 12345678
  Digest-Method = GET
  Digest-URI = /index.html
  Digest-Realm = example.com
  Digest-Qop = auth
  Digest-Algorithm = MD5
  Digest-CNonce = 56593a80
  Digest-Nonce = a3086ac8
  Digest-Nonce-Count = 00000001
  Digest-Response = a4fac45c27a30f4f244c54a2e99fa117
  Digest-Username = 12345678
  Message-Authenticator = 237D85C1478C70C67EEAF22A9C456821

C->B

  Code = Access-Accept (2)
  Packet identifier = 0x7f (127)
  Length = 72
  Authenticator = 6364FA6ED66012847C05A0895607C694
  Digest-Response-Auth = 08c4e942d1d0a191de8b3aa98cd35147
  Message-Authenticator = 43795A3166492AD2A890AD57D5F97D56

B->A

  HTTP/1.1 200 OK
  ...

  <html>
  ...

IANA Considerations

The following values from the RADIUS Attribute Types number space were assigned in [RFC4590]. This document requests that the values in the table below be entered within the existing registry.

Attribute #

---

----

Digest-Response 103 Digest-Realm 104 Digest-Nonce 105 Digest-Response-Auth 106 Digest-Nextnonce 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

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.

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.

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 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.

References

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.

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

         3966, December 2004.

Informative References

[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.

[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.

[RFC3851] Ramsdell, B., Ed., "Secure/Multipurpose Internet Mail

         Extensions (S/MIME) Version 3.1 Message Specification", RFC
         3851, July 2004.

[RFC4346] Dierks, T. and E. Rescorla, "The Transport Layer Security

         (TLS) Protocol Version 1.1", RFC 4346, April 2006.

[RFC4590] Sterman, B., Sadolevsky, D., Schwartz, D., Williams, D.,

         and W. Beck, "RADIUS Extension for Digest Authentication",
         RFC 4590, July 2006.

[RFC4740] Garcia-Martin, M., Ed., Belinchon, M., Pallares-Lopez, M.,

         Canales-Valenzuela, C., and K. Tammi, "Diameter Session
         Initiation Protocol (SIP) Application", RFC 4740, November
         2006.

Appendix A - Changes from RFC 4590

This Appendix lists the major changes between [RFC4590] and this document. Minor changes, including style, grammar, spelling, and editorial changes are not mentioned here.

o The Table of Attributes (Section 5) now indicates that the

  Digest-Method Attribute is required within an Access-Request.
  Also, an entry has been added for the State attribute.  The table
  also includes entries for Accounting-Request messages.  As noted
  in the examples, the User-Name Attribute is not necessary when
  requesting a nonce.

o Two errors in attribute assignment have been corrected within the

  IANA Considerations (Section 7).  Digest-Response-Auth is assigned
  attribute 106, and Digest-Nextnonce is assigned attribute 107.

o Several errors in the examples section have been corrected.

Acknowledgments

The authors would like to thank Mike McCauley for his help in working through the details of the examples.

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.

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]

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