INTERNET DRAFT Pat R. Calhoun
Category: Standards Track Sun Microsystems, Inc.
Title: draft-calhoun-diameter-strong-crypto-03.txt William Bulley
Date: April 2000 Merit Network, Inc.
Stephen Farrell
Baltimore Technologies
DIAMETER Strong Security Extension
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026. Internet-Drafts are working
documents of the Internet Engineering Task Force (IETF), its areas,
and its working groups. Note that other groups may also distribute
working documents as Internet-Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at:
http://www.ietf.org/ietf/1id-abstracts.txt
The list of Internet-Draft Shadow Directories can be accessed at:
http://www.ietf.org/shadow.html.
This document is an individual contribution for consideration by the
AAA Working Group of the Internet Engineering Task Force. Comments
should be submitted to the diameter@diameter.org mailing list.
Distribution of this memo is unlimited.
Copyright (C) The Internet Society 1999. All Rights Reserved.
Calhoun, Bulley, Farrell expires October 2000 [Page 1]
INTERNET DRAFT April 2000
Abstract
The DIAMETER base protocol defines message integrity and AVP
encryption using symmetric transforms to secure the communication
between two DIAMETER nodes. The base protocol also defines a DIAMETER
proxy server, that forwards requests to other servers when it detects
that a given request cannot be satisfied locally.
The ROAMOPS Working Group has defined a requirement that allows for
the DIAMETER servers communicating through the proxy to be able to
provide for end-to-end AVP integrity and confidentiality, making it
difficult for the proxy to be able to modify, and/or be able to view
sensitive information, within the message. The Mobile-IP and NASREQ
Working Groups have stated that strong authentication is a
requirement for AAA data, such as accounting records, for the
purposes of non-repudiation.
This DIAMETER extension specifies how strong AVP authentication,
integrity and encryption can be done using asymmetric transforms, by
encapsulating Cryptographic Message Syntax (CMS) data into DIAMETER
AVPs. The CMS data can also be used to carry X.509 certificates.
Table of Contents
1.0 Introduction
1.1 Certificate Requirements
1.2 Requirements language
2.0 Extended AVP Format
3.0 CMS-Data AVP
4.0 Result-Code AVP Values
5.0 IANA Considerations
6.0 Security Considerations
7.0 References
8.0 Acknowledgements
9.0 Authors' Addresses
10.0 Full Copyright Statement
Calhoun, Bulley, Farrell expires October 2000 [Page 2]
INTERNET DRAFT April 2000
1.0 Introduction
The DIAMETER base protocol [1] defines message integrity and AVP
encryption using symmetric transforms to secure the communication
between two DIAMETER nodes. The base protocol also defines a DIAMETER
proxy server, that forwards requests to other servers when it detects
that a given request cannot be satisfied locally.
The ROAMOPS Working Group has defined a requirement in [10] that
allows for the DIAMETER servers communicating through the proxy to be
able to provide for end-to-end AVP integrity and confidentiality,
making it difficult for the proxy to be able to modify and see
sensitive information within the message. The Mobile-IP and NASREQ
Working Groups have stated in [6, 7, 8] that non-repudiation is a
requirement for AAA data, such as accounting records.
When a chain of proxies use hop-by-hop security, each node in the
proxy chain MUST recompute the Integrity-Value-Check (ICV) [1],
making it easy for a malicious proxy to modify information in a
DIAMETER message. It is virtually impossible for the rest of the
nodes in the proxy chain to know that the message was modified in
mid-stream. Figure 1 shows an example of such a network, where DIA3
modifies the contents of "foo" in both the request and the response.
(Request) (Request) (Request)
[AVP(foo)=x] [AVP(foo)=x] [AVP(foo)=y]
+------+ -----> +------+ -----> +------+ -----> +------+
| | | | | | | |
| NASB +----------+ DIA2 +----------+ DIA3 +----------+ DIA1 |
| | | | | | | |
+------+ <----- +------+ <----- +------+ <----- +------+
(Answer) (Answer) (Answer)
[AVP(foo)=b] [AVP(foo)=b] [AVP(foo)=a]
Figure 1: Proxy Chain
This document describes how strong authentication and encryption can
be provided in the DIAMETER protocol, by encapsulating CMS objects
[3] in AVPs. The CMS object can also be used to carry X.509
certificates and revocation lists.
In the example provided in Figure 1, the originator of the request
and response adds a digital signature that covers a set of AVPs
within the message. The protected AVPs MUST NOT be changed by an
intermediate proxy server (DIA2, DIA3), since the signature
validation performed by the end server would fail.
The DIAMETER base protocol also allows a DIAMETER broker to provide
redirect services, as shown in Figure 2. The DIAMETER broker MAY
Calhoun, Bulley, Farrell expires October 2000 [Page 3]
INTERNET DRAFT April 2000
return information to a requesting server that would allow the
servers to interact directly, bypassing the broker. This optimized
approach reduces the complexity associated with end-to-end security.
+------------------+ +---------+
| DIAMETER | | CRL DB/ |
| Broker | | OCSP |
+------------------+ +---------+
^
Request | Response +
| Result Code =
Local | Redirect Home
ISP v ISP
+----------+ +----------+
| abc.net | | xyz.net |
| DIAMETER |<------------>| DIAMETER |
| Server | | Server |
+----------+ Direct +----------+
Communication
Figure 2: DIAMETER Broker Returning Redirect Indication
When redirect services are used, a network layer security protocol,
such as IP Security, MAY be used to secure the traffic between the
two DIAMETER servers. However, security at the application level may
still be necessary in this network configuration, specifically the
ability to authenticate a select set of AVPs. Brokers that operate in
a redirect mode typically require that both DIAMETER servers sign
accounting records. The accounting record, signed by both parties is
then forwarded to the broker via the local DIAMETER server. This
provides the broker with some assurances that both networks agreed on
the accounting data, which it MAY use for settlement purposes. If the
underlying security protocol provides confidentiality, strong
encryption MAY not be necessary in the redirect case.
Given that asymmetric transform operations are expensive, DIAMETER
servers MAY wish to use them only when dealing with inter-domain
servers, as shown in Figure 3. This configuration is normally
desirable since DIAMETER entities within a given administrative
domain MAY inherently trust each other. Further, it is desirable to
move this functionality to the edges, since NASes do not necessarily
have the CPU power to perform expensive cryptographic operations.
Calhoun, Bulley, Farrell expires October 2000 [Page 4]
INTERNET DRAFT April 2000
+------------------------+
| Foreign Network |
|+-----+ +--------+ | +--------+ +--------+
|| | |DIAMETER| | |DIAMETER| |DIAMETER|
|| NAS +------+ +--------+ +--------+ Home |
|| | | Proxy | | | Broker | | Server |
|+-----+ +--------+ | +--------+ +--------+
| |
+------------------------+
<------------> <-------------------------->
<Hop-by-Hop> <End-to-End>
Figure 3: Mixed DIAMETER Security Models
The Extension number for this draft is two (2). This value is used in
the Extension-Id AVP as defined in [1].
1.1 Certificate Requirements
Certificates used for the purposes of DIAMETER MUST conform to the
PKIX profile [4], and MUST also include a DIAMETER node's NAI, which
is typically added in the Host-Name AVP [1], as one of the values of
the subjectAltName extension of the Certificate. The NAI is to be
encoded as an rfc822Name within the subjectAltName.
These names are used for two purposes:
1. Where a DIAMETER node is verifying a signature it needs to be
able to compare the identity of the signer against the identity
in the Host-Name AVP.
2. Where a DIAMETER node is encrypting AVPs, it needs to be able
to ensure that it uses a public key for the intended recipient.
This requries comparing the identity in a Certificate against
the NAI of the intended recipient (which is assumed to be
known).
In either case, the presence of the required NAI as an rfc822Name
value in the subjectAltName extension of a verified public key
certificate satisfies the matching requirement.
Note that there MAY also be other values in the subjectAltName
extension, (either using rfc822Name or other elements of the CHOICE),
these can be safely ignored, but implementations MUST be able to
handle their presence.
Note also that the PKIX profile [4], section 4.1.2.6, specifies the
Calhoun, Bulley, Farrell expires October 2000 [Page 5]
INTERNET DRAFT April 2000
rules for the relationship between the subjectAltName extension and
the subject field of public key certificates.
1.2 Requirements language
In this document, the key words "MAY", "MUST, "MUST NOT", "optional",
"recommended", "SHOULD", and "SHOULD NOT", are to be interpreted as
described in [13].
2.0 Extended AVP Format
This specification introduces the 'P' bit in the AVP Header, which is
defined in [1]. The 'P' bit, known as the protected AVP bit, is used
to indicate whether the AVP is protected by a digital signature. When
set, the AVP is protected and the contents cannot be changed by a
DIAMETER proxy server without detection.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AVP Code |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AVP Length | Reserved |P|T|V|R|M|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Vendor ID (opt) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag (opt) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Data ...
+-+-+-+-+-+-+-+-+
Figure 4: Extended DIAMETER AVP Header
Note that unless stated otherwise, the 'P' bit can be set on any
DIAMETER AVP. The Proxy-State and Integrity-Check-Value AVPs [1] MUST
NOT have the 'P' bit set. The Encrypted-Payload AVP MAY have the 'P'
bit set if there is no intermediate proxy server. Any additional AVPs
that MUST be removed, or changed, at each hop in a proxy chain MUST
NOT have the 'P' bit set.
3.0 CMS-Data AVP
The CMS-Data AVP (AVP Code 310) is of type data and contains the DER
encoding of a CMS object [3] of type ContentInfo. The profile of CMS
algorithm and structure usage is as specified in the S/MIME v3
message specification [11]. This means that where a set of AVPs is
Calhoun, Bulley, Farrell expires October 2000 [Page 6]
INTERNET DRAFT April 2000
protected using CMS, the set MUST first be encoded according to MIME
encoding rules specified below. This method of encapsulating AVPs
allows existing S/MIME toolkits to be used without changes in order
to produce strongly protected DIAMETER messages. The CMS object MAY
contain any of the three methods; signed-only, enveloped-only and
signed-and-enveloped. Optional certificates and CRLs MAY be present
in all three methods.
To package a set of AVPs as a MIME type, the AVPs are first
concatenated in the order in which they occur in the DIAMETER
message. The entire AVP MUST be input to the signing/encryption
process, from the first byte of the AVP code to the last byte of the
AVP data, including all other fields, length, reserved/flags, and
optional vendor IDs, tags and padding. The AVP MUST be input to the
signing/encryption process in network byte order. If AVPs are to be
enciphered, then the encryptor is free to order AVPs whatever way it
chooses. This value is then used as the value of a new MIME type
application/x-diameter-avps, which MUST be prepared in accordance
with the rules specified in section 3.1 of [11]. If a receiver
detects that the contents of the CMS-Data AVP is invalid, it SHOULD
return the new Result-Code AVP value defined in section 4.0.
Where signing only is performed, the signature is calculated over the
canonical encoding of the application/x-diameter-avps MIME type, but
the AVPs themselves are not carried within the CMS-Data AVP. Instead,
the digest value within the SignedData structure contains the digest
over the canonicalized encoding of application/x-diameter-avps.
Multiple DIAMETER entities MAY add their signatures to an existing
CMS-Data AVP using the countersignature attribute, defined in section
11.4 of [3]. The countersignature attribute requires that the
signatures occur sequentially, meaning that each node's signature
covers the existing signatures in the CMS object.
Where encryption only is performed, the encryptedContent MUST contain
the canonical encoding of the application/x-diameter-avps MIME type.
Where signing and encryption are both performed, signing MUST occur
first, the resulting CMS object MUST then be MIME encoded producing
an application/pkcs7-mime type which is then used as the content of
the EnvelopedData.
There is no need for an 'outer' MIME encoding when only signing, or
only encryption is applied.
Where AVPs are encapsulated within a CMS-Data AVP, the eContentType
of the EncapsulatedContentInfo MUST be id-data [11].
The signing and encryption algorithms supported MUST be those
Calhoun, Bulley, Farrell expires October 2000 [Page 7]
INTERNET DRAFT April 2000
specified in sections 2.2 and 2.3 of [11].
Conformant implementations MUST emit a CMS-Data AVP which contains
only one application/x-diameter-avps MIME type. Implementations which
receive any other MIME type MUST indicate an error.
Where a CMS-Data AVP contains a set of certificates then both public
key certificates (Certificate) and attribute certificates
(AttributeCertificate) are allowed by CMS (as well as one other
legacy format which MUST NOT be used). Support for use of the
Certificate structure is REQUIRED, implementations SHOULD support use
of the AttributeCertificate structure as defined in the PKIX
attribute certificate profile [12]. This allows DIAMETER
implementations to include a certifiate from a trusted party that
they are authorized to emit the AVPs contained in the message.
When a SignedData object is present, the eContent field of the
EncapsulatedContentInfo structure MUST be absent since the
authentication covers data outside of the object. The signature is
computed over all AVPs prior to the AVP that have the 'P' bit
enabled. The order of the AVPs MUST be preserved and the computation
begins with the first AVP immediately following the DIAMETER header.
If the 'T' bit is set, the CMS-Data AVP covers all previous AVP with
the 'T' bit enabled and the same tag value as the one found in the
CMS-Data AVP. An Integrity-Check-Value (ICV) AVP MUST NOT preceed a
CMS-Data AVP containing a SignedData object. If the signature cannot
be verified correctly, a response with the Result-Code AVP set to
DIAMETER_INVALID_AUTH [1] MUST be returned.
When an EnvelopedData object is present, the encryptedContentInfo
field MUST contain the Host-Name AVP, containing the host name of the
encryptor, and one or more additional AVPs.
When a conforming implementation receives a DIAMETER message which
contains encrypted AVPs within a CMS EnvelopedData, then the
recipient MUST check to see if it is on the list of recipients
specified in the RecipientInfos of the EnvelopedData. If not, the
recipient MAY choose to process the message or indicate an error. If
the recipient is in the RecipientInfos and an error occurs during
decryption, then the recipient MUST indicate an error.
A CMS-Data MAY also contain a certs-only CMS structure, which is a
degenerate form of CMS structure containing only PKI related
information (see section 3.6 of [11] for details of the CMS certs-
only structure). This use of the CMS-Data AVP can be used to "push"
public key and attribute certificates and CRLs using DIAMETER, which
MAY be useful in environments where repositories (e.g. LDAP servers)
are either not used or not available (e.g. due to crossing a domain
Calhoun, Bulley, Farrell expires October 2000 [Page 8]
INTERNET DRAFT April 2000
boundary). Conforming implementations MUST be able to emit a certs-
only CMS structure which contains relevant PKI related information
and MUST be able to process a CMS-Data AVP which contains a certs-
only CMS structure. Of course, the recipient of such a certs-only CMS
structure SHOULD NOT use the PKI related information without first
verifying it, e.g. by checking that issuer's are trusted, signatures
verify etc.
When the CMS-Data AVP contains certificates in the certificates field
of the SignedData, a CRL [4] MAY also be provided in the crls field
of the SignedData, which MAY be used to assist in determining whether
a certificate has been revoked. Optionally, the DIAMETER server MAY
check the status of certificates using another mechanism, such as
Online Certificate Status Protocol (OCSP) [9].
This AVP MUST have the 'M' bit enabled, while the 'T' bit MAY be
enabled if the signature covers a set of AVPs. The 'P' and 'V' bits
MUST NOT be enabled.
The following is an example of a message that includes strong
security and hop-by-hop security:
<DIAMETER Msg> ::= <DIAMETER Header>
<Command-Code AVP>
[<Additional AVPs>]
<CMS-Data AVP>
[<Timestamp AVP>
<Nonce AVP>
<Integrity-Check-Value AVP>]
4.0 Result-Code AVP Values
This section defines new Result-Code [1] values that MUST be
supported by all DIAMETER implementations that conform to this
specification.
DIAMETER_INVALID_CMS_DATA 20
This error code is returned when a CMS-Data AVP is received
with an invalid ContentInfo object.
5.0 IANA Considerations
The CMD-Data AVP defined in Section 3 is a DIAMETER AVP whose
identifier was allocated from the AVP numbering space [1], and
extended in [13], [14] and [15]. IANA should assign a value of 310 to
this AVP.
Calhoun, Bulley, Farrell expires October 2000 [Page 9]
INTERNET DRAFT April 2000
The Result-Code values defined in Section 4.0 are error codes as
defined in [1] and extended in [13], [14] and [15]. They correspond
to error values specific to the Strong Security extension. IANA
should record the values as defined in Section 4.0.
6.0 Security Considerations
This document describes how strong security can be achieved in the
DIAMETER protocol by allowing S/MIME Cryptographic Message Syntax [3]
objects to be carried as a DIAMETER AVP.
Section 3.0 states that a certificate received in a CMS-Data AVP
SHOULD NOT be used prior to cert verification. In most cases, the
verification will be according to the rules specified in [4],
however, some communities have indicated that they wish to be allowed
specify alternative certificate verification mechanisms, hence the
"SHOULD NOT" rather than the more typical "MUST NOT". The authors do
however strongly RECOMMEND that the verification procedures specified
in [4] are always applied, regardless of whatever other verification
mechanisms are in use.
7.0 References
[1] P. Calhoun, A. Rubens, H. Akhtar, E. Guttman, "DIAMETER Base
Protocol", draft-calhoun-diameter-14.txt, IETF work in progress,
April 2000.
[2] Kaufman, Perlman, Speciner, "Network Security: Private Communi-
cations in a Public World", Prentice Hall, March 1995, ISBN 0-
13-061466-1.
[3] R. Housley, "Cryptographic Message Syntax", RFC 2630, June 1999.
[4] Housley, Ford, Polk, Solo, "Internet X.509 Public Key Infras-
tructure Certificate and CRL Profile", RFC 2459, January 1999.
[5] S. Bradner, "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[6] M. Beadles, "Criteria for Evaluating Network Access Server Pro-
tocols", draft-ietf-nasreq-criteria-03.txt, IETF work in pro-
gress, October 1999.
[7] T. Hiller et al., "Cdma2000 Wireless Data Requirements for AAA",
draft-hiller-cdma2000-AAA-00.txt, IETF work in progress, October
Calhoun, Bulley, Farrell expires October 2000 [Page 10]
INTERNET DRAFT April 2000
1999.
[8] S. Glass, S. Jacobs, C. Perkins, "Mobile IP Authentication,
Authorization, and Accounting Requirements", draft-ietf-
mobileip-aaa-reqs-01.txt, IETF work in progress, January 2000.
[9] Myers, Ankney, Malpani, Galperin, Adams, "X.509 Internet Public
Key Infrastructure Online Certificate Status Protocol (OCSP)",
RFC 2560, June 1999.
[10] Aboba, Zorn, "Criteria for Evaluating Roaming Protocols", RFC
2477, January 1999.
[11] B. Ramsdell, "S/MIME v2 Message Specification", RFC2633, June
1999.
[12] S. Farrell, R. Housley, "An Internet Attribute Certificate Pro-
file for Authorization", draft-ietf-pkix-ac509prof-01.txt, IETF
work in progress, October 1999.
[13] P. Calhoun, W. Bulley, "DIAMETER NASREQ Extension", draft-
calhoun-diameter-nasreq-03.txt, IETF work in progress, April
2000.
[14] P. Calhoun, C. Perkins, "DIAMETER Mobile IP Extensions", draft-
calhoun-diameter-mobileip-07.txt, IETF work in progress, April
2000.
[15] Arkko, Calhoun, Patel, Zorn, "DIAMETER Accounting Extension",
draft-calhoun-diameter-accounting-05.txt, IETF work in progress,
April 2000.
8.0 Acknowledgements
The authors would also like to acknowledge the following people for
their contribution in the development of the DIAMETER protocol:
Bernard Aboba, Jari Arkko, William Bulley, Daniel C. Fox, Lol Grant,
Ignacio Goyret, Nancy Greene, Peter Heitman, Paul Krumviede, Fergal
Ladley, Ryan Moats, Victor Muslin, Kenneth Peirce, Sumit Vakil, John
R. Vollbrecht, Jeff Weisberg and Glen Zorn
9.0 Authors' Addresses
Questions about this memo can be directed to:
Calhoun, Bulley, Farrell expires October 2000 [Page 11]
INTERNET DRAFT April 2000
Pat R. Calhoun
Network and Security Research Center, Sun Labs
Sun Microsystems, Inc.
15 Network Circle
Menlo Park, California, 94025
USA
Phone: +1 650-786-7733
Fax: +1 650-786-6445
E-mail: pcalhoun@eng.sun.com
William Bulley
Merit Network, Inc.
Building One, Suite 2000
4251 Plymouth Road
Ann Arbor, Michigan, 48105-2785
USA
Phone: +1 734-764-9993
Fax: +1 734-647-5185
E-mail: web@merit.edu
Stephen Farrell
Baltimore Technologies
61/62 Fitzwilliam Lane
Dublin 2,
IRELAND
Phone: +353-1-647-7300
Fax: +353-1-647-7499
E-Mail: stephen.farrell@baltimore.ie
10.0 Full Copyright Statement
Copyright (C) The Internet Society (1999). All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published and
distributed, in whole or in part, without restriction of any kind,
provided that the above copyright notice and this paragraph are
included on all such copies and derivative works. However, this docu-
ment itself may not be modified in any way, such as by removing the
copyright notice or references to the Internet Society or other Inter-
net organizations, except as needed for the purpose of developing
Calhoun, Bulley, Farrell expires October 2000 [Page 12]
INTERNET DRAFT April 2000
Internet standards in which case the procedures for copyrights defined
in the Internet Standards process must be followed, or as required to
translate it into languages other than English. The limited permis-
sions granted above are perpetual and will not be revoked by the
Internet Society or its successors or assigns. This document and the
information contained herein is provided on an "AS IS" basis and THE
INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL
WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WAR-
RANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY
RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A
PARTICULAR PURPOSE."
Calhoun, Bulley, Farrell expires October 2000 [Page 13]