One document matched: draft-ietf-aaa-diameter-e2e-sec-01.txt
Differences from draft-ietf-aaa-diameter-e2e-sec-00.txt
Individual Contribution Pat R. Calhoun
Internet-Draft Sun Microsystems, Inc.
Category: Standards Track Stephen Farrell
<draft-ietf-aaa-diameter-e2e-sec-01.txt> Baltimore Technologies
William Bulley
Merit Network, Inc.
May 2001
Diameter End-2-End 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.
Distribution of this memo is unlimited.
Copyright (C) The Internet Society 2001. All Rights Reserved.
Abstract
The Diameter base protocol leverages either IPsec or SSL for
integrity and confidentiality 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.
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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 a mixture of symmetric and
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 Requirements language
1.2 Advertising extension support
2.0 AVP Format
3.0 Key Management
3.1 Usage Scenario
3.2 Certificate Requirements
3.3 Algorithms
3.4 Reuse of CMS Content Encryption Keys
4.0 Command-Codes Values
4.1 E2E-SA-Setup-Request (ESSR) Command
4.2 E2E-SA-Setup-Answer (ESSA) Command
5.0 End-to-End Security Association Message Flow
6.0 End-to-End Security AVPs
6.1 CMS-Signed-Data AVP
6.2 CMS-Encrypted-Data AVP
6.3 CMS-Cert AVP
6.4 Local-CA-Info AVP
6.4.1 CA-Name AVP
6.4.2 Key-Hash AVP
6.5 OCSP-Nonce AVP
6.6 AAA-Server-Certs AVP
6.7 OCSP-Responses AVP
6.8 CA-Chain AVP
6.9 Expected-Signed-AVP AVP
6.10 Expected-Encrypted-AVP AVP
6.11 AVP-Code AVP
7.0 Result-Code AVP Values
7.1 Transient Failures
7.2 Permanent Failures
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8.0 IANA Considerations
8.1 Command Codes
8.2 AVP Codes
8.3 Result-Code AVP Values
8.4 Extension Identifier
9.0 Security Considerations
10.0 References
11.0 Acknowledgements
12.0 Authors' Addresses
13.0 Full Copyright Statement
14.0 Expiration Date
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1.0 Introduction
The Diameter base protocol [1] leverages either IPsec or SSL for
integrity and confidentiality 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 (e.g. TLS, IPSec), a
proxy may 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 should 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
return information to a requesting server that would allow the
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servers to interact directly, bypassing the broker. This optimized
approach reduces the complexity associated with end-to-end security.
+------------------+
| Diameter |
| Broker |
+------------------+
^
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 the
same set of AVPs, marked with the 'P' bit, in 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.
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+------------------------+
| Foreign Network |
|+-----+ +--------+ | +--------+ +--------+
|| | |Diameter| | |Diameter| |Diameter|
|| NAS +------+ +--------+ +--------+ Home |
|| | | Proxy | | | Broker | | Server |
|+-----+ +--------+ | +--------+ +--------+
| |
+------------------------+
<------------> <-------------------------->
<Hop-by-Hop> <End-to-End>
Figure 3: Mixed Diameter Security Models
1.1 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 [5].
1.2 Advertising extension support
Diameter nodes conforming to this specification MAY advertise support
by including the value of two (2) in either the Device-Reboot-Ind
Command's [2] Auth-Extension-Id or Acct-Extension-Id AVPs.
2.0 AVP Format
The Diameter base protocol [1] details the AVP header, which includes
the 'P' bit, but does not specify how the 'P' bit is used. 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.
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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|R|V|R|M|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Vendor ID (opt) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Data ...
+-+-+-+-+-+-+-+-+
Figure 4: Diameter AVP Header
All Diameter specifications MUST specify whether the 'P' bit can be
set or not, as is done in section 4.5 of [1] and section 6 below.
AVPs that are designed to be changed at each hop (such as the Proxy-
Info AVP) MUST NOT allow the 'P' bit to be set.
3.0 Key Management
For e2e origin authentication, CMS itself already provides sufficient
key management without the need for additional specification.
Basically, the originating Diameter node signs and includes whatever
certificates are necessary for validation of the digital signature.
However, for encryption of AVPs more work is needed. In order to be
able to encrypt AVPs for a recipient, the originating Diameter node
must have a copy of the recipient's public key. There are many well-
known key retrieval schemes (e.g. using LDAP [16]), however, in order
to simplify Diameter implementations a specific Diameter key
distribution mechanism is defined here.
Another issue that must be addressed is how a Diameter node is to
"know" that certain AVPs are required to use the end-to-end security
extension. This is communicated during the End-to-End Security
Association message exchange, listed in section 4.0.
Finally, this section addresses the certificate profile to be used
for this Diameter extension, which is a simplified profile of [4].
3.1 Usage Scenario
When a Diameter node is about to send a message which MAY use end-
to-end security, it must determine whether to use the end-to-end
security service or not. We assume the Diameter node knows the user's
NAI, which determines the user's realm.
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In the present discussion we assume that the Diameter node has not
cached any information. Where information can be cached this is
noted.
We use Diameter E2E-SA-Setup-Request (ESSR) and E2E-SA-Setup-Answer
(ESSA) messages to establish whether end-to-end security is required
and if so, for which AVPs and which public key(s) to use.
The originating node sends the ESSR message to a server in the
destination realm. The ESSR message contains:
- the realm part of the user's NAI
- the list of direct trust CA's that the originating Diameter
node has configured into it for certificate validation. A
"direct trust" CA is one that the node is willing to use as the
"top" of a certificate chain, sometimes confusingly known as a
"root CA."
- a list of AVPs that expected to be protected (and how) for this
realm
- (optionally) a flag indicating that the originating Diameter
node wishes to receive certificate status information (using
OCSP messages) in which case a nonce to be used by the
destination Diameter node in OCSP requests MAY also be
supplied. See [9] for details of the certificate status
protocol and messages.
The destination node returns the ESSA message which contains:
- TTL for this SA (seconds)
- a chain of CA certificates (possibly empty)
- public key certificates for the AAA servers in the realm, all
of which MUST validate up to one of the CA's contained in the
ESSR message, via the chain of CA certificates above;
- a list of AVPs that expected to be protected (and how) for this
realm
- (optionally, if nonce received and OCSP supported) a list of
OCSP responses for the certificates in question, each of which
uses the nonce from the ESSR message
[Issue: If one OCSP responder is used, do we need to append to the
nonce for each request?]
The originating Diameter node now has to check the response. Any
failure results in error messages and auditing and not sending the
Diameter message.
Checks:
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- the certificate chain selected is cryptographically correct,
passes the (relevant parts of the) rfc2459 path validation
algorithm and terminates at a CA mentioned in the ESSR message
- the realm part of the user's NAI must occur as a subjectAltName
(with the rfc822Address option) in the AAA server's
certificate. This rfc822Address MUST be of the form "Diameter-
<XXX>@<domain>" where <domain> is the NAI's domain component
and <XXX> can be anything (e.g. "Diameter-1@baltimore.com",
"Diameter-west@sun.com") chosen by the AAA server
administrator.
- the ESSA message MUST be digitally signed and the signature
MUST be validated and the signer's certificate chain MUST
terminate as a CA mentioned in the ESSR message
If certificate status (revocation) is an issue for the Diameter
node, then the ESSR message MAY contain a nonce value. The idea
is that the sender of the ESSA makes OCSP requests on behalf of
the Diameter node and returns the OCSP responses to the
Diameter node as part of the ESSA message. The use of the nonce
value ensures that the sender of the ESSA cannot return cached
or otherwise fake OCSP responses to the Diameter node.
The nonce value is to be (the beginning of) the nonce in the
OCSP response.
[Issue The reason for "beginning" above is that an OCSP
responder might produce an error if presented with the same
nonce more than once.]
The ESSR MAY be signed. If the originating node has a private
key and protection expectations for AVPs are specified, then
the ESSR SHOULD be signed.
The ESSA MUST be signed to prevent an intermediate node from
modifying the protection expectations for AVPs. The ESSA MUST
be signed a Diameter node from the destination realm (based on
the signer's name).
If e2e confidentiality or digial signature is required, then
the originating node prepares the CMS related AVPs as required.
3.2 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
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encoded as an rfc822Name within the subjectAltName.
For Diameter nodes (capable of acting as recipients for e2e
confidentiality), the NAI MUST be of the form "Diameter-
<xxx>@<realm>". Other Diameter nodes MAY use this naming scheme. Note
that this naming constraint is for PKI purposes only, and in no way
restricts a Diameter's host name.
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 requires 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
rules for the relationship between the subjectAltName extension and
the subject field of public key certificates.
[Issue: Future versions of this draft may specify a restricted
profile of [4] in order to simplify implementation.]
3.3 Algorithms
For all uses of CMS in this specification the mandatory to implement
algorithms are as follows:
- Asymmetric: RSA
- Hashing: SHA-1
- Signature: RSAwithSHA1
- Symmetric Encryption: 3DES
At some point in future, AES will replace 3DES.
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3.4 Reuse of CMS Content Encryption Keys
Once a CMS-Encrypted-Data AVP has been exchanged between two Diameter
nodes, then they share a symmetric cryptographic key (the content
encryption key) which can be used to encrypt further Diameter AVPs
between the nodes by using the scheme specified in [15]. Normally,
the nodes first take part in an ESSR/ESSA exchange in order to
distribute the required asymmetric keys.
[15] leaves open some issues, namely how to handle loss of a shared
secret (say following a node re-boot) and for how long to continue to
use a shared secret (the maximum number of decryptions required).
Where a Diameter node receives a CMS-Encrypted-Data AVP, but doesn't
have the required shared secret, that node should return the
DIAMETER_KEY_UNKNOWN error message. The Diameter nodes may then use
the ESSR/ESSA exchange, or cached asymmetric keys to rebuild their
security association.
In [15], the default value for the maximum number of decryptions
allowed (CEKMaxDecrypts) when re-using a content encryption key is
one. In general this default SHOULD be used, but if a Diameter node
"knows" that more than one CMS-Encrypted-Data AVP will be exchanged
between the nodes (based on the Expected-Encrypted-AVP settings
exchanged during the ESSR/ESSA exchange) then the CEKMaxDecrypts
setting MAY be set higher. Diameter nodes MUST be able to support a
maxDecrypts setting of 1000.
[Issue: Are there reasonable expectations for the highest MUST
support for maxDecrypts?]
4.0 Command-Codes Values
This section defines new Command-Code [1] values that MUST be
supported by all Diameter implementations that conform to this
specification. The following Command Codes are currently defined in
this document:
Command-Name Abbrev. Code Reference
--------------------------------------------------------
E2E-SA-Setup-Request ESSR 304 4.1
E2E-SA-Setup-Answer ESSA 305 4.2
4.1 E2E-SA-Setup-Request (ESSR) Command
The E2E-SA-Setup-Request command, indicated by the Command-Code field
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set to 304, is sent by a Diameter node to establish a Diameter End-
to-End Security Association.
<E2E-SA-Setup-Request> ::= < Diameter-Header: 304 >
{ Origin-FQDN }
{ Origin-Realm }
{ Destination-Realm }
+ { Local-CA-info }
{ Auth-Extension-Id }
[ Destination-FQDN ]
* [ Expected-Signed-AVP ]
* [ Expected-Encrypted-AVP ]
* [ OCSP-Nonce ]
0*1[ CMS-Signed-Data ]
* [ Proxy-Info ]
* [ Route-Record ]
4.2 E2E-SA-Setup-Answer (ESSA) Command
The E2E-SA-Setup-Answer command, indicated by the Command-Code field
set to 305, is sent by a Diameter node in response to an ESSR
message.
<E2E-SA-Setup-Answer> ::= < Diameter-Header: 305 >
{ Origin-FQDN }
{ Origin-Realm }
0*1{ CA-Chain }
+ { AAA-Server-Certs }
* { OCSP-Responses }
{ Destination-FQDN }
{ Auth-Extension-Id }
* [ Expected-Signed-AVP ]
* [ Expected-Encrypted-AVP ]
[ CMS-Signed-Data ]
* [ Proxy-Info ]
* [ Route-Record ]
5.0 End-to-End Security Association Message Flow
This section contains an example of a NAS in domain xyz.com,
communicating with its local proxy, which in turn communicates with a
Diameter server in ABC.COM's network. In the following example, once
the initial capabilities exchange is complete, the NAS receives a
request for access from alice@abc.com, which causes an end-to-end
security association message exchange, followed by an authentication
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request.
+-------+ +-------+ +---------+
| NAS | | Proxy | | abc.com |
| | | Srv | |Home Srv |
+-------+ +-------+ +---------+
| | |
|DRI extensions 1, 2 | |
(a) |------------------->| |
|DRI extension 1, -1 | |
(b) |<-------------------| |
| . |DRI extensions 1, 2 |
(c) | |<-------------------|
| |DRI extension 1, -1 |
(d) | |------------------->|
->| User alice@abc.com | |
(e) | Requests Access | |
| | |
| ESSR | |
| Dest-Realm=abc.com | |
| CMS-Cert | |
(f) |--------------------+------------------->|
| | ESSA |
| | Origin-FQDN=foo |
| | CMS-Cert |
(g) |<-------------------+--------------------|
| Auth-Request + | |
| CMS-Signed-Data | |
| Dest-FQDN=foo | |
(h) |--------------------+------------------->|
| | Auth-Answer + |
| | CMS-Encrypted-Data |
(i) |<-------------------+--------------------|
Figure 5: Example of an End-to-End Security Association Setup
(a) NAS sends a DRI message to its proxy server indicating that it
supports extensions 1 (NASREQ) and 2 (E2E Security).
(b) The proxy server sends a DRI message to the NAS indicating
that it supports extension 1 (NASREQ), as well as the wildcard
extension.
(c) ABC.COM's Home Server sends a DRI message to a proxy server
indicating that it supports extensions 1 (NASREQ) and 2 (E2E
Security).
(d) The proxy server sends a DRI message to ABC.COM's Home Server
indicating that it supports extension 1 (NASREQ), as well as
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the wildcard extension.
(e) The NAS receives a request for access from a user
(alice@abc.com).
(f) The NAS issues an ESSR message, with the Destination-Realm AVP
set to abc.com, and its certificate in the CMS-Cert AVP. The
ESSR includes the set of AVPs that the NAS expects to be
encrypted, in the event that the home server returns messages
that contain these AVPs.
(g) ABC.COM's Home Server processes the ESSR message, and replies
with the ESSA message. The ESSA also includes the set of AVPs
that the home server is expecting to be authenticated, as well
as its certificate in the CMS-Cert AVP.
(h) The NAS issues an authentication request with the
Destination-FQDN AVP set to the value of the Origin-FQDN AVP
in the ESSA. The message includes the CMS-Signed-AVP, which
authenticates the AVPs that were requested by the Home Server
in the ESSA.
(i) The Home Server successfully authenticates the user, and
returns a reply, which includes the CMS-Encrypted-Data AVP,
whose contents include the AVPs that were specified by the NAS
in the ESSR.
6.0 End-to-End Security AVPs
This section contains AVPs that are used to establish a Diameter
End-to-End Security Association.
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+---------------------+
| AVP Flag rules |
|----+-----+----+-----|----+
AVP Section | | |SHLD| MUST|MAY |
Attribute Name Code Defined Value Type |MUST| MAY | NOT| NOT|Encr|
-----------------------------------------|----+-----+----+-----|----|
AAA-Server-Certs 351 6.6 OctetString| M | P | | V | N |
AVP-Code 352 6.11 Unsigned32 | M | P | | V | N |
CA-Chain 353 6.8 OctetString| M | P | | V | N |
CA-Name 349 6.4.1 OctetString| M | P | | V | N |
CMS-Cert 354 6.3 OctetString| M | | | P,V | N |
CMS-Encrypted- 355 6.2 OctetString| M | P | | V | N |
Data | | | | | |
CMS-Signed-Data 310 6.1 OctetString| M | | | P,V | N |
Key-Hash 350 6.4.2 OctetString| M | P | | V | N |
Expected-Signed- 356 6.9 Grouped |M,P | | | V | N |
AVP | | | | | |
Expected- 357 6.10 Grouped |M,P | | | V | N |
Encrypted-AVP | | | | | |
Local-CA-Info 348 6.4 Grouped | M | P | | V | N |
OCSP-Nonce 358 6.5 OctetString| M | P | | V | N |
OCSP-Responses 359 6.7 OctetString| M | P | | V | N |
6.1 CMS-Signed-Data AVP
The CMS-Signed-Data AVP (AVP Code 310) is of type OctetString and
contains the Basic Encoding Rules (BER) 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 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.
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 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, and padding. The AVP MUST be input to the signing
process in network byte order.
The signature is calculated over the catenation of all the 'P' bit
AVPs, but the AVPs themselves are not carried within the CMS-Signed-
Data AVP. Instead, the digest value within the SignedData structure
contains the digest over these AVPs. Multiple Diameter entities MAY
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add their signatures to an existing CMS-Signed-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. A countersignature MUST cover all AVPs
in the message that have the 'P' bit enabled (i.e. the same AVPs as
the first signature). Receiving Diameter nodes MAY, but need not, be
able to support the use of the countersignature attribute.
If a receiver detects that the contents of the CMS-Signed-Data AVP
are invalid, it SHOULD return the new Result-Code AVP value defined
in section 7.0.
When AVPs are to be both encrypted and signed, the CMS-Encrypted-Data
AVP MUST be created first. The resulting CMS object MUST then be MIME
encoded producing an application/pkcs7-mime MIME type which is then
used as the content of the EnvelopedData. This means that signing is
"outside" encryption.
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 signature cannot be verified correctly, a
response with the Result-Code AVP set to DIAMETER_INVALID_AUTH [1]
MUST be returned.
No more than one CMS-Signed-Data AVP MUST be present in any given
Diameter message.
6.2 CMS-Encrypted-Data AVP
The CMS-Encrypted-Data AVP (AVP Code 355) is of type OctetString and
contains the Basic Encoding Rules (BER) encoding of a CMS object [3]
of type ContentInfo. This means that where a set of AVPs is protected
using CMS, the set MUST first be catenated a sequence of encoded
AVPs.
The entire AVP MUST be input to the 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, and padding. The AVP MUST be input to the encryption
process in network byte order, and the encryptor is free to order
AVPs whatever way it chooses. This value is then encrypted and used
as the value of the EncryptedContent field within CMSEnvelopedData.
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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 7.0.
When AVPs are to be both encrypted and authenticated, the CMS-
Encrypted-Data AVP MUST be created first.
Where AVPs are encapsulated within a CMS-Encrypted-Data AVP, the
eContentType of the EncapsulatedContentInfo MUST be id-data [11].
CMS-Encrypted-Data MAY contain more than one CMS object, that is,
implementations are REQUIRED to be able to add a new CMS-Encrypted-
Data AVP value and are also REQUIRED to be able to decrypt all CMS-
Encrypted-Data AVP values which are encrypted for them.
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.
Diameter nodes SHOULD implement content encryption key re-use (see
section 3.4 above).
Zero or more CMS-Encrypted-Data AVP MAY be present in any Diameter
message.
6.3 CMS-Cert AVP
The CMS-Cert AVP (AVP Code 354) is of type OctetString and contains 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).
The CMS-Cert AVP contains one or more public key certificates
(Certificate) and MAY optionally contains attribute certificates
(AttributeCertificate) as allowed by CMS. Other legacy formats
supported by CMS MUST NOT be used.
Support for use of the Certificate structure is REQUIRED, while
implementations MAY support use of the AttributeCertificate structure
as defined in the PKIX attribute certificate profile [12]. The latter
allows Diameter implementations to include a certificate from a
trusted party that they are authorized to emit the AVPs contained in
the message.
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This use of the CMS-Cert 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 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-Cert 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.
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 node MAY check the status of
certificates using another mechanism, such as Online Certificate
Status Protocol (OCSP) [9].
6.4 Local-CA-Info AVP
The Local-CA-Info AVP (AVP Code 348) is of type Grouped. The Grouped
Data field has the following ABNF grammar:
Local-CA-Info = CA-Name Key-Hash
CA-Name = ; See Section 6.4.1
Key-Hash = ; See Section 6.4.2
The Local-CA-Info AVP Data field contains the Certificate Authority's
name in the CA-Name AVP, as well as a hash of the key in the Key-Hash
AVP.
+---------------------------------------------------------------+
| AVP Header (AVP Code = 348) |
+---------------------------------------------------------------+
| CA-Name AVP |
+---------------------------------------------------------------+
| Key-Hash AVP |
+---------------------------------------------------------------+
6.4.1 CA-Name AVP
The CA-Name AVP (AVP Code 349) is of type OctetString, encoded in the
UTF-8 [24] format. The AVP contains the DN (in LDAP string syntax) of
the Certificate Authority, e.g. "CN=CA;O=Baltimore
Technologies;C=IE".
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6.4.2 Key-Hash AVP
The Key-Hash AVP (AVP Code 350) is of type OctetString, and contains
a SHA-1 hash of the key.
The hash MUST be calculated over the representation of the CA public
key which would be present in an X.509 public key certificate,
specifically, the input for the hash algorithm MUST be the DER
encoding of a SubjectPublicKeyInfo representation of the key. Note:
This includes the AlgorithmIdentifier as well as the BIT STRING. The
rules given in [4] for encoding keys MUST be followed.
Since this AVP is used for indexing and not for security (since
Diameter nodes SHOULD validate certificates), there is no need to
support more than one hash algorithm here.
6.5 OCSP-Nonce AVP
The OCSP-Nonce AVP (AVP Code 358) is of type OctetString, and
contains a random value (RECOMMENDED 128 bits) generated by the
Diameter node.
[Issue: Currently the nonce value also indicates the wish to receive
OCSP responses. It might be better to make this a grouped AVP with a
flag and optional nonce.]
6.6 AAA-Server-Certs AVP
The AAA-Server-Certs AVP (AVP Code 351) is of type OctetString and
contains the certificates of the AAA Servers in the home domain.
Note: this AVP contains no CA certificates, just those for AAA
servers.
6.7 OCSP-Responses AVP
The OCSP-Responses AVP (AVP Code 359) is of type OctetString, and
contains an OCSP response message from an OCSP responder. This AVP
MUST only be included in an ESSA message for which the corresponding
ESSR message contained an OCSP nonce.
6.8 CA-Chain AVP
The CA-Chain AVP (AVP Code 353) is of type OctetString, and contains
a certificate chain, from one of the nominated locally trusted CAs
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down to the (one and only) CA which has issued the end entity
certificates in the AAA-Server-Certs AVP.
To produce this AVP in an ESSA message, one (and only one) of the
Local-CA-info values from the corresponding ESSR message is selected
(call this the "top" CA for the purposes of this description). This
AVP then contains a certificate path (in order) from the "top" CA
down to the (one and only) CA which has issued all the end entity
certificates in the AAA-Servers-AVP. The (typically self-signed),
certificate of the "top" CA MAY be included, or MAY be omitted.
[Issue: Whether the "top" CA cert should be included or not can be
determined later.]
6.9 Expected-Signed-AVP AVP
The Expected-Signed-AVP AVP (AVP Code 356) is of type Grouped. The
Grouped Data field has the following ABNF grammar:
Expected-Signed-AVP = AVP-Code Vendor-Id
AVP-Code = ; See Section 6.11
Vendor-Id = ; See [1]
A Diameter node adds the Expected-Signed-AVP AVP to inform the ESSR/A
peer that any message received which contains the AVP specified in
this AVP MUST be authenticated via the CMS-Signed-Data AVP. The
Vendor-Id MAY contain a non-zero value if the AVP specified in the
AVP-Code AVP is vendor-specific.
+---------------------------------------------------------------+
| AVP Header (AVP Code = 356) |
+---------------------------------------------------------------+
| Vendor-Id AVP |
+---------------------------------------------------------------+
| AVP-Code AVP |
+---------------------------------------------------------------+
6.10 Expected-Encrypted-AVP AVP
The Expected-Encrypted-AVP AVP (AVP Code 357) is of type Grouped.
The Grouped Data field has the following ABNF grammar:
Expected-Encrypted-AVP = AVP-Code Vendor-Id
AVP-Code = ; See Section 6.11
Vendor-Id = ; See [1]
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A Diameter node adds the Expected-Encrypted-AVP AVP to inform the
ESSR/A peer that any message received which contains the AVP
specified in this AVP MUST be encrypted via the CMS-Encrypted-Data
AVP. The Vendor-Id MAY contain a non-zero value if the AVP specified
in the AVP-Code AVP is vendor-specific.
+---------------------------------------------------------------+
| AVP Header (AVP Code = 357) |
+---------------------------------------------------------------+
| Vendor-Id AVP |
+---------------------------------------------------------------+
| AVP-Code AVP |
+---------------------------------------------------------------+
6.11 AVP-Code AVP
The AVP-Code AVP (AVP Code 352) is of type Unsigned32, and contains
the AVP Code of the AVP that is to be authenticated or encrypted.
7.0 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.
7.1 Transient Failures
Errors that fall within the transient failures category are used to
inform a peer that the request could not be satisfied at the time it
was received, but MAY be able to satisfy the request in the future.
DIAMETER_KEY_UNKNOWN 4007
This error code is returned when a CMS-Signed-Data or CMS-
Encrypted-Data AVP is received that was generated using a key
that is not locally recognized. This error could be caused if
one of the endpoints of an end-to-end security association lost
a previously agreed upon key, perhaps as a result of a reboot.
7.2 Permanent Failures
Errors that fall within the permanent failures category are used to
inform the peer that the request failed, and should not be attempted
again.
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DIAMETER_INVALID_CMS_DATA 5018
This error code is returned when a CMS-Data AVP is received
with an invalid ContentInfo object.
8.0 IANA Considerations
This section contains the namespaces that have either been created in
this specification, or the values assigned to existing namespaces
managed by IANA.
8.1 Command Codes
This specification assigns the values 304-305 from the Command Code
namespace defined in [1], and extended in [13] and [14]. See section
4.0 for the assignment of the namespace in this specification.
8.2 AVP Codes
This specification assigns the values 348-359 from the AVP Code
namespace defined in [1], and extended in [13] and [14]. See section
6.0 for the assignment of the namespace in this specification.
8.3 Result-Code AVP Values
This specification assigns the values 4007, 5018 from the Result-Code
AVP (AVP Code 268) value namespace defined in [1], and extended in
[14]. See section 7.0 for the assignment of the namespace in this
specification.
8.4 Extension Identifier
This specification assigns the value two (2) to the Extension
Identifier namespace defined in [1]. See section 1.2 for more
information.
9.0 Security Considerations
This document describes how end-to-end 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 6.3 states that a certificate received in a CMS-Cert AVP
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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
to 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.
10.0 References
[1] P. Calhoun, A. Rubens, H. Akhtar, E. Guttman, "Diameter Base
Protocol", draft-ietf-aaa-Diameter-03.txt, IETF work in pro-
gress, May 2001.
[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, D. Mitton, "Criteria for Evaluating Network Access
Server Protocols", draft-ietf-nasreq-criteria-05.txt, IETF work
in progress, June 2000.
[7] T. Hiller et al., "Cdma2000 Wireless Data Requirements for AAA",
draft-hiller-cdma2000-AAA-02.txt, IETF work in progress, Sep-
tember 2000.
[8] S. Glass, S. Jacobs, C. Perkins, "Mobile IP Authentication,
Authorization, and Accounting Requirements". RFC 2977. October
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.
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[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-06.txt, IETF
work in progress, January 2001.
[13] P. Calhoun, W. Bulley, G. Zorn, "Diameter NASREQ Extension",
draft-ietf-aaa-Diameter-nasreq-03.txt, IETF work in progress,
May 2001.
[14] P. Calhoun, C. Perkins, "Diameter Mobile IP Extensions", draft-
ietf-aaa-Diameter-mobileip-03.txt, IETF work in progress, May
2001.
[15] Farrell, Turner, "Reuse of CMS Content Encryption Keys", draft-
ietf-smime-rcek-02.txt, IETF work in progress, May 2001.
[16] Boyen, Howes, Richard, "Internet X.509 Public Key Infrastructure
Operational Protocols - LDAPv2", RFC 2559, April 1999.
11.0 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
12.0 Authors' Addresses
Questions about this memo can be directed to:
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
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Stephen Farrell
Baltimore Technologies
39 Parkgate Street,
Dublin 8,
IRELAND
Phone: +353-1-881-6000
Fax: +353-1-881-7000
E-Mail: stephen.farrell@baltimore.ie
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
13.0 Full Copyright Statement
Copyright (C) The Internet Society (2001). 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 restric-
tion 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 Internet standards in which case
the procedures for copyrights defined in the Internet Standards pro-
cess 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 con-
tained herein is provided on an "AS IS" basis and THE INTERNET
SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL WARRAN-
TIES, 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 2001 [Page 25]
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14.0 Expiration Date
This memo is filed as <draft-ietf-aaa-diameter-e2e-sec-01.txt> and
expires in October 2001.
Calhoun, Bulley, Farrell expires October 2001 [Page 26]
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