Internet Draft Jesse Walker
Expiration: July 2003 Amol Kulkarni
File: draft-ietf-rap-cops-tls-05.txt Intel Corp.
COPS Over TLS
Last Updated: February 6, 2003
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.
Conventions used in this document
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 [RFC-2119].
Abstract
This memo describes how to use TLS to secure COPS connections over
the Internet.
Please send comments on this document to the rap@ops.ietf.org
mailing list.
Walker et al. [Page 1]
Internet Draft COPS Over TLS February 2003
Table of Contents
1 Introduction...................................................3
2 COPS Over TLS..................................................3
3 Separate Ports versus Upward Negotiation........................3
3.1 The COPS/TLS approach.........................................4
3.2.1 The ClientSI object format..................................4
3.2.2 Error Codes and Sub-Codes...................................5
4 Usage Scenarios.................................................5
4.1 Security Required By Client and Server........................5
4.2 Security Required By Client and Optional on Server............5
4.3 Security Optional on Client and Required on Server............6
4.4 Security Optional on Client and Server........................6
4.5 Security Supported by Client but not by Server................6
4.6 Security supported by Server but not by Client................6
4.7 Security not Supported by either Client or Server.............6
5 Secure Connection Initiation....................................6
6 Connection Closure..............................................7
6.1. PEP System Behavior.........................................7
6.2. PDP System Behavior.........................................7
7 Port Number.....................................................8
8 Endpoint Identification and Access Control.....................8
8.1 PDP Identity.................................................8
8.2 PEP Identity.................................................9
9 Other Considerations...........................................10
9.1 Backward Compatibility.......................................10
9.2 IANA Considerations..........................................10
10 Security Considerations......................................10
11 Acknowledgements.............................................10
12 References....................................................10
12.1 Normative References........................................10
12.2 Informative References......................................10
13 Authors' Addresses...........................................11
Walker et al. Expires July 2003 [Page 2]
Internet Draft COPS Over TLS February 2003
1 Introduction
COPS [COPS] was designed to distribute clear-text policy information
from a centralized Policy Decision Point (PDP) to a set of Policy
Enforcement Points (PEP) in the Internet. COPS provides its own
security mechanisms to protect the per-hop integrity of the deployed
policy. However, the use of COPS for sensitive applications such as
some types of security policy distribution requires additional
security measures, such as data privacy. This is because some
organizations find it necessary to hide some or all of their
security policies, e.g., because policy distribution to devices such
as mobile platforms can cross domain boundaries.
TLS [TLS] was designed to provide channel-oriented security. TLS
standardizes SSL and may be used with any connection-oriented
service. TLS provides mechanisms for both one- and two-way
authentication, dynamic session keying, and data stream privacy and
integrity.
This document describes how to use COPS over TLS. "COPS over TLS" is
abbreviated COPS/TLS.
2 COPS Over TLS
COPS/TLS is very simple: use COPS over TLS similar to how you would
use COPS over TCP (COPS/TCP). Apart from a specific procedure used
to initialize the connection, there is no difference between
COPS/TLS and COPS/TCP.
3 Separate Ports versus Upward Negotiation
There are two ways in which insecure and secure versions of the same
protocol can be run simultaneously.
In the first method, the secure version of the protocol is also
allocated a well-known port. This strategy of having well-known port
numbers for both, the secure and insecure versions, is known as
'Separate Ports'. The clients requiring security can simply connect
to the well-known secure port. The main advantage of this strategy
is that it is very simple to implement, with no modifications needed
to existing insecure implementations. Thus it is the most popular
approach. The disadvantage, however, is that it doesn't scale well,
with a new port required for each secure implementation. Hence, the
IESG discourages designers from using the strategy.
The second method is known as 'Upward Negotiation'. In this method,
the secure and insecure versions of the protocol run on the same
port. The client connects to the server, both discover each others'
capabilities, and start security negotiations if desired. This
method usually requires some changes in the protocol being secured
so that it can support the upward negotiation. There is also a high
handshake overhead involved in this method.
Walker et al. Expires July 2003 [Page 3]
Internet Draft COPS Over TLS February 2003
3.1 The COPS/TLS approach
COPS/TLS uses a combination of both these approaches to achieve
simultaneous operation with COPS/TCP. Initially, the authors had
hoped to use the Separate Ports strategy for implementing COPS/TLS,
however, due to the reluctance of the IESG to assign a well-known
port, they settled on the following approach.
When the COPS/TLS server is initialized, it SHOULD bind to any non-
well-known port of its choice. The standard COPS server running over
TCP MUST know the TCP port on which COPS/TLS is running. How this is
achieved is outside the scope of this document.
The system acting as the PEP also acts as the TLS client. It needs
to first connect to the COPS/TCP server, from where it can be
redirected to the COPS/TLS server.
3.2 Object Format and Error Codes
This section describes the ClientSI object sent in the ClientOpen
message and the error codes the server returns.
3.2.1 The ClientSI object format
0 1 2 3
+----------+----------+----------+----------+
| Length (Octets) | C-Num=9 | C-Type=2 |
+----------+----------+----------+----------+
| Protocol | Flags |
+----------+----------+----------+----------+
| : : : |
// : : : //
+----------+----------+----------+----------+
| Protocol | Flags |
+----------+----------+----------+----------+
Protocol:
1 = TLS
Flags:
0 = Protocol Support Optional
1 = Protocol Support Required
This ClientSI object MUST be included with the ClientOpen message
(Client Type = 0) when the client supports security. For each
supported protocol, there MUST be a 32 bit Protocol+Flags pair
appended to the object. At present, only one protocol (TLS) is
described. However, the ClientSI object definition is general enough
to allow addition of new protocols in the future.
Walker et al. Expires July 2003 [Page 4]
Internet Draft COPS Over TLS February 2003
If multiple protocols are supported by the client, it MUST ensure
that no more than one has the 'Protocol Support Required' flag set.
Note that it is also valid to mark all protocols as optional.
3.2.2 Error Codes and Sub-Codes
This section adds to, and modifies, the error codes described in
section 2.2.8 (Error Object) of [COPS].
Error Code: 12 = Redirect to Preferred Server:
Sub-code:
0 = Regular redirect (no security necessary)
1 = Use TLS
Error Code: 16 = Security Failure
17 = Security Required
A new error sub-code has been added to the pre-existing error code
12. The sub-code informs the client that it SHOULD use TLS when
connecting to the redirected server. In the future, more sub-codes
may be added to specify additional protocols.
Error Code 17 MAY be used by either Client or Server if they require
security but the other side doesn't support it.
4 Usage Scenarios
When the client needs to open a secure connection with the server,
it SHOULD first connect to the non-secure port, and send a Client
Open message with a ClientType=0. Included in this message, MUST be
a ClientSI object, which lists the security capabilities of the
client.
The following scenarios occur:
4.1 Security Required By Client and Server
If the server's internal policies allow the client to connect, the
server MUST send a ClientClose message with a Redirect object,
redirecting the client to the COPS/TLS secure port. Additionally,
the error object included in the ClientClose message MUST have the
error code = 12 and sub code = 1.
If the server's internal policies do not allow the client to
connect, the server MUST send a ClientClose with an appropriate
error code.
4.2 Security Required By Client and Optional on Server
If the server's internal policies allow the client to connect
securely, the server MUST send a ClientClose message with a Redirect
object, redirecting the client to the COPS/TLS secure port.
Additionally, the error object included in the ClientClose message
MUST have the error code = 12 and sub code = 1.
Walker et al. Expires July 2003 [Page 5]
Internet Draft COPS Over TLS February 2003
If the server's internal policies do not allow the client to connect
securely, the server MUST send a ClientClose with error code 16 or
another more appropriate error code.
4.3 Security Optional on Client and Required on Server
Depending upon its internal policies, the server MAY send a
ClientClose message with a Redirect object, redirecting the client
to the COPS/TLS secure port.
4.4 Security Optional on Client and Server
Depending upon its internal policies, the server MAY send a
ClientClose message with a Redirect object, redirecting the client
to the COPS/TLS secure port.
Optionally, the server MAY proceed to establish an insecure
connection over COPS/TCP.
4.5 Security Supported by Client but not by Server
If the Client's capabilities specify that security is optional, the
server MAY proceed to establish an insecure connection. Otherwise,
it MUST send a ClientClose with the error code 16.
4.6 Security supported by Server but not by Client
If security is required by the server it MUST send a ClientClose
with the error code 16. If security is optional on the server, it
MAY establish an insecure connection with the client.
4.7 Security not Supported by either Client or Server
This is the regular COPS/TCP case as described in [COPS]. In this
case, only an insecure connection is possible.
5 Secure Connection Initiation
Once the PEP receives a redirect from the COPS/TCP server, it
initiates a connection to the PDP to the secure COPS port. When this
succeeds, the PEP system sends the TLS ClientHello to begin the TLS
handshake. When the TLS handshake completes, the PEP MAY initiate
the first COPS message. All COPS data MUST be sent as TLS
"application data". Normal COPS behavior follows.
All PEP implementations of COPS/TLS MUST support an access control
mechanism to identify authorized PDPs. This requirement provides a
level of assurance that the policy arriving at the PEP is actually
valid. The access control mechanism implemented is outside the scope
of this document. PEP implementations SHOULD require the use of this
access control mechanism for operation of COPS over TLS. When access
control is enabled, the PEP implementation MUST NOT initiate
Walker et al. Expires July 2003 [Page 6]
Internet Draft COPS Over TLS February 2003
COPS/TLS connections to systems not authorized as PDPs by the access
control mechanism.
Similarly, PDP COPS/TLS implementations MUST support an access
control mechanism permitting them to restrict their services to
authorized PEP systems only. However, implementations MUST NOT
require the use of an access control mechanism at the PDP, as
organizations might not consider the types of policy being deployed
as sensitive, and therefore do not need to incur the expense of
managing credentials for the PEP systems. If access controls are
used, however, the PDP implementation MUST terminate COPS/TLS
connections from unauthorized PEP systems and log an error if an
auditable logging mechanism is present.
6 Connection Closure
TLS provides facilities to securely close its connections. Reception
of a valid closure alert assures an implementation that no further
data will arrive on that connection. The TLS specification requires
TLS implementations to initiate a closure alert exchange before
closing a connection. It also permits TLS implementations to close
connections without waiting to receive closure alerts from the peer,
provided they send their own first. A connection closed in this way
is known as an "incomplete close". TLS allows implementations to
reuse the session in this case, but COPS/TLS makes no use of this
capability.
A connection closed without first sending a closure alert is known
as a "premature close". Note that a premature close does not call
into question the security of the data already received, but simply
indicates that subsequent data might have been truncated. Because
TLS is oblivious to COPS message boundaries, it is necessary to
examine the COPS data itself (specifically the Message header) to
determine whether truncation occurred.
6.1. PEP System Behavior
PEP implementations MUST treat premature closes as errors and any
data received as potentially truncated. The COPS protocol allows the
PEP system to find out whether truncation took place. A PEP system
detecting an incomplete close SHOULD recover gracefully.
PEP systems MUST send a closure alert before closing the connection.
Clients unprepared to receive any more data MAY choose not to wait
for the PDP system's closure alert and simply close the connection,
thus generating an incomplete close on the PDP side.
6.2. PDP System Behavior
COPS permits a PEP to close the connection at any time, and requires
PDPs to recover gracefully. In particular, PDPs SHOULD be prepared
to receive an incomplete close from the PEP, since a PEP often shuts
Walker et al. Expires July 2003 [Page 7]
Internet Draft COPS Over TLS February 2003
down for operational reasons unrelated to the transfer of policy
information between the PEP and PDP.
Implementation note: The PDP ordinarily expects to be able to
signal end of data by closing the connection. However, the PEP
may have already sent the closure alert and dropped the
connection.
PDP systems MUST attempt to initiate an exchange of closure alerts
with the PEP system before closing the connection. PDP systems MAY
close the connection after sending the closure alert, thus
generating an incomplete close on the PEP side.
7 Port Number
The first data a PDP expects to receive from the PEP is a Client-
Open message. The first data a TLS server (and hence a COPS/TLS
server) expects to receive is the ClientHello. Consequently,
COPS/TLS runs over a separate port in order to distinguish it from
COPS alone. When COPS/TLS runs over a TCP/IP connection, the TCP
port is any non-well-known port of the PDP's choice. This port MUST
be communicated to the COPS/TCP server running on the well-known
COPS TCP port. The PEP may use any TCP port. This does not preclude
COPS/TLS from running over another transport. TLS only presumes a
reliable connection-oriented data stream.
8 Endpoint Identification and Access Control
Implementations of COPS/TLS MUST use X.509 v3 certificates
conforming to [PKIX] to identify PDP and PEP systems. COPS/TLS
systems MUST perform certificate verification processing conforming
to [PKIX].
If a subjectAltName extension of type dNSName or iPAddress is
present in the PDP's certificate, that MUST be used as the PDP
identity. Otherwise, the most specific Common Name field in the
Subject field of the certificate MUST be used.
Matching is performed using the matching rules specified by [PKIX].
If more than one identity of a given type is present in the
certificate (e.g. more than one dNSName name, a match in any one of
the set is considered acceptable.), the COPS system uses the first
name to match, except as noted below in the IP address checking
requirements. Names may contain the wildcard character * which is
considered to match any single domain name component or component
fragment. For example, *.a.com matches foo.a.com but not
bar.foo.a.com. f*.com matches foo.com but not foo.bar.com.
8.1 PDP Identity
Generally, COPS/TLS requests are generated by the PEP consulting
bootstrap policy information identifying authorized PDPs. As a
consequence, the hostname or IP address for the PDP is known to the
Walker et al. Expires July 2003 [Page 8]
Internet Draft COPS Over TLS February 2003
PEP. How this bootstrap policy information arrives at the PEP is
outside the scope of this document. However, all PEP implementations
MUST provide a mechanism to securely deliver or configure the
bootstrap policy. In particular, all PEP implementations MUST
support a mechanism to securely acquire the signing certificate of
the authorized certificate authorities issuing PDP certificates, and
MUST support a mechanism to securely acquire an access control list
or filter identifying its set of authorized PDPs.
PEP implementations that participate in multiple domains, such as
those on mobile platforms, MAY use different certificate authorities
and access control lists in each domain.
Organizations may choose to deliver some or all of the bootstrap
policy configuration from an untrusted source, such as DHCP. In this
circumstance, COPS over TLS provides no protection from attack when
this untrusted source is compromised.
If the PDP hostname or IP address is available via the access
control mechanism, the PEP MUST check it against the PDP's identity
as presented in the PDP's TLS Certificate message.
In some cases the bootstrap policy will identify the authorized PDP
only by an IP address of the PDP system. In this case, the
subjectAltName MUST be present in the certificate, and it MUST
include an iPAdress format matching the expected name of the policy
server.
If the hostname of the PDP does not match the identity in the
certificate, a PEP on a user oriented system MUST either notify the
user (PEP systems MAY afford the user the opportunity to continue
with the connection in any case) or terminate the connection with a
bad certificate error. PEPs on unattended systems MUST log the error
to an appropriate audit log (if available) and MUST terminate the
connection (with a bad certificate error). Unattended PEP systems
MAY provide a configuration setting that disables this check, but
then MUST provide a setting which enables it.
8.2 PEP Identity
When PEP systems are not access controlled, the PDP need have no
external knowledge of what the PEP's identity ought to be and so
checks are neither possible nor necessary. In this case, there is no
requirement for PEP systems to register with a certificate
authority, and COPS over TLS uses one-way authentication, of the PDP
to the PEP.
When PEP systems are access controlled, PEPs must be PKI clients in
the sense of [PKIX]. In this case, COPS over TLS uses two-way
authentication, and the PDP MUST perform the same identity checks
for the PEPs as described above for the PDP.
Walker et al. Expires July 2003 [Page 9]
Internet Draft COPS Over TLS February 2003
When access controls are in effect at the PDP, PDP implementations
MUST have a mechanism to securely acquire the signing certificates
of the certificate authorities issuing certificates to any of the
PEPs they support.
9 Other Considerations
9.1 Backward Compatibility
The client and server SHOULD be backward compatible with peers that
do not support security. A client SHOULD be able to handle errors
generated by a server which does not understand the ClientSI object
mentioned above. Similarly, if a server receives a ClientOpen for
Client type=0, which does not contain the ClientSI object, it SHOULD
assume that the client wishes to open a non-secure connection and
proceed accordingly.
9.2 IANA Considerations
This draft defines some new error codes and sub codes which require
IANA approval. Section 3.2.2 has more details on these codes.
10 Security Considerations
This entire document concerns security.
11 Acknowledgements
This document freely plagiarizes and adapts Eric Rescorla's similar
document RFC2818 that specifies how HTTP runs over TLS. Discussions
with David Durham, Scott Hahn and Ylian Sainte-Hillaire also lead to
improvements in this document.
12 References
12.1 Normative References
[RFC2026] Bradner, S., "The Internet Standards Process - Revision
3", RFC 2026, October 1996
[RFC2119] Bradner, S., "Key Words for use in RFCs to indicate
Requirement Levels", RFC 2119, March 1997.
[COPS] Durham, D., Boyle, J., Cohen, R., Herzog, R., Rajan, R.,
Sastry, A., "The COPS (Common Open Policy Service) Protocol", RFC
2748, January 200.
[PKIX] Housley, R., Ford, W., Polk, W., Solo, D., "Internet
Public Key Infrastructure: Part I: X.509 Certificate and CRL
Profile", RFC 2459, January 1999.
[TLS] Dierks, T., Allen, C., "The TLS Protocol", RFC2246, January
1999.
12.2 Informative References
Walker et al. Expires July 2003 [Page 10]
Internet Draft COPS Over TLS February 2003
[RFC2818] Rescorla, E., "HTTP Over TLS", RFC2818, May 2000.
13 Authors' Addresses
Jesse R. Walker
Intel Corporation
2111 N.E. 25th Avenue
Hillsboro, OR 97214
USA
jesse.walker@intel.com
Amol Kulkarni
Intel Corporation
JF3-206
2111 N.E. 25th Avenue
Hillsboro, OR 97214
USA
amol.kulkarni@intel.com
Walker et al. Expires July 2003 [Page 11]
