One document matched: draft-ietf-rap-cops-tls-07.txt
Differences from draft-ietf-rap-cops-tls-06.txt
Internet Draft Jesse Walker
Expiration: May 2004 Amol Kulkarni, Ed.
File: draft-ietf-rap-cops-tls-07.txt Intel Corp.
COPS Over TLS
Last Updated: November 24, 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
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documents at any time. It is inappropriate to use Internet-Drafts
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progress."
The list of current Internet-Drafts can be accessed at
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The list of Internet-Draft Shadow Directories can be accessed at
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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 [RFC2119].
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.
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Table Of Contents
Glossary..........................................................3
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..................................5
3.2.2 Error Codes and Sub-Codes...................................5
4 Usage Scenarios.................................................6
4.1 Security Mandatory on both, Client and Server.................6
4.2 Security Mandatory on Client and Optional on Server...........7
4.3 Security Optional on Client and Mandatory on Server...........7
4.4 Security Optional on both, Client and Server..................7
4.5 Security Mandatory on Client but not supported by Server......7
4.6 Security Optional on Client but not supported by Server.......7
4.7 Security Mandatory on Server but not supported by Client......7
4.8 Security Optional on Server but not supported by Client.......7
5 Secure Connection Initiation....................................7
6 Connection Closure..............................................8
6.1. PEP System Behavior.........................................8
6.2. PDP System Behavior.........................................9
7 Port Number.....................................................9
8 Endpoint Identification and Access Control.....................9
8.1 PDP Identity................................................10
8.2 PEP Identity................................................11
9 Other Considerations...........................................11
9.1 Backward Compatibility.......................................11
9.2 IANA Considerations..........................................11
10 Security Considerations......................................11
11 Acknowledgements.............................................11
12 References....................................................12
12.1 Normative References........................................12
12.2 Informative References......................................12
13 Author Addresses.............................................12
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Glossary
COPS - Common Open Policy Service. See [RFC2748].
COPS/TCP - A plain-vanilla implementation of COPS.
COPS/TLS - A secure implementation of COPS using TLS.
PDP - Policy Decision Point. Also referred to as the Policy
Server. See [RFC2753].
PEP - Policy Enforcement Point. Also referred to as the Policy
Client. See [RFC2753].
1 Introduction
COPS [RFC2748] 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 [RFC2246] 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,
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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.
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.
During the initial negotiation with the COPS/TCP server, the Message
Integrity Object MUST be used to authenticate the validity of the
COPS messages. As specified in [RFC2748], the integrity object
contains a sequence number, a Key Id and a message digest. The
sequence number is used to foil replay attacks while the Key Id
identifies a secret key shared between the client and the server.
COPS uses the HMAC-MD5-96 algorithm to generate a digest of the
entire COPS message, up to and including the sequence number and Key
Id.
The specifics of key distribution and maintenance are outside the
scope of this document.
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.
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3.2.1 The ClientSI object format
0 1 2 3
+----------+----------+----------+----------+
| Length (Octets) | C-Num=9 | C-Type=1 |
+----------+----------+----------+----------+
| 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.
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. This
is used by the client to notify the server that a secure connection
is not mandatory.
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 [RFC2748].
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.
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Error Code 17 SHOULD 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.
'Bootstrap' policies implemented on the client dictate whether
security is mandatory or optional.
If the policies specify that security is mandatory, the above-
mentioned ClientSI object MUST be included in the Client Open
message. This object MUST list one protocol as Required by setting
the corresponding flag to 1.
If the policies do not explicitly specify that a secure connection
is required, the client SHOULD include the ClientSI object, listing
protocol support as Optional.
Note that if the client's policies specifically prohibit a secure
connection, it MAY attempt to establish an insecure connection.
Based on the client's policies and the server's policy requirements
for the client, a number of usage scenarios are possible. The figure
below shows the type of connections established for the scenarios.
The sections following the figure explain the various scenarios in
greater detail.
+---------+------------+------------+-------------+
|\SERVER | | | |
|C\ | | | Security |
|L \ | Security | Security | Not |
|I \ | Mandatory | Optional | Supported |
|E \ | | | |
|N \ | | | |
|T \ | | | |
+---------+------------+------------+-------------+
|Mandatory| Secure | Secure | Disconnect |
+---------+------------+------------+-------------+
|Optional | Secure | Secure / | Insecure |
| | | Insecure | |
+---------+------------+------------+-------------+
|Not | | | |
|Supported| Disconnect | Insecure | Insecure |
+---------+------------+------------+-------------+
4.1 Security Mandatory on both, Client and Server
The server MUST send a ClientClose message with a Redirect object,
redirecting the client to the COPS/TLS secure port. Additionally,
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the error object included in the ClientClose message MUST have the
error code = 12 and sub code = 1.
4.2 Security Mandatory on Client and Optional on Server
The server SHOULD 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 does not redirect the client to the secure port, it
MUST send a ClientClose with the error code 16.
4.3 Security Optional on Client and Mandatory on Server
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.
4.4 Security Optional on both, Client and Server
The server SHOULD 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.
Optionally, the server MAY proceed to establish an insecure
connection over COPS/TCP.
4.5 Security Mandatory on Client but not supported by Server
The server MUST send a ClientClose with the error code 16.
4.6 Security Optional on Client but not supported by Server
The server SHOULD attempt to establish a non-secure connection with
the client.
4.7 Security Mandatory on Server but not supported by Client
If security is required by the server it MUST send a ClientClose
with the error code 16.
4.8 Security Optional on Server but not supported by Client
The server it MAY attempt to establish a non-secure connection with
the client.
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
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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. 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
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 MAY choose not
to use 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.
Section 8 provides more details on access control.
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
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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
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 [RFC2459] to identify PDP and PEP systems. COPS/TLS
systems MUST perform certificate verification processing conforming
to [RFC2459]. In case the Certificate Authority cannot be accessed,
the COPS/TLS systems MAY use a Web of Trust to verify the identity,
or the communication MAY revert to insecure.
If a subjectAltName extension of type dNSName or iPAddress is
present in the PDP's certificate, it MUST be used as the PDP
identity. Otherwise, the most specific Common Name field in the
Subject field of the certificate MUST be used.
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Matching is performed using the matching rules specified by
[RFC2459]. 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 that identifies PDPs that the PEP is
authorized to connect to. This policy provides the PEP with the
hostname or IP address of the PDP. 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.
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.
All PEP implementations MUST be able to securely acquire the signing
certificates of authorized Certificate Authorities that issue PDP
certificates. Also, the PEPs MUST support a mechanism to securely
acquire an access control list or filter identifying the CA's set of
authorized PDPs.
PEP implementations that participate in multiple domains, such as
those on mobile platforms, MAY use different CAs and access control
lists in each domain.
If the PDP hostname or IP address is available via the bootstrap
policy, 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
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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 [RFC2459]. 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.
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
have not been modified to support COPS/TLS.
A client SHOULD be able to handle errors generated by a COPS/TCP
server which does not understand the ClientSI object mentioned
above. Similarly, if a COPS/TCP 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.
The authors wish to thank Uri Blumenthal for doing a thorough
security review of the document.
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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.
[RFC2748] Durham, D., Boyle, J., Cohen, R., Herzog, R., Rajan,
R., Sastry, A., "The COPS (Common Open Policy Service) Protocol",
RFC 2748, January 2000.
[RFC2459] Housley, R., Ford, W., Polk, W., Solo, D., "Internet
Public Key Infrastructure: Part I: X.509 Certificate and CRL
Profile", RFC 2459, January 1999.
[RFC2246] Dierks, T., Allen, C., "The TLS Protocol", RFC 2246,
January 1999.
12.2 Informative References
[RFC2818] Rescorla, E., "HTTP Over TLS", RFC2818, May 2000.
13 Author Addresses
Jesse R. Walker
Intel Corporation
2111 N.E. 25th Avenue
Hillsboro, OR 97214
USA
jesse.walker[at]intel.com
Amol Kulkarni
Intel Corporation
JF3-206
2111 N.E. 25th Avenue
Hillsboro, OR 97214
USA
amol.kulkarni[at]intel.com
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