Network Working Group T. Kause
Internet-Draft SSH
Updates: 4210 (if approved) M. Peylo
Intended status: Standards Track NSN
Expires: January 10, 2011 July 09, 2010
Internet X.509 Public Key Infrastructure -- Transport Protocols for CMP
draft-ietf-pkix-cmp-transport-protocols-09.txt
Abstract
This document describes how to layer the Certificate Management
Protocol over various transport protocols. It is the "CMPtrans"
document referenced in RFC 4210 and therefore updates the reference
given therein.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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This Internet-Draft will expire on January 10, 2011.
Copyright Notice
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described in the Simplified BSD License.
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Contributions published or made publicly available before November
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. TCP-Based Management Protocol . . . . . . . . . . . . . . . . 6
3.1. General Form . . . . . . . . . . . . . . . . . . . . . . . 6
3.2. Version . . . . . . . . . . . . . . . . . . . . . . . . . 7
3.2.1. Version Negotiation . . . . . . . . . . . . . . . . . 7
3.2.2. Detection and Interoperation with RFC2510
Conformant Implementations . . . . . . . . . . . . . . 8
3.3. Flags . . . . . . . . . . . . . . . . . . . . . . . . . . 8
3.3.1. Connection Close Flag . . . . . . . . . . . . . . . . 8
3.4. Message-Types . . . . . . . . . . . . . . . . . . . . . . 9
3.4.1. pkiReq . . . . . . . . . . . . . . . . . . . . . . . . 9
3.4.2. pkiRep . . . . . . . . . . . . . . . . . . . . . . . . 10
3.4.3. pollReq . . . . . . . . . . . . . . . . . . . . . . . 10
3.4.4. pollRep . . . . . . . . . . . . . . . . . . . . . . . 11
3.4.5. finRep . . . . . . . . . . . . . . . . . . . . . . . . 11
3.4.6. errorMsgRep . . . . . . . . . . . . . . . . . . . . . 11
3.4.6.1. VersionNotSupported . . . . . . . . . . . . . . . 12
3.4.6.2. GeneralClientError . . . . . . . . . . . . . . . . 13
3.4.6.3. InvalidMessageType . . . . . . . . . . . . . . . . 13
3.4.6.4. InvalidPollID . . . . . . . . . . . . . . . . . . 14
3.4.6.5. GeneralServerError . . . . . . . . . . . . . . . . 14
4. HTTP-Based Protocol . . . . . . . . . . . . . . . . . . . . . 15
4.1. HTTP Versions . . . . . . . . . . . . . . . . . . . . . . 15
4.2. Persistent Connections . . . . . . . . . . . . . . . . . . 15
4.3. General Form . . . . . . . . . . . . . . . . . . . . . . . 15
4.4. Media Type . . . . . . . . . . . . . . . . . . . . . . . . 16
4.5. Communication Workflow . . . . . . . . . . . . . . . . . . 16
4.6. HTTP Request-URI . . . . . . . . . . . . . . . . . . . . . 16
4.7. Announcements . . . . . . . . . . . . . . . . . . . . . . 17
4.7.1. Pushing of Announcements . . . . . . . . . . . . . . . 17
4.7.2. Polling of Announcements . . . . . . . . . . . . . . . 18
4.7.2.1. CA Key Update Announcement . . . . . . . . . . . . 18
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4.7.2.2. Revocation Announcement . . . . . . . . . . . . . 19
4.7.2.3. CRL Announcement . . . . . . . . . . . . . . . . . 19
4.8. HTTP Considerations . . . . . . . . . . . . . . . . . . . 20
4.9. Compatibility Issues with Legacy Implementations . . . . . 20
5. File-Based Protocol . . . . . . . . . . . . . . . . . . . . . 21
6. Mail-Based Protocol . . . . . . . . . . . . . . . . . . . . . 22
7. Security Considerations . . . . . . . . . . . . . . . . . . . 23
8. Information Security Considerations . . . . . . . . . . . . . 24
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 25
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 26
10.1. Normative References . . . . . . . . . . . . . . . . . . . 26
10.2. Informative References . . . . . . . . . . . . . . . . . . 26
Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . . 27
Appendix B. Registration of the application/pkixcmp Media Type . 28
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 30
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1. Introduction
The Certificate Management Protocol (CMP) [RFC4210] requires well
defined transport mechanisms to enable End Entities, RAs and CAs to
pass PKIMessage sequences between them. This document defines the
transport mechanisms which were removed from the main CMP
specification with the second release and referred to be in a
separate document.
The first version of the CMP specification [RFC2510] included a brief
description of a simple TCP-based transport protocol. Its features
are simple transport level error-handling and a mechanism to poll for
outstanding PKI messages. Additionally, it was mentioned that PKI
messages could also be conveyed using file-, E-mail- and HTTP-based
transport.
The current version of the CMP specification incorporated an own
polling mechanism and thus the need for a transport protocol
providing this functionality vanished. The remaining features CMP
requires from its transport protocols are connection- and error-
handling.
During the long time it existed as draft, this RFC was undergoing
drastic changes. The TCP-based transport specification was enhanced
and a TCP-Messages-over-HTTP transport specification appeared. Both
proved to be needless and cumbersome, implementers preferred to use
plain HTTP transport. This specification now aims to reflect that.
HTTP transport is generally easy to implement, traverses network
borders utilizing ubiquitous proxies and is already commonly found in
existing implementations. TCP-based transport is only documented for
information and optional downward compatibility. E-Mail or file
transfer are also mentioned and may be used to convey PKIMessage
sequences - provided that scenarios are identified where they are
better suited than HTTP.
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2. Requirements
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].
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3. TCP-Based Management Protocol
The so-called "TCP-based transport" is OPTIONAL and its use is
deprecated. Its description appears here only for information and
downward compatibility. HTTP-based transport, as described in
Section 4, should be preferred when transporting CMP messages as
defined in [RFC4210]. The reasoning for that is given in Section 1.
While this section is called TCP-based and the messages are called
TCP-Messages, the same protocol can be used over any reliable,
connection oriented transport protocol (e.g. SNA, DECnet, etc.).
This protocol is suitable for cases where an end entity (or an RA)
initiates a transaction and can poll to pick up the results.
The client sends a TCP-Message to the server, and the server responds
with another TCP-Message. A response MUST be sent for every request,
even if the encapsulated CMP message in the request does not have a
corresponding response.
The protocol requires a listener process on an RA or CA which can
accept TCP-Messages on a well-defined port (default TCP port number
is 829). Typically a client initiates the connection to the server
and instantly submits a TCP-Message. The server replies with a TCP-
Message containing either a CMP message or a reference number to be
used later when polling for the actual CMP response message.
If a polling-reference was supplied, the client SHOULD send a polling
request using this polling-reference after waiting for at least the
time specified along with the reference number. The server may again
reply with a new polling-reference or with the actual CMP message
response.
When the final CMP response message has been picked up by the client,
no new polling reference is supplied.
3.1. General Form
The format of a TCP-Message is shown below:
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Version = 10 | Flags | Message-Type | \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ /
\ \
/ Value (variable length) /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Length: 32 bits (unsigned integer)
This field contains the number of remaining octets of the TCP-
Message (i.e. number of octets of the Value field plus 3). All
bit values in this protocol are specified to be in network byte
order.
Version: 8-bits (unsigned integer)
The version of the TCP-Message is 10 in for this document. It
MUST be incremented in each future specification modification
e.g. changing the Flags field in a way that is not fully
backwards compatible.
Flags: 8 bits
TCP-Message specific flags as described in Section 3.3.
Message-Type: 8 bits
A value indicating the type of the TCP-Message.
Value: variable length
Message-type dependent data is stored here. The usage of this
field is described along with the respective message-type
3.2. Version
The TCP-Message version is 10 for this document. The number has
deliberately been chosen to prevent [RFC2510] compliant applications
from treating it as a valid message type. Applications receiving a
version less than 10 SHOULD interpret the message as being an
[RFC2510] style message.
3.2.1. Version Negotiation
If a client knows the protocol version(s) supported by the server
(e.g. from a previous TCP-Message exchange or via some out-of-band
means) then it SHOULD send a TCP-Message with the highest version
supported both by it and the server. If a client does not know what
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version(s) the server supports then it SHOULD send a TCP-Message
using the highest version it supports.
If a server receives a TCP-Message version that it supports, then it
MUST reply with a TCP-Message of the same version. If the version
received is higher than what the server supports, it MUST send back a
VersionNotSupported errorMsgRep containing the highest version it
supports, see Section 3.4.6.
3.2.2. Detection and Interoperation with RFC2510 Conformant
Implementations
Servers wishing to interoperate with clients conforming to [RFC2510]
can do so by treating any received message with a version less than
10 as an [RFC2510] message and responding in that format. Servers
not wishing to support [RFC2510] messages MUST respond with a
[RFC2510] errorMsgRep.
If a client receives a [RFC2510] errorMsgRep (message-type 06)
message, it MAY automatically resend the same request on the same
connection, falling back to the [RFC2510] format; if the received
message is not an errorMsgRep, it MUST terminate the connection. It
MAY then retry the communication falling back completely to the
[RFC2510] format.
Naturally, a client MUST abort the connection attempt if the server
does not support any of the client's supported versions. It SHOULD
retry the version negotiation after a delay to check if the server
was updated.
3.3. Flags
The LSB of the Flags field is used to indicate a connection close;
all other bits in the Flags octet MUST be ignored by receivers, and
MUST be set to zero by senders.
3.3.1. Connection Close Flag
By default connections are kept open after the receipt of a response.
Either party (client or server) MAY set the connection close bit at
any time. If the connection close bit is set on a request, then the
server MUST set the bit in the response and close the connection
after sending the response. If the bit is set on a response from the
server, the client MUST NOT send any further requests on that
connection. Applications MAY decide to close an idle connection (one
on which no response is outstanding) after some time-out. Because of
the problem where a client sends a request and the server closes the
connection while the request is still in flight, clients SHOULD
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automatically retry a request for which no part of the response could
be read due to a connection close or reset.
If the connection is kept open, it MUST only be used for subsequent
request/response transactions started by the client - the server MUST
NOT use it to send requests to the client. Different transactions
may be freely interwoven on the same connection. E.g. a CR/CP need
not immediately be followed by the Confirm, but may be followed by
any other request from a different transaction.
3.4. Message-Types
Message-Types 0-127 are reserved and are to be issued under IANA
auspices. Message-types 128-255 are reserved for application use.
The Message-Types currently defined are:
ID Value Message Name
-------- ------------
'00'H pkiReq
'01'H pollRep
'02'H pollReq
'03'H finRep
'05'H pkiRep
'06'H errorMsgRep
If a server receives an unknown message-type, it MUST reply with an
InvalidMessageType errorMsgRep. If a client receives an unknown
message-type, it MUST abort the current CMP transaction and terminate
the connection.
The different TCP-Message-types are discussed in the following
sections:
3.4.1. pkiReq
A pkiReq message conveys a PKIMessage from a client to a server. The
Value field of this TCP-Message contains a DER-encoded PKIMessage.
The type of PKIMessages that can be carried by pkiReq TCP-Messages
are (in the order they are defined in [RFC4210]):
[0] Initialization Request
[2] Certification Request
[4] PKCS-10 Request
[6] pop Response
[7] Key Update Request
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[9] Key Recovery Request
[11] Revocation Request
[13] Cross-Certification Request
[15] CA Key Update Announcement
[16] Certificate Announcement
[17] Revocation Announcement
[18] CRL Announcement
[20] Nested Message
[21] General Message
[23] Error Message
[24] Certificate Confirmation
[25] Polling Request
3.4.2. pkiRep
TCP-Messages of this type are used to send a response to the
requestor. The Value field of the pkiRep contains a DER encoded
PKIMessage.
The type of PKIMessages that can be carried by such pkiRep messages
are (in the order they are defined in [RFC4210]):
[1] Initialization Response
[3] Certification Response
[5] pop Challenge
[8] Key Update Response
[10] Key Recovery Response
[12] Revocation Response
[14] Cross-Certificate Response
[19] Confirmation
[22] General Response
[23] Error Message
[26] Polling Response
3.4.3. pollReq
A pollReq is used by a client to check the status of a pending TCP-
Message. The Value portion of a pollReq contains:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Polling-Reference |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Polling-Reference: 32 bits (unsigned integer)
This polling-reference MUST be the one returned via the
respective pollRep TCP-Message.
3.4.4. pollRep
A pollRep is sent by the server to the client as response in case
there is no PKIMessage ready yet. The Value portion of the pollRep
looks as follows:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Polling-Reference |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Time-to-Check-Back |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Polling-Reference: 32 bits (unsigned integer)
A unique 32-bit number identifying the transaction.
Time-to-Check-Back: 32 bits (unsigned integer)
The time in seconds indicating the minimum interval after which
the client SHOULD check the status again. The duration for which
the server keeps the polling-reference unique is left to the
implementation.
3.4.5. finRep
A finRep is sent by the server whenever no other response applies,
such as after receiving a CMP pkiConf. The Value portion of the
finRep SHALL contain:
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
| '00'H |
+-+-+-+-+-+-+-+-+
'00'H: 8 bits
All bits set to zero.
3.4.6. errorMsgRep
This TCP-Message is sent when a TCP-Message level protocol error is
detected. It is imperative that PKIError messages MUST NOT be sent
using this message type. Examples of TCP-Message level errors are:
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o Invalid protocol version
o Invalid TCP message-type
o Invalid polling reference number
The Value field of the errorMsgRep TCP-Message MUST contain:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Error-Type | Data-Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ Data (variable length) /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Error-Type: 16 bits A value (format described below) indicating the
type of the error.
Data-Length: 16 bits (unsigned integer) Contains the length of the
Data field in number of octets. Error messages not conveying
additional information MUST set Data-Length to 0.
Data: <data-length> octets
An UTF8 text string for user readable error messages, containing
additional information about the error. Note that it does not
contain a terminating NULL character at the end. It SHOULD
include an [RFC5646] language tag, as described in [RFC2482]
The Error-Type is in the format MMNN where M and N are hex digits
(0-F) and MM represents the major category and NN the minor. The
major categories defined by this specification are:
ID Value Major Categories
-------- ----------------
'01'H TCP-Message version negotiation
'02'H client errors
'03'H server errors
The major categories '80'H-'FF'H are reserved for application use.
The different error-types are discussed in the following sections:
3.4.6.1. VersionNotSupported
The VersionNotSupported errorMsgRep is defined as follows:
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+------------------+------------------------+
| Field | Value |
+------------------+------------------------+
| Error-Type | '0101'H |
| | |
| Data-Length | 1 |
| | |
| Data | <version> |
| | |
| UTF8-text String | implementation defined |
+------------------+------------------------+
where <version> is the highest TCP-Message protocol version the
server supports.
3.4.6.2. GeneralClientError
The GeneralClientError errorMsgRep is defined as follows:
+------------------+------------------------+
| Field | Value |
+------------------+------------------------+
| Error-Type | '0200'H |
| | |
| Data-Length | 0 |
| | |
| Data | <empty> |
| | |
| UTF8-text String | implementation defined |
+------------------+------------------------+
3.4.6.3. InvalidMessageType
The InvalidMessageType errorMsgRep is defined as follows:
+------------------+------------------------+
| Field | Value |
+------------------+------------------------+
| Error-Type | '0201'H |
| | |
| Data-Length | 1 |
| | |
| Data | <message-type> |
| | |
| UTF8-text String | implementation defined |
+------------------+------------------------+
where <message-type> is the invalid Message-Type ID received by the
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server.
3.4.6.4. InvalidPollID
The InvalidPollID errorMsgRep is defined as follows:
+------------------+------------------------+
| Field | Value |
+------------------+------------------------+
| Error-Type | '0202'H |
| | |
| Data-Length | 4 |
| | |
| Data | <polling-reference> |
| | |
| UTF8-text String | implementation defined |
+------------------+------------------------+
where <polling-reference> is the polling-reference received by the
server, identifying the transaction.
3.4.6.5. GeneralServerError
The GeneralServerError errorMsgRep is defined as follows:
+------------------+------------------------+
| Field | Value |
+------------------+------------------------+
| Error-Type | '0300'H |
| | |
| Data-Length | 0 |
| | |
| Data | <empty> |
| | |
| UTF8-text String | implementation defined |
+------------------+------------------------+
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4. HTTP-Based Protocol
For direct interaction between two entities, where a reliable
transport protocol like TCP is available, HTTP SHOULD be utilized for
conveying CMP messages.
With its status codes, HTTP provides needed error reporting
capabilities. General problems on the server side as well as those
directly caused by the respective request can be reported to the
client.
As CMP implements a transaction ID, identifying transactions
consisting of more than just a single request/response pair, the
statelessness of HTTP is not blocking its usage as transport protocol
for CMP messages.
4.1. HTTP Versions
Either HTTP/1.0 as described in [RFC1945] or HTTP/1.1 as in [RFC2616]
MAY be used. Naturally, the newer version should be preferred. To
support legacy implementations, both server and client MUST be able
to interact with counterparts utilizing the other HTTP protocol
version.
4.2. Persistent Connections
HTTP permits to reuse a connection for subsequent requests.
Implementations may use this functionality for messages within the
same transaction but MUST NOT rely on that, as e.g. intermediate HTTP
proxies might terminate the connection after each request/response
pair.
In contrast to HTTP/1.1, persistent connections are explicitly
negotiated in HTTP/1.0. To avoid the problems described in chapter
19.6.2 in [RFC2616], HTTP/1.0 implementations must not send Keep-
Alive when talking to proxies.
4.3. General Form
An ASN.1 DER-encoded PKIMessage is sent as the entity-body of an HTTP
POST request. If this HTTP request is successful, the server returns
the CMP reply in the body of the HTTP response. The response status
code in this case MUST be 200; other 2xx codes MUST NOT be used for
this purpose. The HTTP responses with empty message body to CMP
Announcement messages also utilize the status codes 201 and 202 to
identify if the information was properly processed.
Note that a server may return any 1xx, 3xx, 4xx, or 5xx status code
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if the HTTP request needs further handling or is otherwise not
acceptable.
4.4. Media Type
The Internet Media Type "application/pkixcmp" MUST be set in the HTTP
header when conveying a PKIMessage.
4.5. Communication Workflow
In CMP most communication is initiated by the end entities where
every CMP request triggers a CMP response message from the CA or RA.
The CMP Announcement messages described in Section 4.7 are an
exception. Their creation may be triggered by events or generated on
a regular basis by a CA. The recipient of the Announcement only
replies with an HTTP status code acknowledging the receipt or
indicating an error but not with a CMP response.
The receipt of every HTTP message is confirmed by the counterpart
using HTTP means or it MUST be assumed by the sender that it was not
successfully delivered to its destination.
4.6. HTTP Request-URI
The Request-URI is formed as specified in [RFC3986].
Client requests containing a PKI message MUST be directed to an
Request-URI depicting a directory. A server implementation MUST
handle Request-URIs with or without a trailing slash as identical.
The following list contains all such CMP message types. The prefixed
numbers reflect ASN.1 numbering of the respective element.
[0] Initialization Request
[2] Certification Request
[4] PKCS-10 Request
[6] pop Response
[7] Key Update Request
[9] Key Recovery Request
[11] Revocation Request
[13] Cross-Certification Request
[15] CA Key Update Announcement
[16] Certificate Announcement
[17] Revocation Announcement
[18] CRL Announcement
[20] Nested Message
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[21] General Message
[23] Error Message
[24] Certificate Confirmation
[25] Polling Request
An example of a Request-Line and a Host header field in an HTTP/1.1
header, sending a CMP request to a server, located in the "/cmp"
directory of the host example.com, would be
POST /cmp HTTP/1.1
Host: example.com
or in the absoluteURI form
POST http://example.com/cmp/ HTTP/1.1
Host: example.com
A CMP server may be logically located either inside the root- or
within subdirectories of an HTTP server. As default, the path should
end in a "cmp" directory.
4.7. Announcements
A CMP server may create event-triggered announcements or generate
them on a regular basis. It MAY also utilize HTTP transport to
convey them to a suitable recipient. They can either be pushed to
the recipient or polled from the HTTP CMP server.
4.7.1. Pushing of Announcements
The ASN.1 encoded structures are sent as the entity-body of an HTTP
POST request.
Suitable recipients for CMP announcements might e.g. be repositories
storing the announced information such as directory services. Those
listen for incoming messages, utilizing the same HTTP Request-URI
scheme as defined in Section 4.6.
The following PKIMessages are announcements that may be pushed by a
CA. The prefixed numbers reflect ASN.1 numbering of the respective
element.
[15] CA Key Update Announcement
[16] Certificate Announcement
[17] Revocation Announcement
[18] CRL Announcement
CMP announcement messages do not require any CMP response. However,
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the recipient MUST acknowledge receipt with a HTTP message having an
appropriate status code and an empty body. The sending side should
assume the delivery unsuccessful without such reply and retry if
applicable after waiting for an appropriate time span.
If the announced issue was successfully stored in a database or was
already present, the answer MUST be an HTTP message with a "201
Created" status code and empty message body.
In case the announced issue was only stored for further processing,
the status code of the returned HTTP message must be "202 Accepted".
After an appropriate delay, the server may then try to send the
Announcement again and may repeat this until it receives a
confirmation that it had been successfully stored. The appropriate
duration of the delay and the option to increase it between
consecutive attempts should be carefully considered.
A receiver MUST answer with a suitable 4xx or 5xx HTTP error code
when a problem occurs.
4.7.2. Polling of Announcements
As an OPTIONAL feature a CA may provide CA Key Update Announcement,
Revocation Announcement and CRL Announcement messages for polling
using HTTP GET requests.
The server replies with the requested Announcement as the body of a
HTTP response having a 200 status code. If no suitable announcement
message is available, an HTTP "404 Not Found" error code MUST be
returned.
Query components are formed according to [RFC3986]. Their start is
indicated by the first question mark in the Request-URI and they are
containing "key=value" pairs. Hexadecimal representations of ASN.1
strings used as value MAY contain lower or upper case letters and are
neither grouped nor prefixed.
The given examples are for a self-signed certificate with the common
name (OID 2.5.4.3) "Example CA", the keyIdentifier in hexadecimal
representation BE911E711EDB685BF94D9B176A1BC715CE51D794 and the
serial number 008F8B7E383D88327C.
4.7.2.1. CA Key Update Announcement
When updating its key pair, a CA can produce a CA Key Update
Announcement Message that can be made available to the relevant end
entities. This is described as "Root CA Key Update" in E.4 of
[RFC4210].
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A CMP server may provide this message via an HTTP GET request for the
CAKeyUpdAnn.PKI file in the respective server's path. The
identification of the old key in question is created according to the
Authority Key Identifier as defined in chapter 4.2.1.1 of [RFC5280].
The query component then cosists of one single "key=value" pair,
having the string "AuthorityKeyIdentifier" as key, and the
hexadecimal representation of the ASN.1 AuthorityKeyIdentifier
sequence as value.
An example of the query component, when requesting a CA Key Update
Announcement Message for an old key identified with the
AuthorityKeyIdentifier 303C8014BE911E711EDB685BF94D9B176A1BC715CE51D7
94A119A4173015311330110603550403130A4578616D706C652043418209008F8B7E3
83D88327C
?AuthorityKeyIdentifier=303C8014BE911E711EDB685BF94D9B176A1BC715CE
51D794A119A4173015311330110603550403130A4578616D706C65204341820900
8F8B7E383D88327C
4.7.2.2. Revocation Announcement
A CMP server MAY permit subjects to poll for a Revocation
Announcement using HTTP means. This enables a subject to determine
if its certificate is about to be (or has been) revoked.
The Request-URI of the HTTP GET targets the RevAnn.PKI file in the
respective server's path. The query component contains two
"key=value" pairs identifying the certificate in question:
o an "issuer" key with the hexadecimal representation of the
certificate's issuer's GeneralNames ASN.1 sequence as value
o a "serialNumber" key with the hexadecimal representation of the
certificate's serial number
An example of the query component, when requesting a Revocation
Announcement of a certificate issued by "Example CA" having the
decimal serialNumber 6699 would be:
?issuer=3015311330110603550403130A4578616D706C65204341&
serialNumber=1A2B
4.7.2.3. CRL Announcement
A CMP server MAY offer the possibility to poll for the latest CRL
Announcement of a specific CA.
The Request-URI targets the CRLAnn.PKI file. The query component
consists of one one "key=value" pair containing an "issuer" key with
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the hexadecimal representation of the CA's GeneralNames' ASN.1
sequence as value.
An example of a Request-URI for the latest CRL Announcement of
"Example CA" from a CMP server located in the "/cmp" directory of the
host example.com would be
http://example.com/cmp/
CRLAnn.PKI?issuer=3015311330110603550403130A4578616D706C65204341
4.8. HTTP Considerations
In general, CMP messages are not cachable; requests and responses
MUST include a "Cache-Control: no-cache" (and, if either side uses
HTTP/1.0, a "Pragma: no-cache") to prevent the client from getting
cached responses.
Connection management is based on the HTTP provided mechanisms
(Connection and Proxy-Connection header fields).
While an implementation MAY make use of all defined features of the
HTTP protocol, it SHOULD keep the protocol utilization as simple as
possible.
There is no need for the clients to send an Expect request-header
field with the "100-continue" expectation and wait for a 100
(Continue) status as described in chapter 8.2.3 of [RFC2616]. The
CMP payload sent by a client is relatively small, so having extra
messages exchanged is more inefficient as the server will anyway only
seldomly reject the message without looking at the body.
Content codings MAY be applied.
4.9. Compatibility Issues with Legacy Implementations
As this document was subject of multiple changes during the long
period of time it was created in, implementations using a different
approach for HTTP transport may exist. While only those
implementations according to this specification are compliant,
implementers should to be aware that there might be existing ones
which behave differently.
Legacy implementations might also use an unregistered "application/
pkixcmp-poll" MIME type as it was specified in earlier drafts of this
document. Here, the entity-body of an HTTP POST request contains a
TCP-Message instead of a plain DER-encoded PKIMessage. Effectively,
this is conveying PKIMessage over TCP-Message over HTTP.
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5. File-Based Protocol
A file containing a PKIMessage MUST contain only the DER encoding of
one PKIMessage, there MUST NOT be extraneous header or trailer
information in the file.
Such files can be used to transport PKIMessage sequences using e.g.
FTP.
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6. Mail-Based Protocol
This subsection specifies a means for conveying ASN.1-encoded
messages for the protocol exchanges via Internet mail [RFC5321]. A
simple MIME object is specified as follows.
Content-Type: application/pkixcmp
Content-Transfer-Encoding: base64
<<the ASN.1 DER-encoded PKIX-CMP message, base64-encoded>>
This MIME object can be sent and received using common MIME
processing engines and provides a simple Internet mail transport for
PKIX-CMP messages. Implementations MAY wish to also recognize and
use the "application/x-pkixcmp" MIME type (specified in earlier
versions of this document) in order to support backward compatibility
wherever applicable.
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7. Security Considerations
Four aspects need to be considered by server side implementers:
1. There is the risk for denial of service attacks through resource
consumption by opening many connections, therefore idle
connections should be terminated after an appropriate timeout,
maybe also depending on the available free resources. After
sending a CMP Error Message, the server should close the
connection even if the CMP transaction is not yet fully
completed.
2. There is no security at the TCP and HTTP protocol level (unless
tunneled via SSL/TLS) and thus information from TCP-Messages or
the HTTP protocol SHOULD NOT be used to change state of the
transaction. Change of state SHOULD be triggered by the signed
PKIMessages which are carried within the TCP-Message.
3. If the server is going to be sending messages with sensitive
information (not meant for public consumption) in the clear, it
is RECOMMENDED that the server sends back the message directly
and not use the TCP-Message pollRep.
4. The TCP-Message polling request/response mechanism can be used
for all kinds of denial of service attacks. It is RECOMMENDED
that a server does not change the polling-reference between
polling requests.
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8. Information Security Considerations
CMP provides inbuilt integrity protection and authentication. Due to
the nature of a PKI, from a security perspective the information
communicated unencrypted does not contain sensitive information.
However, it might be possible for an interceptor to utilize the
available information to gather confidential technical or business
critical information. Therefore, users of the HTTP CMP transport
might want to use HTTP over TLS according to [RFC2818] or should
consider to use virtual private networks created e.g. utilizing
Internet Protocol Security according to [RFC4301].
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9. IANA Considerations
The IANA has already registered TCP and UDP port 829 for "PKIX-3
CA/RA" and the MIME media type "application/pkixcmp" for identifying
CMP sequences.
No further action by the IANA is necessary for this document or any
anticipated updates.
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10. References
10.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, January 2005.
[RFC4210] Adams, C., Farrell, S., Kause, T., and T. Mononen,
"Internet X.509 Public Key Infrastructure Certificate
Management Protocol (CMP)", RFC 4210, September 2005.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, May 2008.
[RFC5321] Klensin, J., "Simple Mail Transfer Protocol", RFC 5321,
October 2008.
[RFC5646] Phillips, A. and M. Davis, "Tags for Identifying
Languages", BCP 47, RFC 5646, September 2009.
10.2. Informative References
[RFC1945] Berners-Lee, T., Fielding, R., and H. Nielsen, "Hypertext
Transfer Protocol -- HTTP/1.0", RFC 1945, May 1996.
[RFC2482] Whistler, K. and G. Adams, "Language Tagging in Unicode
Plain Text", RFC 2482, January 1999.
[RFC2510] Adams, C. and S. Farrell, "Internet X.509 Public Key
Infrastructure Certificate Management Protocols",
RFC 2510, March 1999.
[RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000.
[RFC4301] Kent, S. and K. Seo, "Security Architecture for the
Internet Protocol", RFC 4301, December 2005.
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Appendix A. Acknowledgments
Until the fifth draft version of this document, released in November
24th 2000, the sole authors were Amit Kapoor and Ronald Tschlaer from
Certicom. Up to this point, besides editorial changes, the now
deprecated TCP-Based transport was described as it is still included
herein. They are not available for this working on this document
anymore at the time it is entering the "Authors Final Review state
AUTH48". As they therefore cannot approve this document as it would
be necessary, their names were moved to this section. Their contact
data, as originally stated by them, is as follows:
Amit Kapoor
Certicom
25801 Industrial Blvd
Hayward, CA
US
Email: amit@trustpoint.com
Ronald Tschalaer
Certicom
25801 Industrial Blvd
Hayward, CA
US
Email: ronald@trustpoint.com
The authors gratefully acknowledge the contributions of various
members of the IETF PKIX Working Group and the ICSA CA-talk mailing
list (a list solely devoted to discussing CMP interoperability
efforts).
By providing ideas, giving hints and doing invaluable review work,
the following individuals, listed alphabetically, have significantly
contributed to this document:
Tomas Gustavsson, Primekey
Peter Gutmann, University of Auckland
Wolf-Dietrich Moeller, Nokia Siemens Networks
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Appendix B. Registration of the application/pkixcmp Media Type
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To: ietf-types@iana.org
Subject: Registration of MIME media type application/pkixcmp
MIME media type name: application
MIME subtype name: pkixcmp
Required parameters: -
Optional parameters: -
Encoding considerations:
Content may contain arbitrary octet values (the ASN.1 DER encoding
of a PKIMessage sequence, as defined in the IETF PKIX Working Group
specifications). base64 encoding is required for MIME e-mail; no
encoding is necessary for HTTP.
Security considerations:
This MIME type may be used to transport Public-Key Infrastructure
(PKI) messages between PKI entities. These messages are defined by
the IETF PKIX Working Group and are used to establish and maintain
an Internet X.509 PKI. There is no requirement for specific
security mechanisms to be applied at this level if the PKI messages
themselves are protected as defined in the PKIX specifications.
Interoperability considerations: -
Published specification: this document
Applications which use this media type: Applications using
certificate management, operational, or ancillary protocols (as
defined by the IETF PKIX Working Group) to send PKI messages via
E-Mail or HTTP.
Additional information:
Magic number (s): -
File extension (s): ".PKI"
Macintosh File Type Code (s): -
Person and email address to contact for further information:
Martin Peylo, martin.peylo@nsn.com
Intended usage: COMMON
Author/Change controller: Martin Peylo
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Authors' Addresses
Tomi Kause
SSH Communications Security Corp.
Fredrikinkatu 42
Helsinki 00100
Finland
Email: toka@ssh.com
Martin Peylo
Nokia Siemens Networks
Linnoitustie 6
Espoo 02600
Finland
Email: martin.peylo@nsn.com
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