RFC2585 - Internet X.509 Public Key Infrastructure Operational Protocols: FTP an

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　　Network Working Group R. Housley
Request for Comments: 2585 SPYRUS
Category: Standards Track P. Hoffman
IMC
May 1999

Internet X.509 Public Key Infrastructure
Operational Protocols: FTP and HTTP

Status of this Memo

This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.

Copyright Notice

Copyright (C) The Internet Society (1999). All Rights Reserved.

Abstract

The protocol conventions described in this document satisfy some of
the operational requirements of the Internet Public Key
Infrastructure (PKI). This document specifies the conventions for
using the File Transfer Protocol (FTP) and the Hypertext Transfer
Protocol (HTTP) to obtain certificates and certificate revocation
lists (CRLs) from PKI repositories. Additional mechanisms addressing
PKIX operational requirements are specified in separate documents.

1 Introduction

This specification is part of a multi-part standard for the Internet
Public Key Infrastructure (PKI) using X.509 certificates and
certificate revocation lists (CRLs). This document specifies the
conventions for using the File Transfer Protocol (FTP) and the
Hypertext Transfer Protocol (HTTP) to obtain certificates and CRLs
from PKI repositories. Additional mechanisms addressing PKI
repository access are specified in separate documents.

1.1. Model

The following is a simplified view of the architectural model assumed
by the Internet PKI specifications.

+---+
| C | +------------+
| e | <-------------------->| End entity |
| r | Operational +------------+
| t | transactions ^
| | and management | Management
| / | transactions | transactions
| | | PKI users
| C | v
| R | -------------------+--+-----------+-----------------
| L | ^ ^
| | | | PKI management
| | v | entities
| R | +------+ |
| e | <---------------------| RA | <---+ |
| p | Publish certificate +------+ | |
| o | | |
| s | | |
| I | v v
| t | +------------+
| o | <------------------------------| CA |
| r | Publish certificate +------------+
| y | Publish CRL ^
| | |
+---+ Management |
transactions |
v
+------+
| CA |
+------+

The components in this model are:

End Entity: user of PKI certificates and/or end user system that is
the subject of a certificate;

CA: certification authority;

RA: registration authority, i.e., an optional system to
which a CA delegates certain management functions;

Repository: a system or collection of distributed systems that store
certificates and CRLs and serves as a means of
distributing these certificates and CRLs to end
entities.

1.2. Certificate and CRL Repository

Some CAs mandate the use of on-line validation services, while others
distribute CRLs to allow certificate users to perform certificate
validation themselves. In general, CAs make CRLs available to
certificate users by publishing them in the Directory. The Directory
is also the normal distribution mechanism for certificates. However,
Directory Services are not available in many parts of the Internet
today. The File Transfer Protocol (FTP) defined in RFC959 and the
Hypertext Transfer Protocol (HTTP) defined in RFC2068 offer
alternate methods for certificate and CRL distribution.

End entities and CAs may retrieve certificates and CRLs from the
repository using FTP or HTTP. End entities may publish their own
certificate in the repository using FTP or HTTP, and RAs and CAs may
publish certificates and CRLs in the repository using FTP or HTTP.

2 FTP Conventions

Within certificate extensions and CRL extensions, the URI form of
GeneralName is used to specify the location where issuer certificates
and CRLs may be obtained. For instance, a URI identifying the
subject of a certificate may be carried in subjectAltName certificate
extension. An IA5String describes the use of anonymous FTP to fetch
certificate or CRL information. For example:

ftp://ftp.netcom.com/sp/spyrus/housley.cer
ftp://ftp.your.org/pki/id48.cer
ftp://ftp.your.org/pki/id48.no42.crl

Internet users may publish the URI reference to a file that contains
their certificate on their business card. This practice is useful
when there is no Directory entry for that user. FTP is widely
deployed, and anonymous FTP are accommodated by many firewalls.
Thus, FTP is an attractive alternative to Directory access protocols
for certificate and CRL distribution. While this service satisfies
the requirement to retrieve information related to a certificate
which is already identified by a URI, it is not intended to satisfy
the more general problem of finding a certificate for a user about
whom some other information, such as their electronic mail address or
corporate affiliation, is known.

For convenience, the names of files that contain certificates should
have a suffix of ".cer". Each ".cer" file contains exactly one
certificate, encoded in DER format. Likewise, the names of files
that contain CRLs should have a suffix of ".crl". Each ".crl" file
contains exactly one CRL, encoded in DER format.

3 HTTP Conventions

Within certificate extensions and CRL extensions, the URI form of
GeneralName is used to specify the location where issuer certificates
and CRLs may be obtained. For instance, a URI identifying the
subject of a certificate may be carried in subjectAltName certificate
extension. An IA5String describes the use of HTTP to fetch
certificate or CRL information. For example:

http://www.netcom.com/sp/spyrus/housley.cer
http://www.your.org/pki/id48.cer
http://www.your.org/pki/id48.no42.crl

Internet users may publish the URI reference to a file that contains
their certificate on their business card. This practice is useful
when there is no Directory entry for that user. HTTP is widely
deployed, and HTTP is accommodated by many firewalls. Thus, HTTP is
an attractive alternative to Directory access protocols for
certificate and CRL distribution. While this service satisfies the
requirement to retrieve information related to a certificate which is
already identified by a URI, it is not intended to satisfy the more
general problem of finding a certificate for a user about whom some
other information, such as their electronic mail address or corporate
affiliation, is known.

For convenience, the names of files that contain certificates should
have a suffix of ".cer". Each ".cer" file contains exactly one
certificate, encoded in DER format. Likewise, the names of files
that contain CRLs should have a suffix of ".crl". Each ".crl" file
contains exactly one CRL, encoded in DER format.

4 MIME registrations

Two MIME types are defined to support the transfer of certificates
and CRLs. They are:

application/pkix-cert
application/pkix-crl

4.1. application/pkix-cert

To: ietf-types@iana.org
Subject: Registration of MIME media type application/pkix-cert

MIME media type name: application

MIME subtype name: pkix-cert

Required parameters: None

Optional parameters: version (default value is "1")

Encoding considerations: will be none for 8-bit transports and most
likely Base64 for SMTP or other 7-bit transports

Security considerations: Carries a cryptographic certificate

Interoperability considerations: None

Published specification: draft-ietf-pkix-ipki-part1

Applications which use this media type: Any MIME-complaint transport

Additional information:
Magic number(s): None
File extension(s): .CER
Macintosh File Type Code(s): none

Person & email address to contact for further information:
Russ Housley <housley@spyrus.com>

Intended usage: COMMON

Author/Change controller:
Russ Housley <housley@spyrus.com>

4.2. application/pkix-crl

To: ietf-types@iana.org
Subject: Registration of MIME media type application/pkix-crl

MIME media type name: application

MIME subtype name: pkix-crl

Required parameters: None

Optional parameters: version (default value is "1")

Encoding considerations: will be none for 8-bit transports and most
likely Base64 for SMTP or other 7-bit transports

Security considerations: Carries a cryptographic certificate
revocation list

Interoperability considerations: None

Published specification: draft-ietf-pkix-ipki-part1

Applications which use this media type: Any MIME-complaint transport

Additional information:
Magic number(s): None
File extension(s): .CRL
Macintosh File Type Code(s): none

Person & email address to contact for further information:
Russ Housley <housley@spyrus.com>

Intended usage: COMMON

Author/Change controller:
Russ Housley <housley@spyrus.com>

References

[RFC959] Postel, J. and J. Reynolds, "File Transfer Protocol (FTP)",
STD 5, RFC959, October 1985.

[RFC1738] Berners-Lee, T., Masinter, L. and M. McCahill, "Uniform
Resource Locators (URL)", RFC1738, December 1994.

[RFC2068] Fielding, R., Gettys, J., Mogul, J., Frystyk, H. and
T. Berners-Lee; "Hypertext Transfer Protocol -- HTTP/1.1",
RFC2068, January 1997.

Security Considerations

Since certificates and CRLs are digitally signed, no additional
integrity service is necessary. Neither certificates nor CRLs need
be kept secret, and anonymous access to certificates and CRLs is
generally acceptable. Thus, no privacy service is necessary.

HTTP caching proxies are common on the Internet, and some proxies do
not check for the latest version of an object correctly. If an HTTP
request for a certificate or CRL goes through a misconfigured or
otherwise broken proxy, the proxy may return an out-of-date response.

Operators of FTP sites and World Wide Web servers should authenticate
end entities who publish certificates as well as CAs and RAs who
publish certificates and CRLs. However, authentication is not
necessary to retrieve certificates and CRLs.

Authors' Addresses

Russell Housley
SPYRUS
381 Elden Street, Suite 1120
Herndon, VA 20170 USA

EMail: housley@spyrus.com

Paul Hoffman
Internet Mail Consortium
127 Segre Place
Santa Cruz, CA 95060 USA

EMail: phoffman@imc.org

Full Copyright Statement

Copyright (C) The Internet Society (1999). All Rights Reserved.

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Acknowledgement

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