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.

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.

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RFC 2585 PKIX Operational Protocols: FTP and HTTP May 1999

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 |

+------+

| 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;

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RFC 2585 PKIX Operational Protocols: FTP and HTTP May 1999

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 RFC 959 and the

Hypertext Transfer Protocol (HTTP) defined in RFC 2068 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.

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RFC 2585 PKIX Operational Protocols: FTP and HTTP May 1999

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

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RFC 2585 PKIX Operational Protocols: FTP and HTTP May 1999

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

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RFC 2585 PKIX Operational Protocols: FTP and HTTP May 1999

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

[RFC 959] Postel, J. and J. Reynolds, "File Transfer Protocol (FTP)",

STD 5, RFC 959, October 1985.

[RFC 1738] Berners-Lee, T., Masinter, L. and M. McCahill, "Uniform

Resource Locators (URL)", RFC 1738, December 1994.

[RFC 2068] Fielding, R., Gettys, J., Mogul, J., Frystyk, H. and

T. Berners-Lee; "Hypertext Transfer Protocol -- HTTP/1.1",

RFC 2068, 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.

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RFC 2585 PKIX Operational Protocols: FTP and HTTP May 1999

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

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RFC 2585 PKIX Operational Protocols: FTP and HTTP May 1999

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Acknowledgement

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Housley & Hoffman Standards Track [Page 8]