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Keywords: X.509, LDAP, lightweight directory access protocol, IPKI, Internet X.509 Public Key Infrastructure
Network Working Group S. Boeyen
Request for Comments: 2559 Entrust
Updates: 1778 T. Howes
Category: Standards Track Netscape
P. Richard
Xcert
April 1999
Internet X.509 Public Key Infrastructure
Operational Protocols - LDAPv2
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.
1. Abstract
The protocol described in this document is designed to satisfy some
of the operational requirements within the Internet X.509 Public Key
Infrastructure (IPKI). Specifically, this document addresses
requirements to provide access to Public Key Infrastructure (PKI)
repositories for the purposes of retrieving PKI information and
managing that same information. The mechanism described in this
document is based on the Lightweight Directory Access Protocol (LDAP)
v2, defined in RFC 1777, defining a profile of that protocol for use
within the IPKI and updates encodings for certificates and revocation
lists from RFC 1778. Additional mechanisms addressing PKIX
operational requirements are specified in separate documents.
The key words 'MUST', 'REQUIRED', 'SHOULD', 'RECOMMENDED', and 'MAY'
in this document are to be interpreted as described in RFC 2119.
2. Introduction
This specification is part of a multi-part standard for development
of a Public Key Infrastructure (PKI) for the Internet. This
specification addresses requirements to provide retrieval of X.509
PKI information, including certificates and CRLs from a repository.
This specification also addresses requirements to add, delete and
Boeyen, et al. Standards Track [Page 1]
RFC 2559 PKIX Operational Protocols - LDAPv2 April 1999
modify PKI information in a repository. A profile based on the LDAP
version 2 protocol is provided to satisfy these requirements.
3. Model
The PKI components, as defined in PKIX Part 1, which are involved in
PKIX operational protocol interactions include:
- End Entities
- Certification Authorities (CA)
- Repository
End entities and CAs using LDAPv2, retrieve PKI information from the
repository using a subset of the LDAPv2 protocol.
CAs populate the repository with PKI information using a subset of
the LDAPv2 protocol.
4. Lightweight Directory Access Protocol (LDAP)
The following sections examine the retrieval of PKI information from
a repository and management of PKI information in a repository. A
profile of the LDAPv2 protocol is defined for providing these
services.
Section 5 satisfies the requirement to retrieve PKI information (a
certificate, CRL, or other information of interest) from an entry in
the repository, where the retrieving entity (either an end entity or
a CA) has knowledge of the name of the entry. This is termed
"repository read".
Section 6 satisfies the same requirement as 5 for the situation where
the name of the entry is not known, but some other related
information which may optionally be used as a filter against
candidate entries in the repository, is known. This is termed
"repository search".
Section 7 satisfies the requirement of CAs to add, delete and modify
PKI information information (a certificate, CRL, or other information
of interest)in the repository. This is termed "repository modify".
The subset of LDAPv2 needed to support each of these functions is
described below. Note that the repository search service is a
superset of the repository read service in terms of the LDAPv2
functionality needed.
Note that all tags are implicit by default in the ASN.1 definitions
that follow.
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RFC 2559 PKIX Operational Protocols - LDAPv2 April 1999
5. LDAP Repository Read
To retrieve information from an entry corresponding to the subject or
issuer name of a certificate, requires a subset of the following
three LDAP operations:
BindRequest (and BindResponse)
SearchRequest (and SearchResponse)
UnbindRequest
The subset of each REQUIRED operation is given below.
5.1. Bind
5.1.1. Bind Request
The full LDAP v2 Bind Request is defined in RFC 1777.
An application providing a LDAP repository read service MUST
implement the following subset of this operation:
BindRequest ::=
[APPLICATION 0] SEQUENCE {
version INTEGER (2),
name LDAPDN, -- MUST accept NULL LDAPDN
simpleauth [0] OCTET STRING -- MUST accept NULL simple
}
An application providing a LDAP repository read service MAY implement
other aspects of the BindRequest as well.
Different services may have different security requirements. Some
services may allow anonymous search, others may require
authentication. Those services allowing anonymous search may choose
only to allow search based on certain criteria and not others.
A LDAP repository read service SHOULD implement some level of
anonymous search access. A LDAP repository read service MAY implement
authenticated search access.
5.1.2. Bind Response
The full LDAPv2 BindResponse is described in RFC 1777.
An application providing a LDAP repository read service MUST
implement this entire protocol element, though only the following
error codes may be returned from a Bind operation:
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RFC 2559 PKIX Operational Protocols - LDAPv2 April 1999
success (0),
operationsError (1),
protocolError (2),
authMethodNotSupported (7),
noSuchObject (32),
invalidDNSyntax (34),
inappropriateAuthentication (48),
invalidCredentials (49),
busy (51),
unavailable (52),
unwillingToPerform (53),
other (80)
5.2. Search
5.2.1. Search Request
The full LDAPv2 SearchRequest is defined in RFC 1777.
An application providing a LDAP repository read service MUST
implement the following subset of the SearchRequest.
SearchRequest ::=
[APPLICATION 3] SEQUENCE {
baseObject LDAPDN,
scope ENUMERATED {
baseObject (0),
},
derefAliases ENUMERATED {
neverDerefAliases (0),
},
sizeLimit INTEGER (0),
timeLimit INTEGER (0),
attrsOnly BOOLEAN, -- FALSE only
filter Filter,
attributes SEQUENCE OF AttributeType
}
Filter ::=
CHOICE {
present [7] AttributeType, -- "objectclass" only
}
This subset of the LDAPv2 SearchRequest allows the LDAPv2 "read"
operation: a base object search with a filter testing for the
existence of the objectClass attribute.
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An application providing a LDAP repository read service MAY implement
other aspects of the SearchRequest as well.
5.2.2.
The full LDAPv2 SearchResponse is defined in RFC 1777.
An application providing a LDAP repository read service over LDAPv2
MUST implement the full SearchResponse.
Note that in the case of multivalued attributes such as
userCertificate a SearchResponse containing this attribute will
include all values, assuming the requester has sufficient access
permissions. The application/relying party may need to select an
appropriate value to be used. Also note that retrieval of a
certificate from a named entry does not guarantee that the
certificate will include that same Distinguished Name (DN) and in
some cases the subject DN in the certificate may be NULL.
5.3. Unbind
The full LDAPv2 UnbindRequest is defined in RFC 1777.
An application providing a LDAP repository read service MUST
implement the full UnbindRequest.
6. LDAP Repository Search
To search, using arbitrary criteria, for an entry in a repository
containing a certificate, CRL, or other information of interest,
requires a subset of the following three LDAP operations:
BindRequest (and BindResponse)
SearchRequest (and SearchResponse)
UnbindRequest
The subset of each operation REQUIRED is given below.
6.1. Bind
The BindRequest and BindResponse subsets needed are the same as those
described in Section 5.1.
The full LDAP v2 Bind Request is defined in RFC 1777.
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6.2. Search
6.2.1. Search Request
The full LDAPv2 SearchRequest is defined in RFC 1777.
An application providing a LDAP repository search service MUST
implement the following subset of the SearchRequest protocol unit.
SearchRequest ::=
[APPLICATION 3] SEQUENCE {
baseObject LDAPDN,
scope ENUMERATED {
baseObject (0),
singleLevel (1),
wholeSubtree (2)
},
derefAliases ENUMERATED {
neverDerefAliases (0),
},
sizeLimit INTEGER (0 .. maxInt),
timeLimit INTEGER (0 .. maxInt),
attrsOnly BOOLEAN, -- FALSE only
filter Filter,
attributes SEQUENCE OF AttributeType
}
All aspects of the SearchRequest MUST be supported, except for the
following:
- Only the neverDerefAliases value of derefAliases needs to be
supported
- Only the FALSE value for attrsOnly needs to be supported
This subset provides a more general search capability. It is a
superset of the SearchRequest subset defined in Section 5.2.1. The
elements added to this service are:
- singleLevel and wholeSubtree scope needs to be supported
- sizeLimit is included
- timeLimit is included
- Enhanced filter capability
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An application providing a LDAP repository search service MAY
implement other aspects of the SearchRequest as well.
6.2.2. Search Response
The full LDAPv2 SearchResponse is defined in RFC 1777.
An application providing a LDAP repository search service over LDAPv2
MUST implement the full SearchResponse.
6.3. Unbind
An application providing a LDAP repository search service MUST
implement the full UnbindRequest.
7. LDAP Repository Modify
To add, delete and modify PKI information in a repository requires a
subset of the following LDAP operations:
BindRequest (and BindResponse)
ModifyRequest (and ModifyResponse)
AddRequest (and AddResponse)
DelRequest (and DelResponse
UnbindRequest
The subset of each operation REQUIRED is given below.
7.1. Bind
The full LDAP v2 Bind Request is defined in RFC 1777.
An application providing a LDAP repository modify service MUST
implement the following subset of this operation:
BindRequest ::=
[APPLICATION 0] SEQUENCE {
version INTEGER (2),
name LDAPDN,
simpleauth [0] OCTET STRING
}
A LDAP repository modify service MUST implement authenticated access.
The BindResponse subsets needed are the same as those described in
Section 5.1.2.
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7.2. Modify
7.2.1. Modify Request
The full LDAPv2 ModifyRequest is defined in RFC 1777.
An application providing a LDAP repository modify service MUST
implement the following subset of the ModifyRequest protocol unit.
ModifyRequest ::=
[APPLICATION 6] SEQUENCE {
object LDAPDN,
modification SEQUENCE OF SEQUENCE {
operation ENUMERATED {
add (0),
delete (1)
},
modification SEQUENCE {
type AttributeType,
values SET OF
AttributeValue
}
}
}
All aspects of the ModifyRequest MUST be supported, except for the
following:
- Only the add and delete values of operation need to be supported
7.2.2. Modify Response
The full LDAPv2 ModifyResponse is defined in RFC 1777.
An application providing a LDAP repository modify service MUST
implement the full ModifyResponse.
7.3. Add
7.3.1. Add Request
The full LDAPv2 AddRequest is defined in RFC 1777.
An application providing a LDAP repository modify service MUST
implement the full AddRequest.
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7.3.2. Add Response
The full LDAPv2 AddResponse is defined in RFC 1777.
An application providing a LDAP repository modify service MUST
implement the full AddResponse.
7.4. Delete
7.4.1. Delete Request
The full LDAPv2 DelRequest is defined in RFC 1777.
An application providing a LDAP repository modify service MUST
implement the full DelRequest.
7.4.2. Delete Response
The full LDAPv2 DelResponse is defined in RFC 1777.
An application providing a LDAP repository modify service MUST
implement the full DelResponse.
7.5. Unbind
An application providing a LDAP repository modify service MUST
implement the full UnbindRequest.
8. Non-standard attribute value encodings
When conveyed in LDAP requests and results, attributes defined in
X.500 are to be encoded using string representations defined in RFC
1778, The String Representation of Standard Attribute Syntaxes.
These string encodings were based on the attribute definitions from
X.500(1988). Thus, the string representations of the PKI information
elements are for version 1 certificates and version 1 revocation
lists. Since this specification uses version 3 certificates and
version 2 revocation lists, as defined in X.509(1997), the RFC 1778
string encoding of these attributes is inappropriate.
For this reason, these attributes MUST be encoded using a syntax
similar to the syntax "Undefined" from section 2.1 of RFC 1778:
values of these attributes are encoded as if they were values of type
"OCTET STRING", with the string value of the encoding being the DER-
encoding of the value itself. For example, when writing a
userCertificate to the repository, the CA generates a DER-encoding of
the certificate and uses that encoding as the value of the
userCertificate attribute in the LDAP Modify request.This encoding
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RFC 2559 PKIX Operational Protocols - LDAPv2 April 1999
style is consistent with the encoding scheme proposed for LDAPv3,
which is now being defined within the IETF.
Note that certificates and revocation lists will be transferred using
this mechanism rather than the string encodings in RFC 1778 and
client systems which do not understand this encoding may experience
problems with these attributes.
9. Transport
An application providing a LDAP repository read service, LDAP
repository search service, or LDAP repository modify service MUST
support LDAPv2 transport over TCP, as defined in Section 3.1 of RFC
1777.
An application providing a LDAP repository read service, LDAP
repository search service, or LDAP repository modify service MAY
support LDAPv2 transport over other reliable transports as well.
10. Security Considerations
Since the elements of information which are key to the PKI service
(certificates and CRLs) are both digitally signed pieces of
information, additional integrity service is NOT REQUIRED. As
neither information element need be kept secret and anonymous access
to such information, for retrieval purposes is generally acceptable,
privacy service is NOT REQUIRED for information retrieval requests.
CAs have additional requirements, including modification of PKI
information. Simple authentication alone is not sufficient for these
purposes. It is RECOMMENDED that some stronger means of
authentication and/or (if simple authentication is used) some means
of protecting the privacy of the password is used, (e.g. accept
modifications only via physically secure networks, use IPsec, use SSH
or TLS or SSL tunnel). Without such authentication, it is possible
that a denial-of-service attack could occur where the attacker
replaces valid certificates with bogus ones.
For the LDAP repository modify service, profiled in section 7, there
are some specific security considerations with respect to access
control. These controls apply to a repository which is under the same
management control as the CA. Organizations operating directories are
NOT REQUIRED to provide external CAs access permission to their
directories.
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The CA MUST have access control permissions allowing it to:
For CA entries:
- add, modify and delete all PKI attributes for its own
directory entry;
- add, modify and delete all values of these attributes.
For CRL distribution point entries (if used):
- create, modify and delete entries of object class
cRLDistributionPoint immediately subordinate to its own
entry;
- add, modify and delete all attributes, and all values of
these attributes for these entries.
For subscriber (end-entity) entries:
- add, modify and delete the attribute userCertificate and all
values of that attribute, issued by this CA to/from these
entries.
The CA is the ONLY entity with these permissions.
An application providing LDAP repository read, LDAP repository
search, or LDAP repository modify service as defined in this
specification is NOT REQUIRED to implement any additional security
features other than those described herein, however an implementation
SHOULD do so.
11. References
[1] Yeong, Y., Howes, T. and S. Kille, "Lightweight Directory Access
Protocol", RFC 1777, March 1995.
[2] Howes, T., Kille, S., Yeong, W. and C. Robbins, "The String
Representation of Standard Attribute Syntaxes", RFC 1778, March
1995.
[3] Bradner, S., "Key Words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
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12. Authors' Addresses
Sharon Boeyen
Entrust Technologies Limited
750 Heron Road
Ottawa, Ontario
Canada K1V 1A7
EMail: sharon.boeyen@entrust.com
Tim Howes
Netscape Communications Corp.
501 E. Middlefield Rd.
Mountain View, CA 94043
USA
EMail: howes@netscape.com
Patrick Richard
Xcert Software Inc.
Suite 1001, 701 W. Georgia Street
P.O. Box 10145
Pacific Centre
Vancouver, B.C.
Canada V7Y 1C6
EMail: patr@xcert.com
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RFC 2559 PKIX Operational Protocols - LDAPv2 April 1999
13. Full Copyright Statement
Copyright (C) The Internet Society (1999). All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph are
included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than
English.
The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns.
This document and the information contained herein is provided on an
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Boeyen, et al. Standards Track [Page 13]