RFC 4526

Lightweight Directory Access Protocol (LDAP) Absolute True and False Filters

📅 published June 2006, from ietf

Lightweight Directory Access Protocol (LDAP) Absolute True and False Filters 🎀

Okay bestie, this is RFC 4526 from the Network Working Group 🌸 It's a Standards Track document, which means it's an actual Internet standard, not just a vibe. Kurt D. Zeilenga wrote it for the OpenLDAP Foundation, and it's dated June 2006. The header doesn't list anything it obsoletes or updates, so it's not replacing or patching any other RFC. It's a fresh add-on. ✨

Status of This Memo 📜

This document specifies an Internet standards track protocol for the Internet community, and it's asking everyone to talk about it and suggest improvements 💬 For the standardization state and status of this protocol, check the current edition of the "Internet Official Protocol Standards" (STD 1). Distribution of this memo is unlimited, so share it with everyone 🦋

Copyright Notice ©️

Abstract 💜

This document extends the Lightweight Directory Access Protocol (LDAP) so it can do absolute True and False filters 🔥 These are based on similar capabilities that already exist in X.500 directory systems. It also extends the String Representation of LDAP Search Filters so those filters can be written as strings too 💅

Table of Contents 🗂️

   1. Background ......................................................1
   2. Absolute True and False Filters .................................2
   3. Security Considerations .........................................2
   4. IANA Considerations .............................................3
   5. References ......................................................3
      5.1. Normative References .......................................3
      5.2. Informative References .....................................3

1. Background 🧚

Okay so the X.500 Directory Access Protocol (DAP) [X.511] already supports absolute True and False assertions 👑 An 'and' filter with zero elements always evaluates to True. An 'or' filter with zero elements always evaluates to False. These come up a lot when you're asking for DSA-specific Entries (DSEs), which don't necessarily have 'objectClass' attributes. That's why "(objectClass=*)" might evaluate to False in those cases 🙈

LDAPv2 [RFC1777][RFC3494] put no limit on how many elements 'and' and 'or' filter sets could have, but the LDAPv2 string representation [RFC1960][RFC3494] couldn't represent empty 'and' and 'or' filter sets at all. Because of that, absolute True or False filters were (unfortunately) dropped from LDAPv3 [RFC4510] 😭

This document fixes that by extending LDAPv3 to support absolute True and False assertions. It lets empty 'and' and 'or' show up in Search filters [RFC4511], and it extends the filter string representation [RFC4515] so empty filter lists are allowed 💖

Heads up: certain search operations, like the ones used to retrieve subschema information [RFC4512], need particular filters. This document doesn't change those requirements 👀

This feature is meant to give a more direct mapping between DAP and LDAP, which is what you'd need if you're building DAP-to-LDAP gateways 🌈

In this document, the key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as described in BCP 14 [RFC2119]. ⭐

2. Absolute True and False Filters 💅

Implementations of this extension SHALL allow 'and' and 'or' choices with zero filter elements. ✨

An 'and' filter consisting of an empty set of filters SHALL evaluate to True. This filter is represented by the string "(&)". 🔥

An 'or' filter consisting of an empty set of filters SHALL evaluate to False. This filter is represented by the string "(|)". 🍓

Servers supporting this feature SHOULD publish the Object Identifier 1.3.6.1.4.1.4203.1.5.3 as a value of the 'supportedFeatures' [RFC4512] attribute in the root DSE 🧚

Clients supporting this feature SHOULD NOT use the feature unless they know that the server supports it. Don't be that friend who assumes things 🙅‍♀️

3. Security Considerations 🔐

The (re)introduction of absolute True and False filters is not believed to raise any new security considerations. Phew 😌

Implementors of this (or any) LDAPv3 extension should be familiar with general LDAPv3 security considerations [RFC4510]. Read those before you ship anything 💀

4. IANA Considerations 🎀

Registration of this feature has been completed by the IANA [RFC4520]. It's official, bestie 👑

The registration template looks like this:

   Subject: Request for LDAP Protocol Mechanism Registration Object
   Identifier: 1.3.6.1.4.1.4203.1.5.3 Description: True/False filters
   Person & email address to contact for further information:
        Kurt Zeilenga <kurt@openldap.org> Usage: Feature Specification:
   RFC 4526 Author/Change Controller: IESG Comments: none

This OID was assigned [ASSIGN] by OpenLDAP Foundation, under its IANA-assigned private enterprise allocation [PRIVATE], for use in this specification 🦋

5. References 📚

5.1. Normative References

   [RFC2119]     Bradner, S., "Key words for use in RFCs to Indicate
                 Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC4510]     Zeilenga, K., Ed, "Lightweight Directory Access
                 Protocol (LDAP): Technical Specification Road Map", RFC
                 4510, June 2006.

   [RFC4511]     Sermersheim, J., Ed., "Lightweight Directory Access
                 Protocol (LDAP): The Protocol", RFC 4511, June 2006.

   [RFC4512]     Zeilenga, K., "Lightweight Directory Access Protocol
                 (LDAP): Directory Information Models", RFC 4512, June
                 2006.

   [RFC4515]     Smith, M., Ed. and T. Howes, "Lightweight Directory
                 Access Protocol (LDAP): String Representation of Search
                 Filters", RFC 4515, June 2006.

5.2. Informative References

   [RFC1777]     Yeong, W., Howes, T., and S. Kille, "Lightweight
                 Directory Access Protocol", RFC 1777, March 1995.

   [RFC1960]     Howes, T., "A String Representation of LDAP Search
                 Filters", RFC 1960, June 1996.

   [RFC3494]     Zeilenga, K., "Lightweight Directory Access Protocol
                 version 2 (LDAPv2) to Historic Status", RFC 3494, March
                 2003.

   [RFC4520]     Zeilenga, K., "Internet Assigned Numbers Authority
                 (IANA) Considerations for the Lightweight Directory
                 Access Protocol (LDAP)", BCP 64, RFC 4520, June 2006.

   [X.500]       International Telecommunication Union -
                 Telecommunication Standardization Sector, "The
                 Directory -- Overview of concepts, models and
                 services," X.500(1993) (also ISO/IEC 9594-1:1994).

   [X.501]       International Telecommunication Union -
                 Telecommunication Standardization Sector, "The
                 Directory -- Models," X.501(1993) (also ISO/IEC 9594-
                 2:1994).

   [X.511]       International Telecommunication Union -
                 Telecommunication Standardization Sector, "The
                 Directory: Abstract Service Definition", X.511(1993)
                 (also ISO/IEC 9594-3:1993).

   [ASSIGN]      OpenLDAP Foundation, "OpenLDAP OID Delegations",
                 http://www.openldap.org/foundation/oid-delegate.txt.

   [PRIVATE]     IANA, "Private Enterprise Numbers",
                 http://www.iana.org/assignments/enterprise-numbers.

Author's Address 🖊️

   Kurt D. Zeilenga
   OpenLDAP Foundation

   EMail: Kurt@OpenLDAP.org

This document is subject to the rights, licenses and restrictions contained in BCP 78. Except as BCP 78 says otherwise, the authors keep all their rights 🫶

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Acknowledgement 🌷

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