oids

An object identifier (OID) is a globally unique, hierarchical identifier used to name objects in many information technology standards and protocols. OIDs provide a language-independent way to refer to concepts such as attributes, algorithms, and entities across diverse systems, ensuring interoperability.

Structure and notation: OIDs are organized as trees. Each node in the tree is assigned by a standards body, and the path from the root to a leaf uniquely identifies an object. OIDs are written as a dotted sequence of integers, such as 2.5.4.3, where each number represents an arc in the tree. A common example in X.509 certificates is 2.5.4.3, which denotes the commonName attribute. OIDs can thus represent a wide range of items, including attribute types, algorithm identifiers, and MIB objects in SNMP.

Encoding: In data encoded with ASN.1, OIDs are serialized using BER, CER, or DER. The textual form is transformed into a binary representation in which the first two components are packed into a single value using 40 times the first arc plus the second (to optimize for common prefixes). The remaining components are encoded as base-128 integers with continuation bits. DER uses definite lengths, which is important for certificate and protocol parsing.

Usage: OIDs appear in many areas, including X.509 certificates (attribute types, extension identifiers, and signature algorithms), SNMP MIBs, LDAP schemas, and various ISO and ITU-T standards. They offer a stable, extensible mechanism to identify concepts without dependence on software vendors or specific implementations.

Administration: The OID namespace is managed by international bodies such as ISO and ITU-T, with registration and allocation performed through member organizations. Private-use numbers are allocated under the 1.3.6.1.4.1 subtree for enterprise-specific needs, helping to prevent collisions across organizations.