OiD

An object identifier (OID) is a globally unique identifier used to name objects in many information technology standards. An OID represents a path through a hierarchical tree of nodes, with each node identified by an integer. The conventional form is a dotted decimal string, such as 1.2.840.113549.1.1.5, which encodes a specific object within the standardization hierarchy.

Structure and notation: OIDs are organized as a tree, with the root nodes controlled by standards bodies and subdivided into branches by delegated authorities. Each subsequent arc refines the object’s location in the tree. This hierarchical arrangement allows wide reuse of a small number of root arcs to describe a vast and expanding set of objects, from algorithms and protocols to vendor-specific objects.

Encoding and usage: In practice, OIDs are used within many ASN.1-based systems. They are encoded in binary form for transmission using BER or DER encodings, where the first two arcs are combined (40*A + B) and subsequent arcs are encoded as base-128 integers with continuation bits. This encoding enables compact representation while preserving a globally unique path to the object.

Applications: OIDs identify a wide range of items, including algorithm identifiers in X.509 certificates, object classes and attributes in LDAP schemas, managed objects in SNMP MIBs, and various protocol and data format specifications. They provide interoperability by ensuring that the same identifier consistently refers to the same object across implementations and standards.

Administration and examples: OIDs are distributed by standardization organizations. Root arcs and sub-branches are assigned to ISO, ITU-T, and other bodies, with private enterprise numbers under 1.3.6.1.4.1 assigned to organizations for vendor-specific objects. For example, 1.3.6.1.4.1 is the private-enterprise subtree used by many vendors to create locally defined OIDs.