UUIDs

UUID stands for Universally Unique Identifier. It is a 128-bit value intended to uniquely identify information in distributed systems. The canonical textual form consists of 32 hexadecimal digits, displayed in five groups separated by hyphens (8-4-4-4-12), for example 550e8400-e29b-41d4-a716-446655440000. This format is described in RFC 4122 and is widely used across programming languages and platforms.

A UUID may be generated in several ways, corresponding to different versions. The most common versions are 1 (time-based, using a timestamp and a node identifier such as a MAC address), 3 (name-based using MD5 hashing of a namespace and name), 4 (random), and 5 (name-based using SHA-1). Version 2 (DCE security) exists but is rarely used. Newer variants have been proposed or implemented in some systems to improve ordering or privacy. In many environments the term GUID (Globally Unique Identifier) is used interchangeably, especially in Microsoft ecosystems.

In practice, UUIDs provide a very high degree of uniqueness: even with random sources, the probability of collision is negligible for typical volumes. They are commonly used as primary keys in databases, as identifiers for resources in APIs, and as transaction or session identifiers in distributed systems. They can be stored as 16-byte binary values or as their textual representation, depending on the database or API requirements.

Privacy and security considerations vary by version. Version 1 can reveal generation time and device information due to its MAC address component, while random-based (version 4) or carefully designed name-based variants reduce exposure of such metadata.