Universally Unique Identifier (UUID)

A Universally Unique Identifier (UUID) is a 128-bit label used for information in computer systems. The term Globally Unique Identifier (GUID) is also used, particularly in Microsoft ecosystems.

When generated according to standard methods, UUIDs are for practical purposes unique. Their uniqueness does not depend on a central registration authority or coordination between the parties generating them, unlike most other numbering schemes.

Format

A UUID is typically represented as a string of 32 hexadecimal digits, displayed in five groups separated by hyphens, in the form 8-4-4-4-12 for a total of 36 characters (32 alphanumeric characters and 4 hyphens).

Example: 123e4567-e89b-12d3-a456-426614174000

Versions

There are several versions of UUIDs, each generated using a different algorithm:

• Version 1 (Time-based): Generated from the current time and the MAC address of the computer generating the UUID. It guarantees uniqueness but leaks the MAC address and creation time, which might be a privacy concern.
• Version 3 (Name-based with MD5): Generated from a "namespace" and a "name" using MD5 hashing. Identical namespaces and names will always generate the same UUID.
• Version 4 (Random): Generated entirely randomly (or pseudo-randomly). This is the most common version used today for generating unique keys in databases and applications.
• Version 5 (Name-based with SHA-1): Similar to Version 3, but uses the more secure SHA-1 hashing algorithm.
• Version 7 (Time-ordered): A newer standard designed for database usage. It combines a Unix timestamp with random data, resulting in UUIDs that are sortable by creation time (unlike v4) while maintaining uniqueness and privacy.