uuidv4

UUIDv4 is a version of the Universally Unique Identifier (UUID) standard defined in RFC 4122. It is generated using random numbers to create a globally unique 128-bit identifier.

A UUIDv4 is represented as 32 hexadecimal digits in five groups separated by hyphens: 8-4-4-4-12, for a total of 36 characters. In the 128-bit value, the 4-bit version field is set to 4, and the variant field is set to the RFC 4122 variant (the two most significant bits of the relevant octet are 10). This leaves 122 bits of randomness.

Generation is typically via a cryptographically secure random number generator provided by the operating system. Libraries generate 16 random bytes, then set the version and variant bits appropriately, ensuring a random and unique result.

Use and properties: UUIDv4 is well suited for unique identifiers in distributed systems, databases, and session tokens without requiring a central authority. The probability of collision is vanishingly small for practical purposes. It has no time component and is not inherently ordered, which can be a consideration for certain indexing or sorting needs.

Security and limitations: UUIDv4 IDs are not private or secret tokens and do not convey sensitive information. They should be treated as opaque identifiers. For cryptographic secrecy or authentication, dedicated secure tokens should be used in addition to or instead of UUIDv4 where appropriate.

Alternatives: Other UUID versions exist, such as v1 (time- and MAC-based) and v3/v5 (name-based, deterministic). UUIDv4 is typically chosen when randomness and global uniqueness are desired without a timestamp component.