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RFC 4122 UUIDs

rfc4122/version1 rfc4122/version2 rfc4122/version3 rfc4122/version4 rfc4122/version5 rfc4122/version6 rfc4122/version7 rfc4122/version8

RFC 4122 defines five versions of UUID, while a new Internet-Draft under review defines three new versions. Each version has different generation algorithms and properties. Which one you choose depends on your use-case. You can find out more about their applications on the specific page for that version.

Version 1: Gregorian Time

This version of UUID combines a timestamp, node value (in the form of a MAC address from the local computer's network interface), and a clock sequence to ensure uniqueness. For more details, see rfc4122/version1.

Version 2: DCE Security

This version of UUID is the same as Version 1, except the clock_seq_low field is replaced with a local domain and the time_low field is replaced with a local identifier. For more details, see rfc4122/version2.

Version 3: Name-based (MD5)

This version of UUID hashes together a namespace and a name to create a deterministic UUID. The hashing algorithm used is MD5. For more details, see rfc4122/version3.

Version 4: Random

This version creates a UUID using truly-random or pseudo-random numbers. For more details, see rfc4122/version4.

Version 5: Named-based (SHA-1)

This version of UUID hashes together a namespace and a name to create a deterministic UUID. The hashing algorithm used is SHA-1. For more details, see rfc4122/version5.

Version 6: Reordered Time

This version of UUID combines the features of a version 1 UUID <rfc4122.version1> with a monotonically increasing UUID. For more details, see rfc4122.version6.

Version 7: Unix Epoch Time

This version of UUID combines a timestamp--based on milliseconds elapsed since the Unix Epoch--and random bytes to create a monotonically increasing, sortable UUID without the privacy and entropy concerns associated with version 1 and version 6 UUIDs. For more details, see rfc4122.version7.

Version 8: Custom

This version of UUID allows applications to generate custom identifiers in an RFC-compatible format. For more details, see rfc4122/version8.