UUID Versions

Version	Method	Use Case	Collision Risk
v1	Time-based	Distributed systems	Very low
v3	MD5 hash of namespace + name	Deterministic IDs	Low (MD5 collisions)
v4	Random	General purpose	Extremely low
v5	SHA-1 hash of namespace + name	Deterministic IDs	Very low

UUID Format

A UUID is a 128-bit number represented as 32 hexadecimal digits, displayed in five groups separated by hyphens:

xxxxxxxx-xxxx-Mxxx-Nxxx-xxxxxxxxxxxx

• M indicates the UUID version (1-5)
• N indicates the UUID variant (usually 8, 9, A, or B)
• The remaining bits are randomly generated or derived from input

Standard Namespaces

Namespace	UUID	Purpose
DNS	6ba7b810-9dad-11d1-80b4-00c04fd430c8	Domain names
URL	6ba7b811-9dad-11d1-80b4-00c04fd430c8	URLs
OID	6ba7b812-9dad-11d1-80b4-00c04fd430c8	ISO OIDs
X.500 DN	6ba7b814-9dad-11d1-80b4-00c04fd430c8	LDAP DNs

Common Use Cases

• Database Primary Keys: Unique identifiers for records
• Session IDs: Unique session identifiers
• API Keys: Unique authentication tokens
• File Names: Unique file identifiers
• Distributed Systems: Unique object identifiers across systems

UUID vs GUID

UUID (Universally Unique Identifier) and GUID (Globally Unique Identifier) are essentially the same thing. Microsoft uses the term GUID, while the rest of the industry uses UUID. They follow the same RFC 4122 standard.