Random UUIDs aka Version 4 UUIDs are generated from random (or pseudo-random) numbers. MD5 hash Name-based UUIDsĪre backward compatible with other systems that generates UUIDs from names. MD5 hash Name-based UUIDs aka Version 3 UUIDs are generated from MD5 hash of provided namespace and name. Recommended to use Time-based UUIDs because they can be traced back to the machines which generated them. Time-based UUIDs aka Version 1 UUIDs are generated using high precision timer and 802 MAC addresses. MD5 hash Name-based UUIDs or SHA1 hash Name-based UUIDs If you need Ids which are namespace scoped, use either If you need unique Ids, use Time-based UUIDs or Random UUIDs. UUIDs with different level of uniqueness. RFC 4122 proposes different algorithms to generate Z's value in the example UUID is 4 making it a Random UUID type. The binary equivalent of 'a' is "10xx" making variant as 2. Randomly or pseudo-randomly generated version "Leach-Salz" UUIDs, after the authors of the original Internet Draft Msb0ĭCE Security version, with embedded POSIX UIDs The following table lists the currently-defined versions for variant 2 UUID also known as RFC 4122/DCE 1.1 UUIDs, or The version field bits are the most significant 4 bits of octet 6 of UUIDs. The type of UUID is determine by the version field bits. Reserved, Microsoft Corporation backward compatibility Leach-Salz, Webtools.Services UUID generator creates only this type of UUID The following table lists the contents of the variant field bits, where the letter "x" indicates a "don't-care" value. Variant bits are the most significant 3 bits of octet 8 of UUIDs. How all other bits in UUIDs be interpreted. The layout of UUIDs are determine by the variant field bits. UUIDs are of multiple types based on algorithm used for their generation.īits sequence in each UUID type are interpreted differently. In memory, UUIDs are saved as 16 octets continuous memory slots in Most Significant Byte first order (also known as network byte order).Įach octet of the UUIDs is interpreted as 8-bit unsigned integer. The hexadecimal values "a" through "f" are output as lower case characters and are case insensitive on input. Used in the Apollo Network Computing System and later in the Open Software Foundations' (OSF) Distributed Computing Environment (DCE), and then inįor human readability, UUIDs are represented as 32 hexadecimal (base 16) string, displayed in five groups separated by hyphens, in the form 8-4-4-4-12. When generated according to the standard methods, UUIDs are unique for practical purposes. UUIDs are 128-bit number used to uniquely UUID (or GUID) is an acronym for 'Universally Unique Identifier' (or 'Globally Unique Identifier'). Versions of UUIDs for software components, database key, or just for anything where unique Webtools - Online UUID (GUID) Generator is a free online tool that helps you generate different
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