5.3. UUID Version 3

UUIDv3 is meant for generating UUIDs from names that are drawn from, and unique within, some namespace as per Section 6.5.

UUIDv3 values are created by computing an MD5 hash [RFC1321] over a given Namespace ID value (Section 6.6) concatenated with the desired name value after both have been converted to a canonical sequence of octets, as defined by the standards or conventions of its namespace, in network byte order. This MD5 value is then used to populate all 128 bits of the UUID layout. The UUID version and variant then replace the respective bits as defined by Sections 4.2 and 4.1. An example of this bit substitution can be found in Appendix A.2.

Information around selecting a desired name's canonical format within a given namespace can be found in Section 6.5 under the heading "A note on names".

Where possible, UUIDv5 SHOULD be used in lieu of UUIDv3. For more information on MD5 security considerations, see [RFC6151].

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                            md5_high                           |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|          md5_high             |  ver  |       md5_mid         |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|var|                        md5_low                            |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                            md5_low                            |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 7: UUIDv3 Field and Bit Layout

Field Definitions:

md5_high: The first 48 bits of the layout are filled with the most significant, leftmost 48 bits from the computed MD5 value. Occupies bits 0 through 47 (octets 0-5).

ver: The 4-bit version field as defined by Section 4.2, set to 0b0011 (3). Occupies bits 48 through 51 of octet 6.

md5_mid: 12 more bits of the layout consisting of the least significant, rightmost 12 bits of 16 bits immediately following md5_high from the computed MD5 value. Occupies bits 52 through 63 (octets 6-7).

var: The 2-bit variant field as defined by Section 4.1, set to 0b10. Occupies bits 64 and 65 of octet 8.

md5_low: The final 62 bits of the layout immediately following the var field to be filled with the least significant, rightmost bits of the final 64 bits from the computed MD5 value. Occupies bits 66 through 127 (octets 8-15).

5.3. UUID Version 3​

5.3. UUID Version 3