🆔 Mix of a time-based and a randomly generated UUID - Mix of v1 and v4
This is an alternative version of a randomly generated UUID, using both the timestamp and pseudo-random bytes.
Maybe I'm wrong about all that but I thought mixing the UUID v1 and v4 methods would make the generated UUID more secure, as it ensures a zero-chance of collision of a single computer and a -really- low chance of collision on multiple computers (because of both probability and time).
The UUID contains 62 randomly generated bits, so there is 2^62 different outcomes for that part of the generated UUID, which means you'd start geeting colisions after about 2^31 generations. That being said, that would only happen if you were able to generate that many UUIDs within 100 nanosecond to 1 microsecond (because the gettimeofday() function used here returns a microsecond-precise timestamp).
This generated UUID format is oooooooo-oooo-Mooo-Nxxx-xxxxxxxxxxxx, it concatenates:
o: The current timestamp (60 bits) (time_low, time_mid, time_high)M: The version (4 bits)N: The variant (2 bits)x: Pseudo-random values (62 bits)
Based on:
- Code from an UUID v1 Generation script: GitHub @ fredriklindberg / class.uuid.php
- Code from an UUID v4 Generation script: Answer to "PHP function to generate v4 UUID" on StackOverflow