3 ms·

> A single AES encryption block is the same size as a UUID and cheap to compute. I didn’t realise this! The UUID spec mandates some values for specific digits,

• jandrewrogers 1y ago
  They would not be valid UUIDs, it is an opaque 128-bit value. To be honest many companies are not using strictly standard conforming UUIDs everywhere, and UUID has become a synonym for opaque 128-bit identifier. Consumers of the value just need them to be unique. All standard UUID versions are sometimes prohibited in environments, except maybe UUIDv8, so this semantic ambiguity is helpful. Technically, you could make it present as a standard UUIDv4 or UUIDv8 by setting a few bits, as long as you remember to add them back if you ever need to decrypt it. The entropy might be a bit off for a UUIDv4 if someone actually checks but you can guarantee the uniqueness. Using AES to produce a UUID-like key is an old but useful trick. Both ARM and x86 do that encryption in hardware — it is cheaper to generate than the standardized UUID versions in most cases.
  • sysysy 1y ago
    Which mode of AES do you mean? AES ECB seems to fit your example, but wouldn't it still expose the incremental nature UUID v7 with enough samples (see https://en.wikipedia.org/wiki/Block_cipher_mode_of_operation https://en.wikipedia.org/wiki/Block_cipher_mode_of_operation, the Linux Tux image example)? Other AES modes produce way longer results, even when the ID is encoded with Base58 or the like.
• deleted 1y ago
  [deleted]