UUID from hash of string

help
1

I'm trying to generate a UUID by hashing a string.

  • Rust playground doesn't have sha3 yet, and the examples in the sha3 docs won't run.
  • The UUID crate understands how to take in a MD5 hash, but not a SHA3 hash.

Is there some elegant way to do this, or do I have to push bytes around until the crates catch up?

2

Is there a reason you can't use an MD5 hash? Is there some set of SHA3 hashes you want to use?

3

Already include sha3 in the project, but avoid using md5 because it's deprecated and don't want it showing in Cargo.toml

4

MD5 is not good enough for security-related contexts, but it's still fine if there aren't any serious consequences from a malicious actor intentionally causing collisions.

1 Like
5

It's not that it "understands" one but not the other, rather the spec for UUIDs specifies a version of UUIDs derived from a md5 hash (and one for UUIDs derived from a sha1 hash) but not from a sha3 hash.

3 Likes
6

The sha3 example works for me. Taking that and turning the first half of the hash into a UUID looks like this:

use sha3::{Digest, Sha3_256};
use uuid::Builder;

fn main() {
    let mut hasher = Sha3_256::new();
    hasher.update(b"abc");
    let result = hasher.finalize();
    let uuid = Builder::from_bytes(result[..16].try_into().unwrap()).into_uuid();

    dbg!(uuid);
}
7

That is not a valid UUID. You are directly using the hashed bytes as UUID, but a UUID requires certain parts of the UUID to have certain values depending on the UUID version.

The options for a hash based UUID are v3 (md5 based), v5 (sha-1 based) or v8 (custom, which allows you to specify 122 bits, with the remaining 6 bits having a fixed value indicating a v8 uuid)

You can use the Uuid::new_v8 method to create a v8 uuid.

11 Likes
8

Got past this. Thanks.