Constant-Time fuzzing results

[phayes]

I built a bunch of constant-time fuzzing targets for blake3 using sidefuzz

The fuzzing targets can be found here: http://github.com/phayes/sidefuzz-targets

Results are as follows:

• hash (input): constant time ✔️
• keyed_hash (input): constant time ✔️
• keyed_hash (key): constant time ✔️
• keyed_hash (key): constant time ✔️
• reference_impl_hash (input): constant time ✔️
• keyed_hash (key_material): constant time ✔️
• keyed_hash (context): fuzzing-failed

So everything looks good except that I couldn't properly fuzz keyed_hash in relation to the context since it takes a string, and sidefuzz produces &[u8]s as it's fuzzing inputs.

So to fuzz keyed_hash in relation to context we would either need to resolve #13 or I would need to improve sidefuzz to have a function that provides a string.

[oconnor663]

Glad to hear we didn't do anything catastrophically wrong :-D

I wonder if you could work around the string issue by just converting the fuzz input to a hexadecimal string, and using that as the context? Or maybe masking off the high bit of each byte to make it valid ASCII, and then converting with std::str::from_utf8? I suppose the fully correct thing to do would be to generate a series of randomly chosen valid Unicode code points, but maybe that's more complicated than it really needs to be.

[phayes]

@oconnor663 - I'll work on adding string support to SideFuzz - that should solve the issue.

Being able to fuzz string inputs is something sidefuzz should have anyways, so this is fine. I'll update this ticket when it's done and I have results.

[oconnor663]

Going to close this one for now, but please do comment again if you get new results.