Implement CollisionResistance for XOFs
#694
Merged
Conversation
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
daxpedda
force-pushed
the
collision-resistance
branch
from
061b555 to
f0c41f3
Compare
newpavlov
approved these changes
May 28, 2025
tarcieri
pushed a commit
to RustCrypto/traits
that referenced
this pull request
May 28, 2025
## Changes to `ExpandMsg` - Move generic parameter `K` from `ExpandMsg` implementers to `trait ExpandMsg` itself. This was necessary to be able to enforce the correct `K` instead of letting users insert an arbitrary one. E.g. `GroupDigest::hash_from_bytes()` can now `where X: ExpandMsg<Self::K>` instead of users calling `hash_from_bytes::<ExpandMsgXmd<Sha256, U0>>()`. However, this made calling `ExpandMsg` implementers directly more difficult. E.g. instead of `ExpandMsgXmd::<Sha256, U32>::expand_msg(...)` users now have to write `<ExpandMsgXmd<Sha256> as ExpandMsg<U32>>::expand_message()`. If we want to address this, I propose adding `RawExpandMsgXmd`. - Add `CollisionResistance` requirement to `ExpandMsgXof`. - Move the lifetime on `ExpandMsg` to the associated `type Expander<'dst>`. - Fix `dst` not actually being checked to be empty, but instead checked for number of slices. - Move `GroupDigest`s `ProjectivePoint: CofactorGroup` bound to super trait bounds. This makes it less "poisoning" so downstream users don't have to write `where ProjectivePoint: CofactorGroup` every time they use `GroupDigest`. - Move `GroupDigest::hash_to_scalar()`s `Scalar: FromOkm` bounds to `GroupDigest`. I believe this was a historical leftover when `FromOkm` wasn't implemented for `Scalar`s yet. - Improved some documentation around hash2curve and updated all mentions of the draft to RFC9380. - Rename parameter names `msgs` and `dsts` to singular `msg` and `dst`. This is to avoid confusion: even though the type is `&[&[u8]]`, it doesn't represent multiple messages or DSTs, but single concated ones. - Remove non-functioning examples. While I don't think the examples are necessary, I'm happy to re-add them if desired, but I would have to add `GroupDigest` to the `Dev` curve. ## Changes to VOPRF While I was at it, I also adjusted a couple of things around `VoprfParameters` (but I'm happy to split this into its own PR): - Renamed all mentions of VOPRF to OPRF. VOPRF was the old name of the draft when it was just a single "mode", the RFC is split into three modes: OPRF, VOPRF and POPRF. The RFC itself is called ["Oblivious Pseudorandom Functions (OPRFs)"](https://www.rfc-editor.org/rfc/rfc9497.html). - Changed associated `const ID` from `&str` to `&[u8]`. - Changed associated `type Hash` from requiring `Digest` to `Default + FixedOutput + Update`. - Updated all mentions of the VOPRF draft to RFC9497. --- Related: RustCrypto/hashes#694. Companion PR: RustCrypto/elliptic-curves#1203.
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
2 participants
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
This PR implements
CollisionResistancefor all XOFs. I started with those to add support forExpandMsgXofinelliptic-curveand will do follow-up PRs for at least SHA2 and SHA3 fixed output hashes.Companion PR: RustCrypto/traits#1862.
See RustCrypto/traits#1816 for previous discussions.