Add DST to bulletproofs, DDH and key consistency proofs#967
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benr-ml
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Jun 2, 2026
Adds a domain-separation-tag (DST) parameter to the range proofs (bulletproofs) and the sigma-protocol proofs used by Contra: - RangeProof prove/verify bind the DST into the Merlin transcript. - DdhTupleNizk (nizk.rs) and ZeroProof / ConsistencyProof / KeyConsistencyProof (twisted_elgamal.rs) bind the DST into their Fiat-Shamir challenge. The DDH, ElGamal and key-consistency challenge constructions are made byte-for-byte compatible with the Move and TypeScript implementations in Contra: blake2b256(dst || canonical-element-bytes... in Move's order) with the top byte zeroed and reduced to a canonical little-endian scalar, exposed as RistrettoScalar::fiat_shamir_challenge. The DDH challenge reduction is abstracted behind a FiatShamirChallenge strategy trait (default Blake2bCanonicalChallenge) so alternative reductions can be plugged in; ZeroProof and KeyConsistencyProof reuse the same strategy.
Daeinar
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Jun 15, 2026
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| fn challenge(x_g: &G, x_h: &G, a: &G, b: &G, dst: &[u8]) -> G::ScalarType { | ||
| let chunks: Vec<Vec<u8>> = vec![ | ||
| dst.to_vec(), | ||
| bcs::to_bytes(x_g).expect("Serialization succeeds"), | ||
| bcs::to_bytes(x_h).expect("Serialization succeeds"), | ||
| bcs::to_bytes(a).expect("Serialization succeeds"), | ||
| bcs::to_bytes(b).expect("Serialization succeeds"), | ||
| ]; |
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Nit: Should we pass parameters to challenge in the same order as they are processed, i.e., move dst to the front?
Daeinar
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Jun 15, 2026
| let mut digest = Blake2b256::digest(bcs::to_bytes(msg).unwrap()).digest; | ||
| digest[31] = 0; | ||
| RistrettoScalar::from_byte_array(&digest).expect("Always in field") | ||
| /// Derive an internal batching coefficient labelled `label` from the challenge `c` and (optional) |
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This should not be derived from the challenge c but from a fresh random value. I know that this will be fixed in another PR (right?) but I'm wondering if it would make sense to write here already that the batching coefficient will be derived from randomness r instead of challenge c (i.e. update the name of the input parameter etc)?
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Adds a domain-separation-tag (
dst) to the bulletproof range proofs and the Twisted ElGamal / DDH sigma proofs (DdhTupleNizk,ZeroProof,ConsistencyProof,KeyConsistencyProof).The sigma-proof challenges are made byte-for-byte compatible with Contra's Move/TS implementations:
blake2b256(dst || canonical-element-bytes…), top byte zeroed, canonical LE scalar (RistrettoScalar::fiat_shamir_challenge). Breaking change: prove/verify call sites now require adst.This changes range proof verification, so Sui must be updated.
Test plan
cargo test -p fastcrypto --lib(nizk, twisted_elgamal, bulletproofs)cargo fmt --check+cargo xclippy -D warnings