feat!: put merlin behind feature (#180)

# Rationale for this change

See #161 for rationale.

# What changes are included in this PR?

NOTE: the individual commits may be good to review individually

* `DoryMessages` accepts `impl Transcript` instead of
`merlin::Transcript`. This is a breaking change, making the proofs
non-backward compatible. The API deos not change.
* Changed `CommitmentEvaluationProof` to accept `impl Transcript` rather
than `merlin::Transcript`.
* Replaced `merlin::Transcript` with `Keccak256Transcript` within
`QueryProof`. Although the proof could be made generic, there is no real
use-case for `merlin`. In the future, we can easily support other
transcripts, but I think it is best to keep it concrete for now.
* Dropped dead code and renamed the old `merlin` module.
* Put `merlin` behind the `blitzar` feature flag since it is still
required for the `blitzar::InnerProductProof`.

* The tests are _NOT_ refactored to remove `merlin`. This can be done in
a separate PR.

# Are these changes tested?

Yes. Existing tests cover the changes.

crates/proof-of-sql/Cargo.toml

@@ -36,7 +36,7 @@ derive_more = { workspace = true }
 indexmap = { workspace = true, features = ["serde"] }
 itertools = { workspace = true }
 lazy_static = { workspace = true }
-merlin = { workspace = true }
+merlin = { workspace = true, optional = true }
 num-traits = { workspace = true }
 num-bigint = { workspace = true, default-features = false }
 postcard = { workspace = true, features = ["alloc"] }
@@ -58,6 +58,7 @@ blitzar = { workspace = true }
 clap = { workspace = true, features = ["derive"] }
 criterion = { workspace = true, features = ["html_reports"] }
 # forge-script = { workspace = true }
+merlin = { workspace = true }
 opentelemetry = { workspace = true }
 opentelemetry-jaeger = { workspace = true }
 rand = { workspace = true, default-features = false }
@@ -75,6 +76,7 @@ development = ["arrow-csv"]
 [features]
 default = ["arrow", "blitzar", "rayon"]
 arrow = ["dep:arrow"]
+blitzar = ["dep:blitzar", "dep:merlin"]
 test = ["dep:rand"]
 
 [lints]

crates/proof-of-sql/src/base/commitment/commitment_evaluation_proof.rs

@@ -1,12 +1,11 @@
 use super::Commitment;
-use crate::base::{proof::Transcript as _, scalar::Scalar};
+use crate::base::{proof::Transcript, scalar::Scalar};
 #[cfg(feature = "blitzar")]
 use crate::base::{scalar::MontScalar, slice_ops};
 #[cfg(feature = "blitzar")]
 use blitzar::proof::{InnerProductProof, ProofError};
 #[cfg(feature = "blitzar")]
 use curve25519_dalek::RistrettoPoint;
-use merlin::Transcript;
 use serde::{Deserialize, Serialize};
 
 /// A trait for using commitment schemes generically. Specifically, this trait is for the evaluation proof of a commitment scheme.
@@ -31,7 +30,7 @@ pub trait CommitmentEvaluationProof {
     /// `b_point` are the values for the variables that are being evaluated.
     /// The resulting evaluation is the the inner product of `a` and `b`, where `b` is the expanded vector form of `b_point`.
     fn new(
-        transcript: &mut Transcript,
+        transcript: &mut impl Transcript,
         a: &[Self::Scalar],
         b_point: &[Self::Scalar],
         generators_offset: u64,
@@ -45,7 +44,7 @@ pub trait CommitmentEvaluationProof {
     #[allow(clippy::too_many_arguments)]
     fn verify_proof(
         &self,
-        transcript: &mut Transcript,
+        transcript: &mut impl Transcript,
         a_commit: &Self::Commitment,
         product: &Self::Scalar,
         b_point: &[Self::Scalar],
@@ -68,7 +67,7 @@ pub trait CommitmentEvaluationProof {
     #[allow(clippy::too_many_arguments)]
     fn verify_batched_proof(
         &self,
-        transcript: &mut Transcript,
+        transcript: &mut impl Transcript,
         commit_batch: &[Self::Commitment],
         batching_factors: &[Self::Scalar],
         product: &Self::Scalar,
@@ -87,7 +86,7 @@ impl CommitmentEvaluationProof for InnerProductProof {
     type ProverPublicSetup<'a> = ();
     type VerifierPublicSetup<'a> = ();
     fn new(
-        transcript: &mut Transcript,
+        transcript: &mut impl Transcript,
         a: &[Self::Scalar],
         b_point: &[Self::Scalar],
         generators_offset: u64,
@@ -115,7 +114,7 @@ impl CommitmentEvaluationProof for InnerProductProof {
 
     fn verify_batched_proof(
         &self,
-        transcript: &mut Transcript,
+        transcript: &mut impl Transcript,
         commit_batch: &[Self::Commitment],
         batching_factors: &[Self::Scalar],
         product: &Self::Scalar,

crates/proof-of-sql/src/base/commitment/test_evaluation_proof.rs

@@ -1,5 +1,5 @@
 use super::{naive_commitment::NaiveCommitment, CommitmentEvaluationProof};
-use crate::base::scalar::test_scalar::TestScalar;
+use crate::base::{proof::Transcript, scalar::test_scalar::TestScalar};
 
 /// This should only be used for the purpose of unit testing.
 pub struct TestEvaluationProof {}
@@ -21,7 +21,7 @@ impl CommitmentEvaluationProof for TestEvaluationProof {
     type VerifierPublicSetup<'a> = ();
 
     fn new(
-        _transcript: &mut merlin::Transcript,
+        _transcript: &mut impl Transcript,
         _a: &[Self::Scalar],
         _b_point: &[Self::Scalar],
         _generators_offset: u64,
@@ -32,7 +32,7 @@ impl CommitmentEvaluationProof for TestEvaluationProof {
 
     fn verify_batched_proof(
         &self,
-        _transcript: &mut merlin::Transcript,
+        _transcript: &mut impl Transcript,
         _commit_batch: &[Self::Commitment],
         _batching_factors: &[Self::Scalar],
         _product: &Self::Scalar,

crates/proof-of-sql/src/base/proof/merlin_transcript_core.rs

@@ -0,0 +1,30 @@
+impl super::transcript_core::TranscriptCore for merlin::Transcript {
+    fn new() -> Self {
+        merlin::Transcript::new(b"TranscriptCore::new")
+    }
+    fn raw_append(&mut self, message: &[u8]) {
+        self.append_message(b"TranscriptCore::raw_append", message)
+    }
+    fn raw_challenge(&mut self) -> [u8; 32] {
+        let mut result = [0u8; 32];
+        self.challenge_bytes(b"TranscriptCore::raw_challenge", &mut result);
+        result
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::super::transcript_core::test_util::*;
+    #[test]
+    fn we_get_equivalent_challenges_with_equivalent_merlin_transcripts() {
+        we_get_equivalent_challenges_with_equivalent_transcripts::<merlin::Transcript>()
+    }
+    #[test]
+    fn we_get_different_challenges_with_different_keccak256_transcripts() {
+        we_get_different_challenges_with_different_transcripts::<merlin::Transcript>()
+    }
+    #[test]
+    fn we_get_different_nontrivial_consecutive_challenges_from_keccak256_transcript() {
+        we_get_different_nontrivial_consecutive_challenges_from_transcript::<merlin::Transcript>()
+    }
+}

crates/proof-of-sql/src/base/proof/mod.rs

@@ -4,10 +4,8 @@ mod error;
 pub use error::ProofError;
 
 /// Contains an extension trait for `merlin::Transcript`, which is used to construct a proof.
-mod transcript_protocol;
-#[cfg(test)]
-mod transcript_protocol_test;
-pub use transcript_protocol::{MessageLabel, TranscriptProtocol};
+#[cfg(any(test, feature = "blitzar"))]
+mod merlin_transcript_core;
 
 mod transcript;
 pub use transcript::Transcript;