simplify trait requirements (#143)

* simplify trait requirements

* update version

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "nova-snark"
-version = "0.14.0"
+version = "0.15.0"
 authors = ["Srinath Setty <srinath@microsoft.com>"]
 edition = "2021"
 description = "Recursive zkSNARKs without trusted setup"

src/lib.rs

@@ -44,7 +44,7 @@ use r1cs::{
 use serde::{Deserialize, Serialize};
 use traits::{
   circuit::StepCircuit,
-  commitment::{CommitmentEngineTrait, CompressedCommitmentTrait},
+  commitment::{CommitmentEngineTrait, CommitmentTrait},
   snark::RelaxedR1CSSNARKTrait,
   AbsorbInROTrait, Group, ROConstants, ROConstantsCircuit, ROConstantsTrait, ROTrait,
 };
@@ -317,7 +317,7 @@ where
           Some(r_snark.zi_primary.clone()),
           Some(r_snark.r_U_secondary.clone()),
           Some(r_snark.l_u_secondary.clone()),
-          Some(nifs_secondary.comm_T.decompress()?),
+          Some(Commitment::<G2>::decompress(&nifs_secondary.comm_T)?),
         );
 
         let circuit_primary: NovaAugmentedCircuit<G2, C1> = NovaAugmentedCircuit::new(
@@ -351,7 +351,7 @@ where
           Some(r_snark.zi_secondary.clone()),
           Some(r_snark.r_U_primary.clone()),
           Some(l_u_primary.clone()),
-          Some(nifs_primary.comm_T.decompress()?),
+          Some(Commitment::<G1>::decompress(&nifs_primary.comm_T)?),
         );
 
         let circuit_secondary: NovaAugmentedCircuit<G1, C2> = NovaAugmentedCircuit::new(
@@ -727,7 +727,7 @@ where
 
 type CommitmentGens<G> = <<G as traits::Group>::CE as CommitmentEngineTrait<G>>::CommitmentGens;
 type Commitment<G> = <<G as Group>::CE as CommitmentEngineTrait<G>>::Commitment;
-type CompressedCommitment<G> = <<G as Group>::CE as CommitmentEngineTrait<G>>::CompressedCommitment;
+type CompressedCommitment<G> = <<<G as Group>::CE as CommitmentEngineTrait<G>>::Commitment as CommitmentTrait<G>>::CompressedCommitment;
 type CE<G> = <G as Group>::CE;
 
 #[cfg(test)]

src/nifs.rs

@@ -6,11 +6,8 @@ use crate::{
   constants::{NUM_CHALLENGE_BITS, NUM_FE_FOR_RO},
   errors::NovaError,
   r1cs::{R1CSGens, R1CSInstance, R1CSShape, R1CSWitness, RelaxedR1CSInstance, RelaxedR1CSWitness},
-  traits::{
-    commitment::{CommitmentTrait, CompressedCommitmentTrait},
-    AbsorbInROTrait, Group, ROTrait,
-  },
-  CompressedCommitment,
+  traits::{commitment::CommitmentTrait, AbsorbInROTrait, Group, ROTrait},
+  Commitment, CompressedCommitment,
 };
 use core::marker::PhantomData;
 use serde::{Deserialize, Serialize};
@@ -101,7 +98,7 @@ impl<G: Group> NIFS<G> {
     U2.absorb_in_ro(&mut ro);
 
     // append `comm_T` to the transcript and obtain a challenge
-    let comm_T = self.comm_T.decompress()?;
+    let comm_T = Commitment::<G>::decompress(&self.comm_T)?;
     comm_T.absorb_in_ro(&mut ro);
 
     // compute a challenge from the RO

src/provider/pasta.rs

@@ -190,8 +190,8 @@ macro_rules! impl_traits {
         Some($name_curve::from_bytes(&self.repr).unwrap())
       }
 
-      fn as_bytes(&self) -> &[u8] {
-        &self.repr
+      fn as_bytes(&self) -> Vec<u8> {
+        self.repr.to_vec()
       }
     }
   };

src/provider/pedersen.rs

@@ -2,9 +2,7 @@
 use crate::{
   errors::NovaError,
   traits::{
-    commitment::{
-      CommitmentEngineTrait, CommitmentGensTrait, CommitmentTrait, CompressedCommitmentTrait,
-    },
+    commitment::{CommitmentEngineTrait, CommitmentGensTrait, CommitmentTrait},
     AbsorbInROTrait, AppendToTranscriptTrait, CompressedGroup, Group, ROTrait,
     TranscriptEngineTrait,
   },
@@ -35,13 +33,12 @@ pub struct Commitment<G: Group> {
 /// A type that holds a compressed commitment
 #[derive(Clone, Copy, Debug, PartialEq, Eq, Serialize, Deserialize)]
 #[serde(bound = "")]
-pub struct CompressedCommitment<C: CompressedGroup> {
-  comm: C,
+pub struct CompressedCommitment<G: Group> {
+  comm: G::CompressedGroupElement,
 }
 
 impl<G: Group> CommitmentGensTrait<G> for CommitmentGens<G> {
   type Commitment = Commitment<G>;
-  type CompressedCommitment = CompressedCommitment<G::CompressedGroupElement>;
 
   fn new(label: &'static [u8], n: usize) -> Self {
     CommitmentGens {
@@ -63,9 +60,9 @@ impl<G: Group> CommitmentGensTrait<G> for CommitmentGens<G> {
 }
 
 impl<G: Group> CommitmentTrait<G> for Commitment<G> {
-  type CompressedCommitment = CompressedCommitment<G::CompressedGroupElement>;
+  type CompressedCommitment = CompressedCommitment<G>;
 
-  fn compress(&self) -> CompressedCommitment<G::CompressedGroupElement> {
+  fn compress(&self) -> Self::CompressedCommitment {
     CompressedCommitment {
       comm: self.comm.compress(),
     }
@@ -74,19 +71,9 @@ impl<G: Group> CommitmentTrait<G> for Commitment<G> {
   fn to_coordinates(&self) -> (G::Base, G::Base, bool) {
     self.comm.to_coordinates()
   }
-}
 
-impl<G: Group> Default for Commitment<G> {
-  fn default() -> Self {
-    Commitment { comm: G::zero() }
-  }
-}
-
-impl<C: CompressedGroup> CompressedCommitmentTrait<C> for CompressedCommitment<C> {
-  type Commitment = Commitment<C::GroupElement>;
-
-  fn decompress(&self) -> Result<Self::Commitment, NovaError> {
-    let comm = self.comm.decompress();
+  fn decompress(c: &Self::CompressedCommitment) -> Result<Self, NovaError> {
+    let comm = c.comm.decompress();
     if comm.is_none() {
       return Err(NovaError::DecompressionError);
     }
@@ -96,6 +83,12 @@ impl<C: CompressedGroup> CompressedCommitmentTrait<C> for CompressedCommitment<C
   }
 }
 
+impl<G: Group> Default for Commitment<G> {
+  fn default() -> Self {
+    Commitment { comm: G::zero() }
+  }
+}
+
 impl<G: Group> AppendToTranscriptTrait<G> for Commitment<G> {
   fn append_to_transcript(&self, label: &'static [u8], transcript: &mut G::TE) {
     let (x, y, is_infinity) = self.comm.to_coordinates();
@@ -123,16 +116,9 @@ impl<G: Group> AbsorbInROTrait<G> for Commitment<G> {
   }
 }
 
-impl<C: CompressedGroup> AppendToTranscriptTrait<C::GroupElement> for CompressedCommitment<C> {
-  fn append_to_transcript(
-    &self,
-    label: &'static [u8],
-    transcript: &mut <C::GroupElement as Group>::TE,
-  ) {
-    let comm = self.decompress().unwrap();
-    <Commitment<C::GroupElement> as AppendToTranscriptTrait<C::GroupElement>>::append_to_transcript(
-      &comm, label, transcript,
-    );
+impl<G: Group> AppendToTranscriptTrait<G> for CompressedCommitment<G> {
+  fn append_to_transcript(&self, label: &'static [u8], transcript: &mut G::TE) {
+    transcript.absorb_bytes(label, &self.comm.as_bytes());
   }
 }
 
@@ -225,7 +211,6 @@ pub struct CommitmentEngine<G: Group> {
 impl<G: Group> CommitmentEngineTrait<G> for CommitmentEngine<G> {
   type CommitmentGens = CommitmentGens<G>;
   type Commitment = Commitment<G>;
-  type CompressedCommitment = CompressedCommitment<G::CompressedGroupElement>;
 
   fn commit(gens: &Self::CommitmentGens, v: &[G::Scalar]) -> Self::Commitment {
     gens.commit(v)
@@ -251,7 +236,7 @@ pub(crate) trait CommitmentGensExtTrait<G: Group>: CommitmentGensTrait<G> {
 
   /// Reinterprets commitments as commitment keys
   fn reinterpret_commitments_as_gens(
-    c: &[<<Self as CommitmentGensExtTrait<G>>::CE as CommitmentEngineTrait<G>>::CompressedCommitment],
+    c: &[<<<Self as CommitmentGensExtTrait<G>>::CE as CommitmentEngineTrait<G>>::Commitment as CommitmentTrait<G>>::CompressedCommitment],
   ) -> Result<Self, NovaError>
   where
     Self: Sized;
@@ -320,12 +305,10 @@ impl<G: Group> CommitmentGensExtTrait<G> for CommitmentGens<G> {
   }
 
   /// reinterprets a vector of commitments as a set of generators
-  fn reinterpret_commitments_as_gens(
-    c: &[CompressedCommitment<G::CompressedGroupElement>],
-  ) -> Result<Self, NovaError> {
+  fn reinterpret_commitments_as_gens(c: &[CompressedCommitment<G>]) -> Result<Self, NovaError> {
     let d = (0..c.len())
       .into_par_iter()
-      .map(|i| c[i].decompress())
+      .map(|i| Commitment::<G>::decompress(&c[i]))
       .collect::<Result<Vec<Commitment<G>>, NovaError>>()?;
     let gens = (0..d.len())
       .into_par_iter()

src/traits/commitment.rs

@@ -2,7 +2,7 @@
 //! We require the commitment engine to provide a commitment to vectors with a single group element
 use crate::{
   errors::NovaError,
-  traits::{AbsorbInROTrait, AppendToTranscriptTrait, CompressedGroup, Group},
+  traits::{AbsorbInROTrait, AppendToTranscriptTrait, Group},
 };
 use core::{
   fmt::Debug,
@@ -18,9 +18,6 @@ pub trait CommitmentGensTrait<G: Group>:
   /// Holds the type of the commitment that can be produced
   type Commitment;
 
-  /// Holds the type of the compressed commitment
-  type CompressedCommitment;
-
   /// Samples a new commitment key of a specified size
   fn new(label: &'static [u8], n: usize) -> Self;
 
@@ -77,32 +74,24 @@ pub trait CommitmentTrait<G: Group>:
   + ScalarMul<G::Scalar>
 {
   /// Holds the type of the compressed commitment
-  type CompressedCommitment;
+  type CompressedCommitment: Clone
+    + Debug
+    + PartialEq
+    + Eq
+    + Send
+    + Sync
+    + Serialize
+    + for<'de> Deserialize<'de>
+    + AppendToTranscriptTrait<G>;
 
   /// Compresses self into a compressed commitment
   fn compress(&self) -> Self::CompressedCommitment;
 
   /// Returns the coordinate representation of the commitment
   fn to_coordinates(&self) -> (G::Base, G::Base, bool);
-}
 
-/// This trait defines the behavior of a compressed commitment
-pub trait CompressedCommitmentTrait<C: CompressedGroup>:
-  Clone
-  + Debug
-  + PartialEq
-  + Eq
-  + Send
-  + Sync
-  + Serialize
-  + for<'de> Deserialize<'de>
-  + AppendToTranscriptTrait<C::GroupElement>
-{
-  /// Holds the type of the commitment that can be decompressed into
-  type Commitment;
-
-  /// Decompresses self into a commitment
-  fn decompress(&self) -> Result<Self::Commitment, NovaError>;
+  /// Decompresses a compressed commitment into a commitment
+  fn decompress(c: &Self::CompressedCommitment) -> Result<Self, NovaError>;
 }
 
 /// A trait that ties different pieces of the commitment generation together
@@ -110,20 +99,10 @@ pub trait CommitmentEngineTrait<G: Group>:
   Clone + Send + Sync + Serialize + for<'de> Deserialize<'de>
 {
   /// Holds the type of the commitment key
-  type CommitmentGens: CommitmentGensTrait<
-    G,
-    Commitment = Self::Commitment,
-    CompressedCommitment = Self::CompressedCommitment,
-  >;
+  type CommitmentGens: CommitmentGensTrait<G, Commitment = Self::Commitment>;
 
   /// Holds the type of the commitment
-  type Commitment: CommitmentTrait<G, CompressedCommitment = Self::CompressedCommitment>;
-
-  /// Holds the type of the compressed commitment
-  type CompressedCommitment: CompressedCommitmentTrait<
-    G::CompressedGroupElement,
-    Commitment = Self::Commitment,
-  >;
+  type Commitment: CommitmentTrait<G>;
 
   /// Commits to the provided vector using the provided generators
   fn commit(gens: &Self::CommitmentGens, v: &[G::Scalar]) -> Self::Commitment;

src/traits/mod.rs

@@ -106,7 +106,7 @@ pub trait CompressedGroup:
   fn decompress(&self) -> Option<Self::GroupElement>;
 
   /// Returns a byte array representing the compressed group element
-  fn as_bytes(&self) -> &[u8];
+  fn as_bytes(&self) -> Vec<u8>;
 }
 
 /// A helper trait to absorb different objects in RO