feat: add TranscriptVar trait (#42)

* feat: add TranscriptVar trait

* Update src/transcript/poseidon.rs

Co-authored-by: arnaucube <root@arnaucube.com>

---------

Co-authored-by: arnaucube <root@arnaucube.com>

src/transcript/mod.rs

@@ -1,5 +1,8 @@
 use crate::Error;
 use ark_ec::CurveGroup;
+use ark_ff::PrimeField;
+use ark_r1cs_std::{boolean::Boolean, fields::fp::FpVar};
+use ark_relations::r1cs::{ConstraintSystemRef, SynthesisError};
 use ark_std::fmt::Debug;
 
 pub mod poseidon;
@@ -16,3 +19,16 @@ pub trait Transcript {
     fn get_challenge_nbits(&mut self, nbits: usize) -> Vec<bool>;
     fn get_challenges(&mut self, n: usize) -> Vec<C::ScalarField>;
 }
+
+pub trait TranscriptVar<F: PrimeField> {
+    type TranscriptVarConfig: Debug;
+
+    fn new(cs: ConstraintSystemRef<F>, poseidon_config: &Self::TranscriptVarConfig) -> Self;
+    fn absorb(&mut self, v: FpVar<F>) -> Result<(), SynthesisError>;
+    fn absorb_vec(&mut self, v: &[FpVar<F>]) -> Result<(), SynthesisError>;
+    fn get_challenge(&mut self) -> Result<FpVar<F>, SynthesisError>;
+    /// returns the bit representation of the challenge, we use its output in-circuit for the
+    /// `GC.scalar_mul_le` method.
+    fn get_challenge_nbits(&mut self, nbits: usize) -> Result<Vec<Boolean<F>>, SynthesisError>;
+    fn get_challenges(&mut self, n: usize) -> Result<Vec<FpVar<F>>, SynthesisError>;
+}

src/transcript/poseidon.rs

@@ -12,6 +12,8 @@ use ark_std::{One, Zero};
 use crate::transcript::Transcript;
 use crate::Error;
 
+use super::TranscriptVar;
+
 /// PoseidonTranscript implements the Transcript trait using the Poseidon hash
 pub struct PoseidonTranscript<C: CurveGroup>
 where
@@ -84,18 +86,20 @@ fn prepare_point(p: &C) -> Result, Error> {
 pub struct PoseidonTranscriptVar<F: PrimeField> {
     sponge: PoseidonSpongeVar<F>,
 }
-impl<F: PrimeField> PoseidonTranscriptVar<F> {
-    pub fn new(cs: ConstraintSystemRef<F>, poseidon_config: &PoseidonConfig<F>) -> Self {
+impl<F: PrimeField> TranscriptVar<F> for PoseidonTranscriptVar<F> {
+    type TranscriptVarConfig = PoseidonConfig<F>;
+
+    fn new(cs: ConstraintSystemRef<F>, poseidon_config: &Self::TranscriptVarConfig) -> Self {
         let sponge = PoseidonSpongeVar::<F>::new(cs, poseidon_config);
         Self { sponge }
     }
-    pub fn absorb(&mut self, v: FpVar<F>) -> Result<(), SynthesisError> {
+    fn absorb(&mut self, v: FpVar<F>) -> Result<(), SynthesisError> {
         self.sponge.absorb(&v)
     }
-    pub fn absorb_vec(&mut self, v: &[FpVar<F>]) -> Result<(), SynthesisError> {
+    fn absorb_vec(&mut self, v: &[FpVar<F>]) -> Result<(), SynthesisError> {
         self.sponge.absorb(&v)
     }
-    pub fn get_challenge(&mut self) -> Result<FpVar<F>, SynthesisError> {
+    fn get_challenge(&mut self) -> Result<FpVar<F>, SynthesisError> {
         let c = self.sponge.squeeze_field_elements(1)?;
         self.sponge.absorb(&c[0])?;
         Ok(c[0].clone())
@@ -103,10 +107,10 @@ impl PoseidonTranscriptVar {
 
     /// returns the bit representation of the challenge, we use its output in-circuit for the
     /// `GC.scalar_mul_le` method.
-    pub fn get_challenge_nbits(&mut self, nbits: usize) -> Result<Vec<Boolean<F>>, SynthesisError> {
+    fn get_challenge_nbits(&mut self, nbits: usize) -> Result<Vec<Boolean<F>>, SynthesisError> {
         self.sponge.squeeze_bits(nbits)
     }
-    pub fn get_challenges(&mut self, n: usize) -> Result<Vec<FpVar<F>>, SynthesisError> {
+    fn get_challenges(&mut self, n: usize) -> Result<Vec<FpVar<F>>, SynthesisError> {
         let c = self.sponge.squeeze_field_elements(n)?;
         self.sponge.absorb(&c)?;
         Ok(c)