From 82b7fabd9d66f3c9581b0271365d8255f05c511c Mon Sep 17 00:00:00 2001
From: Srinath Setty <srinath@microsoft.com>
Date: Fri, 13 May 2022 11:48:53 +0530
Subject: [PATCH] absorb running instance separately (for clarity) (#52)

---
 src/circuit.rs      |  4 ++--
 src/gadgets/r1cs.rs |  5 +++--
 src/poseidon.rs     | 22 ++++++++++++----------
 3 files changed, 17 insertions(+), 14 deletions(-)

diff --git a/src/circuit.rs b/src/circuit.rs
index 619a943..6c1f474 100644
--- a/src/circuit.rs
+++ b/src/circuit.rs
@@ -203,7 +203,7 @@ where
   ) -> Result<(AllocatedRelaxedR1CSInstance<G>, AllocatedBit), SynthesisError> {
     // Check that u.x[0] = Hash(params, U, i, z0, zi)
     let mut ro: PoseidonROGadget<G::Base> = PoseidonROGadget::new(self.poseidon_constants.clone());
-    ro.absorb(params);
+    ro.absorb(params.clone());
     ro.absorb(i);
     ro.absorb(z_0);
     ro.absorb(z_i);
@@ -220,7 +220,7 @@ where
     // Run NIFS Verifier
     let U_fold = U.fold_with_r1cs(
       cs.namespace(|| "compute fold of U and u"),
-      hash, // hash of the (params, U, i, z0, zi)
+      params,
       u,
       T,
       self.poseidon_constants.clone(),
diff --git a/src/gadgets/r1cs.rs b/src/gadgets/r1cs.rs
index 2b4ce43..7cab720 100644
--- a/src/gadgets/r1cs.rs
+++ b/src/gadgets/r1cs.rs
@@ -216,7 +216,7 @@ where
   pub fn fold_with_r1cs<CS: ConstraintSystem<<G as Group>::Base>>(
     &self,
     mut cs: CS,
-    hash: AllocatedNum<G::Base>, // hash of (params, running_instance, i, z0, zi)
+    params: AllocatedNum<G::Base>, // hash of R1CSShape of F'
     u: AllocatedR1CSInstance<G>,
     T: AllocatedPoint<G::Base>,
     poseidon_constants: NovaPoseidonConstants<G::Base>,
@@ -225,7 +225,8 @@ where
   ) -> Result<AllocatedRelaxedR1CSInstance<G>, SynthesisError> {
     // Compute r:
     let mut ro: PoseidonROGadget<G::Base> = PoseidonROGadget::new(poseidon_constants);
-    ro.absorb(hash);
+    ro.absorb(params);
+    self.absorb_in_ro(cs.namespace(|| "absorb running instance"), &mut ro)?;
     u.absorb_in_ro(&mut ro);
     ro.absorb(T.x.clone());
     ro.absorb(T.y.clone());
diff --git a/src/poseidon.rs b/src/poseidon.rs
index 0725e52..92aa8f4 100644
--- a/src/poseidon.rs
+++ b/src/poseidon.rs
@@ -12,7 +12,7 @@ use bellperson::{
 };
 use core::marker::PhantomData;
 use ff::{PrimeField, PrimeFieldBits};
-use generic_array::typenum::{U27, U9};
+use generic_array::typenum::{U27, U32};
 use neptune::{
   circuit::poseidon_hash,
   poseidon::{Poseidon, PoseidonConstants},
@@ -25,8 +25,8 @@ pub struct NovaPoseidonConstants<Scalar>
 where
   Scalar: PrimeField,
 {
-  constants9: PoseidonConstants<Scalar, U9>,
   constants27: PoseidonConstants<Scalar, U27>,
+  constants32: PoseidonConstants<Scalar, U32>,
 }
 
 impl<Scalar> HashFuncConstantsTrait<Scalar> for NovaPoseidonConstants<Scalar>
@@ -36,11 +36,11 @@ where
   /// Generate Poseidon constants for the arities that Nova uses
   #[allow(clippy::new_without_default)]
   fn new() -> Self {
-    let constants9 = PoseidonConstants::<Scalar, U9>::new_with_strength(Strength::Strengthened);
     let constants27 = PoseidonConstants::<Scalar, U27>::new_with_strength(Strength::Strengthened);
+    let constants32 = PoseidonConstants::<Scalar, U32>::new_with_strength(Strength::Strengthened);
     Self {
-      constants9,
       constants27,
+      constants32,
     }
   }
 }
@@ -65,10 +65,12 @@ where
 {
   fn hash_inner(&self) -> Base {
     match self.state.len() {
-      9 => Poseidon::<Base, U9>::new_with_preimage(&self.state, &self.constants.constants9).hash(),
       27 => {
         Poseidon::<Base, U27>::new_with_preimage(&self.state, &self.constants.constants27).hash()
       }
+      32 => {
+        Poseidon::<Base, U32>::new_with_preimage(&self.state, &self.constants.constants32).hash()
+      }
       _ => {
         panic!(
           "Number of elements in the RO state does not match any of the arities used in Nova: {:?}",
@@ -169,16 +171,16 @@ where
     CS: ConstraintSystem<Scalar>,
   {
     let out = match self.state.len() {
-      9 => poseidon_hash(
-        cs.namespace(|| "Posideon hash"),
-        self.state.clone(),
-        &self.constants.constants9,
-      )?,
       27 => poseidon_hash(
         cs.namespace(|| "Poseidon hash"),
         self.state.clone(),
         &self.constants.constants27,
       )?,
+      32 => poseidon_hash(
+        cs.namespace(|| "Posideon hash"),
+        self.state.clone(),
+        &self.constants.constants32,
+      )?,
       _ => {
         panic!(
           "Number of elements in the RO state does not match any of the arities used in Nova: {}",