feat: use RLN with RC instead of Poseidon

.gitmodules

@@ -0,0 +1,3 @@
+[submodule "lib/rc-impls"]
+	path = lib/rc-impls
+	url = https://github.com/rymnc/reinforced-concrete-impls

README.md

@@ -3,13 +3,52 @@
     <img src="https://github.com/Rate-Limiting-Nullifier/rln-circuits-v2/workflows/Test/badge.svg" width="110">
 </p>
 
-<div align="center">
+___
 
-*The project was audited by Veridise, yAcademy fellows and internally.*
+## This is a fork of RLN
 
-</div>
+This fork of RLN makes use of [RC hash function](https://rc-hash.info) as a drop in replacement to poseidon.
 
-___
+
+### Constraint differences
+
+1. RLN Circuit =>
+
+```diff
+circom compiler 2.1.5
+-template instances: 216
++template instances: 48
+-non-linear constraints: 5820
++non-linear constraints: 957
+linear constraints: 0
+public inputs: 2
+public outputs: 3
+private inputs: 43
+private outputs: 0
+-wires: 5844
++wires: 1053
+-labels: 18553
++labels: 24733
+```
+
+2. Withdraw Circuit =>
+
+```diff
+circom compiler 2.1.5
+-template instances: 71
++template instances: 42
+-non-linear constraints: 214
++non-linear constraints: 37
+linear constraints: 0
+public inputs: 1
+public outputs: 1
+private inputs: 1
+private outputs: 0
+-wires: 217
++wires: 43
+-labels: 585
++labels: 1021
+```
 
 ## What's RLN?
 

circuits/rln.circom

@@ -1,7 +1,7 @@
 pragma circom 2.1.0;
 
 include "./utils.circom";
-include "../node_modules/circomlib/circuits/poseidon.circom";
+include "../lib/rc-impls/rc-circom/circuits/reinforcedConcrete.circom";
 
 template RLN(DEPTH, LIMIT_BIT_SIZE) {
     // Private signals
@@ -20,8 +20,8 @@ template RLN(DEPTH, LIMIT_BIT_SIZE) {
     signal output root;
     signal output nullifier;
 
-    signal identityCommitment <== Poseidon(1)([identitySecret]);
-    signal rateCommitment <== Poseidon(2)([identityCommitment, userMessageLimit]);
+    signal identityCommitment <== ReinforcedConcreteHash()([identitySecret, 0]);
+    signal rateCommitment <== ReinforcedConcreteHash()([identityCommitment, userMessageLimit]);
 
     // Membership check
     root <== MerkleTreeInclusionProof(DEPTH)(rateCommitment, identityPathIndex, pathElements);
@@ -30,11 +30,14 @@ template RLN(DEPTH, LIMIT_BIT_SIZE) {
     RangeCheck(LIMIT_BIT_SIZE)(messageId, userMessageLimit);
 
     // SSS share calculations
-    signal a1 <== Poseidon(3)([identitySecret, externalNullifier, messageId]);
+    component rcPermutation = ReinforcedConcretePermutation();
+    signal a1;
+    rcPermutation.state <== [identitySecret, externalNullifier, messageId];
+    a1 <== rcPermutation.hash[0];
     y <== identitySecret + a1 * x;
 
     // nullifier calculation
-    nullifier <== Poseidon(1)([a1]);
+    nullifier <== ReinforcedConcreteHash()([a1, 0]);
 }
 
 component main { public [x, externalNullifier] } = RLN(20, 16);

circuits/utils.circom

@@ -1,6 +1,6 @@
 pragma circom 2.1.0;
 
-include "../node_modules/circomlib/circuits/poseidon.circom";
+include "../lib/rc-impls/rc-circom/circuits/reinforcedConcrete.circom";
 include "../node_modules/circomlib/circuits/mux1.circom";
 include "../node_modules/circomlib/circuits/bitify.circom";
 include "../node_modules/circomlib/circuits/comparators.circom";
@@ -27,7 +27,7 @@ template MerkleTreeInclusionProof(DEPTH) {
             pathIndex[i]
         );
 
-        levelHashes[i + 1] <== Poseidon(2)([mux[i][0], mux[i][1]]);
+        levelHashes[i + 1] <== ReinforcedConcreteHash()([mux[i][0], mux[i][1]]);
     }
 
     root <== levelHashes[DEPTH];

circuits/withdraw.circom

@@ -1,12 +1,12 @@
 pragma circom 2.1.0;
 
-include "../node_modules/circomlib/circuits/poseidon.circom";
+include "../lib/rc-impls/rc-circom/circuits/reinforcedConcrete.circom";
 
 template Withdraw() {
     signal input identitySecret;
     signal input address;
 
-    signal output identityCommitment <== Poseidon(1)([identitySecret]);
+    signal output identityCommitment <== ReinforcedConcreteHash()([identitySecret, 0]);
 
     // Dummy constraint to prevent compiler optimizing it
     signal addressSquared <== address * address;