Rln-Relay: Change tree depth to 20 (#726)

* adds instructions on how to generate parameters for a different tree size

* updates the depth of tree

* modifies the Merkle root

* updates parameters for the new tree size

* fixes failing tests

* updates the comment

tests/v2/test_waku_rln_relay.nim

@@ -246,7 +246,7 @@ procSuite "Waku rln relay":
     debug "expected root ", expectedRoot
 
     # start rln-relay
-    node.mountRelay()
+    node.mountRelay(@[RLNRELAY_PUBSUB_TOPIC])
     await node.mountRlnRelay(ethClientAddrOpt = some(EthClient), ethAccAddrOpt =  some(ethAccountAddress), memContractAddOpt =  some(membershipContractAddress), groupOpt = some(group), memKeyPairOpt = some(keypair.get()),  memIndexOpt = some(index), pubsubTopic = RLNRELAY_PUBSUB_TOPIC)
     let calculatedRoot = node.wakuRlnRelay.rlnInstance.getMerkleRoot().value().toHex
     debug "calculated root ", calculatedRoot
@@ -280,7 +280,7 @@ procSuite "Waku rln relay":
     let index = MembershipIndex(5)
 
     # -------- mount rln-relay in the off-chain mode
-    node.mountRelay()
+    node.mountRelay(@[RLNRELAY_PUBSUB_TOPIC])
     await node.mountRlnRelay(groupOpt = some(groupIDCommitments), memKeyPairOpt = some(groupKeyPairs[index]),  memIndexOpt = some(index), onchainMode = false, pubsubTopic = RLNRELAY_PUBSUB_TOPIC)
     
     # get the root of Merkle tree which is constructed inside the mountRlnRelay proc

waku/v2/protocol/waku_rln_relay/waku_rln_relay_types.nim

@@ -44,7 +44,7 @@ type MembershipIndex* = uint
 const 
   MEMBERSHIP_FEE* = 5.u256
   #  the current implementation of the rln lib only supports a circuit for Merkle tree with depth 32
-  MERKLE_TREE_DEPTH* = 32
+  MERKLE_TREE_DEPTH* = 20
   # TODO the ETH_CLIENT should be an input to the rln-relay, though hardcoded for now
   # the current address is the address of ganache-cli when run locally
   ETH_CLIENT* = "ws://localhost:8540/"
@@ -67,5 +67,5 @@ const
   # STATIC_GROUP_MERKLE_ROOT is the root of the Merkle tree constructed from the STATIC_GROUP_KEYS above
   # only identity commitments are used for the Merkle tree construction
   # the root is created locally, using createMembershipList proc from waku_rln_relay_utils module, and the result is hardcoded in here 
-  STATIC_GROUP_MERKLE_ROOT* = "25e03b7d551c3016cb21c057a113be5bf27eaa9b2529e806715bc0a1ef221e07"  
+  STATIC_GROUP_MERKLE_ROOT* = "a1877a553eff12e1b21632a0545a916a5c5b8060ad7cc6c69956741134397b2d"  
 

waku/v2/protocol/waku_rln_relay/waku_rln_relay_utils.nim

@@ -28,11 +28,15 @@ proc createRLNInstance*(d: int = MERKLE_TREE_DEPTH): RLNResult
   var  
     rlnInstance: RLN[Bn256]
     merkleDepth: csize_t = uint(d)
-    # parameters.key contains the parameters related to the Poseidon hasher
-    # to generate this file, clone this repo https://github.com/kilic/rln 
-    # and run the following command in the root directory of the cloned project
-    # cargo run --example export_test_keys
-    # the file is generated separately and copied here
+    ## parameters.key contains the prover and verifier keys
+    ## to generate this file, clone this repo https://github.com/kilic/rln 
+    ## and run the following command in the root directory of the cloned project
+    ## cargo run --example export_test_keys
+    ## the file is generated separately and copied here
+    ## parameters are function of tree depth and poseidon hasher
+    ## to generate parameters for a different tree depth, change the tree size in the following line of rln library
+    ## https://github.com/kilic/rln/blob/3bbec368a4adc68cd5f9bfae80b17e1bbb4ef373/examples/export_test_keys/main.rs#L4
+    ## and then proceed as explained above
     parameters = readFile("waku/v2/protocol/waku_rln_relay/parameters.key")
     pbytes = parameters.toBytes()
     len : csize_t = uint(pbytes.len)