diff --git a/src/index.ts b/src/index.ts
index ae89bec..d0eed69 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -6,6 +6,7 @@ import {
 } from "./constants.js";
 import { createRLN } from "./create.js";
 import { Keystore } from "./keystore/index.js";
+import { extractMetaMaskSigner } from "./metamask.js";
 import {
   IdentityCredential,
   Proof,
@@ -29,4 +30,5 @@ export {
   RLN_STORAGE_ABI,
   RLN_REGISTRY_ABI,
   SEPOLIA_CONTRACT,
+  extractMetaMaskSigner,
 };
diff --git a/src/keystore/index.ts b/src/keystore/index.ts
index fc85b09..5dc3b56 100644
--- a/src/keystore/index.ts
+++ b/src/keystore/index.ts
@@ -1,3 +1,5 @@
 import { Keystore } from "./keystore.js";
+import type { KeystoreEntity } from "./types.js";
 
 export { Keystore };
+export type { KeystoreEntity };
diff --git a/src/keystore/keystore.ts b/src/keystore/keystore.ts
index 4232aad..accd33f 100644
--- a/src/keystore/keystore.ts
+++ b/src/keystore/keystore.ts
@@ -14,12 +14,12 @@ import _ from "lodash";
 import { v4 as uuidV4 } from "uuid";
 
 import { buildBigIntFromUint8Array } from "../byte_utils.js";
-import type { IdentityCredential } from "../rln.js";
 
 import { decryptEipKeystore, keccak256Checksum } from "./cipher.js";
 import { isCredentialValid, isKeystoreValid } from "./schema_validator.js";
 import type {
   Keccak256Hash,
+  KeystoreEntity,
   MembershipHash,
   MembershipInfo,
   Password,
@@ -57,11 +57,6 @@ type KeystoreCreateOptions = {
   appIdentifier?: string;
 };
 
-type IdentityOptions = {
-  identity: IdentityCredential;
-  membership: MembershipInfo;
-};
-
 export class Keystore {
   private data: NwakuKeystore;
 
@@ -105,7 +100,7 @@ export class Keystore {
   }
 
   public async addCredential(
-    options: IdentityOptions,
+    options: KeystoreEntity,
     password: Password
   ): Promise<MembershipHash> {
     const membershipHash: MembershipHash = Keystore.computeMembershipHash(
@@ -138,7 +133,7 @@ export class Keystore {
   public async readCredential(
     membershipHash: MembershipHash,
     password: Password
-  ): Promise<null | IdentityOptions> {
+  ): Promise<null | KeystoreEntity> {
     const nwakuCredential = this.data.credentials[membershipHash];
 
     if (!nwakuCredential) {
@@ -235,9 +230,7 @@ export class Keystore {
     };
   }
 
-  private static fromBytesToIdentity(
-    bytes: Uint8Array
-  ): null | IdentityOptions {
+  private static fromBytesToIdentity(bytes: Uint8Array): null | KeystoreEntity {
     try {
       const str = bytesToUtf8(bytes);
       const obj = JSON.parse(str);
@@ -302,7 +295,7 @@ export class Keystore {
 
   // follows nwaku implementation
   // https://github.com/waku-org/nwaku/blob/f05528d4be3d3c876a8b07f9bb7dfaae8aa8ec6e/waku/waku_keystore/protocol_types.nim#L98
-  private static fromIdentityToBytes(options: IdentityOptions): Uint8Array {
+  private static fromIdentityToBytes(options: KeystoreEntity): Uint8Array {
     return utf8ToBytes(
       JSON.stringify({
         treeIndex: options.membership.treeIndex,
diff --git a/src/keystore/types.ts b/src/keystore/types.ts
index 4873f97..b792920 100644
--- a/src/keystore/types.ts
+++ b/src/keystore/types.ts
@@ -1,3 +1,5 @@
+import type { IdentityCredential } from "../rln.js";
+
 export type MembershipHash = string;
 export type Sha256Hash = string;
 export type Keccak256Hash = string;
@@ -10,3 +12,8 @@ export type MembershipInfo = {
   address: string;
   treeIndex: number;
 };
+
+export type KeystoreEntity = {
+  identity: IdentityCredential;
+  membership: MembershipInfo;
+};
diff --git a/src/metamask.ts b/src/metamask.ts
index e171205..f35423d 100644
--- a/src/metamask.ts
+++ b/src/metamask.ts
@@ -1,15 +1,16 @@
 import { ethers } from "ethers";
 
-export const extractMetaMaskAccount =
-  async (): Promise<ethers.providers.Web3Provider> => {
-    const ethereum = (window as any).ethereum;
+export const extractMetaMaskSigner = async (): Promise<ethers.Signer> => {
+  const ethereum = (window as any).ethereum;
 
-    if (!ethereum) {
-      throw Error(
-        "Missing or invalid Ethereum provider. Please install a Web3 wallet such as MetaMask."
-      );
-    }
+  if (!ethereum) {
+    throw Error(
+      "Missing or invalid Ethereum provider. Please install a Web3 wallet such as MetaMask."
+    );
+  }
 
-    await ethereum.request({ method: "eth_requestAccounts" });
-    return new ethers.providers.Web3Provider(ethereum, "any");
-  };
+  await ethereum.request({ method: "eth_requestAccounts" });
+  const provider = new ethers.providers.Web3Provider(ethereum, "any");
+
+  return provider.getSigner();
+};
diff --git a/src/rln.ts b/src/rln.ts
index f96bdc4..4f87a39 100644
--- a/src/rln.ts
+++ b/src/rln.ts
@@ -1,12 +1,21 @@
+import { createDecoder, createEncoder } from "@waku/core";
 import type { IRateLimitProof } from "@waku/interfaces";
+import type {
+  ContentTopic,
+  IDecodedMessage,
+  EncoderOptions as WakuEncoderOptions,
+} from "@waku/interfaces";
 import init from "@waku/zerokit-rln-wasm";
 import * as zerokitRLN from "@waku/zerokit-rln-wasm";
 import { ethers } from "ethers";
 
 import { buildBigIntFromUint8Array, writeUIntLE } from "./byte_utils.js";
+import type { RLNDecoder, RLNEncoder } from "./codec.js";
+import { createRLNDecoder, createRLNEncoder } from "./codec.js";
 import { SEPOLIA_CONTRACT } from "./constants.js";
 import { dateToEpoch, epochIntToBytes } from "./epoch.js";
-import { extractMetaMaskAccount } from "./metamask.js";
+import type { KeystoreEntity } from "./keystore/index.js";
+import { extractMetaMaskSigner } from "./metamask.js";
 import verificationKey from "./resources/verification_key.js";
 import { RLNContract } from "./rln_contract.js";
 import * as wc from "./witness_calculator.js";
@@ -164,34 +173,138 @@ export function sha256(input: Uint8Array): Uint8Array {
 
 type StartRLNOptions = {
   /**
-   * If not set - will extract MetaMask account and get provider from it.
+   * If not set - will extract MetaMask account and get signer from it.
    */
-  provider?: ethers.providers.Provider;
+  signer?: ethers.Signer;
   /**
    * If not set - will use default SEPOLIA_CONTRACT address.
    */
   registryAddress?: string;
+  /**
+   * Credentials to use for generating proofs and connecting to the contract and network.
+   * If provided used for validating the network chainId and connecting to registry contract.
+   */
+  credentials?: KeystoreEntity;
 };
 
+type RegisterMembershipOptions =
+  | { signature: string }
+  | { identity: IdentityCredential };
+
 export class RLNInstance {
-  private _contract: null | RLNContract = null;
+  private started = false;
+  private starting = false;
+
+  private _contract: undefined | RLNContract;
+  private _signer: undefined | ethers.Signer;
+  private _credentials: undefined | KeystoreEntity;
 
   constructor(
     private zkRLN: number,
     private witnessCalculator: WitnessCalculator
   ) {}
 
-  public get contract(): null | RLNContract {
+  public get contract(): undefined | RLNContract {
     return this._contract;
   }
 
-  public async start(options: StartRLNOptions = {}): Promise<void> {
-    const provider = options.provider || (await extractMetaMaskAccount());
-    const registryAddress = options.registryAddress || SEPOLIA_CONTRACT.address;
+  public get signer(): undefined | ethers.Signer {
+    return this._signer;
+  }
 
-    this._contract = await RLNContract.init(this, {
+  public async start(options: StartRLNOptions = {}): Promise<void> {
+    if (this.started || this.starting) {
+      return;
+    }
+
+    this.starting = true;
+
+    try {
+      const { signer, credentials, registryAddress } =
+        await this.determineStartOptions(options);
+
+      this._signer = signer!;
+      this._credentials = credentials;
+      this._contract = await RLNContract.init(this, {
+        registryAddress: registryAddress!,
+        signer: signer!,
+      });
+      this.started = true;
+    } finally {
+      this.starting = false;
+    }
+  }
+
+  private async determineStartOptions(
+    options: StartRLNOptions
+  ): Promise<StartRLNOptions> {
+    let chainId = options.credentials?.membership.chainId;
+    const registryAddress =
+      options.credentials?.membership.address ||
+      options.registryAddress ||
+      SEPOLIA_CONTRACT.address;
+
+    if (registryAddress === SEPOLIA_CONTRACT.address) {
+      chainId = SEPOLIA_CONTRACT.chainId;
+    }
+
+    const signer = options.signer || (await extractMetaMaskSigner());
+    const currentChainId = await signer.getChainId();
+
+    if (chainId && chainId !== currentChainId) {
+      throw Error(
+        `Failed to start RLN contract, chain ID of contract is different from current one: contract-${chainId}, current network-${currentChainId}`
+      );
+    }
+
+    return {
+      signer,
       registryAddress,
-      provider,
+      credentials: options.credentials,
+    };
+  }
+
+  public async registerMembership(
+    options: RegisterMembershipOptions
+  ): Promise<undefined | KeystoreEntity> {
+    if (!this.contract) {
+      throw Error("RLN Contract is not initialized.");
+    }
+
+    if (!options.identity || !options.signature) {
+      throw Error("Missing signature or identity to register membership.");
+    }
+
+    let identity = options.identity;
+
+    if (options.signature) {
+      identity = await this.generateSeededIdentityCredential(signature);
+    }
+
+    return this.contract.registerWithIdentity(identity);
+  }
+
+  public createEncoder(options: WakuEncoderOptions): RLNEncoder {
+    if (!this._credentials) {
+      throw Error(
+        "Failed to create Encoder: missing RLN credentials. Use createRLNEncoder directly."
+      );
+    }
+
+    return createRLNEncoder({
+      encoder: createEncoder(options),
+      rlnInstance: this,
+      index: this._credentials.membership.treeIndex,
+      credential: this._credentials.identity,
+    });
+  }
+
+  public createDecoder(
+    contentTopic: ContentTopic
+  ): RLNDecoder<IDecodedMessage> {
+    return createRLNDecoder({
+      rlnInstance: this,
+      decoder: createDecoder(contentTopic),
     });
   }
 
diff --git a/src/rln_contract.ts b/src/rln_contract.ts
index 6a53fa9..6fc82e5 100644
--- a/src/rln_contract.ts
+++ b/src/rln_contract.ts
@@ -3,7 +3,8 @@ import { ethers } from "ethers";
 
 import { zeroPadLE } from "./byte_utils.js";
 import { RLN_REGISTRY_ABI, RLN_STORAGE_ABI } from "./constants.js";
-import { IdentityCredential, RLNInstance } from "./rln.js";
+import type { KeystoreEntity } from "./keystore/index.js";
+import { type IdentityCredential, RLNInstance } from "./rln.js";
 import { MerkleRootTracker } from "./root_tracker.js";
 
 type Member = {
@@ -11,10 +12,10 @@ type Member = {
   index: ethers.BigNumber;
 };
 
-type Provider = ethers.Signer | ethers.providers.Provider;
+type Signer = ethers.Signer;
 
 type RLNContractOptions = {
-  provider: Provider;
+  signer: Signer;
   registryAddress: string;
 };
 
@@ -47,7 +48,7 @@ export class RLNContract {
   ): Promise<RLNContract> {
     const rlnContract = new RLNContract(rlnInstance, options);
 
-    await rlnContract.initStorageContract(options.provider);
+    await rlnContract.initStorageContract(options.signer);
     await rlnContract.fetchMembers(rlnInstance);
     rlnContract.subscribeToMembers(rlnInstance);
 
@@ -56,20 +57,20 @@ export class RLNContract {
 
   constructor(
     rlnInstance: RLNInstance,
-    { registryAddress, provider }: RLNContractOptions
+    { registryAddress, signer }: RLNContractOptions
   ) {
     const initialRoot = rlnInstance.getMerkleRoot();
 
     this.registryContract = new ethers.Contract(
       registryAddress,
       RLN_REGISTRY_ABI,
-      provider
+      signer
     );
     this.merkleRootTracker = new MerkleRootTracker(5, initialRoot);
   }
 
   private async initStorageContract(
-    provider: Provider,
+    signer: Signer,
     options: RLNStorageOptions = {}
   ): Promise<void> {
     const storageIndex = options?.storageIndex
@@ -85,7 +86,7 @@ export class RLNContract {
     this.storageContract = new ethers.Contract(
       storageAddress,
       RLN_STORAGE_ABI,
-      provider
+      signer
     );
     this._membersFilter = this.storageContract.filters.MemberRegistered();
 
@@ -207,19 +208,9 @@ export class RLNContract {
     );
   }
 
-  public async registerWithSignature(
-    rlnInstance: RLNInstance,
-    signature: string
-  ): Promise<Member | undefined> {
-    const identityCredential =
-      await rlnInstance.generateSeededIdentityCredential(signature);
-
-    return this.registerWithKey(identityCredential);
-  }
-
-  public async registerWithKey(
-    credential: IdentityCredential
-  ): Promise<Member | undefined> {
+  public async registerWithIdentity(
+    identity: IdentityCredential
+  ): Promise<KeystoreEntity | undefined> {
     if (this.storageIndex === undefined) {
       throw Error(
         "Cannot register credential, no storage contract index found."
@@ -228,7 +219,7 @@ export class RLNContract {
     const txRegisterResponse: ethers.ContractTransaction =
       await this.registryContract["register(uint16,uint256)"](
         this.storageIndex,
-        credential.IDCommitmentBigInt,
+        identity.IDCommitmentBigInt,
         { gasLimit: 100000 }
       );
     const txRegisterReceipt = await txRegisterResponse.wait();
@@ -245,9 +236,17 @@ export class RLNContract {
       memberRegistered.data
     );
 
+    const network = await this.registryContract.provider.getNetwork();
+    const address = this.registryContract.address;
+    const membershipId = decodedData.index.toNumber();
+
     return {
-      idCommitment: decodedData.idCommitment,
-      index: decodedData.index,
+      identity,
+      membership: {
+        address,
+        treeIndex: membershipId,
+        chainId: network.chainId,
+      },
     };
   }