Message Signing

Message signing allows users to cryptographically prove their identity and provide data without paying transaction fees. This makes it perfect for authentication, feedback collection, surveys, and any scenario where you need verified user input but don’t require on-chain storage.

Key Concepts

Authentication

Users sign messages with their wallet to authenticate themselves

Cryptographic Proof

Signatures provide cryptographic proof of wallet ownership

Instant Verification

No blockchain confirmation time - instant verification

When to Use Message Signing vs Transactions

Feature	Message Signing	Blockchain Transaction
Cost	Free	Requires SOL for fees
Speed	Instant	Requires confirmation (~400ms)
Storage	Off-chain (database)	On-chain (permanent)
Use Cases	Authentication, feedback, surveys	Payments, NFT minting, DeFi
Verification	Cryptographic signature	Blockchain consensus

Two Approaches to Message Signing

There are two primary approaches to implementing message signing in Blinks:

1. Plain Text Signing

Simple message signing with a static string. Best for basic authentication and use-cases where you don’t need the enhanced security of the structured approach.

src/app/api/actions/sign-plain/route.ts

import {
  ActionGetResponse,
  ActionPostRequest,
  ActionPostResponse,
  ActionError,
  ACTIONS_CORS_HEADERS,
  BLOCKCHAIN_IDS
} from "@solana/actions";
import { PublicKey } from "@solana/web3.js";
import nacl from "tweetnacl";
import * as bs58 from "bs58";

const blockchain = BLOCKCHAIN_IDS.mainnet;
const headers = {
  ...ACTIONS_CORS_HEADERS,
  'X-Blockchain-Ids': blockchain,
  'X-Action-Version': '2.4'
};

// The message users will sign
const MESSAGE = "Please sign this message to verify your wallet";

export const OPTIONS = async () => new Response(null, { headers });

export const GET = async (req: Request) => {
  const payload: ActionGetResponse = {
    type: "action",
    icon: new URL("/sign-icon.jpg", req.url).toString(),
    title: "Sign Message Demo",
    description: "Sign a message to verify your wallet ownership",
    label: "Sign Message",
    links: {
      actions: [
        {
          type: "message", // Use 'message' type instead of 'transaction'
          href: "/api/actions/sign-plain",
          label: "Sign Message"
        }
      ]
    }
  };

  return new Response(JSON.stringify(payload), { headers });
};

export const POST = async (req: Request) => {
  try {
    const request: ActionPostRequest = await req.json();
    const { account, signature } = request;

    if (!signature) {
      const error: ActionError = {
        message: "Signature is required for verification"
      };
      return new Response(JSON.stringify(error), { 
        status: 400, 
        headers 
      });
    }

    // Verify the signature
    const isValid = verifySignature(MESSAGE, signature, account);

    if (!isValid) {
      const payload: ActionGetResponse = {
        type: "action",
        icon: new URL("/sign-icon.jpg", req.url).toString(),
        title: "❌ Signature Invalid",
        description: `Invalid signature for account: ${account}`,
        label: "Try Again",
        links: { actions: [] }
      };
      return new Response(JSON.stringify(payload), { headers });
    }

    // Success response
    const payload: ActionGetResponse = {
      type: "action",
      icon: new URL("/sign-icon.jpg", req.url).toString(),
      title: "✅ Signature Verified",
      description: `Successfully verified signature for: ${account}`,
      label: "Completed",
      links: { actions: [] }
    };

    return new Response(JSON.stringify(payload), { headers });

  } catch (error) {
    console.error("Signature verification error:", error);
    const errorResponse: ActionError = {
      message: "Failed to verify signature"
    };
    return new Response(JSON.stringify(errorResponse), { 
      status: 500, 
      headers 
    });
  }
};

// Signature verification utility
function verifySignature(message: string, signature: string, account: string): boolean {
  try {
    const messageBytes = new TextEncoder().encode(message);
    const signatureBytes = bs58.decode(signature);
    const publicKeyBytes = new PublicKey(account).toBytes();
    
    return nacl.sign.detached.verify(
      messageBytes,
      signatureBytes,
      publicKeyBytes
    );
  } catch {
    return false;
  }
}

2. Structured Message Signing (Recommended)

Uses the SIWS (Sign-In With Solana) standard with anti-replay protection and domain binding. Best for production applications requiring enhanced security.

Main Endpoint

src/app/api/actions/sign-structured/route.ts

import {
  ActionGetResponse,
  ActionPostRequest,
  ActionPostResponse,
  ActionError,
  ACTIONS_CORS_HEADERS,
  BLOCKCHAIN_IDS,
  SignMessageData,
  SignMessageResponse
} from "@solana/actions";
import { Keypair, PublicKey } from "@solana/web3.js";
import { createSignMessageText } from "@solana/actions";
import nacl from "tweetnacl";
import * as bs58 from "bs58";

const blockchain = BLOCKCHAIN_IDS.mainnet;
const headers = {
  ...ACTIONS_CORS_HEADERS,
  'X-Blockchain-Ids': blockchain,
  'X-Action-Version': '2.4'
};

// Server signing keypair (store securely in production!)
const SERVER_KEYPAIR = nacl.sign.keyPair.fromSecretKey(
  bs58.decode("YOUR_SECRET_KEY_HERE") // Replace with your secret key
);

export const OPTIONS = async () => new Response(null, { headers });

export const GET = async (req: Request) => {
  const payload: ActionGetResponse = {
    type: "action",
    icon: new URL("/sign-icon.jpg", req.url).toString(),
    title: "Secure Message Signing",
    description: "Sign a structured message with enhanced security",
    label: "Sign Secure Message",
    links: {
      actions: [
        {
          type: "message",
          href: "/api/actions/sign-structured",
          label: "Sign Message"
        }
      ]
    }
  };

  return new Response(JSON.stringify(payload), { headers });
};

export const POST = async (req: Request) => {
  try {
    const request: ActionPostRequest = await req.json();
    const { account, signature, state } = request;

    if (!signature) {
      // First request - generate structured message data
      const signMessageData: SignMessageData = {
        address: account,
        domain: new URL(req.url).hostname,
        statement: "Please sign this message to verify your wallet ownership",
        issuedAt: new Date().toISOString(),
        nonce: Keypair.generate().publicKey.toString(), // Anti-replay protection
      };

      // Create standardized message text
      const message = createSignMessageText(signMessageData);
      
      // Server signs the message to prevent tampering
      const serverSignature = bs58.encode(
        nacl.sign.detached(
          new TextEncoder().encode(message),
          SERVER_KEYPAIR.secretKey
        )
      );

      // Store message and server signature in state
      const stateData = {
        message,
        serverSignature
      };

      const response: SignMessageResponse = {
        type: "message",
        data: signMessageData,
        state: JSON.stringify(stateData),
        links: {
          next: {
            type: "post",
            href: "/api/actions/sign-structured/verify"
          }
        }
      };

      return new Response(JSON.stringify(response), { headers });
    }

    // This shouldn't happen in the main endpoint, but handle gracefully
    return new Response(JSON.stringify({
      message: "Use the verify endpoint for signature verification"
    } as ActionError), { status: 400, headers });

  } catch (error) {
    console.error("Sign message error:", error);
    return new Response(JSON.stringify({
      message: "Failed to process sign message request"
    } as ActionError), { status: 500, headers });
  }
};

Verification Endpoint

src/app/api/actions/sign-structured/verify/route.ts

import {
  ActionGetResponse,
  ActionPostRequest,
  ActionError,
  ACTIONS_CORS_HEADERS,
  BLOCKCHAIN_IDS
} from "@solana/actions";
import { PublicKey } from "@solana/web3.js";
import nacl from "tweetnacl";
import * as bs58 from "bs58";

const blockchain = BLOCKCHAIN_IDS.mainnet;
const headers = {
  ...ACTIONS_CORS_HEADERS,
  'X-Blockchain-Ids': blockchain,
  'X-Action-Version': '2.4'
};

// Same server keypair as above
const SERVER_KEYPAIR = nacl.sign.keyPair.fromSecretKey(
  bs58.decode("YOUR_SECRET_KEY_HERE")
);

export const OPTIONS = async () => new Response(null, { headers });

export const POST = async (req: Request) => {
  try {
    const request: ActionPostRequest = await req.json();
    const { account, signature, state } = request;

    if (!signature || !state) {
      return new Response(JSON.stringify({
        message: "Signature and state are required"
      } as ActionError), { status: 400, headers });
    }

    // Parse state data
    const { message, serverSignature } = JSON.parse(state) as {
      message: string;
      serverSignature: string;
    };

    // Verify server signature (anti-tampering)
    const serverSignatureValid = verifySignature(
      message,
      serverSignature,
      bs58.encode(SERVER_KEYPAIR.publicKey)
    );

    // Verify user signature
    const userSignatureValid = verifySignature(message, signature, account);

    const isValid = serverSignatureValid && userSignatureValid;

    if (!isValid) {
      const payload: ActionGetResponse = {
        type: "action",
        icon: new URL("/sign-icon.jpg", req.url).toString(),
        title: "❌ Signature Verification Failed",
        description: `Invalid signature. Server: ${serverSignatureValid}, User: ${userSignatureValid}`,
        label: "Try Again",
        links: { actions: [] }
      };
      return new Response(JSON.stringify(payload), { headers });
    }

    // Success - you can now save data to database, authenticate user, etc.
    const payload: ActionGetResponse = {
      type: "action",
      icon: new URL("/sign-icon.jpg", req.url).toString(),
      title: "✅ Signature Verified Successfully",
      description: `Message verified for wallet: ${account}`,
      label: "Completed",
      links: { actions: [] }
    };

    return new Response(JSON.stringify(payload), { headers });

  } catch (error) {
    console.error("Verification error:", error);
    return new Response(JSON.stringify({
      message: "Signature verification failed"
    } as ActionError), { status: 500, headers });
  }
};

function verifySignature(message: string, signature: string, account: string): boolean {
  try {
    const messageBytes = new TextEncoder().encode(message);
    const signatureBytes = bs58.decode(signature);
    const publicKeyBytes = new PublicKey(account).toBytes();
    
    return nacl.sign.detached.verify(
      messageBytes,
      signatureBytes,
      publicKeyBytes
    );
  } catch {
    return false;
  }
}

This structured approach uses the SIWS (Sign-In With Solana) standard and provides enhanced security through:

Domain binding - Message is tied to your specific domain
Anti-replay protection - Unique nonce prevents message reuse
Timestamp validation - issuedAt helps detect stale requests
Server signature - Prevents message tampering

Security Considerations

Production Security Requirements

Store server keypairs securely (use environment variables)
Validate all inputs thoroughly
Implement rate limiting to prevent spam
Use HTTPS in production
Consider nonce expiration for time-sensitive operations
Log security events for monitoring

Common Use Cases

Message signing is ideal for:

Wallet Based Login/Authentication - Sign in to dApps and platforms
Token Holder Verification - Prove ownership of specific tokens or NFTs for access
Multi-Step Flows - Combine with action chaining
Whitelist Registration - Sign up for airdrops, presales, or exclusive events
DAO Governance - Off-chain voting and proposal participation
Settings Management - Change notification preferences, update profile settings

Integration with Action Chaining

Message signing works seamlessly with action chaining for multi-step flows:

const response: ActionPostResponse = {
  type: "message",
  message: "Thank you for signing!",
  links: {
    next: {
      type: "post", 
      href: "/api/actions/next-step"
    }
  }
};

For a complete working example, see our Feedback Blink guide which implements message signing with database storage and action chaining.

GETTING STARTED

CLIENT

PROVIDER (API)

STARTERS

API REFERENCE

Key Concepts

Authentication

Cryptographic Proof

Instant Verification

When to Use Message Signing vs Transactions

Two Approaches to Message Signing

1. Plain Text Signing

2. Structured Message Signing (Recommended)

Main Endpoint

Verification Endpoint

Security Considerations

Common Use Cases

Integration with Action Chaining

GETTING STARTED

CLIENT

PROVIDER (API)

STARTERS

API REFERENCE

Documentation Index

​Key Concepts

Authentication

Cryptographic Proof

Instant Verification

​When to Use Message Signing vs Transactions

​Two Approaches to Message Signing

​1. Plain Text Signing

​2. Structured Message Signing (Recommended)

​Main Endpoint

​Verification Endpoint

​Security Considerations

​Common Use Cases

​Integration with Action Chaining

Key Concepts

When to Use Message Signing vs Transactions

Two Approaches to Message Signing

1. Plain Text Signing

2. Structured Message Signing (Recommended)

Main Endpoint

Verification Endpoint

Security Considerations

Common Use Cases

Integration with Action Chaining