How to verify signed Tx and signer's address?

[golddydev]

Hello everybody. I am now facing an issue while I tried to verify the signed Tx.

I was trying to verify this signed Tx in the same way I verify the signed Data using

@emurgo/cardano-message-signing-nodejs
@emurgo/cardano-serialization-lib-nodejs

I send the signedData like this

const signedData = {
    signature: transaction string,
    key: signed transaction
}

But I got error like this.

Deserialization failed in TransactionWitnessSet because: Invalid cbor: not the right type, expected Map' byte received Array'.

I think it is because the transaction format and the message (signedData) format is different. But how to fix this?

Can anyone help?

Thank you.

[lisicky]

Hi @eageringdev ! Unfortunately I can not help with additional information like a code example, cbor of transaction

[golddydev]

At least, verifying signed transaction is doable? The blockchain itself certainly do. But how can we do on our own code?

[lisicky]

You can check it by CSL:

1. Use FixedTransaction type to deserialize a transaction
2. get raw_body from FixedTransaction and and body hash by TransactionHash.from_bytes(blake2b(32).update(raw_body).digest('binary'))
3. After you can get signatures and public keys from tx witness set and verify it by calling verify from PublicKey type

[golddydev]

Thanks, @lisicky Your answer inspires me. Extract the public key from transaction body.

import { C } from 'lucid-cardano';

export const decodeSignedData = ({ signedData }) => {
  const { signature, data } = signedData;
  const txVkeyWitnesses = C.TransactionWitnessSet.from_bytes(
    Buffer.from(signature, 'hex')
  );
  const pubKeyHash = txVkeyWitnesses
    .vkeys()
    ?.get(0)
    .vkey()
    .public_key()
    .hash()
    .to_hex();

  const tx = C.Transaction.from_bytes(Buffer.from(data, 'hex'));
  const txSignerPubKeyHash = tx.body().required_signers()?.get(0).to_hex();

  const isVerified = pubKeyHash?.length > 0 && pubKeyHash == txSignerPubKeyHash;

  const rewardAddress = C.RewardAddress.new(
    C.NetworkInfo.mainnet().network_id(),
    C.StakeCredential.from_keyhash(C.Ed25519KeyHash.from_hex(pubKeyHash))
  );
  return {
    isVerified,
    signerAddress: rewardAddress.to_address().to_bech32(),
  };
};

This is the code snippet to verify the signed transaction. Where the signedData.signature is signed transaction and signedData.data is transaction data (hex string).

What do you think?