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I am trying to broadcast a Tezos transaction on the Babylon testnet.

I'm using an external military-grade hardware security module (HSM) located on a remote server. Its purpose is to never expose the private key to the outside, but it will sign payloads that I send to it and returns those to me. It uses the SECP256K1 elliptic curve methodology for signing and as such I have to use 'tz2' addresses, as they lie on the SECP256K1 curve.

For building and transmitting the transaction I use the Taquito library. The address I'm trying to send from is: https://babylonnet.tzstats.com/tz2RzEYWusHfd1ZCrEKfMFPaL4pCaYV61eeL Its public key is:

{
    x: 'da17e06b2c2be5cf311eb08061681864e13dafd4bac36ba659a3821a6805bf3c',
    y: '34182f94d154f0761d91712913cf317c0491219db7c986316fbaa28e56c9cbab'
}

Taquito allows you to implement your own Signer object: https://github.com/ecadlabs/taquito/blob/master/packages/taquito/src/signer/interface.ts. The custom signer connects to the HSM, the HSM signs the payload and returns a DER signature, and the custom signer adds the R and S of the DER signature to the payload in the 'sbytes' property used for broadcasting.

Here is my custom Signer class and sign function (I left out the 3 other interface functions here). Most of it is just copied from the Taquito signer: https://github.com/ecadlabs/taquito/blob/master/packages/taquito-signer/src/taquito-signer.ts

export class XtzCustomSigner implements Signer {

  async sign(bytes: string, watermark?: Uint8Array) {
    try {
      let bb = hex2buf(bytes);
      if (typeof watermark !== 'undefined') {
        bb = mergebuf(watermark, bb);
      }

      const payload: string = bufferToHexString(Buffer.from(bb));
      await sodium.ready;
      const payloadHash = bufferToHexString(Buffer.from(sodium.crypto_generichash(32, 
       payload)))

      // This line signs the payload with the HSM
      const signature = await this.hsmCommunicationService.requestSign(this.modelPortfolio,
          this.authKey, this.coinAccount, this._publicKey, payloadHash, this.derivationPath);

      // Get R + (canonical) S from signature
      const signatureBuffer = extractRSFromDERSignature(signature, true);
      const sbytes = bytes + buf2hex(signatureBuffer);

      const result = {
        bytes: undefined,
        sig: undefined,
        prefixSig: b58cencode(signatureBuffer, prefix[Prefix.SPSIG]),
        sbytes,
      };
      return result;
    } catch (ex) {
      console.log(ex);
      throw ex;
    }
  }
}

This sign function is called by taquito automatically if the customer signer is passed into the Provider. The code that calls this signer:

public async buildTransaction(input: ICoinTransactionInput): Promise<void> {
    // Set up connection to Babylonnet using custom signer
    Tezos.setProvider({ rpc: 'https://api.tez.ie/rpc/babylonnet', signer: this.xtzCustomSigner });

    // Modifies the custom signer with correct input credentials
    this.setData(input.senderCredentials, input.senderCoinAccount);

    const receivingAddress = 'tz2H81kw4NahMKoenoGSizWxes82B9PiLiyG';

    // Here we get a fee estimate and the amount to transfer (in units of Tezos, so not the 10^-6 unit).
    const { amount, estimate } = await this.adjustTransactionAmountFee(input.amount, receivingAddress);

    // Here we do the transaction broadcasting
    let op: TransactionOperation;
    try {
      op = await Tezos.contract.transfer({
        to: receivingAddress,
        amount,
        fee: estimate.suggestedFeeMutez,
        gasLimit: estimate.gasLimit,
        storageLimit: estimate.storageLimit,
      });
    } catch (e) {
      console.log(e);
    }

    // Wait for at least 1 confirmation of the transaction
    const blockHeight = await op.confirmation(1);
  }

Upon attempting to broadcast, Babylon returns the following error:

    HttpResponseError {
      message:
       'Http error response: (500) [{"kind":"permanent","id":"proto.005-PsBabyM1.operation.invalid_signature"}]\n',
      status: 500,
      statusText: 'Internal Server Error',
      body:
       '[{"kind":"permanent","id":"proto.005-PsBabyM1.operation.invalid_signature"}]\n',
      name: 'HttpResponse' }

So it says the signature is invalid. To rule some things out:

  • I've implemented BTC and ETH transactions using the same signing function with the HSM (hsmCommunicationService.requestSign()). Signing and broadcasting works successfully for both coins.
  • The HSM and the botan library that I use to verify the DER signature both don't throw an error, meaning that the public key is successfully used to verify the signature.
  • I am aware of the prefixes that Tezos uses. For the SECP256K1 elliptic curve you need:

    • 'tz2' prefix before a Tezos address (public key hash)
    • 'sppk' prefix before a Tezos public key
    • 'sig' prefix before the 'sig' property
    • 'spsig' prefix before the 'prefixSig' property
  • I use the same function to extract R and S from the signature that I use for BTC and ETH. For Tezos, I know that you need the 'Lower S' (canonical) form of the signature. Thus I add the following check if canonical is set to true:

export const extractRSFromDERSignature = (signature: string,
                                          canonical: boolean = false): Buffer => {

  let R: string; 
  let S: string;

  // -------------
  // Here is standard code not relevant right now to get R and S from the DER signature
  // -------------

  if (canonical) {
    const bnS = new BigNumber(S);

    // This is the order of the elliptic curve N
    const bnN = new BigNumber('FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFEBAAEDCE6AF48A03BBFD25E8CD0364141', 16);

    // if S > N / 2
    if (bnS.isGreaterThan(bnN.div(new BigNumber(2)))) {
      // then S = N - S
      S = bnN.minus(bnS).toString(16);
    }

    const RS: string = R + S;
    return hexStringToBuffer(RS.toLowerCase());
  }

I used the Taquito default signer to successfully sign and broadcast from a 'tz1' address to 'tz2' addresses: https://babylonnet.tzstats.com/tz1NZuMdXsXhDQHVRX1yHEyViKrkYmKB5TPw. All I did was comment out my custom signer and use the default signer and it worked. I checked the signatures' format to compare:

Signing with the taquito default signer (tz1 address, uses Edward's curve), 'sig' property is:

sighWTZ1HNXf3u5BsmFvGfWrW3rQFMYbf3htFLXiftx5PM5CemciKG6DCchVP24sJuDB6MPv67VVwtPjYnHZG7uJXz34ej6e

'prefixSig' property is:

edsighWTZ1HNXf3u5BsmFvGfWrW3rQFMYbf3htFLXiftx5PM5CemciKG6DCchVP24sJuDB6MPv67VVwtPjYnHZG7uJXz34ej6e

Signing with my custom signer, 'sig' property is:

sigsAujsNePapNNGsVotTvcKWMNNJja9B4a2FfAe8vExzFhEgEo1GTQStiif22uSA6iNxPGCGsXsRyeLHzeLbJL2y8CnYuNe

'prefixSig' property is:

spsigsAujsNePapNNGsVotTvcKWMNNJja9B4a2FfAe8vExzFhEgEo1GTQStiif22uSA6iNxPGCGsXsRyeLHzeLbJL2y8CnYuNe

The prefix is correct, the length is correct. Does anyone have an idea what the problem might be? Any tips on what parts of code I should check out to find the error?

  • Are you sure that you derived the public key hash in the correct manner, because if that is wrong, then it will return invalid signature as well. – Tjappo Feb 29 at 12:16
2

I ran your code, and found out that your payload hash is not correct; these lines of code:

const payload: string = bufferToHexString(Buffer.from(bb));
await sodium.ready;
const payloadHash = bufferToHexString(Buffer.from(sodium.crypto_generichash(32, 
       payload)))

. The function sodium.crypto_generichash involving the hashing of a uint8array and the hashing of a string do not yield the same result. If you convert the payload to a uint8array, it does work. In other words, you can change the lines above to:

await sodium.ready;
const payloadHash = bufferToHexString(Buffer.from(sodium.crypto_generichash(32, 
       bb)))

. You do not have to convert the bb (uint8array) to a buffer and then to a hex string.

  • Can't believe it was actually something that simple :) – CoderApprentice Mar 1 at 22:25
1

Util Link: base58.ml

The pre-apply RPC call validates the signature prefix, while the inject operation call doesn't.

You should use the specific curve prefix.

sig([4, 130, 43]) # sig(96) generic signature (Used after the operation injection)

edsig([9, 245, 205, 134, 18]) # edsig(99) ED25519 signature (Used for tz1 signatures)

spsig1([13, 115, 101, 19, 63]) # spsig1(99) SECP256K1 signature (Used for tz2 signatures)

p2sig([54, 240, 44, 52]) # p2sig(98) SECP256R1 signature (Used for tz3 signatures)

  • Apologies, the signature examples I posted were the generic 'sig' property values returned by the Signer's 'sign' function. I just now added the 'prefixSig' property values. This line of code -> prefixSig: b58cencode(signatureBuffer, prefix[Prefix.SPSIG]) does add [13, 115, 101, 19, 63] to the signature. – CoderApprentice Feb 28 at 20:00

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