Gnosis Safe – EIP-1271 Signatures with Gnosis Safe Off-Chain

I am trying to generate an EIP-1271 contract signature off-chain, and propose a transaction using safe-api-kit. My first question is, is there support for creating EIP-1271 signatures using safe-core-sdk? I assume not simply because of this commit that is merged recently into develop which brings support for contract signatures. But if there are like helper(ish) functions with the current version I don't know of that I can use, it would be greatly appreciated.

Since I couldn't find any, I implemented my own signature by implementing the SafeSignature interface:

import { SafeSignature } from "@safe-global/safe-core-sdk-types";
import { addressToBytes32, intToBytes32 } from "./utils";

export const EIP1271_IMPL_CONTRACT_ADDRESS = "0x1E69533f104F7868DD280bf7E77b06F7De0b3063";

export class EIP1271SafeSignature implements SafeSignature {
    signer: string = EIP1271_IMPL_CONTRACT_ADDRESS;
    data: string = "0x00000000000000000000000000000000000000000000000000000000deadbeef";

    // EIP1271 implementing contract address
    private readonly r = addressToBytes32(EIP1271_IMPL_CONTRACT_ADDRESS);
    // offset of the dynamic data, for demo purposes we can put constant here
    private readonly s = intToBytes32(65);
    // signature type 0
    private readonly v = "00";
    // dynamic part of the signature in which can be any bytes, and will be sent to the EIP1271 implementing contract
    private dynamic = "000000000000000000000000000000000000000000000000000000000000002000000000000000000000000000000000000000000000000000000000deadbeef";

    staticPart(): string {
        return this.r + this.s.substring(2) + this.v;
    }

    dynamicPart(): string {
        return this.dynamic;
    }

    build() {
        return (this.staticPart() + this.dynamicPart()).toLowerCase();
    }
}

I know that offset (s part of the signature) requires a bit more work due to concatenation of multiple signatures into one, but currently, I am testing with only 1 threshold, and I am just trying to propose and execute a transaction, hence I hardcoded it as 65.

I first create a transaction as follows:

  const safeTransaction = await safeSdkOwner1.createTransaction({ 
    transactions: [{
      to: await owner1Signer.getAddress(),
      data: "0x",
      value: weiAmount,
    }],
  });

Then I get the Safe hash of this transaction:

  const safeTxHash = await safeSdkOwner1.getTransactionHash(safeTransaction);

Then I propose the transaction as following:

  const contractSignature = new EIP1271SafeSignature();
  await safeApiKit.proposeTransaction({
    safeAddress,
    safeTransactionData: safeTransaction.data,
    safeTxHash,
    senderAddress: contractSignature.signer,
    senderSignature: contractSignature.build(),
  });

I receive the following error from the proposeTransaction method of safe-api-kit:

Error:
Signature=0x0000000000000000000000001e69533f104f7868dd280bf7e77b06f7de0b3063000000000000000000000000000000000000000000000000000000000000004100
for owner=0x1E69533f104F7868DD280bf7E77b06F7De0b3063 is not valid

And here is the signature I am getting by calling contractSignature.build():

0x0000000000000000000000001e69533f104f7868dd280bf7e77b06f7de0b3063000000000000000000000000000000000000000000000000000000000000004100000000000000000000000000000000000000000000000000000000000000002000000000000000000000000000000000000000000000000000000000deadbeef

Any idea what I am doing wrong?

Versions

Safe: 1.3.0
Safe API Kit: 2.0.0
Safe Protocol Kit: 2.0.0