signArb.ts

import { makeADR36AminoSignDoc, serializeSignDoc } from "@keplr-wallet/cosmos";
import { Hash, PrivKeySecp256k1 } from "@keplr-wallet/crypto";

function signArbFn(address: string, privateKey: string) {
  const cryptoPrivKey = new PrivKeySecp256k1(fromHex(privateKey));

  return async (message: string | Uint8Array): Promise<string> => {
    const signDoc = makeADR36AminoSignDoc(address, message);
    const serializedSignDoc = serializeSignDoc(signDoc);
    const digest = Hash.sha256(serializedSignDoc);

    const signature = cryptoPrivKey.signDigest32(digest);
    return Buffer.from(
      new Uint8Array([...signature.r, ...signature.s])
    ).toString("base64");
  };
}