json_sig_2.ts

import * as secp from "@noble/secp256k1"
import { blake3 } from "@noble/hashes/blake3"
import canonicalize from "canonicalize"
import { Address } from "micro-eth-signer"
import { base58, base64 } from "@scure/base"

// enables sync mode
import { hmac } from "@noble/hashes/hmac"
import { sha256 } from "@noble/hashes/sha256"
secp.etc.hmacSha256Sync = (k, ...m) =>
  hmac(sha256, k, secp.etc.concatBytes(...m))

export type SignedObject = {
  _sig: [string, string, number]
  [x: string]: any
}

export const SIG_KEY = "_sig"

export function signedObjSync(privateKey: Uint8Array, obj: any) {
  const wallet = Address.fromPrivateKey(privateKey)
  const hash = blake3(canonicalize(obj) as string)
  const sig = secp.sign(hash, privateKey)
  const sigEncoded = base64.encode(sig.toCompactRawBytes())
  const withSig = { ...obj, [SIG_KEY]: [wallet, sigEncoded, sig.recovery] }
  return withSig
}

export function verifyObjSync(obj: SignedObject) {
  // pull out signature data
  const [wallet, sigEncoded, recovery] = obj[SIG_KEY]

  const objCopy = { ...obj } as any
  delete objCopy[SIG_KEY]

  // recovery pubkey + address
  const hash = blake3(canonicalize(objCopy) as string)
  const sig = secp.Signature.fromCompact(base64.decode(sigEncoded))
  const pubkey = sig.addRecoveryBit(recovery).recoverPublicKey(hash)
  const recoveredWallet = Address.fromPublicKey(pubkey.toRawBytes())

  if (recoveredWallet != wallet) {
    throw new Error(
      `recovered wallet : ${recoveredWallet} doesn't match _sig[0] wallet: ${wallet}`
    )
  }

  return obj
}

signature_codec.ts

/*

a simple codec for signed JSON messages.
a special `_sig` property is added to the encoded JSON, but it is otherwise the same as what you'd get from JSON.stringify:

  {"action":"track.repost","id":123,"_sig":["0x09953a07689ee1959c6C13fB52AdEE57d4f74d38","L3yekPZL2pdOtoGlwa2jb4b9EhqEYgOyQo5D++WZ7bpalvFP3WUultzn7cZDRgpnKxymzYER+C1FQdnQ1dxvMw==",0]}

Using JSON Canonicalization Scheme (JCS) + blake3 means it is not dependant on orig JSON encoding.
It can for instance be stored in a JSONB column (which may change order of properties)
but signature can still be verified later.

*/

import * as secp from "@noble/secp256k1";
import { blake3 } from "@noble/hashes/blake3";
import canonicalize from "canonicalize";
import { Address } from "micro-eth-signer";
import { base64 } from "@scure/base";

const SIG_KEY = "_sig";

export async function encode(privateKey: Uint8Array, obj: any) {
  const hash = blake3(canonicalize(obj) as string);
  const address = Address.fromPrivateKey(privateKey);
  const sig = await secp.signAsync(hash, privateKey);
  const sigEncoded = base64.encode(sig.toCompactRawBytes());
  const withSig = { ...obj, [SIG_KEY]: [address, sigEncoded, sig.recovery] };
  return JSON.stringify(withSig);
}

export async function decode(j: string) {
  const obj = JSON.parse(j);

  // pull out signature data
  const [address, sigEncoded, recovery] = obj[SIG_KEY];
  delete obj[SIG_KEY];

  // recovery pubkey + address
  const hash = blake3(canonicalize(obj) as string);
  const sig = secp.Signature.fromCompact(base64.decode(sigEncoded));
  const pubkey = sig.addRecoveryBit(recovery).recoverPublicKey(hash);
  const recoveredAddress = Address.fromPublicKey(pubkey.toRawBytes());

  if (recoveredAddress != address) {
    throw new Error(
      `recovered address ${recoveredAddress} doesn't match signing address ${address}`
    );
  }

  return [obj, recoveredAddress];
}

//
// test
//
(async () => {
  const privKey = secp.utils.randomPrivateKey();

  const encoded = await encode(privKey, { action: "track.repost", id: 123 });
  console.log(encoded);

  const decoded = await decode(encoded);
  console.log(decoded);

  // try modify message
  {
    const bad = encoded.replace("123", "456");

    try {
      const decoded = await decode(bad);
      console.log(decoded);
    } catch (e) {
      console.log(" !!! tsk tsk", (e as Error).message);
    }
  }

  // try to modify the signer address
  {
    const address = Address.fromPrivateKey(privKey);
    const badWallet = "0x358Bc2D66EE2A585BB2E3f4075b235eA04893064";
    const bad = encoded.replace(address, badWallet);

    try {
      const decoded = await decode(bad);
      console.log(decoded);
    } catch (e) {
      console.log(" !!! tsk tsk", (e as Error).message);
    }
  }
})();