zod-backend/src/auth/utils/crypt.ts

import * as crypto from 'crypto';

export function verifySignature(
  publicKeyBase64: string,
  signatureBase64: string,
  message: string,
  algorithm: 'SHA1' | 'SHA384',
) {
  const signatureBuffer = Buffer.from(signatureBase64, 'base64');

  const publicKeyPEM = '-----BEGIN PUBLIC KEY-----\n' + publicKeyBase64 + '\n-----END PUBLIC KEY-----';
  const verifier = crypto.createVerify(algorithm);
  verifier.update(message, 'utf8');
  return verifier.verify(
    {
      key: publicKeyPEM,
      padding: crypto.constants.RSA_PKCS1_PADDING,
    },
    signatureBuffer,
  );
}

export function removePadding(originalSignature: string) {
  const buffer = Buffer.from(originalSignature, 'base64');
  return buffer.toString('base64');
}