React Native

ECDSA Sign and Verify

See more ECC Examples

Demonstrates how to create an ECDSA signature on the SHA256 hash of some data, and then verify. React Native

import { Asn, BinData, Crypt2, Ecc, PrivateKey, Prng, PublicKey, Xml } from '@chilkat/react-native'

function chilkatExample() {
  // This example assumes the Chilkat API to have been previously unlocked.
  // See Global Unlock Sample for sample code.

  // First load an ECDSA private key to be used for signing.
  const privKey = new PrivateKey();
  try {
    privKey.loadEncryptedPemFile('qa_data/ecc/secp256r1-key-pkcs8-secret.pem', 'secret');
  } catch {
    console.log(privKey.lastErrorText);
    return;
  }

  // Sign the SHA256 hash of some data.
  const bd = new BinData();
  try {
    bd.loadFile('qa_data/hamlet.xml');
  } catch {
    console.log('Failed to load file to be hashed.');
    return;
  }

  const crypt = new Crypt2();
  crypt.hashAlgorithm = 'sha256';
  crypt.encodingMode = 'base64';
  const hashStr = crypt.hashBdENC(bd);

  const ecdsa = new Ecc();
  const prng = new Prng();
  // Returns ASN.1 signature as a base64 string.
  const sig = ecdsa.signHashENC(hashStr, 'base64', privKey, prng);
  console.log(`sig = ${sig}`);

  // The signature is in ASN.1 format (which may be described as the "encoded DSS signature").
  // SEQUENCE (2 elem)
  //   INTEGER (255 bit) 4849395540832462044300553275435608522154141569743642905628579547100940...
  //   INTEGER (255 bit) 3680701124244788134409868118208591399799457104230118295614152238560005...

  // If you wish, you can get the r and s components of the signature like this:
  const asn = new Asn();
  asn.loadEncoded(sig, 'base64');
  const xml = new Xml();
  xml.loadXml(asn.asnToXml());

  console.log(xml.getXml());

  // We now have this:
  // <?xml version="1.0" encoding="utf-8"?>
  // <sequence>
  //     <int>6650D422D86BA4A228B5617604E59052591B9B2C32EF324C44D09EF67E5F0060</int>
  //     <int>0CFD9F6AC85042FC70F672C141BA6B2A4CAFBB906C3D907BCCC1BED62B28326F</int>
  // </sequence>

  // Get the "r" and "s" as hex strings
  const r = xml.getChildContentByIndex(0);
  const s = xml.getChildContentByIndex(1);

  console.log(`r = ${r}`);
  console.log(`s = ${s}`);

  // --------------------------------------------------------------------
  // Now verify against the hash of the original data.

  // Get the corresponding public key.
  const pubKey = new PublicKey();
  try {
    pubKey.loadFromFile('qa_data/ecc/secp256r1-pub.pem');
  } catch {
    console.log(pubKey.lastErrorText);
    return;
  }

  // We already have the SHA256 hash of the original data (hashStr) so no need to re-do it..
  const ecc2 = new Ecc();
  const result = ecc2.verifyHashENC(hashStr, sig, 'base64', pubKey);
  if (result !== 1) {
    console.log(ecc2.lastErrorText);
    return;
  }

  console.log('Verified!');

  // Note: If we have only r,s and wish to reconstruct the ASN.1 signature, we do it like this:
  const xml2 = new Xml();
  xml2.tag = 'sequence';
  xml2.newChild2('int', r);
  xml2.newChild2('int', s);

  const asn2 = new Asn();
  asn2.loadAsnXml(xml2.getXml());
  const encodedSig = asn2.getEncodedDer('base64');
  console.log(`encoded DSS signature: ${encodedSig}`);

  // You can go to https://lapo.it/asn1js/  and copy/paste the base64 encodedSig into the online tool, then press the "decode" button.
  // You will see the ASN.1 such as this:

  // SEQUENCE (2 elem)
  //   INTEGER (255 bit) 4849395540832462044300553275435608522154141569743642905628579547100940...
  //   INTEGER (255 bit) 3680701124244788134409868118208591399799457104230118295614152238560005...
}