Node.js

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. Node.js

NODEJS_PRELUDE

function chilkatExample() {

    var success = false;

    // 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.
    var privKey = new chilkat.PrivateKey();
    success = privKey.LoadEncryptedPemFile("qa_data/ecc/secp256r1-key-pkcs8-secret.pem","secret");
    if (success == false) {
        console.log(privKey.LastErrorText);
        return;
    }

    // Sign the SHA256 hash of some data.
    var bd = new chilkat.BinData();
    success = bd.LoadFile("qa_data/hamlet.xml");
    if (success == false) {
        console.log("Failed to load file to be hashed.");
        return;
    }

    var crypt = new chilkat.Crypt2();
    crypt.HashAlgorithm = "sha256";
    crypt.EncodingMode = "base64";
    var hashStr = crypt.HashBdENC(bd);

    var ecdsa = new chilkat.Ecc();
    var prng = new chilkat.Prng();
    // Returns ASN.1 signature as a base64 string.
    var 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:
    var asn = new chilkat.Asn();
    asn.LoadEncoded(sig,"base64");
    var xml = new chilkat.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
    var r = xml.GetChildContentByIndex(0);
    var 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.
    var pubKey = new chilkat.PublicKey();
    success = pubKey.LoadFromFile("qa_data/ecc/secp256r1-pub.pem");
    if (success == false) {
        console.log(pubKey.LastErrorText);
        return;
    }

    // We already have the SHA256 hash of the original data (hashStr) so no need to re-do it..
    var ecc2 = new chilkat.Ecc();
    var 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:
    var xml2 = new chilkat.Xml();
    xml2.Tag = "sequence";
    xml2.NewChild2("int",r);
    xml2.NewChild2("int",s);

    var asn2 = new chilkat.Asn();
    asn2.LoadAsnXml(xml2.GetXml());
    var 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...

}

chilkatExample();