Node.js

ECDSA Sign Data and Get Raw R and S Values

See more ECC Examples

Demonstrates getting the raw R and S value of an ECDSA signature. Node.js

NODEJS_PRELUDE

function chilkatExample() {

    var success = false;

    // This example requires the Chilkat API to have been previously unlocked.
    // See Global Unlock Sample for sample code.

    // To create an ECDSA signature, the data first needs to be hashed.  Then the hash
    // is signed.

    var crypt = new chilkat.Crypt2();
    crypt.HashAlgorithm = "SHA256";
    crypt.Charset = "utf-8";
    crypt.EncodingMode = "base64";

    // Hash a string.
    var hash1 = crypt.HashStringENC("The quick brown fox jumps over the lazy dog");
    console.log("hash1 = " + hash1);

    // -----------------------------------------------------------
    // An ECDSA private key is used for signing.  The public key is for signature verification.
    // Load our ECC private key.
    // Our private key file contains this:

    // 	// -----BEGIN PRIVATE KEY-----
    // 	MIGHAgEAMBMGByqGSM49AgEGCCqGSM49AwEHBG0wawIBAQQg3J8q/24D1sEKGdP9
    // 	72MGYElLGpw/a56Y3t6pfON3uhShRANCAATlSmoizyhAwoYZAOuFBATl07/1RR54
    // 	a1Dzfm16grxJe666AGKR+bSs24hk7TEpaeCTvT8YOOM3l+xKFg7zq6Q9
    // 	-----END PRIVATE KEY-----

    var privKey = new chilkat.PrivateKey();
    success = privKey.LoadPemFile("qa_data/ecc/secp256r1-key-pkcs8.pem");
    if (success !== true) {
        console.log(privKey.LastErrorText);
        return;
    }

    // Sign the hash..
    var prng = new chilkat.Prng();
    var ecdsa = new chilkat.Ecc();
    var ecdsaSigBase64 = ecdsa.SignHashENC(hash1,"base64",privKey,prng);
    if (ecdsa.LastMethodSuccess !== true) {
        console.log(ecdsa.LastErrorText);
        return;
    }

    // The ECDSA signature is ASN.1 that contains a sequence of 2 large integers (r and s)
    // For example:
    // SEQUENCE (2 elem)
    //   INTEGER (255 bit) 792134D9B4AD82D5431ED03835A88E2596EB35E5B13054BD9B05A0069281ACC9
    //   INTEGER (255 bit) 481E758CC1E3CBF825537EC3D9A2CA627E5FAD1137BBEA65DF38658DCB0A9ED5

    console.log("Base64 ECDSA signature = " + ecdsaSigBase64);

    // If the raw R and S values are needed, here's how to get them:
    var asn = new chilkat.Asn();
    success = asn.LoadEncoded(ecdsaSigBase64,"base64");
    if (success == false) {
        console.log(asn.LastErrorText);
        return;
    }

    // The R and X will be in hexidecimal in the XML.
    var xml = new chilkat.Xml();
    xml.LoadXml(asn.AsnToXml());
    console.log(xml.GetXml());

    // The XML looks like this:
    // <sequence>
    // <int>792134D9B4AD82D5431ED03835A88E2596EB35E5B13054BD9B05A0069281ACC9</int>
    // <int>481E758CC1E3CBF825537EC3D9A2CA627E5FAD1137BBEA65DF38658DCB0A9ED5</int>
    // </sequence>

    // Copy raw R and S hex values into a Chilkat BinData object.
    var bd = new chilkat.BinData();
    var r = xml.GetChildContent("int[0]");
    var s = xml.GetChildContent("int[1]");
    bd.AppendEncoded(r,"hex");
    bd.AppendEncoded(s,"hex");

    console.log("Number of bytes in bd: " + bd.NumBytes);

}

chilkatExample();