(Node.js) ECDSA Sign Data and Get Raw R and S Values

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

Install Chilkat for Node.js and Electron using npm at Chilkat npm packages for Node.js Chilkat npm packages for Electron on Windows, Linux, MacOSX, and ARM

var os = require('os');
if (os.platform() == 'win32') {  
    if (os.arch() == 'ia32') {
        var chilkat = require('@chilkat/ck-node21-win-ia32');
    } else {
        var chilkat = require('@chilkat/ck-node21-win64'); 
    }
} else if (os.platform() == 'linux') {
    if (os.arch() == 'arm') {
        var chilkat = require('@chilkat/ck-node21-arm');
    } else if (os.arch() == 'x86') {
        var chilkat = require('@chilkat/ck-node21-linux32');
    } else {
        var chilkat = require('@chilkat/ck-node21-linux64');
    }
} else if (os.platform() == 'darwin') {
    if (os.arch() == 'arm64') {
        var chilkat = require('@chilkat/ck-node21-mac-m1');
    } else {
        var chilkat = require('@chilkat/ck-node21-macosx');
    }
}

function chilkatExample() {

    // 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();
    var 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();