(Node.js) Get RSA Key Modulus from .cer or .key

Demonstrates how to get the RSA key modulus from either the certificate (.cer) or RSA key (.key). OpenSSL commands to do the same would be:

openssl x509 -inform DER -in "test.cer"  -modulus -noout 

openssl pkcs8 -inform DER -in​ "test.key"​ -outform PEM -passin pass:"12345​678a​"
   | openssl rsa -inform PEM -modulus -noout 

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() {

    var privKey = new chilkat.PrivateKey();

    var password = "12345678a";
    var success = privKey.LoadPkcs8EncryptedFile("qa_data/certs/test_12345678a.key",password);
    if (success !== true) {
        console.log(privKey.LastErrorText);
        return;
    }

    var xml = new chilkat.Xml();
    xml.LoadXml(privKey.GetXml());

    // The XML contains the parts of the key in base64.
    console.log("Private Key XML:");
    console.log(xml.GetXml());

    // We can get the base64 modulus like this:
    var modulus = xml.GetChildContent("Modulus");
    console.log("base64 modulus = " + modulus);

    // To convert to hex:
    var binDat = new chilkat.BinData();
    binDat.AppendEncoded(modulus,"base64");
    var hexModulus = binDat.GetEncoded("hex");
    console.log("hex modulus = " + hexModulus);

    // Now get the modulus from the cert:
    var cert = new chilkat.Cert();

    success = cert.LoadFromFile("qa_data/certs/test_12345678a.cer");
    if (success !== true) {
        console.log(cert.LastErrorText);
        return;
    }

    // The cert contains the public key, which is composed of the
    // modulus + exponent (for RSA keys).
    // pubKey: PublicKey
    var pubKey = cert.ExportPublicKey();

    xml.LoadXml(pubKey.GetXml());
    console.log("Public Key XML:");
    console.log(xml.GetXml());

    // Proceed in the same way as before....
    modulus = xml.GetChildContent("Modulus");
    console.log("base64 modulus = " + modulus);

    // To convert to hex:
    binDat.Clear();
    binDat.AppendEncoded(modulus,"base64");
    hexModulus = binDat.GetEncoded("hex");
    console.log("hex modulus = " + hexModulus);


}

chilkatExample();