JavaScript

About RSA Public/Private Keys

See more RSA Examples

This example provides some additional information for understanding public/private key pairs. In demonstrates how a private key is a superset of the public key. A public key contains the modulus and exponent. The matching private key also contains the modulus and exponent, but also contains the additional private key parts. JavaScript

var success = false;

var cert = new CkCert();

// Load a digital certificate.
success = cert.LoadFromFile("digitalCert.cer");
if (success == false) {
    console.log(cert.LastErrorText);
    return;
}

// A .cer file does not contain the private key.  It should contain
// the public key...
var pubKey = new CkPublicKey();
cert.GetPublicKey(pubKey);

// Let's have a look at it (in XML format).
console.log("Public Key from Certificate:");
console.log(pubKey.GetXml());

// An RSA public key consists of a modulus and exponent.

// An RSA private key includes both the modulus and exponent,
// as well as other "big" numbers: P, Q, D, etc.

// Let's load an RSA private key from a DER-encoded file:
var privKey = new CkPrivateKey();

success = privKey.LoadAnyFormatFile("PrivateKey.key","");
if (success !== true) {
    console.log(privKey.LastErrorText);
    return;
}

// If this private key is the matching half to the public key from
// the certificate, then the modulus and exponent should
// be identical.  (Thus, a "private key" really contains both the public part as well as the private parts...).
console.log("Private Key from DER:");
console.log(privKey.GetXml());