(C# UWP/WinRT) 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 

Chilkat Universal Windows Platform (UWP) / WinRT Downloads Chilkat for the Universal Windows Platform (UWP)

Chilkat.PrivateKey privKey = new Chilkat.PrivateKey();

string password = "12345678a";
bool success = privKey.LoadPkcs8EncryptedFile("qa_data/certs/test_12345678a.key",password);
if (success != true) {
    Debug.WriteLine(privKey.LastErrorText);
    return;
}

Chilkat.Xml xml = new Chilkat.Xml();
xml.LoadXml(privKey.GetXml());

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

// We can get the base64 modulus like this:
string modulus = xml.GetChildContent("Modulus");
Debug.WriteLine("base64 modulus = " + modulus);

// To convert to hex:
Chilkat.BinData binDat = new Chilkat.BinData();
binDat.AppendEncoded(modulus,"base64");
string hexModulus = binDat.GetEncoded("hex");
Debug.WriteLine("hex modulus = " + hexModulus);

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

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

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

xml.LoadXml(pubKey.GetXml());
Debug.WriteLine("Public Key XML:");
Debug.WriteLine(xml.GetXml());

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

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