(MFC) 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 C/C++ Library Downloads MS Visual C/C++ Libs

See Also: Using MFC CString in Chilkat

#include <CkPrivateKey.h>
#include <CkXml.h>
#include <CkBinData.h>
#include <CkCert.h>
#include <CkPublicKey.h>

void ChilkatSample(void)
    {
    CkString strOut;

    CkPrivateKey privKey;

    const char *password = "12345678a";
    bool success = privKey.LoadPkcs8EncryptedFile("qa_data/certs/test_12345678a.key",password);
    if (success != true) {
        strOut.append(privKey.lastErrorText());
        strOut.append("\r\n");
        SetDlgItemText(IDC_EDIT1,strOut.getUnicode());
        return;
    }

    CkXml xml;
    xml.LoadXml(privKey.getXml());

    // The XML contains the parts of the key in base64.
    strOut.append("Private Key XML:");
    strOut.append("\r\n");
    strOut.append(xml.getXml());
    strOut.append("\r\n");

    // We can get the base64 modulus like this:
    const char *modulus = xml.getChildContent("Modulus");
    strOut.append("base64 modulus = ");
    strOut.append(modulus);
    strOut.append("\r\n");

    // To convert to hex:
    CkBinData binDat;
    binDat.AppendEncoded(modulus,"base64");
    const char *hexModulus = binDat.getEncoded("hex");
    strOut.append("hex modulus = ");
    strOut.append(hexModulus);
    strOut.append("\r\n");

    // Now get the modulus from the cert:
    CkCert cert;

    success = cert.LoadFromFile("qa_data/certs/test_12345678a.cer");
    if (success != true) {
        strOut.append(cert.lastErrorText());
        strOut.append("\r\n");
        SetDlgItemText(IDC_EDIT1,strOut.getUnicode());
        return;
    }

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

    xml.LoadXml(pubKey->getXml());
    strOut.append("Public Key XML:");
    strOut.append("\r\n");
    strOut.append(xml.getXml());
    strOut.append("\r\n");

    // Proceed in the same way as before....
    modulus = xml.getChildContent("Modulus");
    strOut.append("base64 modulus = ");
    strOut.append(modulus);
    strOut.append("\r\n");

    // To convert to hex:
    binDat.Clear();
    binDat.AppendEncoded(modulus,"base64");
    hexModulus = binDat.getEncoded("hex");
    strOut.append("hex modulus = ");
    strOut.append(hexModulus);
    strOut.append("\r\n");

    delete pubKey;


    SetDlgItemText(IDC_EDIT1,strOut.getUnicode());

    }