(Unicode C) About RSA Public/Private Keys

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.

Chilkat C/C++ Library Downloads
MS Visual C/C++ Linux/CentOS C/C++ Alpine Linux C/C++ MAC OS X C/C++	armhf/aarch64 C/C++ C++ Builder iOS C/C++ Android C/C++	Solaris C/C++ MinGW C/C++

#include <C_CkCertW.h>
#include <C_CkPublicKeyW.h>
#include <C_CkPrivateKeyW.h>

void ChilkatSample(void)
    {
    HCkCertW cert;
    BOOL success;
    HCkPublicKeyW pubKey;
    HCkPrivateKeyW privKey;

    cert = CkCertW_Create();

    // Load a digital certificate.
    success = CkCertW_LoadFromFile(cert,L"digitalCert.cer");
    if (success != TRUE) {
        wprintf(L"%s\n",CkCertW_lastErrorText(cert));
        CkCertW_Dispose(cert);
        return;
    }

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

    // Let's have a look at it (in XML format).
    wprintf(L"Public Key from Certificate:\n");
    wprintf(L"%s\n",CkPublicKeyW_getXml(pubKey));

    // 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:
    privKey = CkPrivateKeyW_Create();

    success = CkPrivateKeyW_LoadAnyFormatFile(privKey,L"PrivateKey.key",L"");
    if (success != TRUE) {
        wprintf(L"%s\n",CkPrivateKeyW_lastErrorText(privKey));
        CkPublicKeyW_Dispose(pubKey);
        CkCertW_Dispose(cert);
        CkPrivateKeyW_Dispose(privKey);
        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...).
    wprintf(L"Private Key from DER:\n");
    wprintf(L"%s\n",CkPrivateKeyW_getXml(privKey));

    CkPublicKeyW_Dispose(pubKey);


    CkCertW_Dispose(cert);
    CkPrivateKeyW_Dispose(privKey);

    }