(C) RSA Sign with PKCS8 Encrypted Key

Demonstrates how to load a private key from an encrypted PKCS8 file and create an RSA digital signature (and then verify it).

Note: This example requires Chilkat v11.0.0 or greater.

Chilkat C/C++ Library Downloads
MS Visual C/C++ C++ Builder Linux C/C++ Alpine Linux C/C++	MacOS C/C++ iOS C/C++ Android C/C++ MinGW C/C++

#include <C_CkPrivateKey.h>
#include <C_CkRsa.h>
#include <C_CkCert.h>
#include <C_CkPublicKey.h>

void ChilkatSample(void)
    {
    BOOL success;
    HCkPrivateKey privKey;
    HCkRsa rsa;
    const char *strData;
    const char *hexSig;
    HCkCert cert;
    HCkPublicKey pubKey;
    HCkRsa rsa2;

    success = FALSE;

    // This example assumes the Chilkat API to have been previously unlocked.
    // See Global Unlock Sample for sample code.

    privKey = CkPrivateKey_Create();

    // Load the private key from an RSA PEM file:
    success = CkPrivateKey_LoadAnyFormatFile(privKey,"raul_privateKey.key","a0123456789");
    if (success == FALSE) {
        printf("%s\n",CkPrivateKey_lastErrorText(privKey));
        CkPrivateKey_Dispose(privKey);
        return;
    }

    rsa = CkRsa_Create();

    // Import the private key into the RSA component:
    success = CkRsa_UsePrivateKey(rsa,privKey);
    if (success == FALSE) {
        printf("%s\n",CkRsa_lastErrorText(rsa));
        CkPrivateKey_Dispose(privKey);
        CkRsa_Dispose(rsa);
        return;
    }

    // This example will sign a string, and receive the signature
    // in a hex-encoded string.  Therefore, set the encoding mode
    // to "hex":
    CkRsa_putEncodingMode(rsa,"hex");

    strData = "This is the string to be signed.";

    // Sign the string using the sha256 hash algorithm.
    // Other valid choices are sha1, sha384, sha512 and others.
    hexSig = CkRsa_signStringENC(rsa,strData,"sha256");
    if (CkRsa_getLastMethodSuccess(rsa) == FALSE) {
        printf("%s\n",CkRsa_lastErrorText(rsa));
        CkPrivateKey_Dispose(privKey);
        CkRsa_Dispose(rsa);
        return;
    }

    printf("%s\n",hexSig);

    // Now verify with the public key.
    // This example shows how to use the public key from 
    // a digital certificate (.cer file)
    cert = CkCert_Create();
    success = CkCert_LoadFromFile(cert,"raul_publicKey.cer");
    if (success == FALSE) {
        printf("%s\n",CkCert_lastErrorText(cert));
        CkPrivateKey_Dispose(privKey);
        CkRsa_Dispose(rsa);
        CkCert_Dispose(cert);
        return;
    }

    pubKey = CkPublicKey_Create();
    CkCert_GetPublicKey(cert,pubKey);

    rsa2 = CkRsa_Create();
    success = CkRsa_UsePublicKey(rsa2,pubKey);
    if (success == FALSE) {
        printf("%s\n",CkRsa_lastErrorText(rsa2));
        CkPrivateKey_Dispose(privKey);
        CkRsa_Dispose(rsa);
        CkCert_Dispose(cert);
        CkPublicKey_Dispose(pubKey);
        CkRsa_Dispose(rsa2);
        return;
    }

    // Verify the signature against the original data:
    CkRsa_putEncodingMode(rsa2,"hex");
    success = CkRsa_VerifyStringENC(rsa2,strData,"sha256",hexSig);
    if (success == FALSE) {
        printf("%s\n",CkRsa_lastErrorText(rsa2));
        CkPrivateKey_Dispose(privKey);
        CkRsa_Dispose(rsa);
        CkCert_Dispose(cert);
        CkPublicKey_Dispose(pubKey);
        CkRsa_Dispose(rsa2);
        return;
    }

    printf("Signature verified!\n");

    // Verify with incorrect data:
    success = CkRsa_VerifyStringENC(rsa2,"something else","sha256",hexSig);
    if (success != TRUE) {
        printf("Signature not verified! (which was expected in this case)\n");
    }
    else {
        printf("Hmmm... that's not right...\n");
    }



    CkPrivateKey_Dispose(privKey);
    CkRsa_Dispose(rsa);
    CkCert_Dispose(cert);
    CkPublicKey_Dispose(pubKey);
    CkRsa_Dispose(rsa2);

    }