(C) RSA Encrypt and Decrypt Credit Card Numbers

C sample code to RSA public-key encrypt and decrypt credit card numbers. The RSA key is loaded from an unencrypted PKCS8 file. Chilkat provides many ways of setting the key -- loading from both encrypted and unencrypted PEM, PKCS8, DER, PVK, etc. Keys may be loaded from files or in-memory representations. (The RSA component also provides the ability to generate RSA keys.)

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

void ChilkatSample(void)
    {
    HCkRsa rsa;
    HCkPrivateKey key;
    BOOL success;
    const char *keyXml;
    const char *ccNumber;
    BOOL usePrivateKey;
    const char *encryptedStr;
    HCkRsa rsaDecryptor;
    const char *decryptedStr;

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

    rsa = CkRsa_Create();

    key = CkPrivateKey_Create();

    // Load an RSA private key from a PKCS8 file:
    success = CkPrivateKey_LoadPkcs8File(key,"rsaPrivateKey.p8");
    if (success != TRUE) {
        printf("%s\n",CkPrivateKey_lastErrorText(key));
        CkRsa_Dispose(rsa);
        CkPrivateKey_Dispose(key);
        return;
    }

    // Get the key as XML:

    keyXml = CkPrivateKey_getXml(key);

    // We'll encrypt with the public key and decrypt with the private
    // key.  (It's also possible to do the reverse.)
    // Note: An RSA private key is composed of different parts internally: modulus, exponent, P, Q, etc.
    // An RSA public-key is a sub-set of the private key.
    // Therefore, when you have a private key, you really have
    // both public and private keys.
    success = CkRsa_ImportPublicKey(rsa,keyXml);
    if (success != TRUE) {
        printf("%s\n",CkRsa_lastErrorText(rsa));
        CkRsa_Dispose(rsa);
        CkPrivateKey_Dispose(key);
        return;
    }

    // Encrypt a VISA credit card number:
    // 1234-5678-0000-9999
    ccNumber = "1234567800009999";

    usePrivateKey = FALSE;
    CkRsa_putEncodingMode(rsa,"base64");
    encryptedStr = CkRsa_encryptStringENC(rsa,ccNumber,usePrivateKey);
    printf("Encrypted:\n");
    printf("%s\n",encryptedStr);

    // Now decrypt:
    rsaDecryptor = CkRsa_Create();

    CkRsa_putEncodingMode(rsaDecryptor,"base64");
    success = CkRsa_ImportPrivateKey(rsaDecryptor,keyXml);

    usePrivateKey = TRUE;
    decryptedStr = CkRsa_decryptStringENC(rsaDecryptor,encryptedStr,usePrivateKey);

    printf("Decrypted:\n");
    printf("%s\n",decryptedStr);

    // Important: RSA encryption should only be used to encrypt small amounts of data.
    // It is typically used for encrypting symmetric encryption
    // keys such that a symmetric encryption algorithm, such as 
    // AES is then used to encrypt/decrypt bulk data


    CkRsa_Dispose(rsa);
    CkPrivateKey_Dispose(key);
    CkRsa_Dispose(rsaDecryptor);

    }