(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.)

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

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

void ChilkatSample(void)
    {
    BOOL success;
    HCkRsa rsa;
    HCkPrivateKey privKey;
    HCkPublicKey pubKey;
    const char *ccNumber;
    BOOL usePrivateKey;
    const char *encryptedStr;
    HCkRsa rsaDecryptor;
    const char *decryptedStr;

    success = FALSE;

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

    rsa = CkRsa_Create();

    privKey = CkPrivateKey_Create();

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

    // Get the public part of the private key.
    pubKey = CkPublicKey_Create();
    CkPrivateKey_ToPublicKey(privKey,pubKey);

    success = CkRsa_UsePublicKey(rsa,pubKey);
    if (success == FALSE) {
        printf("%s\n",CkRsa_lastErrorText(rsa));
        CkRsa_Dispose(rsa);
        CkPrivateKey_Dispose(privKey);
        CkPublicKey_Dispose(pubKey);
        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");
    CkRsa_UsePrivateKey(rsaDecryptor,privKey);

    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(privKey);
    CkPublicKey_Dispose(pubKey);
    CkRsa_Dispose(rsaDecryptor);

    }