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

Chilkat.Rsa rsa = new Chilkat.Rsa();

Chilkat.PrivateKey key = new Chilkat.PrivateKey();

// Load an RSA private key from a file:
bool success = key.LoadAnyFormatFile("rsaPrivateKey.key","");
if (success != true) {
    Debug.WriteLine(key.LastErrorText);
    return;
}

// Get the key as XML:
string keyXml;
keyXml = key.GetXml();

// 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 = rsa.ImportPublicKey(keyXml);
if (success != true) {
    Debug.WriteLine(rsa.LastErrorText);
    return;
}

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

bool usePrivateKey = false;
rsa.EncodingMode = "base64";
string encryptedStr = rsa.EncryptStringENC(ccNumber,usePrivateKey);
Debug.WriteLine("Encrypted:");
Debug.WriteLine(encryptedStr);

// Now decrypt:
Chilkat.Rsa rsaDecryptor = new Chilkat.Rsa();

rsaDecryptor.EncodingMode = "base64";
success = rsaDecryptor.ImportPrivateKey(keyXml);

usePrivateKey = true;
string decryptedStr = rsaDecryptor.DecryptStringENC(encryptedStr,usePrivateKey);

Debug.WriteLine("Decrypted:");
Debug.WriteLine(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