(Objective-C) RSA Encrypt and Decrypt Credit Card Numbers

Objective-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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#import <CkoRsa.h>
#import <CkoPrivateKey.h>
#import <NSString.h>

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

CkoRsa *rsa = [[CkoRsa alloc] init];

CkoPrivateKey *key = [[CkoPrivateKey alloc] init];

// Load an RSA private key from a file:
BOOL success = [key LoadAnyFormatFile: @"rsaPrivateKey.key" password: @""];
if (success != YES) {
    NSLog(@"%@",key.LastErrorText);
    return;
}

// Get the key as XML:
NSString *keyXml = 0;
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 != YES) {
    NSLog(@"%@",rsa.LastErrorText);
    return;
}

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

BOOL usePrivateKey = NO;
rsa.EncodingMode = @"base64";
NSString *encryptedStr = [rsa EncryptStringENC: ccNumber bUsePrivateKey: usePrivateKey];
NSLog(@"%@",@"Encrypted:");
NSLog(@"%@",encryptedStr);

// Now decrypt:
CkoRsa *rsaDecryptor = [[CkoRsa alloc] init];

rsaDecryptor.EncodingMode = @"base64";
success = [rsaDecryptor ImportPrivateKey: keyXml];

usePrivateKey = YES;
NSString *decryptedStr = [rsaDecryptor DecryptStringENC: encryptedStr bUsePrivateKey: usePrivateKey];

NSLog(@"%@",@"Decrypted:");
NSLog(@"%@",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