AES128 in PHP and Objective-C (iOS)

Question

I have a code, writed on PHP:

function aes128Encrypt($key, $data) {
    $iv = rand(1,9999999);
    $size = mcrypt_get_iv_size(MCRYPT_RIJNDAEL_128, MCRYPT_MODE_CBC);
    $iv = mcrypt_create_iv($size,$iv);
    $key = md5($key);
    return base64_encode($iv.mcrypt_encrypt(MCRYPT_RIJNDAEL_128, pack("H*", $key) , $data, MCRYPT_MODE_CBC, $iv));
    return $data;
}

//Function for decryption of AES-128
function aes128Decrypt($key, $data) {
    $data = base64_decode($data);
    $iv = substr($data, 0, 16);
    $data = substr_replace($data, null, 0, 16);
    $key = md5($key);
    $decrypted = urlencode(mcrypt_decrypt(MCRYPT_RIJNDAEL_128, pack("H*", $key) , $data, MCRYPT_MODE_CBC, $iv));
    $decrypted = str_replace('%00','',$decrypted);
    return urldecode($decrypted);
}

I need to make the same code on iOS, using Objective-C. How can i do it? I'm new in Objective-C, so help please :)

Answer 1

There are several problems with the php cryptography.

1. The rand() function documentation: "This function does not generate cryptographically secure values, and should not be used for cryptographic purposes . If you need a cryptographically secure value". See: mcrypt_create_iv.

2. If the input key is text, such as a password, using md5 to derive a key is no longer considered acceptable, use a function such as PBKDF2. See: hash_pbkdf2.

For iOS use Apple's Common Crypto library.

Note that Base64 encoding/decoding is separate from Common Crypto and part of NSData in iOS7 and above.

The Common Crypto functions you will need are:

CCCryptorStatus CCCrypt(
    CCOperation op,         /* kCCEncrypt, etc. */
    CCAlgorithm alg,        /* kCCAlgorithmAES128, etc. */
    CCOptions options,      /* kCCOptionPKCS7Padding, etc. */
    const void *key, size_t keyLength,
    const void *iv,         /* optional initialization vector */
    const void *dataIn, size_t dataInLength,
    void *dataOut,          /* data RETURNED here */
    size_t dataOutAvailable,
    size_t *dataOutMoved)

int 
CCKeyDerivationPBKDF(
    CCPBKDFAlgorithm algorithm,
    const char *password, size_t passwordLen,
    const uint8_t *salt, size_t saltLen,
    CCPseudoRandomAlgorithm prf, uint rounds, 
    uint8_t *derivedKey, size_t derivedKeyLen)

The Base64 methods you will need:

- (NSString *)base64EncodedStringWithOptions:(NSDataBase64EncodingOptions)options
- (NSData *)base64EncodedDataWithOptions:(NSDataBase64EncodingOptions)options