So my question for you stackoverflow geniuses is: if there a way (native, library, framework, whatever..) to encrypt data with AES (preferably 128 but could be 256 too) using a strong Authenticated encryption algorithm, let's say GCM mode?
Question is short, I have done some research and I only found one library that seems to support it ( RNCryptor ) but it also seems to use password to crypt instead of keys (like you provide a password and the library made the key) and I don't like that a lot, I prefer to manage my keys myself.
I also look at CommonCryptor.h and I found that line, which seems to me the only reference of GCM in commoncryptor source code (but I could be wrong, actually I am probably wrong) :
case kCCModeGCM: if((ref->symMode[direction].gcm = getCipherMode(cipher, mode, direction).gcm) == NULL) return kCCUnimplemented;
Thanks to owlstead suggest I take a look deeper into RNCryptor and found a solution.
First of all after lots of googling it's seems that Zaph were right and iOS doesn't provide GCM but use it in iOS. ref there: iOS Security feb 2014
Second, RNCryptor doesn't use GCM but use AES256 in CBC mode (Cipher Block Chaining), which is fine, and then authenticate with HMAC+SHA1. This fits my requirements.
To encrypt with a key and to skip the password derivation part, RNCryptor provide this function:
NSData *encryptedData = [RNEncryptor encryptData:yourData withSettings:kRNCryptorAES256Settings encryptionKey:encryptionKey HMACKey:HMACKey error:&error];
and then decrypt with this
NSData *decryptedData = [RNDecryptor decryptData:encryptedData withEncryptionKey:encryptionKey HMACKey:HMACKey error:&decryptionError];
RNCryptor also provide random generation methods for keys.