Swift AES encryption using CommonCrypto

Question

I am working on an iOS app on XCode 7.1 with Swift 2.1 and I am trying to do simple encryption with AES 128 bit and PKCS7 padding using CommonCrypto library.

The code works but every time I try to cast the NSData object to NSString then to String I get a nil and the app crashes.

I debugged the app and the NSData object is not nil.

The error occurs when I try to unwrap the String optional.

How to resolve this issue? and convert the NSData object to a String correctly? Here is my code

static func AESEncryption(phrase: String,key: String,ivKey: String,encryptOrDecrypt: Bool) -> String {

let phraseData = phrase.dataUsingEncoding(NSUTF8StringEncoding)
let ivData = ivKey.dataUsingEncoding(NSUTF8StringEncoding)
    let keyData: NSData! = key.dataUsingEncoding(NSUTF8StringEncoding, allowLossyConversion: false)!
    let keyBytes         = UnsafePointer<Void>(keyData.bytes)
    let keyLength        = size_t(kCCKeySizeAES128)
    let dataLength       = Int(phraseData!.length)
    let dataBytes        = UnsafePointer<Void>(phraseData!.bytes)
    let bufferData       = NSMutableData(length: Int(dataLength) + kCCBlockSizeAES128)!
    let bufferPointer    = UnsafeMutablePointer<Void>(bufferData.mutableBytes)
    let bufferLength     = size_t(bufferData.length)
    let ivBuffer         = UnsafePointer<Void>(ivData!.bytes)
    var bytesDecrypted   = Int(0)

    let operation = encryptOrDecrypt ? UInt32(kCCEncrypt) : UInt32(kCCDecrypt)

    let algorithm:  CCAlgorithm = UInt32(kCCAlgorithmAES128)
    let options:   CCOptions   = UInt32(kCCOptionPKCS7Padding)

    let cryptStatus = CCCrypt(
        operation,
        algorithm,
        options,
        keyBytes,
        keyLength,
        ivBuffer,
        dataBytes,
        dataLength,
        bufferPointer,
        bufferLength,
        &bytesDecrypted)
    if Int32(cryptStatus) == Int32(kCCSuccess) {
        bufferData.length = bytesDecrypted

        let data = bufferData as NSData
        let stringData =  String(data: data,encoding: NSUTF8StringEncoding)
        print("After Operation: \(stringData)")
        return stringData!
    } else {
        print("Encryption Error: \(cryptStatus)")
    }
    return "";
}

Answer 1

The encrypted data will not be a valid UTF-8 string as it should be indistinguishable from random bits. If you need it in a string form you need to do something like base64 encode it or write out the hex values of the bytes.

NSData has a base64EncodedDataWithOptions method which should produce a String.