AES.swift

//
//  AES.swift
//  CommonCryptoSwift
//
//  Created by Khoa Pham on 27/07/16.
//  Copyright © 2016 Fantageek. All rights reserved.
//

import Foundation
import CommonCrypto

public struct AES {

    // MARK: - Data

    public static func encrypt(_ data: Data, key: Data, keySize: Int = kCCKeySizeAES128) -> Data? {
        return perform(data, key: key, keySize: keySize, encrypting: true)
    }

    public static func decrypt(_ data: Data, key: Data, keySize: Int = kCCKeySizeAES128) -> Data? {
        return perform(data, key: key, keySize: keySize, encrypting: false)
    }

    // MARK: - String

    public static func encrypt(_ string: String, key: String, keySize: Int = kCCKeySizeAES128) -> String? {
        guard let data = string.data(using: String.Encoding.utf8),
              let keyData = key.data(using: String.Encoding.utf8) else { return nil }

        let encrypted = perform(data, key: keyData, keySize: keySize, encrypting: true)
        return encrypted?.base64EncodedString(options: .lineLength64Characters)
    }

    public static func decrypt(_ string: String, key: String, keySize: Int = kCCKeySizeAES128) -> String? {
        guard let data = Data(base64Encoded: string, options: .ignoreUnknownCharacters),
              let keyData = key.data(using: String.Encoding.utf8) else { return nil }

        guard let decrypted = perform(data, key: keyData, keySize: keySize, encrypting: false) else { return nil }
        return String(data: decrypted, encoding: String.Encoding.utf8)
    }

    // MARK: - Private

    fileprivate static func perform(_ data: Data, key: Data, keySize: Int = kCCKeySizeAES128, encrypting: Bool) -> Data? {
        guard let out = NSMutableData(length: data.count + kCCBlockSizeAES128) else { return nil }

        let hashData = Hash.SHA384(key)

        // kCCKeySizeAES128 by default
        var keyRange: Range<Int> = 0..<16
        var ivRange: Range<Int> = 16..<32

        switch keySize {
        case kCCKeySizeAES192:
            keyRange = 0..<24
            ivRange = 24..<40
        case kCCKeySizeAES256:
            keyRange = 0..<32
            ivRange = 32..<48
        default: ()
        }

        let hashKeyData = hashData.subdata(in: keyRange)
        let ivData = hashData.subdata(in: ivRange)
        
        let operation = encrypting ? kCCEncrypt : kCCDecrypt
        var dataOutMovedLength: size_t = 0

        let status = CCCrypt(
            CCOperation(operation),
            CCAlgorithm(kCCAlgorithmAES128),
            CCOptions(kCCOptionPKCS7Padding),
            (hashKeyData as NSData).bytes,
            keySize,
            (ivData as NSData).bytes,
            (data as NSData).bytes,
            size_t(data.count),
            out.mutableBytes,
            size_t(out.length),
            &dataOutMovedLength)

        guard Int(status) == Int(kCCSuccess) else { return nil }

        out.length = dataOutMovedLength
        return out as Data
    }
}