CryptoSwift/Sources/CryptoSwift/BlockMode/CBC.swift

//
//  CBC.swift
//  CryptoSwift
//
//  Copyright (C) 2014-2017 Marcin Krzyżanowski <marcin@krzyzanowskim.com>
//  This software is provided 'as-is', without any express or implied warranty.
//
//  In no event will the authors be held liable for any damages arising from the use of this software.
//
//  Permission is granted to anyone to use this software for any purpose,including commercial applications, and to alter it and redistribute it freely, subject to the following restrictions:
//
//  - The origin of this software must not be misrepresented; you must not claim that you wrote the original software. If you use this software in a product, an acknowledgment in the product documentation is required.
//  - Altered source versions must be plainly marked as such, and must not be misrepresented as being the original software.
//  - This notice may not be removed or altered from any source or binary distribution.
//

//  Cipher-block chaining (CBC)
//

struct CBCModeWorker: BlockModeWorker {
    typealias Element = Array<UInt8>

    let cipherOperation: CipherOperationOnBlock
    private let iv: Element
    private var prev: Element?

    init(iv: Array<UInt8>, cipherOperation: @escaping CipherOperationOnBlock) {
        self.iv = iv
        self.cipherOperation = cipherOperation
    }

    mutating func encrypt(_ plaintext: ArraySlice<UInt8>) -> Array<UInt8> {
        guard let ciphertext = cipherOperation(xor(prev ?? iv, plaintext)) else {
            return Array(plaintext)
        }
        prev = ciphertext
        return ciphertext
    }

    mutating func decrypt(_ ciphertext: ArraySlice<UInt8>) -> Array<UInt8> {
        guard let plaintext = cipherOperation(Array(ciphertext)) else {
            return Array(ciphertext)
        }
        let result = xor(prev ?? iv, plaintext)
        prev = Array(ciphertext)
        return result
    }
}