SHA256.swift

//
// This is a heavily altered version of SHA2.swift found in CryptoSwift.
// I tried to remove everything that is not about SHA256.
//
// --========================================================================--
//
//  SHA2.swift
//  CryptoSwift
//
//  Created by Marcin Krzyzanowski on 24/08/14.
//  Copyright (c) 2014 Marcin Krzyzanowski. All rights reserved.
//
//  Copyright (C) 2014 Marcin Krzyżanowski <marcin.krzyzanowski@gmail.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.

import Foundation

public extension Data {
    func sha256() -> Data {
        let bytes: Array<UInt8> = Array(self)
        let result = SHA256(bytes).calculate32()
        return Data(bytes: result)
    }
}

final public class SHA256 {
    
    let message: Array<UInt8>

    init(_ message: Array<UInt8>) {
        self.message = message
    }
    
    func calculate32() -> Array<UInt8> {
        var tmpMessage = bitPadding(to: self.message, blockSize: 64, allowance: 64 / 8)

        // hash values
        var hh = Array<UInt32>()
        h.forEach {(h) -> () in
            hh.append(UInt32(h))
        }

        // append message length, in a 64-bit big-endian integer. So now the message length is a multiple of 512 bits.
        tmpMessage += arrayOfBytes(value: message.count * 8, length: 64 / 8)

        // Process the message in successive 512-bit chunks:
        let chunkSizeBytes = 512 / 8 // 64
        for chunk in BytesSequence(chunkSize: chunkSizeBytes, data: tmpMessage) {
            // break chunk into sixteen 32-bit words M[j], 0 ≤ j ≤ 15, big-endian
            // Extend the sixteen 32-bit words into sixty-four 32-bit words:
            var M = Array<UInt32>(repeating: 0, count: k.count)
            for x in 0..<M.count {
                switch x {
                case 0...15:
                    let start = chunk.startIndex + (x * MemoryLayout<UInt32>.size)
                    let end = start + MemoryLayout<UInt32>.size
                    let le = chunk[start..<end].toUInt32Array()[0]
                    M[x] = le.bigEndian
                    break
                default:
                    let s0 = rotateRight(M[x-15], by: 7) ^ rotateRight(M[x-15], by: 18) ^ (M[x-15] >> 3)
                    let s1 = rotateRight(M[x-2], by: 17) ^ rotateRight(M[x-2], by: 19) ^ (M[x-2] >> 10)
                    M[x] = M[x-16] &+ s0 &+ M[x-7] &+ s1
                    break
                }
            }

            var A = hh[0]
            var B = hh[1]
            var C = hh[2]
            var D = hh[3]
            var E = hh[4]
            var F = hh[5]
            var G = hh[6]
            var H = hh[7]

            // Main loop
            for j in 0..<k.count {
                let s0 = rotateRight(A, by: 2) ^ rotateRight(A, by: 13) ^ rotateRight(A, by: 22)
                let maj = (A & B) ^ (A & C) ^ (B & C)
                let t2 = s0 &+ maj
                let s1 = rotateRight(E, by: 6) ^ rotateRight(E, by: 11) ^ rotateRight(E, by: 25)
                let ch = (E & F) ^ ((~E) & G)
                let t1 = H &+ s1 &+ ch &+ UInt32(k[j]) &+ M[j]

                H = G
                G = F
                F = E
                E = D &+ t1
                D = C
                C = B
                B = A
                A = t1 &+ t2
            }

            hh[0] = (hh[0] &+ A)
            hh[1] = (hh[1] &+ B)
            hh[2] = (hh[2] &+ C)
            hh[3] = (hh[3] &+ D)
            hh[4] = (hh[4] &+ E)
            hh[5] = (hh[5] &+ F)
            hh[6] = (hh[6] &+ G)
            hh[7] = (hh[7] &+ H)
        }

        // Produce the final hash value (big-endian) as a 160 bit number:
        var result = Array<UInt8>()
        result.reserveCapacity(hh.count / 4)
        ArraySlice(hh).forEach {
            let item = $0.bigEndian
            let toAppend: [UInt8] = [UInt8(item & 0xff), UInt8((item >> 8) & 0xff), UInt8((item >> 16) & 0xff), UInt8((item >> 24) & 0xff)]
            result += toAppend
        }
        return result
    }
    
    private lazy var h: Array<UInt64> = {
        return [0x6a09e667, 0xbb67ae85, 0x3c6ef372, 0xa54ff53a, 0x510e527f, 0x9b05688c, 0x1f83d9ab, 0x5be0cd19]
    }()
    
    private lazy var k: Array<UInt64> = {
        return [0x428a2f98, 0x71374491, 0xb5c0fbcf, 0xe9b5dba5, 0x3956c25b, 0x59f111f1, 0x923f82a4, 0xab1c5ed5,
                0xd807aa98, 0x12835b01, 0x243185be, 0x550c7dc3, 0x72be5d74, 0x80deb1fe, 0x9bdc06a7, 0xc19bf174,
                0xe49b69c1, 0xefbe4786, 0x0fc19dc6, 0x240ca1cc, 0x2de92c6f, 0x4a7484aa, 0x5cb0a9dc, 0x76f988da,
                0x983e5152, 0xa831c66d, 0xb00327c8, 0xbf597fc7, 0xc6e00bf3, 0xd5a79147, 0x06ca6351, 0x14292967,
                0x27b70a85, 0x2e1b2138, 0x4d2c6dfc, 0x53380d13, 0x650a7354, 0x766a0abb, 0x81c2c92e, 0x92722c85,
                0xa2bfe8a1, 0xa81a664b, 0xc24b8b70, 0xc76c51a3, 0xd192e819, 0xd6990624, 0xf40e3585, 0x106aa070,
                0x19a4c116, 0x1e376c08, 0x2748774c, 0x34b0bcb5, 0x391c0cb3, 0x4ed8aa4a, 0x5b9cca4f, 0x682e6ff3,
                0x748f82ee, 0x78a5636f, 0x84c87814, 0x8cc70208, 0x90befffa, 0xa4506ceb, 0xbef9a3f7, 0xc67178f2]
    }()
    
    private func rotateRight(_ value: UInt32, by: UInt32) -> UInt32 {
        return (value >> by) | (value << (32 - by))
    }
    
    private func arrayOfBytes<T>(value: T, length: Int? = nil) -> Array<UInt8> {
        let totalBytes = length ?? MemoryLayout<T>.size
        
        let valuePointer = UnsafeMutablePointer<T>.allocate(capacity: 1)
        valuePointer.pointee = value
        
        let bytesPointer = UnsafeMutablePointer<UInt8>(OpaquePointer(valuePointer))
        var bytes = Array<UInt8>(repeating: 0, count: totalBytes)
        for j in 0..<min(MemoryLayout<T>.size, totalBytes) {
            bytes[totalBytes - 1 - j] = (bytesPointer + j).pointee
        }
        
        valuePointer.deinitialize(count: 1)
        valuePointer.deallocate()
        
        return bytes
    }
}

internal extension Collection where Self.Iterator.Element == UInt8, Self.Index == Int {
    func toUInt32Array() -> Array<UInt32> {
        var result = Array<UInt32>()
        result.reserveCapacity(16)
        for idx in stride(from: self.startIndex, to: self.endIndex, by: MemoryLayout<UInt32>.size) {
            var val: UInt32 = 0
            val |= self.count > 3 ? UInt32(self[idx.advanced(by: 3)]) << 24 : 0
            val |= self.count > 2 ? UInt32(self[idx.advanced(by: 2)]) << 16 : 0
            val |= self.count > 1 ? UInt32(self[idx.advanced(by: 1)]) << 8  : 0
            val |= !self.isEmpty ? UInt32(self[idx]) : 0
            result.append(val)
        }
        
        return result
    }
}

internal func bitPadding(to data: Array<UInt8>, blockSize: Int, allowance: Int = 0) -> Array<UInt8> {
    var tmp = data
    
    // Step 1. Append Padding Bits
    tmp.append(0x80) // append one bit (UInt8 with one bit) to message
    
    // append "0" bit until message length in bits ≡ 448 (mod 512)
    var msgLength = tmp.count
    var counter = 0
    
    while msgLength % blockSize != (blockSize - allowance) {
        counter += 1
        msgLength += 1
    }
    
    tmp += Array<UInt8>(repeating: 0, count: counter)
    return tmp
}

internal struct BytesSequence<D: RandomAccessCollection>: Sequence where D.Iterator.Element == UInt8,
    D.IndexDistance == Int,
    D.SubSequence.IndexDistance == Int,
D.Index == Int {
    let chunkSize: D.IndexDistance
    let data: D
    
    func makeIterator() -> AnyIterator<D.SubSequence> {
        var offset = data.startIndex
        return AnyIterator {
            let end = Swift.min(self.chunkSize, self.data.count - offset)
            let result = self.data[offset..<offset + end]
            offset = offset.advanced(by: result.count)
            if !result.isEmpty {
                return result
            }
            return nil
        }
    }
}