小知识，大挑战！本文正在参与“程序员必备小知识”创作活动。
前言
最近做个项目，在做一个App端向后端发请求的安全校验问题，用到了MD5加密，所以在这里记录一下。
算不上特别有技术含量。
Swift的中MD5加密
说来是个奇怪的事情，在Swift的较早之前的版本中，其实对于MD5加密这种算法支持的不算特别友好，还需要进行桥接：
// XXX-Bridge-Header.h
/// OC转Swift的桥接文件
#import <CommonCrypto/CommonDigest.h>
复制代码不过在Swift5中，这个情况有所转变，直接在项目中import就好了：
import CommonCrypto
复制代码不过就算是直接import了，我们还是需要在String中做一个分类扩展才能完成这个方法：
extension String {
/// 原生md5
public var md5: String {
guard let data = data(using: .utf8) else {
return self
}
var digest = [UInt8](repeating: 0, count: Int(CC_MD5_DIGEST_LENGTH))
#if swift(>=5.0)
_ = data.withUnsafeBytes { (bytes: UnsafeRawBufferPointer) in
return CC_MD5(bytes.baseAddress, CC_LONG(data.count), &digest)
}
#else
_ = data.withUnsafeBytes { bytes in
return CC_MD5(bytes, CC_LONG(data.count), &digest)
}
#endif
return digest.map { String(format: "%02x", $0) }.joined()
}
}
复制代码大家看到了，在Swift5之后，才有Swift自带的库去支持MD5加密，如果有一些第三方Swift库要支持Swift5之前，难道都要用户去自己bridge一把#import <CommonCrypto/CommonDigest.h>？
当然不可能这样，于是得到的答案便是手写MD5加密算法，而其中值得参考的就是Kingfisher，不知道大家注意没有：
在Kingfisher项目中有一个String+MD5.swift文件，而其中便是一个徒手写的MD5加密算法：
import Foundation
import CommonCrypto
extension String: KingfisherCompatibleValue { }
extension KingfisherWrapper where Base == String {
var md5: String {
guard let data = base.data(using: .utf8) else {
return base
}
let message = data.withUnsafeBytes { (bytes: UnsafeRawBufferPointer) in
return [UInt8](bytes)
}
let MD5Calculator = MD5(message)
let MD5Data = MD5Calculator.calculate()
var MD5String = String()
for c in MD5Data {
MD5String += String(format: "%02x", c)
}
return MD5String
}
var ext: String? {
var ext = ""
if let index = base.lastIndex(of: ".") {
let extRange = base.index(index, offsetBy: 1)..<base.endIndex
ext = String(base[extRange])
}
guard let firstSeg = ext.split(separator: "@").first else {
return nil
}
return firstSeg.count > 0 ? String(firstSeg) : nil
}
}
// array of bytes, little-endian representation
func arrayOfBytes<T>(_ value: T, length: Int? = nil) -> [UInt8] {
let totalBytes = length ?? (MemoryLayout<T>.size * 8)
let valuePointer = UnsafeMutablePointer<T>.allocate(capacity: 1)
valuePointer.pointee = value
let bytes = valuePointer.withMemoryRebound(to: UInt8.self, capacity: totalBytes) { (bytesPointer) -> [UInt8] in
var bytes = [UInt8](repeating: 0, count: totalBytes)
for j in 0..<min(MemoryLayout<T>.size, totalBytes) {
bytes[totalBytes - 1 - j] = (bytesPointer + j).pointee
}
return bytes
}
valuePointer.deinitialize(count: 1)
valuePointer.deallocate()
return bytes
}
extension Int {
// Array of bytes with optional padding (little-endian)
func bytes(_ totalBytes: Int = MemoryLayout<Int>.size) -> [UInt8] {
return arrayOfBytes(self, length: totalBytes)
}
}
extension NSMutableData {
// Convenient way to append bytes
func appendBytes(_ arrayOfBytes: [UInt8]) {
append(arrayOfBytes, length: arrayOfBytes.count)
}
}
protocol HashProtocol {
var message: [UInt8] { get }
// Common part for hash calculation. Prepare header data.
func prepare(_ len: Int) -> [UInt8]
}
extension HashProtocol {
func prepare(_ len: Int) -> [UInt8] {
var tmpMessage = message
// Step 1. Append Padding Bits
tmpMessage.append(0x80) // append one bit (UInt8 with one bit) to message
// append "0" bit until message length in bits ≡ 448 (mod 512)
var msgLength = tmpMessage.count
var counter = 0
while msgLength % len != (len - 8) {
counter += 1
msgLength += 1
}
tmpMessage += [UInt8](repeating: 0, count: counter)
return tmpMessage
}
}
func toUInt32Array(_ slice: ArraySlice<UInt8>) -> [UInt32] {
var result = [UInt32]()
result.reserveCapacity(16)
for idx in stride(from: slice.startIndex, to: slice.endIndex, by: MemoryLayout<UInt32>.size) {
let d0 = UInt32(slice[idx.advanced(by: 3)]) << 24
let d1 = UInt32(slice[idx.advanced(by: 2)]) << 16
let d2 = UInt32(slice[idx.advanced(by: 1)]) << 8
let d3 = UInt32(slice[idx])
let val: UInt32 = d0 | d1 | d2 | d3
result.append(val)
}
return result
}
struct BytesIterator: IteratorProtocol {
let chunkSize: Int
let data: [UInt8]
init(chunkSize: Int, data: [UInt8]) {
self.chunkSize = chunkSize
self.data = data
}
var offset = 0
mutating func next() -> ArraySlice<UInt8>? {
let end = min(chunkSize, data.count - offset)
let result = data[offset..<offset + end]
offset += result.count
return result.count > 0 ? result : nil
}
}
struct BytesSequence: Sequence {
let chunkSize: Int
let data: [UInt8]
func makeIterator() -> BytesIterator {
return BytesIterator(chunkSize: chunkSize, data: data)
}
}
func rotateLeft(_ value: UInt32, bits: UInt32) -> UInt32 {
return ((value << bits) & 0xFFFFFFFF) | (value >> (32 - bits))
}
class MD5: HashProtocol {
static let size = 16 // 128 / 8
let message: [UInt8]
init (_ message: [UInt8]) {
self.message = message
}
// specifies the per-round shift amounts
private let shifts: [UInt32] = [7, 12, 17, 22, 7, 12, 17, 22, 7, 12, 17, 22, 7, 12, 17, 22,
5, 9, 14, 20, 5, 9, 14, 20, 5, 9, 14, 20, 5, 9, 14, 20,
4, 11, 16, 23, 4, 11, 16, 23, 4, 11, 16, 23, 4, 11, 16, 23,
6, 10, 15, 21, 6, 10, 15, 21, 6, 10, 15, 21, 6, 10, 15, 21]
// binary integer part of the sines of integers (Radians)
private let sines: [UInt32] = [0xd76aa478, 0xe8c7b756, 0x242070db, 0xc1bdceee,
0xf57c0faf, 0x4787c62a, 0xa8304613, 0xfd469501,
0x698098d8, 0x8b44f7af, 0xffff5bb1, 0x895cd7be,
0x6b901122, 0xfd987193, 0xa679438e, 0x49b40821,
0xf61e2562, 0xc040b340, 0x265e5a51, 0xe9b6c7aa,
0xd62f105d, 0x02441453, 0xd8a1e681, 0xe7d3fbc8,
0x21e1cde6, 0xc33707d6, 0xf4d50d87, 0x455a14ed,
0xa9e3e905, 0xfcefa3f8, 0x676f02d9, 0x8d2a4c8a,
0xfffa3942, 0x8771f681, 0x6d9d6122, 0xfde5380c,
0xa4beea44, 0x4bdecfa9, 0xf6bb4b60, 0xbebfbc70,
0x289b7ec6, 0xeaa127fa, 0xd4ef3085, 0x4881d05,
0xd9d4d039, 0xe6db99e5, 0x1fa27cf8, 0xc4ac5665,
0xf4292244, 0x432aff97, 0xab9423a7, 0xfc93a039,
0x655b59c3, 0x8f0ccc92, 0xffeff47d, 0x85845dd1,
0x6fa87e4f, 0xfe2ce6e0, 0xa3014314, 0x4e0811a1,
0xf7537e82, 0xbd3af235, 0x2ad7d2bb, 0xeb86d391]
private let hashes: [UInt32] = [0x67452301, 0xefcdab89, 0x98badcfe, 0x10325476]
func calculate() -> [UInt8] {
var tmpMessage = prepare(64)
tmpMessage.reserveCapacity(tmpMessage.count + 4)
// hash values
var hh = hashes
// Step 2. Append Length a 64-bit representation of lengthInBits
let lengthInBits = (message.count * 8)
let lengthBytes = lengthInBits.bytes(64 / 8)
tmpMessage += lengthBytes.reversed()
// 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
let M = toUInt32Array(chunk)
assert(M.count == 16, "Invalid array")
// Initialize hash value for this chunk:
var A: UInt32 = hh[0]
var B: UInt32 = hh[1]
var C: UInt32 = hh[2]
var D: UInt32 = hh[3]
var dTemp: UInt32 = 0
// Main loop
for j in 0 ..< sines.count {
var g = 0
var F: UInt32 = 0
switch j {
case 0...15:
F = (B & C) | ((~B) & D)
g = j
break
case 16...31:
F = (D & B) | (~D & C)
g = (5 * j + 1) % 16
break
case 32...47:
F = B ^ C ^ D
g = (3 * j + 5) % 16
break
case 48...63:
F = C ^ (B | (~D))
g = (7 * j) % 16
break
default:
break
}
dTemp = D
D = C
C = B
B = B &+ rotateLeft((A &+ F &+ sines[j] &+ M[g]), bits: shifts[j])
A = dTemp
}
hh[0] = hh[0] &+ A
hh[1] = hh[1] &+ B
hh[2] = hh[2] &+ C
hh[3] = hh[3] &+ D
}
var result = [UInt8]()
result.reserveCapacity(hh.count / 4)
hh.forEach {
let itemLE = $0.littleEndian
let r1 = UInt8(itemLE & 0xff)
let r2 = UInt8((itemLE >> 8) & 0xff)
let r3 = UInt8((itemLE >> 16) & 0xff)
let r4 = UInt8((itemLE >> 24) & 0xff)
result += [r1, r2, r3, r4]
}
return result
}
}
复制代码这里还有一个开源库：SwiftMD5，大家有兴趣也可以看看。
总结
我不是一个做算法的，所以其实对MD5的并不多。
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13168522 查看本文章
这里回想起Swift在MD5中种种，只是想说，在我们开发过程中看似简单的功能，却一步步走的多么不容易，从桥接到Swift系统，到了Swift5才实现。
而手写MD5，也是需要参考很多其他代码资料完成的。
搬砖也是技术活呀。
我们下期见。