Small knowledge, big challenge! This paper is participating in theEssentials for programmers”Creative activities.
preface
Recently, I was working on a project to verify the security of sending requests from the App end to the back end. MD5 encryption was used, so I recorded it here.
Not particularly technical.
MD5 encryption for Swift
Oddly enough, in earlier versions of Swift, MD5 encryption was not particularly friendly and required bridging:
/ / XXX - Bridge - the Header. H / / / OC Swift Bridge file # import < > CommonCrypto/CommonDigest. HCopy the codeIn Swift5, however, this situation is changed and you can import directly from the project:
import CommonCrypto
Copy the codeBut even with direct import, we still need to do a category extension in String to do this:
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() } }Copy the codeYou see, after Swift5, just have Swift’s own library to support the MD5 encryption, if there are some third-party Swift library to support Swift5 before, will all users to their bridge, a # import < CommonCrypto/CommonDigest. H >?
Of course, this is not possible, so the answer is the handwritten MD5 encryption algorithm, and the reference is Kingfisher, I don’t know if you noticed:
There is a String+MD5.swift file in the Kingfisher project, which contains an MD5 encryption algorithm written freehand:
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
}
}
Copy the codeThere is also an open source library called SwiftMD5 that you can check out if you are interested.
conclusion
I’m not an algorithm guy, so I don’t really know much about MD5.
Here I recall all kinds of Swift in MD5. I just want to say that the seemingly simple function in our development process was not easy step by step. It was not realized until Swift5 was connected to the bridge system.
And handwritten MD5, also need to refer to a lot of other code information to complete.
Moving bricks is also a skill.
We’ll see you next time.