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@ikiuo

MD5: RFC 1321 を実装してみる

Last updated at Posted at 2021-08-06

RFC 1321 (The MD5 Message-Digest Algorithm) を見ながら実装してみた。

以下を念頭に置いています

  • ビット単位の入力は考慮しない
  • コンパクトなものにする
  • 凝ったことはあまりしない

データの種類

データのバイト列は、リトル・エンディアンとして扱います。

種類 ビット数 バイト数 ワード数 シンボル
ワード 32 4 1
ブロック 512 64 16 X[ ]
ダイジェスト値 128 16 4 S[ ] または A,B,C,D
ダイジェスト値 A,B,C,D は配列 S と等しいものとします。
例:C++
uint32_t &A = S[0];
uint32_t &B = S[1];
uint32_t &C = S[2];
uint32_t &D = S[3];

入力データと入力の拡張

入力データの後続に、入力の拡張として、「1ビットの"1"」と「入力のビット数」が追加されます。また、ダイジェスト値の計算は、ブロック単位で行われるので、全体がブロック単位となるように "0" で埋めます。

追加されるバイト列データの並びは以下になります。

バイト数 データ
1 0x80
0 〜 55 0x00
8 入力のビット数（64ビット）

ブロック単位の計算

1ブロックに対して、64要素のテーブルを使って計算します。テーブルは

C
T[i] = int(abs(sin(i)) * 4294967296);  /* i はラジアンで 1 から 64 */

とされています。i が 1 からだと都合が悪いので、実際のプログラムでは

C
T[i] = int(abs(sin(i+1)) * 4294967296);  /* i は 0 から 63 */

にします。T に対して、4種類の関数と16ワードで、計64回の計算を実行します。

4種類の関数は

関数 計算
F(x, y, z) (y & x) | (z & ~x)
G(x, y, z) (x & z) | (y & ~z)
H(x, y, z) x ^ y ^ z
I(x, y, z) y ^ (x | ~z)

となっていて、F,G,H,I を総じて Q とします。

これと、32ビット左ローテート(大抵のCPUでは1命令)

C
uint32_t RotateLeft(uint32_t v, int n)
{
  return (v << n) | (v >> (32 - n));
}

が使われます。

ダイジェスト値の初期値

ダイジェスト値 A,B,C,D の初期値は

A = 0x67452301
B = 0xefcdab89
C = 0x98badcfe
D = 0x10325476

となっています。

ダイジェスト値の更新

テーブル T[i] の i を 0 から順に 63 まで使って、ダイジェスト値の更新します。

一回の計算は

Round
// a,b,c,d,k,s および Q は i に応じて決められている
// S[a],S[b],S[c],S[d] は A,B,C,D をシャッフルしたものに相当
S[a] = S[b] + RotateLeft(X[k] + T[i] + S[a] + Q(S[b], S[c], S[d]), s)

として更新されます。

T[i] と各要素の対応

i と Q,a,b,c,d,k,s の対応表（長いので折りたたみ）
i Q a b c d k s
0 F 0 1 2 3 0 7
1 F 3 0 1 2 1 12
2 F 2 3 0 1 2 17
3 F 1 2 3 0 3 22
4 F 0 1 2 3 4 7
5 F 3 0 1 2 5 12
6 F 2 3 0 1 6 17
7 F 1 2 3 0 7 22
8 F 0 1 2 3 8 7
9 F 3 0 1 2 9 12
10 F 2 3 0 1 10 17
11 F 1 2 3 0 11 22
12 F 0 1 2 3 12 7
13 F 3 0 1 2 13 12
14 F 2 3 0 1 14 17
15 F 1 2 3 0 15 22
16 G 0 1 2 3 1 5
17 G 3 0 1 2 6 9
18 G 2 3 0 1 11 14
19 G 1 2 3 0 0 20
20 G 0 1 2 3 5 5
21 G 3 0 1 2 10 9
22 G 2 3 0 1 15 14
23 G 1 2 3 0 4 20
24 G 0 1 2 3 9 5
25 G 3 0 1 2 14 9
26 G 2 3 0 1 3 14
27 G 1 2 3 0 8 20
28 G 0 1 2 3 13 5
29 G 3 0 1 2 2 9
30 G 2 3 0 1 7 14
31 G 1 2 3 0 12 20
32 H 0 1 2 3 5 4
33 H 3 0 1 2 8 11
34 H 2 3 0 1 11 16
35 H 1 2 3 0 14 23
36 H 0 1 2 3 1 4
37 H 3 0 1 2 4 11
38 H 2 3 0 1 7 16
39 H 1 2 3 0 10 23
40 H 0 1 2 3 13 4
41 H 3 0 1 2 0 11
42 H 2 3 0 1 3 16
43 H 1 2 3 0 6 23
44 H 0 1 2 3 9 4
45 H 3 0 1 2 12 11
46 H 2 3 0 1 15 16
47 H 1 2 3 0 2 23
48 I 0 1 2 3 0 6
49 I 3 0 1 2 7 10
50 I 2 3 0 1 14 15
51 I 1 2 3 0 5 21
52 I 0 1 2 3 12 6
53 I 3 0 1 2 3 10
54 I 2 3 0 1 10 15
55 I 1 2 3 0 1 21
56 I 0 1 2 3 8 6
57 I 3 0 1 2 15 10
58 I 2 3 0 1 6 15
59 I 1 2 3 0 13 21
60 I 0 1 2 3 4 6
61 I 3 0 1 2 11 10
62 I 2 3 0 1 2 15
63 I 1 2 3 0 9 21

i と Q（関数）の対応

i の範囲 i >> 4 Q
00 〜 15 0 F
16 〜 31 1 G
32 〜 47 2 H
48 〜 63 3 I

i と a,b,c,d（ダイジェスト値）の対応

i a b c d 備考
4n+0 0 1 2 3 a = 0 % 4
4n+1 3 0 1 2 a = 3 % 4
4n+2 2 3 0 1 a = 6 % 4
4n+3 1 2 3 0 a = 9 % 4

i と k（ブロック）の対応

i 0 1 2 3 4 5 6 7
0x00 0 1 2 3 4 5 6 7
0x10 1 6 11 0 5 10 15 4
0x20 5 8 11 14 1 4 7 10
0x30 0 7 14 5 12 3 10 1
i 8 9 A B C D E F
0x00 8 9 10 11 12 13 14 15
0x10 9 14 3 8 13 2 7 12
0x20 13 0 3 6 9 12 15 2
0x30 8 15 6 13 4 11 2 9

i の範囲 k
0x00 〜 0x0f ((i * 1) + 0) % 16
0x10 〜 0x1f ((i * 5) + 1) % 16
0x20 〜 0x2f ((i * 3) + 5) % 16
0x30 〜 0x3f ((i * 7) + 0) % 16

i と s（ローテート ビット数）の対応

i 0 1 2 3 4 5 6 7
0x00 7 12 17 22 7 12 17 22
0x10 5 9 14 20 5 9 14 20
0x20 4 11 16 23 4 11 16 23
0x30 6 10 15 21 6 10 15 21
i 8 9 A B C D E F
0x00 7 12 17 22 7 12 17 22
0x10 5 9 14 20 5 9 14 20
0x20 4 11 16 23 4 11 16 23
0x30 6 10 15 21 6 10 15 21

横の 4 以降は、0〜3の繰り返しなので

i 0 1 2 3
0x00 7 12 17 22
0x10 5 9 14 20
0x20 4 11 16 23
0x30 6 10 15 21

に注目します。これを

i 0 1 2 3
0x00 4+(5*0)+0+3 4+(5*1)+0+3 4+(5*2)+0+3 4+(5*3)+1+2
0x10 4+(5*0)+0+1 4+(5*1)+0+0 4+(5*2)+0+0 4+(5*3)+1+0
0x20 4+(5*0)+0+0 4+(5*1)+0+2 4+(5*2)+0+2 4+(5*3)+1+3
0x30 4+(5*0)+0+2 4+(5*1)+0+1 4+(5*2)+0+1 4+(5*3)+1+1

に分解すると、最後の加算値は

i 0 1 2 3
0x00 3 3 3 2
0x10 1 0 0 0
0x20 0 2 2 3
0x30 2 1 1 1

となるので、2ビット値にして逆順にすると

i 3 2 1 0 2進数 16進数
0x30 1 1 1 2 01_01_01_10 56
0x20 3 2 2 0 11_10_10_00 e8
0x10 0 0 0 1 00_00_00_01 01
0x00 2 3 3 3 10_11_11_11 bf

2ビット×16 の参照テーブル（0x56e801bf）が出来上がります。

プログラム

C++版
//
// ヘッダ用
//

#include <cstddef>
#include <cstdint>

/*
 * MD5ByteSum
 */

class MD5ByteSum
{
public:
    typedef uint32_t State[4];
    typedef uint32_t Block[16];
    typedef uint8_t Digest[16];
    typedef char HexDigest[33];

protected:
    static const uint8_t padding[64];

    State state;
    uint32_t bytes;
    Block input;
    bool active;

public:
    MD5ByteSum();
    MD5ByteSum(const void *message, size_t size);

    void digest(Digest &out);
    void hexdigest(HexDigest &out);

    void initialize();
    void update(const void *message, size_t size);
    void finalize();

protected:
    void update_state();
};

/*
 * MD5ByteSum - inline
 */

inline MD5ByteSum::MD5ByteSum()
{
    initialize();
}

//
// コンパイル用
//

/*
 * MD5ByteSum::State - update 16-Word block
 */

inline static uint32_t ROL(uint32_t x, int s)
{
    return ((x << s) | (x >> (32 - s)));
}

inline static uint32_t get_block_index(uint32_t index)
{
    /*
     * [y|y|x|x|x|x]
     *  (index * 1 + 0) & 15
     *  (index * 5 + 1) & 15
     *  (index * 3 + 5) & 15
     *  (index * 7 + 0) & 15
     */
    uint32_t x = index & 0x0f;
    uint32_t y = index & 0x30;
    uint32_t y1 = index & 0x10;
    uint32_t y2 = index & 0x20;
    uint32_t xmul = (y1 >> 2) | (y2 >> 4) | 1;
    uint32_t offs = (0x0510 >> (y >> 2)) & 7;
    return (x * xmul + offs) & 15;
}

inline static int get_rotate_bits(uint32_t index)
{
    /*
     * [y|y|.|.|x|x]
     *  7 12 17 22 : 3 8 13 18 : 3 3 3 3 : 3 3 3 2
     *  5  9 14 20 : 1 5 10 16 : 1 0 0 1 : 1 0 0 0
     *  4 11 16 23 : 0 7 12 19 : 0 2 2 4 : 0 2 2 3
     *  6 10 15 21 : 2 6 11 17 : 2 1 1 2 : 2 1 1 1
     *              -4          -(x*5)    -(x==3)
     *
     *  11 11 11 10 : 10_11_11_11 = bf
     *  01 00 00 00 : 00_00_00_01 = 01
     *  00 10 10 11 : 11_10_10_00 = e8
     *  10 01 01 01 : 01_01_01_10 = 56
     */
    uint32_t x = index & 0x03;
    uint32_t y = index & 0x30;
    uint32_t p = x | (y >> 2);
    uint32_t x0 = (0x56e801bf >> (p << 1)) & 3;
    uint32_t x3 = (x + 1) >> 2; // (x == 3) ? 1 : 0;
    uint32_t x5 = x * 5;
    return x0 + x3 + x5 + 4;
}

inline static uint32_t get_state_index(uint32_t index, uint32_t element)
{
    /*
     *  0 1 2 3
     *  3 0 1 2
     *  2 3 0 1
     *  1 2 3 0
     */
    return ((index * 3) + element) & 3;
}

inline static uint32_t md5bs_state_func(uint32_t index, uint32_t x, uint32_t y, uint32_t z)
{
    switch ((index >> 4) & 3)
    {
    case 0: return (y & x) | (z & ~x);
    case 1: return (x & z) | (y & ~z);
    case 2: return x ^ y ^ z;
    case 3: return y ^ (x | ~z);
    }
    return 0;
}

inline static void md5bs_state_update(uint32_t index, uint32_t *S, const MD5ByteSum::Block &X, uint32_t T)
{
    uint32_t a = get_state_index(index, 0);
    uint32_t b = get_state_index(index, 1);
    uint32_t c = get_state_index(index, 2);
    uint32_t d = get_state_index(index, 3);
    uint32_t x = get_block_index(index);
    uint32_t r = get_rotate_bits(index);

    S[a] = S[b] + ROL(X[x] + T + S[a] + md5bs_state_func(index, S[b], S[c], S[d]), r);
}

inline static void md5bs_state_update(uint32_t index, uint32_t *S,
                                      const MD5ByteSum::Block &X,
                                      uint32_t T1, uint32_t T2,
                                      uint32_t T3, uint32_t T4)
{
    md5bs_state_update(index + 0, S, X, T1);
    md5bs_state_update(index + 1, S, X, T2);
    md5bs_state_update(index + 2, S, X, T3);
    md5bs_state_update(index + 3, S, X, T4);
}

void MD5ByteSum::update_state()
{
    State p;

    p[0] = state[0];
    p[1] = state[1];
    p[2] = state[2];
    p[3] = state[3];

    // Round 1.
    md5bs_state_update( 0 * 4, state, input, 0xd76aa478, 0xe8c7b756, 0x242070db, 0xc1bdceee);
    md5bs_state_update( 1 * 4, state, input, 0xf57c0faf, 0x4787c62a, 0xa8304613, 0xfd469501);
    md5bs_state_update( 2 * 4, state, input, 0x698098d8, 0x8b44f7af, 0xffff5bb1, 0x895cd7be);
    md5bs_state_update( 3 * 4, state, input, 0x6b901122, 0xfd987193, 0xa679438e, 0x49b40821);

    // Round 2.
    md5bs_state_update( 4 * 4, state, input, 0xf61e2562, 0xc040b340, 0x265e5a51, 0xe9b6c7aa);
    md5bs_state_update( 5 * 4, state, input, 0xd62f105d, 0x02441453, 0xd8a1e681, 0xe7d3fbc8);
    md5bs_state_update( 6 * 4, state, input, 0x21e1cde6, 0xc33707d6, 0xf4d50d87, 0x455a14ed);
    md5bs_state_update( 7 * 4, state, input, 0xa9e3e905, 0xfcefa3f8, 0x676f02d9, 0x8d2a4c8a);

    // Round 3.
    md5bs_state_update( 8 * 4, state, input, 0xfffa3942, 0x8771f681, 0x6d9d6122, 0xfde5380c);
    md5bs_state_update( 9 * 4, state, input, 0xa4beea44, 0x4bdecfa9, 0xf6bb4b60, 0xbebfbc70);
    md5bs_state_update(10 * 4, state, input, 0x289b7ec6, 0xeaa127fa, 0xd4ef3085, 0x04881d05);
    md5bs_state_update(11 * 4, state, input, 0xd9d4d039, 0xe6db99e5, 0x1fa27cf8, 0xc4ac5665);

    // Round 4.
    md5bs_state_update(12 * 4, state, input, 0xf4292244, 0x432aff97, 0xab9423a7, 0xfc93a039);
    md5bs_state_update(13 * 4, state, input, 0x655b59c3, 0x8f0ccc92, 0xffeff47d, 0x85845dd1);
    md5bs_state_update(14 * 4, state, input, 0x6fa87e4f, 0xfe2ce6e0, 0xa3014314, 0x4e0811a1);
    md5bs_state_update(15 * 4, state, input, 0xf7537e82, 0xbd3af235, 0x2ad7d2bb, 0xeb86d391);

    state[0] += p[0];
    state[1] += p[1];
    state[2] += p[2];
    state[3] += p[3];
}

/*
 * MD5ByteSum
 */

const uint8_t MD5ByteSum::padding[64] = { 0x80 };

MD5ByteSum::MD5ByteSum(const void *message, size_t size)
{
    initialize();
    update(message, size);
    // finalize();
}

void MD5ByteSum::initialize()
{
    state[0] = 0x67452301;
    state[1] = 0xefcdab89;
    state[2] = 0x98badcfe;
    state[3] = 0x10325476;
    bytes = 0;
    for (int i = 0; i < 16; i++)
        input[i] = 0;
    active = true;
}

void MD5ByteSum::finalize()
{
    if (!active)
        return;

    uint32_t l = bytes;
    uint32_t i = l & 0x3f;
    uint32_t n = ((i >= 56) ? 64 : 0) + 56 - i;

    update(padding, n);

    input[14] = l << 3;
    input[15] = l >> 29;
    update_state();

    active = false;
}

void MD5ByteSum::update(const void *message, size_t size)
{
    if (!active)
        initialize();

    const uint8_t *d = reinterpret_cast<const uint8_t *>(message);
    unsigned b = (bytes & 3) << 3;
    unsigned i = (bytes >> 2) & 0x0f;

    bytes += size;
    while (size-- > 0)
    {
        input[i] |= (*d++) << b;

        b = (b + 8) & 0x1f;
        if (b == 0)
        {
            i = (i + 1) & 0x0f;
            if (i == 0)
                update_state();
            input[i] = 0;
        }
    }
}

void MD5ByteSum::digest(Digest &out)
{
    finalize();

    for (int p = 0; p < 4; p++)
    {
        uint32_t s = state[p];

        for (int q = 0; q < 4; q++, s >>= 8)
            out[p * 4 + q] = uint8_t(s);
    }
}

void MD5ByteSum::hexdigest(HexDigest &out)
{
    finalize();

    for (int p = 0; p < 4; p++)
    {
        uint32_t s = state[p];

        for (unsigned q = 0; q < 4; q++, s >>= 8)
        {
            char h = (s >> 4) & 0x0f;
            char l = (s >> 0) & 0x0f;
            out[p * 8 + q * 2 + 0] = h + ((h < 10) ? '0' : ('a' - 10));
            out[p * 8 + q * 2 + 1] = l + ((l < 10) ? '0' : ('a' - 10));
        }
    }
    out[32] = 0;
}

//
// テスト用
//

#include <cstdio>
#include <cstring>

int main(int argc, char **argv)
{
    const char *program = argv[0];

    if (argc != 2)
    {
        printf("usage: %s message\n", program);
        return 1;
    }

    const char *message = argv[1];

    MD5ByteSum md5(message, strlen(message));
    MD5ByteSum::HexDigest res;
    md5.hexdigest(res);
    printf("MD5 (\"%s\") = %s\n", message, res);
    return 0;
}

頭の体操として python/swift でも作ってみた。python では hashlib を、 swift では CommonCrypto を使った方がよいです。

Python版
#!/usr/bin/env python3

import math


def md5s(msg, encoding='utf-8'):
    if type(msg) in (bytes, bytearray):
        inp = bytearray(msg)
    elif type(msg) == str:
        inp = bytearray(msg, encoding)
    else:
        raise Exception('unknown type: %s' % type(msg))

    U32M = 0xffffffff
    def rotate(x, r): return (((U32M >> r) & x) << r) | ((U32M & x) >> (32 - r))
    def round1(a, b, c, d, x, t, r): return U32M & (b + rotate(x + t + a + ((b & c) | (d & (U32M - b))), r))
    def round2(a, b, c, d, x, t, r): return U32M & (b + rotate(x + t + a + ((b & d) | (c & (U32M - d))), r))
    def round3(a, b, c, d, x, t, r): return U32M & (b + rotate(x + t + a + (b ^ c ^ d), r))
    def round4(a, b, c, d, x, t, r): return U32M & (b + rotate(x + t + a + (c ^ (b | (U32M - d))), r))

    dsz = len(inp)
    bsz = dsz << 3
    pos = dsz & 0x3f
    psz = ((pos + 8) & 0x40) + 56 - pos
    inp += bytearray([0x80] + [0] * (psz - 1))
    inp += bytearray([(bsz >> b) & 0xff for b in range(0, 64, 8)])
    inp = tuple([inp[i] + (inp[i + 1] << 8) + (inp[i + 2] << 16) + (inp[i + 3] << 24) for i in range(0, len(inp), 4)])

    Sn = ((0, 1, 2, 3), (3, 0, 1, 2), (2, 3, 0, 1), (1, 2, 3, 0)) * 16
    Fn = (round1, round2, round3, round4)
    X1 = (0, 1, 2, 3) * 4 + (1, 6, 11, 0) * 4 + (13, 0, 3, 6) * 4 + (0, 7, 14, 5) * 4
    X4 = (0, 4, 8, 12) * 2 + (8, 4, 0, 12) + (0, 12, 8, 4)
    T = tuple([int(abs(math.sin(i + 1)) * 0x100000000) for i in range(64)])
    Rn = (7, 12, 17, 22) * 4 + (5, 9, 14, 20) * 4 + (4, 11, 16, 23) * 4 + (6, 10, 15, 21) * 4
    Z = tuple([(Sn[i], Fn[i >> 4], (X1[i] + X4[i >> 2]) & 0x0f, T[i], Rn[i]) for i in range(64)])

    S = [0x67452301, 0xefcdab89, 0x98badcfe, 0x10325476]
    for X in range(0, len(inp), 16):
        ss = S * 1
        for ((a, b, c, d), f, x, t, r) in Z:
            S[a] = f(S[a], S[b], S[c], S[d], inp[X + x], t, r)
        for i in range(4):
            S[i] = U32M & (S[i] + ss[i])

    return bytes([(s >> b) & 0xff for s in S for b in range(0, 32, 8)])


# Test

sample = (
    ('', 'd41d8cd98f00b204e9800998ecf8427e'),
    ('a', '0cc175b9c0f1b6a831c399e269772661'),
    ('abc', '900150983cd24fb0d6963f7d28e17f72'),
    ('message digest', 'f96b697d7cb7938d525a2f31aaf161d0'),
    ('abcdefghijklmnopqrstuvwxyz', 'c3fcd3d76192e4007dfb496cca67e13b'),
    ('ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789', 'd174ab98d277d9f5a5611c2c9f419d9f'),
    ('12345678901234567890123456789012345678901234567890123456789012345678901234567890', '57edf4a22be3c955ac49da2e2107b67a'),
)

for (message, digest) in sample:
    res = md5s(message)
    if res.hex() != digest:
        raise Exception('message "%s":\n   %s != %s' % (message, digest, res.hex()))
    print('MD5 ("%s") = %s' % (message, res.hex()))
Python（縦短横長）版

Sn, X1, X4, Rn は Z 中の計算で求めるようにするなどして、改行を減らして短くなったように見えるもの。

#!/usr/bin/env python3

import math


def md5s(msg, encoding='utf-8'):
    if type(msg) in (bytes, bytearray):
        inp = bytearray(msg)
    elif type(msg) == str:
        inp = bytearray(msg, encoding)
    else:
        raise Exception('unknown type: %s' % type(msg))

    psz = (((len(inp) & 0x3f) + 8) & 0x40) + 56 - (len(inp) & 0x3f)
    inp += bytearray([0x80] + [0] * (psz - 1)) + bytearray([((len(inp) << 3) >> b) & 0xff for b in range(0, 64, 8)])
    inp = tuple([inp[i] + (inp[i + 1] << 8) + (inp[i + 2] << 16) + (inp[i + 3] << 24) for i in range(0, len(inp), 4)])

    Z = tuple([(tuple([(i * 3 + j) & 3 for j in range(4)]), (lambda x, y, z: (x & y) | (z & (0xffffffff - x)), lambda x, y, z: (x & z) | (y & (0xffffffff - z)), lambda x, y, z: x ^ y ^ z, lambda x, y, z: y ^ (x | (0xffffffff - z)))[i >> 4], ((((i >> 2) & 4) | ((i >> 4) & 2) | 1) * (i & 15) + ((0x0510 >> ((i >> 2) & 12)) & 15)) & 15, int(abs(math.sin(i + 1)) * 0x100000000), ((0x56e801bf >> ((((i >> 2) & 12) | (i & 3)) << 1)) & 3) + (((i & 3) + 1) >> 2) + ((i & 3) * 5) + 4) for i in range(64)])

    S = [0x67452301, 0xefcdab89, 0x98badcfe, 0x10325476]
    for X in range(0, len(inp), 16):
        ss = S * 1
        for ((a, b, c, d), f, x, t, r) in Z:
            S[a] = 0xffffffff & (S[b] + (lambda x, r: (((0xffffffff >> r) & x) << r) | ((0xffffffff & x) >> (32 - r)))(inp[X + x] + t + S[a] + f(S[b], S[c], S[d]), r))
        for i in range(4):
            S[i] = 0xffffffff & (S[i] + ss[i])
    return bytes([(s >> b) & 0xff for s in S for b in range(0, 32, 8)])


# Test

sample = (
    ('', 'd41d8cd98f00b204e9800998ecf8427e'),
    ('a', '0cc175b9c0f1b6a831c399e269772661'),
    ('abc', '900150983cd24fb0d6963f7d28e17f72'),
    ('message digest', 'f96b697d7cb7938d525a2f31aaf161d0'),
    ('abcdefghijklmnopqrstuvwxyz', 'c3fcd3d76192e4007dfb496cca67e13b'),
    ('ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789', 'd174ab98d277d9f5a5611c2c9f419d9f'),
    ('12345678901234567890123456789012345678901234567890123456789012345678901234567890', '57edf4a22be3c955ac49da2e2107b67a'),
)

for (message, digest) in sample:
    res = md5s(message)
    if res.hex() != digest:
        raise Exception('message "%s":\n   %s != %s' % (message, digest, res.hex()))
    print('MD5 ("%s") = %s' % (message, res.hex()))
Swift版

Xcode 12.5.1 での Console アプリとして作っています。

main.swift
import Foundation

// ############

infix operator <<<
func <<< (x: UInt32, s: Int) -> UInt32 {
    return (x &<< s) | (x >> (32 - s))
}

extension Data {
    func ToArrayU8() -> [UInt8] {
        return [UInt8](unsafeUninitializedCapacity: count)
        { buffer, initializedCount in
            copyBytes(to: buffer, from: 0..<count)
            initializedCount = count
        }
    }
}

class MD5ByteSum {
    static let Rmap: [[Int]] = [
        [ 7, 12, 17, 22 ],
        [ 5,  9, 14, 20 ],
        [ 4, 11, 16, 23 ],
        [ 6, 10, 15, 21 ],
    ]
    static let Smap: [[Int]] = [
        [ 0, 1, 2, 3 ],
        [ 3, 0, 1, 2 ],
        [ 2, 3, 0, 1 ],
        [ 1, 2, 3, 0 ],
    ]
    static let T: [UInt32] = [UInt32](unsafeUninitializedCapacity: 64)
    { buffer, initializedCount in
        for i in 0..<64 {
            let t = abs(sin(Double(i + 1))) * 4294967296
            buffer[i] = UInt32(UInt64(t) & 0xffffffff)
        }
        initializedCount = 64
    }
    static let state0: [UInt32] = [0x67452301, 0xefcdab89, 0x98badcfe, 0x10325476]
    var state: [UInt32] = MD5ByteSum.state0
    var count: UInt32 = 0
    var input: [UInt32] = Array(repeating: 0, count: 16)
    var close = false
    init() {}
    init(_ message: [UInt8]) {
        update(message)
    }
    init(_ message: String) {
        update(Data(message.utf8).ToArrayU8())
    }
    func fini() {
        if !close {
            let bytes = count
            let i = Int(bytes & 0x3f)
            let n = ((i >= 56) ? 64 : 0) + 56 - i;
            update([0x80])
            if n > 1 {
                update(Array(repeating: 0, count: n - 1))
            }
            input[14] = bytes &<< 3
            input[15] = bytes >> 29
            update_state()
        }
        close = true
    }
    func clear() {
        state = MD5ByteSum.state0
        count = 0
        input[0] = 0
        close = false
    }
    func update(_ message: String) {
        update(Data(message.utf8).ToArrayU8())
    }
    func update(_ message: [UInt8]) {
        if close {
            clear()
        }
        var b = Int((count & 3) << 3)
        var i = Int((count >> 2) & 0x0f)
        count += UInt32(message.count)
        for d in message {
            input[i] |= UInt32(d) << b
            b = (b + 8) & 0x1f
            if b == 0 {
                i = (i + 1) & 0x0f
                if i == 0 {
                    update_state()
                }
                input[i] = 0
            }
        }
    }
    func update_state() {
        let p = state
        update_digest()
        for n in 0..<4 {
            state[n] &+= p[n]
        }
    }
    func update_digest() {
        var k: Int

        // Round 1.
        let R1 = MD5ByteSum.Rmap[0]
        for i in 0..<16 {
            let S = MD5ByteSum.Smap[i & 3]
            let a = S[0], A = state[a]
            let b = S[1], B = state[b]
            let c = S[2], C = state[c]
            let d = S[3], D = state[d]
            k = i
            state[a] = B &+ ((A &+ ((C & B) | (D & ~B)) &+ MD5ByteSum.T[i] &+ input[k]) <<< R1[i & 3])
        }

        // Round 2.
        k = 1
        let R2 = MD5ByteSum.Rmap[1]
        for i in 16..<32 {
            let S = MD5ByteSum.Smap[i & 3]
            let a = S[0], A = state[a]
            let b = S[1], B = state[b]
            let c = S[2], C = state[c]
            let d = S[3], D = state[d]
            state[a] = B &+ ((A &+ ((B & D) | (C & ~D)) &+ MD5ByteSum.T[i] &+ input[k]) <<< R2[i & 3])
            k = (k + 5) & 0x0f
        }

        // Round 3.
        k = 5
        let R3 = MD5ByteSum.Rmap[2]
        for i in 32..<48 {
            let S = MD5ByteSum.Smap[i & 3]
            let a = S[0], A = state[a]
            let b = S[1], B = state[b]
            let c = S[2], C = state[c]
            let d = S[3], D = state[d]
            state[a] = B &+ ((A &+ (B ^ C ^ D) &+ MD5ByteSum.T[i] &+ input[k]) <<< R3[i & 3])
            k = (k + 3) & 0x0f
        }

        // Round 4.
        k = 0
        let R4 = MD5ByteSum.Rmap[3]
        for i in 48..<64 {
            let S = MD5ByteSum.Smap[i & 3]
            let a = S[0], A = state[a]
            let b = S[1], B = state[b]
            let c = S[2], C = state[c]
            let d = S[3], D = state[d]
            state[a] = B &+ ((A &+ (C ^ (B | ~D)) &+ MD5ByteSum.T[i] &+ input[k]) <<< R4[i & 3])
            k = (k + 7) & 0x0f
        }
    }
    func digest() -> [UInt8] {
        fini()
        return [UInt8](unsafeUninitializedCapacity: 16)
        { buffer, initializedCount in
            for i in 0..<4 {
                for j in 0..<4 {
                    buffer[i * 4 + j] = UInt8((state[i] >> (j << 3)) & 0xff)
                }
            }
            initializedCount = 16
        }
    }
    func hexdigest() -> String {
        var s = ""
        for c in digest() {
            s += String(format: "%02x", c)
        }
        return s
    }
}

// ############

func test() {
    let sample: [[String]] = [
        [ "d41d8cd98f00b204e9800998ecf8427e", "" ],
        [ "0cc175b9c0f1b6a831c399e269772661", "a" ],
        [ "900150983cd24fb0d6963f7d28e17f72", "abc" ],
        [ "f96b697d7cb7938d525a2f31aaf161d0", "message digest" ],
        [ "c3fcd3d76192e4007dfb496cca67e13b", "abcdefghijklmnopqrstuvwxyz" ],
        [ "d174ab98d277d9f5a5611c2c9f419d9f", "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789" ],
        [ "57edf4a22be3c955ac49da2e2107b67a", "12345678901234567890123456789012345678901234567890123456789012345678901234567890" ],
    ]
    for t in sample {
        let md5 = MD5ByteSum(t[1])
        let res = md5.hexdigest()
        if res != t[0] {
            print("Message: \"\(t[1])\"")
            print("  Error: \(t[0]) != \(res)")
            exit(1)
        }
        print("MD5 (\"\(t[1])\") = \(res)")
    }
}
test()
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