2sFmewdY

1package main
2
3import (
4	hmaclib "crypto/hmac"
5	"crypto/md5"
6	"encoding/hex"
7	"fmt"
8	"hash"
9)
10
11func ComputeHmacCorrect(message string, secret string) string {
12	h := hmaclib.New(md5.New, []byte(secret))
13	h.Write([]byte(message))
14	sum := h.Sum(nil)
15	return hex.EncodeToString(sum[:])
16}
17
18func ComputeHmacCustom(message string, key_str string) string {
19	key := []byte(key_str)
20	h := md5.New
21
22	hm := new(hmac)
23	// New
24	{
25		hm.outer = h()
26		hm.inner = h()
27		hm.size = hm.inner.Size()
28		hm.blocksize = hm.inner.BlockSize()
29		hm.ipad = make([]byte, hm.blocksize)
30		hm.opad = make([]byte, hm.blocksize)
31		if len(key) > hm.blocksize {
32			// If key is too big, hash it.
33			hm.outer.Write(key)
34			key = hm.outer.Sum(nil)
35		}
36		copy(hm.ipad, key)
37		copy(hm.opad, key)
38		for i := range hm.ipad {
39			hm.ipad[i] ^= 0x36
40		}
41		for i := range hm.opad {
42			hm.opad[i] ^= 0x5c
43		}
44		hm.inner.Write(hm.ipad)
45	}
46
47	// DEBUG: Inner MD5
48	{
49		hm.Write([]byte(message))
50		return hex.EncodeToString(hm.inner.Sum(nil))
51	}
52
53	// Write
54	{
55		hm.Write([]byte(message))
56	}
57
58	// Sum(in)
59	var sum []byte
60	{
61		var in []byte = nil
62		h := hm
63		origLen := len(in)
64		in = h.inner.Sum(in)
65		h.outer.Reset()
66		h.outer.Write(h.opad)
67		h.outer.Write(in[origLen:])
68		//panic(fmt.Sprintf("%v", in[origLen:]))
69		sum = h.outer.Sum(in[:origLen])
70	}
71	return hex.EncodeToString(sum[:])
72}
73
74func main() {
75	secretKey := "secret_key"
76	//secretKey := "ff772e31410ae7f31b93c2109f496006ff772e31410ae7f31b93c2109f496006"
77	fmt.Printf("--------------------------------------------------------\n")
78	fmt.Printf("Normal implementation \n")
79	fmt.Printf("--------------------------------------------------------\n")
80	fmt.Printf("String A - %s\n", ComputeHmacCorrect(string([]byte{'A'}), secretKey))
81	fmt.Printf("String A with zero byte terminator - %s\n", ComputeHmacCorrect(string([]byte{'A', 0}), secretKey))
82	fmt.Printf("Empty string - %s\n", ComputeHmacCorrect("", secretKey))
83	fmt.Printf("Empty string with zero byte - %s\n", ComputeHmacCorrect(string([]byte{0}), secretKey))
84	fmt.Printf("--------------------------------------------------------\n")
85	fmt.Printf("Custom implementation \n")
86	fmt.Printf("--------------------------------------------------------\n")
87	fmt.Printf("String A - %s\n", ComputeHmacCustom(string([]byte{'A'}), secretKey))
88	fmt.Printf("String A with zero byte terminator - %s\n", ComputeHmacCustom(string([]byte{'A', 0}), secretKey))
89	fmt.Printf("Empty string - %s\n", ComputeHmacCustom("", secretKey))
90	fmt.Printf("Empty string with zero byte - %s\n", ComputeHmacCustom(string([]byte{0}), secretKey))
91	panic(".")
92}
93
94// ---
95
96type hmac struct {
97	size         int
98	blocksize    int
99	opad, ipad   []byte
100	outer, inner hash.Hash
101}
102
103func (h *hmac) Sum(in []byte) []byte {
104	origLen := len(in)
105	in = h.inner.Sum(in)
106	//in = []byte(hex.EncodeToString(h.inner.Sum(in)))
107	//fmt.Printf("Inner MD5: %s\n", hex.EncodeToString(in))
108	h.outer.Reset()
109	h.outer.Write(h.opad)
110	h.outer.Write(in[origLen:])
111	return h.outer.Sum(in[:origLen])
112}
113
114func (h *hmac) Write(p []byte) (n int, err error) {
115	return h.inner.Write(p)
116}
117
118func (h *hmac) Size() int { return h.size }
119
120func (h *hmac) BlockSize() int { return h.blocksize }
121
122func (h *hmac) Reset() {
123	h.inner.Reset()
124	h.inner.Write(h.ipad)
125}