因学习需要，在网上找SMS4的C实现，没有找到满意的。所以自己写了一个，现分享之，希望能帮到有需要的朋友。
实现的时候，用到了一些C99的新特性。
接下来，就是SMS4的C语言实现。没有做优化，以后有时间了，会再改进。
一：头文件 "sms4.h"
1 /*
2 * ============================================================================
3 *
4 * Filename: sms4.h
5 *
6 * Description: Public interface for the SMS4 encryption algorithm.
7 *
8 * Version: 1.0
9 * Created: 2012年04月01日 15时18分14秒
10 * Revision: none
11 * Compiler: gcc
12 *
13 * Author: Long, longcpp9@gmail.com
14 * Company: SDU
15 *
16 * ============================================================================
17 */
18 #ifndef SMS4_INCLUDED
19 #define SMS4_INCLUDED
20
21 void sms4_encrypt(void *plaintext, void const *key);
22 void sms4_decrypt(void *ciphertext, void const *key);
23
24 #endif /* SMS4_INCLUDED */
二：实现文件 "sms4.c"
1 /*
2 * ============================================================================
3 *
4 * Filename: sms4.c
5 *
6 * Description: Implementation of SMS4
7 *
8 * Version: 1.0
9 * Created: 2012年04月01日 13时36分06秒
10 * Revision: none
11 * Compiler: gcc
12 *
13 * Author: Long, longcpp9@gmail.com
14 * Company: SDU
15 *
16 * ============================================================================
17 */
18 #include <stdlib.h>
19 #include <stdint.h>
20 #include <inttypes.h>
21 #include <stdio.h>
22 #include <string.h>
23
24 #include "sms4.h"
25
26 #define ROUND 32
27
28 static uint8_t sms4_sbox[256] = {
29 0xd6, 0x90, 0xe9, 0xfe, 0xcc, 0xe1, 0x3d, 0xb7,
30 0x16, 0xb6, 0x14, 0xc2, 0x28, 0xfb, 0x2c, 0x05,
31 0x2b, 0x67, 0x9a, 0x76, 0x2a, 0xbe, 0x04, 0xc3,
32 0xaa, 0x44, 0x13, 0x26, 0x49, 0x86, 0x06, 0x99,
33 0x9c, 0x42, 0x50, 0xf4, 0x91, 0xef, 0x98, 0x7a,
34 0x33, 0x54, 0x0b, 0x43, 0xed, 0xcf, 0xac, 0x62,
35 0xe4, 0xb3, 0x1c, 0xa9, 0xc9, 0x08, 0xe8, 0x95,
36 0x80, 0xdf, 0x94, 0xfa, 0x75, 0x8f, 0x3f, 0xa6,
37 0x47, 0x07, 0xa7, 0xfc, 0xf3, 0x73, 0x17, 0xba,
38 0x83, 0x59, 0x3c, 0x19, 0xe6, 0x85, 0x4f, 0xa8,
39 0x68, 0x6b, 0x81, 0xb2, 0x71, 0x64, 0xda, 0x8b,
40 0xf8, 0xeb, 0x0f, 0x4b, 0x70, 0x56, 0x9d, 0x35,
41 0x1e, 0x24, 0x0e, 0x5e, 0x63, 0x58, 0xd1, 0xa2,
42 0x25, 0x22, 0x7c, 0x3b, 0x01, 0x21, 0x78, 0x87,
43 0xd4, 0x00, 0x46, 0x57, 0x9f, 0xd3, 0x27, 0x52,
44 0x4c, 0x36, 0x02, 0xe7, 0xa0, 0xc4, 0xc8, 0x9e,
45 0xea, 0xbf, 0x8a, 0xd2, 0x40, 0xc7, 0x38, 0xb5,
46 0xa3, 0xf7, 0xf2, 0xce, 0xf9, 0x61, 0x15, 0xa1,
47 0xe0, 0xae, 0x5d, 0xa4, 0x9b, 0x34, 0x1a, 0x55,
48 0xad, 0x93, 0x32, 0x30, 0xf5, 0x8c, 0xb1, 0xe3,
49 0x1d, 0xf6, 0xe2, 0x2e, 0x82, 0x66, 0xca, 0x60,
50 0xc0, 0x29, 0x23, 0xab, 0x0d, 0x53, 0x4e, 0x6f,
51 0xd5, 0xdb, 0x37, 0x45, 0xde, 0xfd, 0x8e, 0x2f,
52 0x03, 0xff, 0x6a, 0x72, 0x6d, 0x6c, 0x5b, 0x51,
53 0x8d, 0x1b, 0xaf, 0x92, 0xbb, 0xdd, 0xbc, 0x7f,
54 0x11, 0xd9, 0x5c, 0x41, 0x1f, 0x10, 0x5a, 0xd8,
55 0x0a, 0xc1, 0x31, 0x88, 0xa5, 0xcd, 0x7b, 0xbd,
56 0x2d, 0x74, 0xd0, 0x12, 0xb8, 0xe5, 0xb4, 0xb0,
57 0x89, 0x69, 0x97, 0x4a, 0x0c, 0x96, 0x77, 0x7e,
58 0x65, 0xb9, 0xf1, 0x09, 0xc5, 0x6e, 0xc6, 0x84,
59 0x18, 0xf0, 0x7d, 0xec, 0x3a, 0xdc, 0x4d, 0x20,
60 0x79, 0xee, 0x5f, 0x3e, 0xd7, 0xcb, 0x39, 0x48
61 };
62
63 static uint32_t sms4_ck[32] = {
64 0x00070e15, 0x1c232a31, 0x383f464d, 0x545b6269,
65 0x70777e85, 0x8c939aa1, 0xa8afb6bd, 0xc4cbd2d9,
66 0xe0e7eef5, 0xfc030a11, 0x181f262d, 0x343b4249,
67 0x50575e65, 0x6c737a81, 0x888f969d, 0xa4abb2b9,
68 0xc0c7ced5, 0xdce3eaf1, 0xf8ff060d, 0x141b2229,
69 0x30373e45, 0x4c535a61, 0x686f767d, 0x848b9299,
70 0xa0a7aeb5, 0xbcc3cad1, 0xd8dfe6ed, 0xf4fb0209,
71 0x10171e25, 0x2c333a41, 0x484f565d, 0x646b7279
72 };
73
74 static inline uint32_t rotate_left(uint32_t x, uint8_t n)
75 {
76 return ((x << n) | (x >> (32 - n)));
77 }
78
79 static inline uint32_t L_trans(uint32_t x)
80 {
81 return (x ^ rotate_left(x, 2) ^ rotate_left(x, 10)
82 ^ rotate_left(x, 18) ^ rotate_left(x, 24));
83 }
84
85 static inline uint32_t key_L_trans(uint32_t x)
86 {
87 return (x ^ rotate_left(x, 13) ^ rotate_left(x, 23));
88 }
89
90 static inline uint32_t s_substitute(uint32_t x)
91 {
92 uint8_t *px = (uint8_t *)&x;
93 px[0] = sms4_sbox[px[0]];
94 px[1] = sms4_sbox[px[1]];
95 px[2] = sms4_sbox[px[2]];
96 px[3] = sms4_sbox[px[3]];
97
98 return x;
99 }
100
101 static inline uint32_t T_trans(uint32_t x)
102 {
103 return (L_trans(s_substitute(x)));
104 }
105
106 static inline uint32_t key_T_trans(uint32_t x)
107 {
108 return (key_L_trans(s_substitute(x)));
109 }
110
111 static inline void sms4_round_func(uint32_t *input, uint32_t sub_key)
112 {
113 uint32_t tmp = input[0];
114
115 input[0] = input[1];
116 input[1] = input[2];
117 input[2] = input[3];
118 input[3] = tmp ^ T_trans(input[0] ^ input[1] ^ input[2] ^ sub_key);
119 }
120
121 static inline void sms4_reverse(uint32_t *input)
122 {
123 uint32_t tmp;
124 tmp = input[0], input[0] = input[3], input[3] = tmp;
125 tmp = input[1], input[1] = input[2], input[2] = tmp;
126 }
127
128 static void sms4_key_schedule(uint32_t const *key, uint32_t *round_key)
129 {
130 int j;
131 uint32_t buf[4];
132 uint32_t *prk = (uint32_t *)round_key;
133
134 memcpy(buf, key, 16);
135
136 buf[0] ^= 0xa3b1bac6; buf[1] ^= 0x56aa3350;
137 buf[2] ^= 0x677d9197; buf[3] ^= 0xb27022dc;
138
139
140 for(j = 0; j < ROUND; ++j){
141 prk[j] = buf[0] ^ key_T_trans(buf[1] ^ buf[2] ^ buf[3] ^ sms4_ck[j]);
142 buf[0] = buf[1];
143 buf[1] = buf[2];
144 buf[2] = buf[3];
145 buf[3] = prk[j];
146 }
147 }
148
149 void sms4_encrypt(void *plaintext, void const *key)
150 {
151 uint32_t round_key[ROUND] = {0};
152 sms4_key_schedule(key, round_key);
153
154 int i;
155 for(i = 0; i < ROUND; ++i)
156 sms4_round_func((uint32_t *)plaintext, round_key[i]);
157
158 sms4_reverse((uint32_t *)plaintext);
159 }
160
161 void sms4_decrypt(void *ciphertext, void const *key)
162 {
163 uint32_t round_key[ROUND] = {0};
164 sms4_key_schedule(key, round_key);
165
166 int i;
167 for(i = 0; i < ROUND; ++i)
168 sms4_round_func((uint32_t *)ciphertext, round_key[31-i]);
169
170 sms4_reverse((uint32_t *)ciphertext);
171 }
在实现SMS4时，本着一个原则来设计函数接口，即：
共用接口的函数，对参数类型的限制尽可能小（因为我们并不知道用户程序究竟会用怎样的数据类型来存储明文），故参数类型设置为void *，而那些用于实现共用接口的函数的参数类型，限制比较多，因为这些是我们可以控制的（我还不很确定这样的到底是否合适，暂且就这样吧）。
三：测试文件 "sms4_test.c"
1 /*
2 * ============================================================================
3 *
4 * Filename: sms4_test.c
5 *
6 * Description: Test the implementation of sms4.
7 *
8 * Version: 1.0
9 * Created: 2012年04月01日 15时20分44秒
10 * Revision: none
11 * Compiler: gcc
12 *
13 * Author: Long, longcpp9@gmail.com
14 * Company: SDU
15 *
16 * ============================================================================
17 */
18 #include <stdio.h>
19 #include <stdlib.h>
20 #include <inttypes.h>
21
22 #include "sms4.h"
23
24 void print(uint32_t *buf, int size)
25 {
26 int i = 0;
27 for(i = 0; i < size; ++i)
28 printf("%08" PRIx32 " ", buf[i]);
29 printf("\n");
30 }
31
32 int main(int argc, const char *argv[])
33 {
34 uint32_t buffer[4] = {0x01234567, 0x89abcdef, 0xfedcba98, 0x76543210};
35 uint32_t key[4] = {0x01234567, 0x89abcdef, 0xfedcba98, 0x76543210};
36
37 printf("the plaintext:\t");
38 print(buffer, 4);
39
40 printf("the key:\t");
41 print(key, 4);
42
43 sms4_encrypt(buffer, key);
44
45 printf("the ciphertext:\t");
46 print(buffer, 4);
47
48 sms4_decrypt(buffer, key);
49
50 printf("the plaintext:\t");
51 print(buffer, 4);
52
53 exit(EXIT_SUCCESS);
54 }
程序所输出的结果，与SMS4的官方文档中给出的示例一样，如下：（改成循环加密1000000次，所得结果与官方文档中也一样，大家可以测试）
1 the plaintext: 01234567 89abcdef fedcba98 76543210
2 the key: 01234567 89abcdef fedcba98 76543210
3 the ciphertext: 681edf34 d206965e 86b3e94f 536e4246
4 the plaintext: 43267f05 e9acb3f8 bf0e4dbd 43604a8b
大概就是这样了，有不合适的地方，请批评指正。
转载请注明出处。:-)