国密SM4分组加密[通俗易懂]

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分享一篇SM4加密算法实现文章，算法用C语言即可实现，只有短短300多行代码。

SMS4是我国无线局域网标准WAPI中所采用的分组密码标准，随后被我国商用密码标准采用，又名SM4（SM是“商密”的缩写，目前公布的其他商密标准包括SM2椭圆曲线公钥密码，SM3密码杂凑算法）。作为我国商用密码的分组密码标准，预计SMS4在国内的敏感但非机密的应用领域会逐渐取代3DES，AES等国外分组密码标准，用于通信加密，数据加密等应用场合。
SM4的密钥长度和分组长度均为128比特，其设计安全性等同于AES-128。

我对加密算法进行了一个封装，可以直接用来加密文件，我的封装方法是：由于SM4的密钥长度和分组长度均为128比特（16个字节），所以我们必须要对密码和明文进行处理，最简单就是补齐16字节，密码规定最大只能是16个字符，不足部分补0（这样做有个BUG，比如密码“123456”和“1234560”是一样的，可以考虑对密码取MD5值解决这个问题）；明文也是
不足部分补0，加密时计算补了多少个字节，计为offset,然后保存数据时，在数据头加一个字节数据offset,明显offset是在0-15之间。解密时读文件第一个字节就知道偏移量，然后解密完就去掉offset个字节。
我的实现文件：链接:https://pan.baidu.com/s/1rmNv4UNb40nl3PhCUloQ6A 提取码:t08r

SM4算法代码如下：

sm4.h文件：

/**
 * \file sm4.h
 */
#ifndef XYSSL_SM4_H
#define XYSSL_SM4_H
 
#ifdef __cplusplus
extern "C" {
#endif

#define SM4_ENCRYPT     1
#define SM4_DECRYPT     0
 
/**
 * \brief          SM4 context structure
 */
typedef struct
{
    int mode;                   /*!<  encrypt/decrypt   */
    unsigned long sk[32];       /*!<  SM4 subkeys       */
}sm4_context;


/**
 * \brief          SM4 key schedule (128-bit, encryption)
 *
 * \param ctx      SM4 context to be initialized
 * \param key      16-byte secret key
 */
void sm4_setkey_enc( sm4_context *ctx, unsigned char key[16] );
/**
 * \brief          SM4 key schedule (128-bit, decryption)
 *
 * \param ctx      SM4 context to be initialized
 * \param key      16-byte secret key
 */
void sm4_setkey_dec( sm4_context *ctx, unsigned char key[16] );
/**
 * \brief          SM4-ECB block encryption/decryption
 * \param ctx      SM4 context
 * \param mode     SM4_ENCRYPT or SM4_DECRYPT
 * \param length   length of the input data
 * \param input    input block
 * \param output   output block
 */
void sm4_crypt_ecb( sm4_context *ctx,
				     int mode,
					 int length,
                     unsigned char *input,
                     unsigned char *output);
#ifdef __cplusplus
}
#endif

#endif /* sm4.h */

sm4.c文件：

/*
* SM4 Encryption alogrithm (SMS4 algorithm)
* GM/T 0002-2012 Chinese National Standard ref:http://www.oscca.gov.cn/ 
* thanks to Xyssl
* thnaks and refers to http://hi.baidu.com/numax/blog/item/80addfefddfb93e4cf1b3e61.html
* author:goldboar
* email:goldboar@163.com
* 2012-4-20
*/
#include "sm4.h"
#include <string.h>
#include <stdio.h>
/*
* 32-bit integer manipulation macros (big endian)
*/
#ifndef GET_ULONG_BE
#define GET_ULONG_BE(n,b,i)                             \
{                                                       \
(n) = ( (unsigned long) (b)[(i)    ] << 24 )        \
| ( (unsigned long) (b)[(i) + 1] << 16 )        \
| ( (unsigned long) (b)[(i) + 2] <<  8 )        \
| ( (unsigned long) (b)[(i) + 3]       );       \
}
#endif
#ifndef PUT_ULONG_BE
#define PUT_ULONG_BE(n,b,i)                             \
{                                                       \
(b)[(i)    ] = (unsigned char) ( (n) >> 24 );       \
(b)[(i) + 1] = (unsigned char) ( (n) >> 16 );       \
(b)[(i) + 2] = (unsigned char) ( (n) >>  8 );       \
(b)[(i) + 3] = (unsigned char) ( (n)       );       \
}
#endif
/*
*rotate shift left marco definition
*
*/
#define  SHL(x,n) (((x) & 0xFFFFFFFF) << n)
#define ROTL(x,n) (SHL((x),n) | ((x) >> (32 - n)))
#define SWAP(a,b) { unsigned long t = a; a = b; b = t; t = 0; }
/*
* Expanded SM4 S-boxes
/* Sbox table: 8bits input convert to 8 bits output*/
static const unsigned char SboxTable[16][16] = 
{
{0xd6,0x90,0xe9,0xfe,0xcc,0xe1,0x3d,0xb7,0x16,0xb6,0x14,0xc2,0x28,0xfb,0x2c,0x05},
{0x2b,0x67,0x9a,0x76,0x2a,0xbe,0x04,0xc3,0xaa,0x44,0x13,0x26,0x49,0x86,0x06,0x99},
{0x9c,0x42,0x50,0xf4,0x91,0xef,0x98,0x7a,0x33,0x54,0x0b,0x43,0xed,0xcf,0xac,0x62},
{0xe4,0xb3,0x1c,0xa9,0xc9,0x08,0xe8,0x95,0x80,0xdf,0x94,0xfa,0x75,0x8f,0x3f,0xa6},
{0x47,0x07,0xa7,0xfc,0xf3,0x73,0x17,0xba,0x83,0x59,0x3c,0x19,0xe6,0x85,0x4f,0xa8},
{0x68,0x6b,0x81,0xb2,0x71,0x64,0xda,0x8b,0xf8,0xeb,0x0f,0x4b,0x70,0x56,0x9d,0x35},
{0x1e,0x24,0x0e,0x5e,0x63,0x58,0xd1,0xa2,0x25,0x22,0x7c,0x3b,0x01,0x21,0x78,0x87},
{0xd4,0x00,0x46,0x57,0x9f,0xd3,0x27,0x52,0x4c,0x36,0x02,0xe7,0xa0,0xc4,0xc8,0x9e},
{0xea,0xbf,0x8a,0xd2,0x40,0xc7,0x38,0xb5,0xa3,0xf7,0xf2,0xce,0xf9,0x61,0x15,0xa1},
{0xe0,0xae,0x5d,0xa4,0x9b,0x34,0x1a,0x55,0xad,0x93,0x32,0x30,0xf5,0x8c,0xb1,0xe3},
{0x1d,0xf6,0xe2,0x2e,0x82,0x66,0xca,0x60,0xc0,0x29,0x23,0xab,0x0d,0x53,0x4e,0x6f},
{0xd5,0xdb,0x37,0x45,0xde,0xfd,0x8e,0x2f,0x03,0xff,0x6a,0x72,0x6d,0x6c,0x5b,0x51},
{0x8d,0x1b,0xaf,0x92,0xbb,0xdd,0xbc,0x7f,0x11,0xd9,0x5c,0x41,0x1f,0x10,0x5a,0xd8},
{0x0a,0xc1,0x31,0x88,0xa5,0xcd,0x7b,0xbd,0x2d,0x74,0xd0,0x12,0xb8,0xe5,0xb4,0xb0},
{0x89,0x69,0x97,0x4a,0x0c,0x96,0x77,0x7e,0x65,0xb9,0xf1,0x09,0xc5,0x6e,0xc6,0x84},
{0x18,0xf0,0x7d,0xec,0x3a,0xdc,0x4d,0x20,0x79,0xee,0x5f,0x3e,0xd7,0xcb,0x39,0x48}
};
/* System parameter */
static const unsigned long FK[4] = {0xa3b1bac6,0x56aa3350,0x677d9197,0xb27022dc};
/* fixed parameter */
static const unsigned long CK[32] =
{
0x00070e15,0x1c232a31,0x383f464d,0x545b6269,
0x70777e85,0x8c939aa1,0xa8afb6bd,0xc4cbd2d9,
0xe0e7eef5,0xfc030a11,0x181f262d,0x343b4249,
0x50575e65,0x6c737a81,0x888f969d,0xa4abb2b9,
0xc0c7ced5,0xdce3eaf1,0xf8ff060d,0x141b2229,
0x30373e45,0x4c535a61,0x686f767d,0x848b9299,
0xa0a7aeb5,0xbcc3cad1,0xd8dfe6ed,0xf4fb0209,
0x10171e25,0x2c333a41,0x484f565d,0x646b7279
};
/*
* private function:
* look up in SboxTable and get the related value.
* args:    [in] inch: 0x00~0xFF (8 bits unsigned value).
*/
static unsigned char sm4Sbox(unsigned char inch)
{
unsigned char *pTable = (unsigned char *)SboxTable;
unsigned char retVal = (unsigned char)(pTable[inch]);
return retVal;
}
/*
* private F(Lt) function:
* "T algorithm" == "L algorithm" + "t algorithm".
* args:    [in] a: a is a 32 bits unsigned value;
* return: c: c is calculated with line algorithm "L" and nonline algorithm "t"
*/
static unsigned long sm4Lt(unsigned long ka)
{
unsigned long bb = 0;
unsigned long c = 0;
unsigned char a[4];
unsigned char b[4];
PUT_ULONG_BE(ka,a,0)
b[0] = sm4Sbox(a[0]);
b[1] = sm4Sbox(a[1]);
b[2] = sm4Sbox(a[2]);
b[3] = sm4Sbox(a[3]);
GET_ULONG_BE(bb,b,0)
c =bb^(ROTL(bb, 2))^(ROTL(bb, 10))^(ROTL(bb, 18))^(ROTL(bb, 24));
return c;
}
/*
* private F function:
* Calculating and getting encryption/decryption contents.
* args:    [in] x0: original contents;
* args:    [in] x1: original contents;
* args:    [in] x2: original contents;
* args:    [in] x3: original contents;
* args:    [in] rk: encryption/decryption key;
* return the contents of encryption/decryption contents.
*/
static unsigned long sm4F(unsigned long x0, unsigned long x1, unsigned long x2, unsigned long x3, unsigned long rk)
{
return (x0^sm4Lt(x1^x2^x3^rk));
}
/* private function:
* Calculating round encryption key.
* args:    [in] a: a is a 32 bits unsigned value;
* return: sk[i]: i{0,1,2,3,...31}.
*/
static unsigned long sm4CalciRK(unsigned long ka)
{
unsigned long bb = 0;
unsigned long rk = 0;
unsigned char a[4];
unsigned char b[4];
PUT_ULONG_BE(ka,a,0)
b[0] = sm4Sbox(a[0]);
b[1] = sm4Sbox(a[1]);
b[2] = sm4Sbox(a[2]);
b[3] = sm4Sbox(a[3]);
GET_ULONG_BE(bb,b,0)
rk = bb^(ROTL(bb, 13))^(ROTL(bb, 23));
return rk;
}
static void sm4_setkey( unsigned long SK[32], unsigned char key[16] )
{
unsigned long MK[4];
unsigned long k[36];
unsigned long i = 0;
GET_ULONG_BE( MK[0], key, 0 );
GET_ULONG_BE( MK[1], key, 4 );
GET_ULONG_BE( MK[2], key, 8 );
GET_ULONG_BE( MK[3], key, 12 );
k[0] = MK[0]^FK[0];
k[1] = MK[1]^FK[1];
k[2] = MK[2]^FK[2];
k[3] = MK[3]^FK[3];
for(; i<32; i++)
{
k[i+4] = k[i] ^ (sm4CalciRK(k[i+1]^k[i+2]^k[i+3]^CK[i]));
SK[i] = k[i+4];
}
}
/*
* SM4 standard one round processing
*
*/
static void sm4_one_round( unsigned long sk[32],
unsigned char input[16],
unsigned char output[16] )
{
unsigned long i = 0;
unsigned long ulbuf[36];
memset(ulbuf, 0, sizeof(ulbuf));
GET_ULONG_BE( ulbuf[0], input, 0 )
GET_ULONG_BE( ulbuf[1], input, 4 )
GET_ULONG_BE( ulbuf[2], input, 8 )
GET_ULONG_BE( ulbuf[3], input, 12 )
while(i<32)
{
ulbuf[i+4] = sm4F(ulbuf[i], ulbuf[i+1], ulbuf[i+2], ulbuf[i+3], sk[i]);
// #ifdef _DEBUG
//        	printf("rk(%02d) = 0x%08x,  X(%02d) = 0x%08x \n",i,sk[i], i, ulbuf[i+4] );
// #endif
i++;
}
PUT_ULONG_BE(ulbuf[35],output,0);
PUT_ULONG_BE(ulbuf[34],output,4);
PUT_ULONG_BE(ulbuf[33],output,8);
PUT_ULONG_BE(ulbuf[32],output,12);
}
/*
* SM4 key schedule (128-bit, encryption)
*/
void sm4_setkey_enc( sm4_context *ctx, unsigned char key[16] )
{
ctx->mode = SM4_ENCRYPT;
sm4_setkey( ctx->sk, key );
}
/*
* SM4 key schedule (128-bit, decryption)
*/
void sm4_setkey_dec( sm4_context *ctx, unsigned char key[16] )
{
int i;
ctx->mode = SM4_ENCRYPT;
sm4_setkey( ctx->sk, key );
for( i = 0; i < 16; i ++ )
{
SWAP( ctx->sk[ i ], ctx->sk[ 31-i] );
}
}
/*
* SM4-ECB block encryption/decryption
*/
void sm4_crypt_ecb( sm4_context *ctx,
int mode,
int length,
unsigned char *input,
unsigned char *output)
{
while( length > 0 )
{
sm4_one_round( ctx->sk, input, output );
input  += 16;
output += 16;
length -= 16;
}
}
/*
*  * SM4-CBC buffer encryption/decryption
*  */
void sm4_crypt_cbc( sm4_context *ctx,
int mode,
int length,
unsigned char iv[16],
unsigned char *input,
unsigned char *output )
{
int i;
unsigned char temp[16];
if( mode == SM4_ENCRYPT )
{
while( length > 0 )
{
for( i = 0; i < 16; i++ )
output[i] = (unsigned char)( input[i] ^ iv[i] );
sm4_one_round( ctx->sk, output, output );
memcpy( iv, output, 16 );
input  += 16;
output += 16;
length -= 16;
}
}
else /* SM4_DECRYPT */
{
while( length > 0 )
{
memcpy( temp, input, 16 );
sm4_one_round( ctx->sk, input, output );
for( i = 0; i < 16; i++ )
output[i] = (unsigned char)( output[i] ^ iv[i] );
memcpy( iv, temp, 16 );
input  += 16;
output += 16;
length -= 16;
}
}
}