xyssl资料整理（一） 对aescrypt2工程的理解

一、xyssl资料下载

xyssl下载链接

xyssl网站

二、main函数的输入参数

1、预设置参数

选中当前项目-->属性-->配置属性-->调试-->命令参数 其中

int main( int argc, char *argv[] )

argc = “在命令参数中输入参数的个数” - 1，因为argc也算一个参数。

2、参数解释

<mode> <input filename> <output filename> <key>

mode：0表示加密操作；1表示解密操作；

input filename：要进行加密操作的文件名（此处不需要加引号，如D：\input.txt）

output filename：输出文件名，在程序中其举例命名是file.aes格式的。///*************************************************

key：key有三种输入格式，文件名（D：\key.txt）、"hex:"开头的十六进制输入（hex:EFD32E）、直接输入（123456）//****************************

三、知识点说明

1、IV

作用：块密码的工作模式

获取方式：根据上面的链接可知，IV如果固定对有些模式的算法安全性是有影响的。在该例子中，程序根据要加密的文件的大小以及文件名获取其sha256的哈希值（32位），并取得其前面的16位作为IV。

2、HMAC

作用：

四、程序处理流程

1、加密

（1）获取输入文件、输出文件指针；

（2）获取输入密钥数据；

（3）获取IV；

（4）将IV写入输出文件的最前面；

（5）根据IV和输入的key进行8192次的哈希，得到相应hash值digest；

（6）根据（5）得到的digest作为AES加密密钥的输入，获取AES加密的密钥；

（7）加密文件数据

（6）对加密的文件数据进行hmac

（8）

五、代码

#ifndef _CRT_SECURE_NO_DEPRECATE
#define _CRT_SECURE_NO_DEPRECATE 1
#endif

#if defined(WIN32)
#include <windows.h>
#include <io.h>
#else
#include <sys/types.h>
#include <unistd.h>
#endif

#include <string.h>
#include <stdlib.h>
#include <stdio.h>
#include <time.h>

#include "xyssl/aes.h"
#include "xyssl/sha2.h"

#define MODE_ENCRYPT    0
#define MODE_DECRYPT    1

#define USAGE   \
"\n  aescrypt2 <mode> <input filename> <output filename> <key>\n" \
"\n   <mode>: 0 = encrypt, 1 = decrypt\n" \
"\n  example: aescrypt2 0 file file.aes hex:E76B2413958B00E193\n" \
"\n"

int main( int argc, char *argv[] )
{
int ret = 1, i, n;
int keylen, mode, lastn;
FILE *fkey, *fin, *fout;

char *p;
unsigned char IV[16];
unsigned char key[512];
unsigned char digest[32];
unsigned char buffer[1024];

aes_context aes_ctx;
sha2_context sha_ctx;

#if defined(WIN32)
LARGE_INTEGER li_size;
__int64 filesize, offset;
#else
off_t filesize, offset;
#endif

/*
* Parse the command-line arguments.
*/
if( argc != 5 )
{
printf( USAGE );

#if defined(WIN32)
printf( "\n  Press Enter to exit this program.\n" );
fflush( stdout ); getchar();
#endif

goto exit;
}

//获取操作是加密还是解密
mode = atoi( argv[1] );

if( mode != MODE_ENCRYPT && mode != MODE_DECRYPT )
{
fprintf( stderr, "invalide operation mode\n" );
goto exit;
}

//输入文件名和输出文件名必须不一致
if( strcmp( argv[2], argv[3] ) == 0 )
{
fprintf( stderr, "input and output filenames must differ\n" );
goto exit;
}

//以二进制、读写方式打开要加密的文件
if( ( fin = fopen( argv[2], "rb" ) ) == NULL )
{
fprintf( stderr, "fopen(%s,rb) failed\n", argv[2] );
goto exit;
}

//以二进制、只写方式打开或新建保存加密文件后的文件
if( ( fout = fopen( argv[3], "wb+" ) ) == NULL )
{
fprintf( stderr, "fopen(%s,wb+) failed\n", argv[3] );
goto exit;
}

/*
* Read the secret key and clean the command line.
*/
if( ( fkey = fopen( argv[4], "rb" ) ) != NULL )
{
//如果密钥为二进制文件
//则读取密钥key大小的数据，存储于key中
keylen = fread( key, 1, sizeof( key ), fkey );
fclose( fkey );
}
else
{
//如果密钥为直接输入的二进制数据
if( memcmp( argv[4], "hex:", 4 ) == 0 )
{
//则剔除前面的"hex:"字符
p = &argv[4][4];
keylen = 0;

//从一个字符串中读进与指定格式相符的数据
/*X 表示以十六进制形式输出
02 表示不足两位，前面补0输出；出过两位，不影响
举例：
printf("%02X", 0x123);  //打印出：123
printf("%02X", 0x1); //打印出：01*/
//如果密钥长度超过512位，则截断后面的字符
while( sscanf( p, "%02X", &n ) > 0 &&
keylen < (int) sizeof( key ) )
{
key[keylen++] = (unsigned char) n;
p += 2;
}
}
else
{
keylen = strlen( argv[4] );

if( keylen > (int) sizeof( key ) )
keylen = (int) sizeof( key );

memcpy( key, argv[4], keylen );
}
}

memset( argv[4], 0, strlen( argv[4] ) );

#if defined(WIN32)
/*
* Support large files (> 2Gb) on Win32
*/
li_size.QuadPart = 0;
li_size.LowPart  =
SetFilePointer( (HANDLE) _get_osfhandle( _fileno( fin ) ),
li_size.LowPart, &li_size.HighPart, FILE_END );//在一个文件中设置当前的读写位置

if( li_size.LowPart == 0xFFFFFFFF && GetLastError() != NO_ERROR )
{
fprintf( stderr, "SetFilePointer(0,FILE_END) failed\n" );
goto exit;
}

filesize = li_size.QuadPart;
#else
if( ( filesize = lseek( fileno( fin ), 0, SEEK_END ) ) < 0 )
{
perror( "lseek" );
goto exit;
}
#endif

//设置文件指针stream的位置
if( fseek( fin, 0, SEEK_SET ) < 0 )
{
fprintf( stderr, "fseek(0,SEEK_SET) failed\n" );
goto exit;
}

if( mode == MODE_ENCRYPT )
{
/*
* Generate the initialization vector as:
* IV = SHA-256( filesize || filename )[0..15]
*/
for( i = 0; i < 8; i++ )
buffer[i] = (unsigned char)( filesize >> ( i << 3 ) );

p = argv[2];

//根据buffer以及文件名获取其哈希值（32位）
sha2_starts( &sha_ctx, 0 );
sha2_update( &sha_ctx, buffer, 8 );
sha2_update( &sha_ctx, (unsigned char *) p, strlen( p ) );
sha2_finish( &sha_ctx, digest );

//取出哈希值的前16位作为IV
memcpy( IV, digest, 16 );

/*
* The last four bits in the IV are actually used
* to store the file size modulo the AES block size.
*/
//IV值的最后4位存储要加密的文件的文件大小
lastn = (int)( filesize & 0x0F );

IV[15] = (unsigned char)
( ( IV[15] & 0xF0 ) | lastn );

/*
* Append the IV at the beginning of the output.
*/
//将获取的IV值写到加密后的文件的头部
if( fwrite( IV, 1, 16, fout ) != 16 )
{
fprintf( stderr, "fwrite(%d bytes) failed\n", 16 );
goto exit;
}

/*
* Hash the IV and the secret key together 8192 times
* using the result to setup the AES context and HMAC.
*/
//HMAC 消息认证码 数据完整性的认证
memset( digest, 0,  32 );
memcpy( digest, IV, 16 );

for( i = 0; i < 8192; i++ )
{
sha2_starts( &sha_ctx, 0 );
sha2_update( &sha_ctx, digest, 32 );
sha2_update( &sha_ctx, key, keylen );
sha2_finish( &sha_ctx, digest );
}

memset( key, 0, sizeof( key ) );
aes_setkey_enc( &aes_ctx, digest, 256 );
sha2_hmac_starts( &sha_ctx, digest, 32, 0 );

/*
* Encrypt and write the ciphertext.
*/
for( offset = 0; offset < filesize; offset += 16 )
{
n = ( filesize - offset > 16 ) ? 16 : (int)
( filesize - offset );

if( fread( buffer, 1, n, fin ) != (size_t) n )
{
fprintf( stderr, "fread(%d bytes) failed\n", n );
goto exit;
}

for( i = 0; i < 16; i++ )
buffer[i] = (unsigned char)( buffer[i] ^ IV[i] );

aes_crypt_ecb( &aes_ctx, AES_ENCRYPT, buffer, buffer );
sha2_hmac_update( &sha_ctx, buffer, 16 );

if( fwrite( buffer, 1, 16, fout ) != 16 )
{
fprintf( stderr, "fwrite(%d bytes) failed\n", 16 );
goto exit;
}

memcpy( IV, buffer, 16 );
}

/*
* Finally write the HMAC.
*/
sha2_hmac_finish( &sha_ctx, digest );

//将消息认证码写到文件中，用于传输过程中检测是否该文件有被修改
if( fwrite( digest, 1, 32, fout ) != 32 )
{
fprintf( stderr, "fwrite(%d bytes) failed\n", 16 );
goto exit;
}
}

if( mode == MODE_DECRYPT )
{
unsigned char tmp[16];

/*
*  The encrypted file must be structured as follows:
*
*        00 .. 15              Initialization Vector
*        16 .. 31              AES Encrypted Block #1
*           ..
*      N*16 .. (N+1)*16 - 1    AES Encrypted Block #N
*  (N+1)*16 .. (N+1)*16 + 32   HMAC-SHA-256(ciphertext)
*/
if( filesize < 48 )
{
fprintf( stderr, "File too short to be encrypted.\n" );
goto exit;
}

if( ( filesize & 0x0F ) != 0 )
{
fprintf( stderr, "File size not a multiple of 16.\n" );
goto exit;
}

/*
* Substract the IV + HMAC length.
*/
filesize -= ( 16 + 32 );

/*
* Read the IV and original filesize modulo 16.
*/
if( fread( buffer, 1, 16, fin ) != 16 )
{
fprintf( stderr, "fread(%d bytes) failed\n", 16 );
goto exit;
}

memcpy( IV, buffer, 16 );
lastn = IV[15] & 0x0F;

/*
* Hash the IV and the secret key together 8192 times
* using the result to setup the AES context and HMAC.
*/
memset( digest, 0,  32 );
memcpy( digest, IV, 16 );

for( i = 0; i < 8192; i++ )
{
sha2_starts( &sha_ctx, 0 );
sha2_update( &sha_ctx, digest, 32 );
sha2_update( &sha_ctx, key, keylen );
sha2_finish( &sha_ctx, digest );
}

memset( key, 0, sizeof( key ) );
aes_setkey_dec( &aes_ctx, digest, 256 );
sha2_hmac_starts( &sha_ctx, digest, 32, 0 );

/*
* Decrypt and write the plaintext.
*/
for( offset = 0; offset < filesize; offset += 16 )
{
if( fread( buffer, 1, 16, fin ) != 16 )
{
fprintf( stderr, "fread(%d bytes) failed\n", 16 );
goto exit;
}

memcpy( tmp, buffer, 16 );

sha2_hmac_update( &sha_ctx, buffer, 16 );
aes_crypt_ecb( &aes_ctx, AES_DECRYPT, buffer, buffer );

for( i = 0; i < 16; i++ )
buffer[i] = (unsigned char)( buffer[i] ^ IV[i] );

memcpy( IV, tmp, 16 );

n = ( lastn > 0 && offset == filesize - 16 )
? lastn : 16;

if( fwrite( buffer, 1, n, fout ) != (size_t) n )
{
fprintf( stderr, "fwrite(%d bytes) failed\n", n );
goto exit;
}
}

/*
* Verify the message authentication code.
*/
sha2_hmac_finish( &sha_ctx, digest );

if( fread( buffer, 1, 32, fin ) != 32 )
{
fprintf( stderr, "fread(%d bytes) failed\n", 32 );
goto exit;
}

if( memcmp( digest, buffer, 32 ) != 0 )
{
fprintf( stderr, "HMAC check failed: wrong key, "
"or file corrupted.\n" );
goto exit;
}
}

ret = 0;

exit:

memset( buffer, 0, sizeof( buffer ) );
memset( digest, 0, sizeof( digest ) );

memset( &aes_ctx, 0, sizeof(  aes_context ) );
memset( &sha_ctx, 0, sizeof( sha2_context ) );

return( ret );
}