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：123printf("%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 );}