OpenSSL编程之摘要

说明：

　　数字摘要是将任意长度的消息变成固定长度的短消息，它类似于一个自变量是消息的函数，也就是Hash函数。数字摘要就是采用单向Hash函数将需要加密的明文“摘要”成一串固定长度（128位）的密文这一串密文又称为数字指纹，它有固定的长度，而且不同的明文摘要成密文，其结果总是不同的，而同样的明文其摘要必定一致。常用的摘要函数有：MD5、SHA1、SHA256等。

　　以下内容是采用OpenSSL中提供的摘要算法对文件内容进行摘要计算，这些方法同样适用于字符串。

md.h

#ifndef _MD_H_
#define _MD_H_

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

#include <openssl/md5.h>
#include <openssl/sha.h>

void calc_fileMD5(const char *filename,unsigned char *dgst);
void calc_fileSHA(const char *filename,unsigned char *dgst);
void calc_fileSHA224(const char *filename,unsigned char *dgst);
void calc_fileSHA256(const char *filename,unsigned char *dgst);
void calc_fileSHA384(const char *filename,unsigned char *dgst);
void calc_fileSHA512(const char *filename,unsigned char *dgst);

void printDgst(unsigned char* dgst,size_t len);

#endif

md.c

#include "md.h"

void calc_fileMD5(const char *filename, unsigned char *dgst)
{
    MD5_CTX ctx;
    char buf[] = {};
    int len = ;

    if (NULL == filename || NULL == dgst)
    {
        printf("Input error...\n");
        return;
    }

    FILE *fp = fopen(filename, "rb");
    if (NULL == fp)
    {
        printf("open file:%s error...\n", filename);
        return;
    }

    MD5_Init(&ctx);
    while ((len = fread(buf, , , fp)) > )
    {
        MD5_Update(&ctx, buf, len);
        memset(buf, , len);
    }
    MD5_Final(dgst, &ctx);
}
void calc_fileSHA(const char *filename, unsigned char *dgst)
{
    SHA_CTX ctx;
    char buf[] = {};
    int len = ;

    if (NULL == filename || NULL == dgst)
    {
        printf("Input error...\n");
        return;
    }

    FILE *fp = fopen(filename, "rb");
    if (NULL == fp)
    {
        printf("open file:%s error...\n", filename);
        return;
    }

    SHA1_Init(&ctx);
    while ((len = fread(buf, , , fp)) > )
    {
        SHA1_Update(&ctx, buf, len);
        memset(buf, , len);
    }
    SHA1_Final(dgst, &ctx);
}
void calc_fileSHA224(const char *filename, unsigned char *dgst)
{
    SHA256_CTX ctx;
    char buf[] = {};
    int len = ;

    if (NULL == filename || NULL == dgst)
    {
        printf("Input error...\n");
        return;
    }

    FILE *fp = fopen(filename, "rb");
    if (NULL == fp)
    {
        printf("open file:%s error...\n", filename);
        return;
    }

    SHA224_Init(&ctx);
    while ((len = fread(buf, , , fp)) > )
    {
        SHA224_Update(&ctx, buf, len);
        memset(buf, , len);
    }
    SHA224_Final(dgst, &ctx);
}
void calc_fileSHA256(const char *filename, unsigned char *dgst)
{
    SHA256_CTX ctx;
    char buf[] = {};
    int len = ;

    if (NULL == filename || NULL == dgst)
    {
        printf("Input error...\n");
        return;
    }

    FILE *fp = fopen(filename, "rb");
    if (NULL == fp)
    {
        printf("open file:%s error...\n", filename);
        return;
    }

    SHA256_Init(&ctx);
    while ((len = fread(buf, , , fp)) > )
    {
        SHA256_Update(&ctx, buf, len);
        memset(buf, , len);
    }
    SHA256_Final(dgst, &ctx);
}
void calc_fileSHA384(const char *filename, unsigned char *dgst)
{
    SHA512_CTX ctx;
    char buf[] = {};
    int len = ;

    if (NULL == filename || NULL == dgst)
    {
        printf("Input error...\n");
        return;
    }

    FILE *fp = fopen(filename, "rb");
    if (NULL == fp)
    {
        printf("open file:%s error...\n", filename);
        return;
    }

    SHA384_Init(&ctx);
    while ((len = fread(buf, , , fp)) > )
    {
        SHA384_Update(&ctx, buf, len);
        memset(buf, , len);
    }
    SHA384_Final(dgst, &ctx);
}
void calc_fileSHA512(const char *filename, unsigned char *dgst)
{
    SHA512_CTX ctx;
    char buf[] = {};
    int len = ;

    if (NULL == filename || NULL == dgst)
    {
        printf("Input error...\n");
        return;
    }

    FILE *fp = fopen(filename, "rb");
    if (NULL == fp)
    {
        printf("open file:%s error...\n", filename);
        return;
    }

    SHA512_Init(&ctx);
    while ((len = fread(buf, , , fp)) > )
    {
        SHA512_Update(&ctx, buf, len);
        memset(buf, , len);
    }
    SHA512_Final(dgst, &ctx);
}

void printDgst(unsigned char *dgst, size_t len)
{
    if (NULL == dgst || len <= )
    {
        printf("Input error...\n");
        return;
    }

    for (size_t i = ; i < len; ++i)
        printf("%x", dgst[i]);
    printf("\n");
}