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[4096] = {0}; int len = 0; 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, 1, 4096, fp)) > 0) { MD5_Update(&ctx, buf, len); memset(buf, 0, len); } MD5_Final(dgst, &ctx); } void calc_fileSHA(const char *filename, unsigned char *dgst) { SHA_CTX ctx; char buf[4096] = {0}; int len = 0; 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, 1, 4096, fp)) > 0) { SHA1_Update(&ctx, buf, len); memset(buf, 0, len); } SHA1_Final(dgst, &ctx); } void calc_fileSHA224(const char *filename, unsigned char *dgst) { SHA256_CTX ctx; char buf[4096] = {0}; int len = 0; 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, 1, 4096, fp)) > 0) { SHA224_Update(&ctx, buf, len); memset(buf, 0, len); } SHA224_Final(dgst, &ctx); } void calc_fileSHA256(const char *filename, unsigned char *dgst) { SHA256_CTX ctx; char buf[4096] = {0}; int len = 0; 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, 1, 4096, fp)) > 0) { SHA256_Update(&ctx, buf, len); memset(buf, 0, len); } SHA256_Final(dgst, &ctx); } void calc_fileSHA384(const char *filename, unsigned char *dgst) { SHA512_CTX ctx; char buf[4096] = {0}; int len = 0; 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, 1, 4096, fp)) > 0) { SHA384_Update(&ctx, buf, len); memset(buf, 0, len); } SHA384_Final(dgst, &ctx); } void calc_fileSHA512(const char *filename, unsigned char *dgst) { SHA512_CTX ctx; char buf[4096] = {0}; int len = 0; 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, 1, 4096, fp)) > 0) { SHA512_Update(&ctx, buf, len); memset(buf, 0, len); } SHA512_Final(dgst, &ctx); } void printDgst(unsigned char *dgst, size_t len) { if (NULL == dgst || len <= 0) { printf("Input error...\n"); return; } for (size_t i = 0; i < len; ++i) printf("%x", dgst[i]); printf("\n"); }