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md5加密问题

Jun 06, 2016 pm 08:25 PM
c c# c++ java php

由于内存有限,嵌入式环境下要计算一个50mb文件的md5码,需要分成10mb的小段,如何计算使得分割的文件最后计算的md5码和通过整个文件计算的md5码相同

回复内容:

由于内存有限,嵌入式环境下要计算一个50mb文件的md5码,需要分成10mb的小段,如何计算使得分割的文件最后计算的md5码和通过整个文件计算的md5码相同

md5函数都支持分段计算,只要你分割的文件不添加额外的文件内容,计算出来的就和未分割之前的是一致的。

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

int main( int argc, char **argv )
{
MD5_CTX ctx;
unsigned char *data="123";
unsigned char md[16];
char buf[33]={'\0'};
char tmp[3]={'\0'};
int i;

MD5_Init(&ctx);
MD5_Update(&ctx,data,strlen(data));//多次调用这个函数就可以了,你可以每次update 1kB的数据
MD5_Final(md,&ctx);//所有的文件都处理完了,调用这个函数就行了

for( i=0; i</string.h></openssl></stdio.h></code>
Copy after login

多次使用update接口

谁说Java MD5一个文件流要把文件都加载到内存中的啊?用一个buffer,大概8KB就可以,一边读,一遍update就可以了,内存消耗是O(1)的。

另外,这不是加密。

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