md5加密问题
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
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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>
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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