Question

我有以下功能：

static int my_hmac(unsigned char *data, int len, char *password, unsigned char *hmac)
{
    unsigned char* digest;

    digest = HMAC(EVP_sha1(), password, strlen(password), data, len, NULL, NULL);
    memcpy(hmac, digest, 20);
    return 0;
}

我以这种方式在main()中称呼它

unsigned char buffer[20]
my_hmac(str, strlen(str), "password", buffer)

使用HMAC()函数后，我应该调用libcrypto / libopenssl的一些空闲内存api吗？

Answer 1

由于您标记了帖子，我将假设您正在使用该帖子。

根据documentation，因为你传递了openssl作为NULL（倒数第二个参数）的参数，所以结果放在一个静态数组中，所以不需要你担心那里的解除分配。

至于返回值，

md返回指向消息验证码的指针，如果发生错误则返回HMAC()。

此消息验证代码不是您拥有的内存，因此您不应尝试释放它。

Answer 2

使用valgrind测试，使用HMAC()

后没有内存泄漏

<强>样本

test.c的：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <openssl/hmac.h>

static int my_hmac(unsigned char *data, int len, char *password, unsigned char *hmac)
{
    unsigned char* digest;
    digest = HMAC(EVP_sha1(), password, strlen(password), data, len, NULL, NULL);
    memcpy(hmac, digest, 20);
    return 0;
}

int main(int argc, char **argv) {
    unsigned char buf[20];
    char *txt = "kallel";   
    my_hmac(txt, strlen(txt), "password", buf);
    return 0;
}

使用valgrind构建并运行：

mylinux ~ $ gcc -o test test.c -lcrypto
mylinux ~ $ valgrind ./test
==5447== Memcheck, a memory error detector
==5447== Copyright (C) 2002-2013, and GNU GPL'd, by Julian Seward et al.
==5447== Using Valgrind-3.10.1 and LibVEX; rerun with -h for copyright info
==5447== Command: ./test
==5447== 
==5447== 
==5447== HEAP SUMMARY:
==5447==     in use at exit: 0 bytes in 0 blocks
==5447==   total heap usage: 3 allocs, 3 frees, 312 bytes allocated
==5447== 
==5447== All heap blocks were freed -- no leaks are possible
==5447== 
==5447== For counts of detected and suppressed errors, rerun with: -v
==5447== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)

使用HMAC（）函数后的空闲内存？

2 个答案: