MD5() 函数在哪个库中? [英] In which library is the MD5() function?

问题描述

当我编写代码以安装到目标机器上时，我想知道依赖项并注意到不需要 openssl 库.我想知道，因为我知道我使用的是 OpenSSL:

#include ...MD5(a, b, c);...

令我惊讶的是，我们似乎只与 libc 建立了链接.MD5 真的是在 libc 中实现的，而不是在某些 libssl 库中实现的吗?

<小时>

objdump 给了我关于链接库的信息:

动态部分:需要 libQtCore.so.4需要 libstdc++.so.6需要 libgcc_s.so.1需要 libc.so.6SONAME libcontent.so

<小时>

根据 noloader 的建议，我尝试使用 ldd，但仍然没有看到对 MD5 有意义的库.libcontent.so 是直接使用 MD5()...

ldd ../BUILD/snapwebsites/plugins/content/libcontent.solinux-vdso.so.1 =>(0x00007fff4f3ff000)libQtCore.so.4 =>/usr/lib/x86_64-linux-gnu/libQtCore.so.4 (0x00007ff37ad0f000)libstdc++.so.6 =>/usr/lib/x86_64-linux-gnu/libstdc++.so.6 (0x00007ff37aa0c000)libgcc_s.so.1 =>/lib/x86_64-linux-gnu/libgcc_s.so.1 (0x00007ff37a7f5000)libc.so.6 =>/lib/x86_64-linux-gnu/libc.so.6 (0x00007ff37a42c000)libpthread.so.0 =>/lib/x86_64-linux-gnu/libpthread.so.0 (0x00007ff37a20f000)libz.so.1 =>/lib/x86_64-linux-gnu/libz.so.1 (0x00007ff379ff7000)libdl.so.2 =>/lib/x86_64-linux-gnu/libdl.so.2 (0x00007ff379df3000)libglib-2.0.so.0 =>/lib/x86_64-linux-gnu/libglib-2.0.so.0 (0x00007ff379af7000)librt.so.1 =>/lib/x86_64-linux-gnu/librt.so.1 (0x00007ff3798ee000)libm.so.6 =>/lib/x86_64-linux-gnu/libm.so.6 (0x00007ff3795e9000)/lib64/ld-linux-x86-64.so.2 (0x00007ff37b5e5000)libpcre.so.3 =>/lib/x86_64-linux-gnu/libpcre.so.3 (0x00007ff3793a9000)

<小时>

另外，为了确保，我在该内容库上尝试了 nm，我可以看到 MD5 条目:

 w _ITM_registerTMCloneTable00000000003c9468 d __JCR_END__00000000003c9468 d __JCR_LIST__w _Jv_RegisterClassesU MD5 <---- 它在这里...你 memcmp@@GLIBC_2.2.5w pthread_cancelupthread_mutex_destroy@@GLIBC_2.2.5

解决方案

MD5() 函数在哪个库中?

OpenSSL 库.链接到 libcrypto.请参阅 md5(3).

<小时><块引用>

MD5 真的是在 libc 中实现的，而不是在某些 libssl 库中实现的吗?

好吧，它不在 Ubuntu 的 libc 中:

$ nm -D/lib/x86_64-linux-gnu/libc.so.6 |grep -i md5$

它在 OpenSSL 的 libcrypto 中:

$ nm -D/usr/lib/x86_64-linux-gnu/libcrypto.so |grep MD50000000000066840 T MD50000000000066640 T MD5_Final0000000000066790 T MD5_Init0000000000066630 T MD5_Transform0000000000066420 T MD5_Update

T 表示符号 (MD5) 在 TEXT 部分中定义并导出.t 表示符号在 TEXT 部分定义，但它没有导出，所以你不能链接它(想想 GCC 的 visibility=private 或静态声明).

如果你得到一个 U，那么这意味着这个符号是必需的但未定义，并且一个库必须提供它.

<小时><块引用>

#include ...MD5(a, b, c, d);

MD5(a, b, c, d); 不是 OpenSSL 的 MD5.OpenSSL 的 MD5 有三个参数，而不是四个.

<小时><块引用>

objdump 给了我关于链接库的信息

ldd 可能会给你不同的结果.它是我用来检查依赖项的(我不使用 objdump):

$ cat t.c#include int main(int argc, char* argv[]){const char 密码[] = "密码";字符哈希[MD5_DIGEST_LENGTH];MD5(密码，大小(密码)，哈希)；返回0；}$ gcc t.c -o t.exe -lcrypto$ ldd t.exelinux-vdso.so.1 =>(0x00007fff435ff000)libcrypto.so.1.0.0 =>/usr/lib/x86_64-linux-gnu/libcrypto.so.1.0.0 (0x00007fbaff01b000)libc.so.6 =>/lib/x86_64-linux-gnu/libc.so.6 (0x00007fbafec90000)libdl.so.2 =>/lib/x86_64-linux-gnu/libdl.so.2 (0x00007fbafea8b000)libz.so.1 =>/lib/x86_64-linux-gnu/libz.so.1 (0x00007fbafe874000)/lib64/ld-linux-x86-64.so.2 (0x00007fbaff429000)

和t.exe的未解析符号:

$ nm t.exe |grep MD5U MD5@@OPENSSL_1.0.0

As I'm writing code to install on a target machine, I was wondering about the dependencies and noticed that there were no openssl library needed. I wondered because I know I am using OpenSSL:

#include <openssl/md5.h>

...
MD5(a, b, c);
...

To my surprise, it seems that we only get linked against libc. Is MD5 really implemented in libc and not in some libssl library?

---

objdump gives me the info about the linked library:

Dynamic Section:
  NEEDED               libQtCore.so.4
  NEEDED               libstdc++.so.6
  NEEDED               libgcc_s.so.1
  NEEDED               libc.so.6
  SONAME               libcontent.so

---

As suggested by noloader I tried with ldd and still fail to see a library that would make sense for MD5. libcontent.so is directly using MD5()...

ldd ../BUILD/snapwebsites/plugins/content/libcontent.so 
    linux-vdso.so.1 =>  (0x00007fff4f3ff000)
    libQtCore.so.4 => /usr/lib/x86_64-linux-gnu/libQtCore.so.4 (0x00007ff37ad0f000)
    libstdc++.so.6 => /usr/lib/x86_64-linux-gnu/libstdc++.so.6 (0x00007ff37aa0c000)
    libgcc_s.so.1 => /lib/x86_64-linux-gnu/libgcc_s.so.1 (0x00007ff37a7f5000)
    libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007ff37a42c000)
    libpthread.so.0 => /lib/x86_64-linux-gnu/libpthread.so.0 (0x00007ff37a20f000)
    libz.so.1 => /lib/x86_64-linux-gnu/libz.so.1 (0x00007ff379ff7000)
    libdl.so.2 => /lib/x86_64-linux-gnu/libdl.so.2 (0x00007ff379df3000)
    libglib-2.0.so.0 => /lib/x86_64-linux-gnu/libglib-2.0.so.0 (0x00007ff379af7000)
    librt.so.1 => /lib/x86_64-linux-gnu/librt.so.1 (0x00007ff3798ee000)
    libm.so.6 => /lib/x86_64-linux-gnu/libm.so.6 (0x00007ff3795e9000)
    /lib64/ld-linux-x86-64.so.2 (0x00007ff37b5e5000)
    libpcre.so.3 => /lib/x86_64-linux-gnu/libpcre.so.3 (0x00007ff3793a9000)

---

Also, just to make sure, I tried nm on that content library and I can see the MD5 entry:

                 w _ITM_registerTMCloneTable
00000000003c9468 d __JCR_END__
00000000003c9468 d __JCR_LIST__
                 w _Jv_RegisterClasses
                 U MD5                       <---- it's here...
                 U memcmp@@GLIBC_2.2.5
                 w pthread_cancel
                 U pthread_mutex_destroy@@GLIBC_2.2.5

解决方案

In which library is the MD5() function?

The OpenSSL library. Link to libcrypto. See md5(3).

---

Is MD5 really implemented in libc and not in some libssl library?

Well, its not in Ubuntu's libc:

$ nm -D  /lib/x86_64-linux-gnu/libc.so.6 | grep -i md5
$

And it is in OpenSSL's libcrypto:

$ nm -D /usr/lib/x86_64-linux-gnu/libcrypto.so | grep MD5
0000000000066840 T MD5
0000000000066640 T MD5_Final
0000000000066790 T MD5_Init
0000000000066630 T MD5_Transform
0000000000066420 T MD5_Update

The T means the symbol (MD5) is defined in the TEXT section and its exported. A t means the symbol is defined in the TEXT section, but its not exported so you cannot link against it (think GCC's visibility=private or a static declaration).

If you get a U, then that means the symbol is required but undefined and a library will have to provide it.

---

#include <openssl/md5.h>

...
MD5(a, b, c, d);

MD5(a, b, c, d); is not OpenSSL's MD5. OpenSSL's MD5 has three parameters, not four.

---

objdump gives me the info about the linked library

ldd might give you different results. Its what I use to check dependencies (and I don't use objdump):

$ cat t.c
#include <openssl/md5.h>

int main(int argc, char* argv[])
{
    const char password[] = "password";
    char hash[MD5_DIGEST_LENGTH];    
    MD5(password, sizeof(password), hash);

    return 0;
}

$ gcc t.c -o t.exe -lcrypto
$ ldd t.exe 
    linux-vdso.so.1 =>  (0x00007fff435ff000)
    libcrypto.so.1.0.0 => /usr/lib/x86_64-linux-gnu/libcrypto.so.1.0.0 (0x00007fbaff01b000)
    libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007fbafec90000)
    libdl.so.2 => /lib/x86_64-linux-gnu/libdl.so.2 (0x00007fbafea8b000)
    libz.so.1 => /lib/x86_64-linux-gnu/libz.so.1 (0x00007fbafe874000)
    /lib64/ld-linux-x86-64.so.2 (0x00007fbaff429000)

And t.exe's unresolved symbol:

$ nm t.exe | grep MD5
    U MD5@@OPENSSL_1.0.0

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