为什么 RSA_generate_key 使用未初始化的值（根据 valgrind）

Question

我一直在研究涉及密码学的东西。我必须承认，我的密码学知识非常基础。所以我决定看看RSA_generate_key从openssl库生成RSA密钥后RSA结构包含什么。但我遇到了分段错误：

const unsigned long e = 3;
const int num = 3072;   
...
RSA *rsa_key = RSA_generate_key(num, e, NULL, NULL);
if (!rsa_key)
{
    printf("Failed to generate RSA key!\n");
    return RSA_ERROR_CODE;
}

printf("rsa->pad=0x%x\n", rsa_key->pad);
printf("rsa->version=0x%lx\n", rsa_key->version);
if (rsa_key->n)
{
    printf("rsa->n->top=0x%x\n", rsa_key->n->top); // HERE I got the seg fault
    ....

这对我来说看起来很奇怪，所以我编写了一个最小的代码来使用valgrind tool 对其进行测试。这是C中的代码：

#include "openssl/rsa.h"
#include <stdio.h>

int main()
{       
    const unsigned long e = 3;   // the exponent, 3 in QVRSA
    const int num = 3072;   

    RSA *rsa_key = RSA_generate_key(num, e, NULL, NULL);

    if (rsa_key == NULL)
    {
        printf("RSA is invalid!\n");
        return 1;
    }

    printf("rsa->pad=0x%x\n", rsa_key->pad);
    printf("rsa->version=0x%lx\n", rsa_key->version);
    if (rsa_key->n)
    {
        printf("rsa->n->top=0x%x\n", rsa_key->n->top);
    }

    RSA_free(rsa_key);
    rsa_key = NULL;
    return 0;
}

编译行：gcc rsa.c -lcrypto -g -O0 -o rsa

这次没有分段错误，输出为：

rsa->pad=0x0 
rsa->version=0x0 
rsa->n->top=0x30

但是 valgrind 触发了大量错误消息：

==6916== Conditional jump or move depends on uninitialised value(s)
==6916==    at 0x4DAEB37: BN_bin2bn (in /usr/lib64/libcrypto.so.0.9.8)
==6916==    by 0x4DB1B62: ??? (in /usr/lib64/libcrypto.so.0.9.8)
==6916==    by 0x4DB4471: BN_generate_prime_ex (in /usr/lib64/libcrypto.so.0.9.8)
==6916==    by 0x4DC8763: RSA_generate_key_ex (in /usr/lib64/libcrypto.so.0.9.8)
==6916==    by 0x4DCB763: RSA_generate_key (in /usr/lib64/libcrypto.so.0.9.8)
==6916==    by 0x40072E: main (rsa.c:9)
==6916==  Uninitialised value was created by a heap allocation
==6916==    at 0x4B23D6D: malloc (vg_replace_malloc.c:270)
==6916==    by 0x4D8936A: CRYPTO_malloc (in /usr/lib64/libcrypto.so.0.9.8)
==6916==    by 0x4DB1AD1: ??? (in /usr/lib64/libcrypto.so.0.9.8)
==6916==    by 0x4DB4471: BN_generate_prime_ex (in /usr/lib64/libcrypto.so.0.9.8)
==6916==    by 0x4DC8763: RSA_generate_key_ex (in /usr/lib64/libcrypto.so.0.9.8)
==6916==    by 0x4DCB763: RSA_generate_key (in /usr/lib64/libcrypto.so.0.9.8)
==6916==    by 0x40072E: main (rsa.c:9)

==6916== Conditional jump or move depends on uninitialised value(s)
==6916==    at 0x4DB44D0: BN_generate_prime_ex (in /usr/lib64/libcrypto.so.0.9.8)
==6916==    by 0x4DC8763: RSA_generate_key_ex (in /usr/lib64/libcrypto.so.0.9.8)
==6916==    by 0x4DCB763: RSA_generate_key (in /usr/lib64/libcrypto.so.0.9.8)
==6916==    by 0x40072E: main (rsa.c:9)
==6916==  Uninitialised value was created by a heap allocation
==6916==    at 0x4B23D6D: malloc (vg_replace_malloc.c:270)
==6916==    by 0x4D8936A: CRYPTO_malloc (in /usr/lib64/libcrypto.so.0.9.8)
==6916==    by 0x4DB1AD1: ??? (in /usr/lib64/libcrypto.so.0.9.8)
==6916==    by 0x4DB4471: BN_generate_prime_ex (in /usr/lib64/libcrypto.so.0.9.8)
==6916==    by 0x4DC8763: RSA_generate_key_ex (in /usr/lib64/libcrypto.so.0.9.8)
==6916==    by 0x4DCB763: RSA_generate_key (in /usr/lib64/libcrypto.so.0.9.8)
==6916==    by 0x40072E: main (rsa.c:9)

还有许多其他的条件跳转或移动取决于未初始化的值标题。

为什么？ openSSL 中是否存在已知错误，或者它只是一个误报，而我的原始分段错误与我原始代码中的一些隐藏错误有关？

我用过：

• gcc v4.5.2

• valgrind v3.8.1

• OpenSSL 0.9.8a

Answer 1

OpenSSL 正在使用一些未初始化的变量来生成随机数据来生成密钥。然后 Valgrind 会抱怨，所以不是误报。

根据openSSL FAQ，要摆脱它，使用-DPURIFY 编译。 但是，您可以讨论测试与生产二进制文件不同的编译二进制文件是否是一个好主意。