如何清除（用随机字节覆盖）std :: string内部缓冲区？ [英] How to cleanse (overwrite with random bytes) std::string internal buffer?

问题描述

考虑一个场景，其中 std :: string 用于存储一个秘密。一旦消耗掉它并且不再需要它，最好将其清理，即覆盖包含它的内存，从而隐藏 secret 。

Consider a scenario, where std::string is used to store a secret. Once it is consumed and is no longer needed, it would be good to cleanse it, i.e overwrite the memory that contained it, thus hiding the secret.

std :: string 提供函数 const char * data（）返回指向的指针（因为C + +11）连续记忆。

std::string provides a function const char* data() returning a pointer to (since C++11) continous memory.

现在，由于内存是连续的，并且由于作用域结束，变量将在清除后立即销毁，这样可以安全：

Now, since the memory is continous and the variable will be destroyed right after the cleanse due to scope end, would it be safe to:

char* modifiable = const_cast<char*>(secretString.data());
OpenSSL_cleanse(modifiable, secretString.size());

根据此处引用的标准：

$ 5.2.11 / 7-注意：根据对象的类型，由 const_cast 丢弃 const限定符 68 可能会产生不确定的行为（7.1.5.1）。

$5.2.11/7 - Note: Depending on the type of the object, a write operation through the pointer, lvalue or pointer to data member resulting from a const_cast that casts away a const-qualifier⁶⁸ may produce undefined behavior (7.1.5.1).

否则可能会有所建议，但是上面的条件（连续的，将要删除的）是否安全？

That would advise otherwise, but do the conditions above (continuous, to-be-just-removed) make it safe?

推荐答案

这可能是安全的。

但是，由于 C ++ 11 ，因此 std ::字符串必须实现为连续数据，以便您可以使用其第一个元素& secretString [0] 的地址安全地访问其内部数组。 / p>

However, since C++11, a std::string must be implemented as contiguous data so you can safely access its internal array using the address of its first element &secretString[0].

if(!secretString.empty()) // avoid UB
{
    char* modifiable = &secretString[0];
    OpenSSL_cleanse(modifiable, secretString.size());
}

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