4bbf5ddd44 Detailed error message for passphrases with null chars (John Moffett)
b4bdabc223 doc: Release notes for 27068 (John Moffett)
4b1205ba37 Test case for passphrases with null characters (John Moffett)
00a0861181 Pass all characters to SecureString including nulls (John Moffett)
Pull request description:
`SecureString` is a `std::string` specialization with a secure allocator. However, in practice it's treated like a C- string (no explicit length and null-terminated). This can cause unexpected and potentially insecure behavior. For instance, if a user enters a passphrase with embedded null characters (which is possible through Qt and the JSON-RPC), it will ignore any characters after the first null, potentially giving the user a false sense of security.
Instead of assigning to `SecureString` via `std::string::c_str()`, assign it via a `std::string_view` of the original. This explicitly captures the size and still doesn't make any extraneous copies in memory.
Note to reviewers, the following all compile identically in recent `GCC` (x86-64 and ARM64) with `-O2` (and `-std=c++17`):
```C++
std::string orig_string;
std::cin >> orig_string;
SecureString s;
s.reserve(100);
// The following all compile identically
s = orig_string;
s = std::string_view{orig_string};
s.assign(std::string_view{orig_string});
s.assign(orig_string.data(), orig_string.size());
```
So it's largely a matter of preference. However, one thing to keep in mind is that we want to avoid making unnecessary copies of any sensitive data in memory.
Something like `SecureString s{orig_string};` is still invalid and probably unwanted in our case, since it'd get treated as a short string and optimized away from the secure allocator. I presume that's the reason for the `reserve()` calls.
Fixes#27067.
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