[Cryptography] Making sure memory erasure is not optimized away

[Peter Gutmann]

Phillip Hallam-Baker <phill at hallambaker.com> writes:

>My problem isn't knowing how to do X so much as preventing the compiler
>optimizing it away.

  https://docs.microsoft.com/en-us/previous-versions/windows/desktop/legacy/aa366877(v=vs.85)

  SecureZeroMemory function

  Use this function instead of ZeroMemory when you want to ensure that your
  data will be overwritten promptly, as some C++ compilers can optimize a call
  to ZeroMemory by removing it entirely.

  https://man7.org/linux/man-pages/man3/explicit_bzero.3.html

  bzero, explicit_bzero - zero a byte string

  The explicit_bzero() function performs the same task as bzero(). It differs
  from bzero() in that it guarantees that compiler optimizations will not
  remove the erase operation if the compiler deduces that the operation is
  "unnecessary".

Peter.