botan.secure_byte_span
local secure_byte_span = require 'botan'.secure_byte_span
local buf = secure_byte_span.new(4096)The module secure_byte_span allows you to create a byte_span that uses
Botan’s secure allocators.
A major concern with mixing modern multi-user OSes and cryptographic code is that at any time the code (including secret keys) could be swapped to disk, where it can later be read by an attacker, or left floating around in memory for later retrieval.
For this reason the library uses a
std::vectorwith a custom allocator that will zero memory before deallocation, named via typedef assecure_vector. Because it is simply a STL vector with a custom allocator, it has an identical API to thestd::vectoryou know and love.Some operating systems offer the ability to lock memory into RAM, preventing swapping from occurring. Typically this operation is restricted to privileged users (root or admin), however some OSes including Linux and FreeBSD allow normal users to lock a small amount of memory. On these systems, allocations first attempt to allocate out of this small locked pool, and then if that fails will fall back to normal heap allocations.
secure_byte_span will use the same allocators from Botan’s
secure_vector. This mitigation is also useful to protect cryptographic secrets
if you have a buggy application that sends uninitialized data elsewhere
(i.e. use-after-free). Consider the following code:
local my_message = byte_span.new(size)
stream.write_all(my_socket, my_message)The developer forgot to initialize my_message with the message he actually
intended to send. byte_span.new() allocates memory. If the allocated memory
was previously used to hold cryptographic secrets, these secrets will be leaked.
However if all the sensitive data had been allocated using secure_byte_span
then no important leaks can happen as the sensitive data would be zeroed before
returned to the allocator for later reuse in unrelated allocations.