Re: using explicit_bzero

On 2019-Jul-11, Thomas Munro wrote:

> Following a trail of crumbs beginning at OpenSSH's fallback
> implementation of this[1], I learned that C11 has standardised
> memset_s[2] for this purpose. Macs have memset_s but no
> explicit_bzero. FreeBSD has both. I wonder if it'd be better to make
> memset_s the function we use in our code, considering its standard
> blessing and therefore likelihood of being available on every system
> eventually.

Sounds like a future-proof way would be to implement memset_s in
src/port if absent from the OS (using explicit_bzero and other tricks),
and use that.

Here's a portable implementation (includes _WIN32 and NetBSD's
explicit_memset) under ISC license:
https://github.com/jedisct1/libsodium/blob/master/src/libsodium/sodium/utils.c#L112
(from https://www.cryptologie.net/article/419/zeroing-memory-compiler-optimizations-and-memset_s/ )

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