arc4random

[patricus3]

Hi.
I have two questions, why you didn't inplement arc4random?
and an other, the discord drama all was a big misunderstanding, check the new issue at superconfigure repo, and see what I actually meant.

[jart]

Cosmopolitan provides a variety of ways to generate random numbers, such as getrandom() and getentropy() which are both recommended for all use cases. No one's found need of arc4random yet, which is why we don't have it. I'm perfectly happy to include that too, if someone wants to copy over the FreeBSD or OpenBSD implementation per the CONTRIBUTING.md process.

[mrdomino]

Some resources:

• {Free,Open}BSD arc4random.c (the libc interface for both is much the same)
• However the FreeBSD kernel arc4random includes Fenestras X, which is based on
• Niels Ferguson’s Windows 10 RNG whitepaper

[mrdomino]

TLDR on Fenestras X + the Windows 10 RNG is:

• The kernel maintains one root randomness pool per logical core so that no synchronization is needed
• Random numbers are generated via AES-CTR, which directly services large requests or else fills up a 128-byte buffer that is pulled from for small requests (to amortize the cost of the AES key expansion.)
• The libc arc4random calls use MAP_INHERIT_ZERO (spelled INHERIT_ZERO in FreeBSD) to reset the buffer state on forks.

There are lots more subtleties in the whitepaper, and also some interesting design choices in Fenestras X in FreeBSD.

However, I think the arc4random family of syscalls might actually be implemented on all the platforms we care about (in Windows it's just spelled ProcessPrng) so at least the initial implementation of this might be pretty boring.

[mrdomino]

Okay, right, they're not syscalls, they're in libc. So there's at least some porting work to be done.

[jart]

The libc arc4random calls use MAP_INHERIT_ZERO (spelled INHERIT_ZERO in FreeBSD) to reset the buffer state on forks.

That would be a good feature for cosmo's memory manager.
We could easily polyfill it in the fork() libc wrapper on platforms that don't support it.