Wrap our PRNG interface(s) in Rust with appropriate traits

Similar to #24659 (moved), we should provide a way to wrap our C code for getting randomness in Rust, while implementing the appropriate traits (from rand) so that we're able to switch in Rust implementations if we want later.

This is also blocking #23886 (moved).

changed milestone to %Tor: 0.3.4.x-final

added 034-included-20180328 034-roadmap-master 034-triage-20180328 component::core tor/tor milestone::Tor: 0.3.4.x-final owner::isis points::2 priority::low resolution::implemented reviewer::nickm rng roadmap rust severity::normal sponsor::Q status::closed tor-crypto type::enhancement labels

(Not sure if this is more Sponsor8 or Sponsor3 or something else.)

Trac:
Sponsor: N/A to Sponsor3-can

Trac:
Cc: N/A to chelseakomlo

I'd like to solve this one, as my first contribution.

Trac:
Username: budabudimir

Cool! Please ask if you have any questions. There is some possibly helpful documentation in the doc/HACKING subdirectory of the Tor repository, and there are frequently helpful people on the #tor-dev IRC channel on OFTC.

Deferring various "new"-status enhancement tickets to 0.3.4

Trac:
Milestone: Tor: 0.3.3.x-final to Tor: 0.3.4.x-final

Marked #25508 (moved) as a potential duplicate of this ticket.

Closed #25508 (moved) as a duplicate and transferred sponsor/tags/cc here.

Trac:
Cc: chelseakomlo to chelseakomlo, catalyst, isis, nickm, teor
Keywords: N/A deleted, rng, roadmap added
Sponsor: Sponsor3-can to SponsorQ

So it looks like the correct traits to implement are those in rand::rand_core (documentation) and then we get the automatic implementation of rand::Rng for free.

Assigning to myself since this is blocking #25381 (moved), #23886 (moved), and #24988 (moved), possibly among others, it's in the March/April 2018 roadmap, and I can probably do it in an afternoon?

Trac:
Points: N/A to 2
Status: new to accepted
Owner: N/A to isis

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Keywords: N/A deleted, 034-roadmap-master added

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Keywords: N/A deleted, 034-triage-20180328 added

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Keywords: N/A deleted, 034-included-20180328 added

I've made an upstream issue asking about the release/stabilisation of the rand_core crate: https://github.com/rust-lang-nursery/rand/issues/386

There's an implementation in my bug24660 branch (Travis mostly passes, just not the cargo offline mode). The added dependency for rand_core is in the master branch of my tor-rust-dependencies repo, but from https://github.com/rust-lang-nursery/rand/issues/386#issuecomment-380489759 it looks like we should wait a few days to vendor rand_core-0.1.0.

Trac:
Status: accepted to needs_review

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Reviewer: N/A to nickm

I've added some comments and questions to the branch on github. Let's discuss more there. Thanks, Isis!

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Status: needs_review to needs_revision

Replying to nickm:

I've added some comments and questions to the branch on github. Let's discuss more there. Thanks, Isis!

Replied to the comments on https://github.com/isislovecruft/tor/commit/5a984badc59927063d9682ffd8cc6f52fc15a44b and made a bunch of fixup commits (Travis fails because we need to pull in the appropriate tor-rust-dependencies changes). A squashed version is in my bug24660_r1 branch.

The requisite tor-rust-dependencies changes are in my add/rand_core branch and add/rand branch.

Trac:
Status: needs_revision to needs_review

Lgtm, except that I instead of exposing only crypto_strongest_rand() as an Rng, I think we should either expose only crypto_rand(), or expose both. Once that's done I think this is merge_ready.

Edited to add: see comment on the pull request for more info.

Trac:
Status: needs_review to needs_revision