urbit/README.md

libent is a cross-platform wrapper around `getentropy(2)`. It exports
one symbol, `ent_getentropy`. If `getentropy` is available, then it's
just a shim around that. Otherwise, it uses `getrandom(2)` (available
since kernel 3.17) on Linux, or `/dev/urandom` on other \*nix.

### Building

It uses meson. `meson ./build && ninja -C build` should do the trick.

#### Build options

It has one option, `ent_compat`, which tells it to be conservative. On
Linux, this means using `getrandom` directly; on other \*nix, it means
reading from `/dev/urandom`. This may make sense if you want your
binaries to run on older versions of the same OS. If your program is
mostly built from source, don't bother.

### Why?

`getentropy` is the wave of the future. It's the correct API for
generating small amounts of entropy to create cryptographic keys or seed
PRNGs. It's good and reasonable and true, it's on Linux, \*BSD, and OS
X, and it only took us fifty years of UNIX to get here.

Sadly, it only just arrived, so nobody has it yet. It didn't land in
Linux until glibc 2.25, which seems to only have made it into Debian 10.

Once `getentropy` is everywhere you care about, you can just do a
s/ent\_//g on all the call sites and discard this shim.

This project began because [Urbit](https://github.com/urbit/urbit)'s
entropy-generation function was bothering me. Then it got out of hand.

### References

* [OpenBSD getentropy](https://man.openbsd.org/cgi-bin/man.cgi/OpenBSD-current/man2/getentropy.2)
* [djb on entropy gathering](https://blog.cr.yp.to/20140205-entropy.html)