Obtaining random numbers

[jonas-schievink]

We need cryptographically secure random numbers for key generation, and also for stuff like inducing random jitter on the advertising interval. We have to use some trait for that and let the user plug in an implementation. There's two choices:

• embedded_hal::blocking::rng::Read
  • "unproven"
  • Doesn't say anything about cryptographic security
• rand_core::CryptoRng
  • Looks like the better choice for us - rand_core is also no_std
• ...any other alternatives?

[fmckeogh]

rand::RngCore is now implemented for nrf528xx_hal::rng::Rng, and an issue has been opened to make it the standard for embedded-hal (here).