[MirageOS-devel] mirage-entropy

[Hannes Mehnert <hannes@xxxxxxxxxxx>]

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Hi,

for our upcoming release of ocaml-tls, we need to seed our random
number generator (which is fortuna, implemented here
https://github.com/mirleft/ocaml-nocrypto/blob/master/src/rng.ml ).

To achieve that, I implemented an ENTROPY device in mirage and
mirage-types (https://github.com/mirage/mirage/pull/256) - which API
is only a single function:
  val entropy : t -> int -> [ `Ok of buffer | `Error of error ] io
  (** [entropy t count] returns a [buffer] of [count] bytes from the
entropy pool [t]. *)

The buffer is a Cstruct.t in the V1_LWT interface.

The purpose is to get (in a non-blocking manner) some entropy bytes.
If no entropy device is available, an error is thrown (type error = [
| `No_entropy_device of string ]).

Furthermore, I implemented a unix version
(https://github.com/mirage/mirage-entropy) which reads the bytes from
/dev/random (any ideas whether there is a POSIX way to get entropy,
not random?). On XEN the stub implementation currently errors out -
the idea is that the host system provides an entropy device for the
virtual machine guests (this code needs to be written, any volunteers?).


Hannes
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