rand.rs

//  Copyright (C) 2017-2019  The AXIOM TEAM Association.
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU Affero General Public License as
// published by the Free Software Foundation, either version 3 of the
// License, or (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU Affero General Public License for more details.
//
// You should have received a copy of the GNU Affero General Public License
// along with this program.  If not, see <https://www.gnu.org/licenses/>.

//! Manage random generation.

use byteorder::ByteOrder;
use ring::rand;

/// An error with absolutely no details.
///
/// *dup-crypto* uses this unit type as the error type in most of its results
/// because (a) usually the specific reasons for a failure are obvious or are
/// not useful to know, and/or (b) providing more details about a failure might
/// provide a dangerous side channel, and/or (c) it greatly simplifies the
/// error handling logic.
///
/// Experience with using and implementing other crypto libraries like has
/// shown that sophisticated error reporting facilities often cause significant
/// bugs themselves, both within the crypto library and within users of the
/// crypto library. This approach attempts to minimize complexity in the hopes
/// of avoiding such problems. In some cases, this approach may be too extreme,
/// and it may be important for an operation to provide some details about the
/// cause of a failure. Users of *dup-crypto* are encouraged to report such cases so
/// that they can be addressed individually.
#[derive(Copy, Clone, Debug, PartialEq)]
pub struct UnspecifiedRandError;

#[inline]
/// Generate random u32
pub fn gen_u32() -> Result<u32, UnspecifiedRandError> {
    let rng = rand::SystemRandom::new();
    let random_bytes = rand::generate::<[u8; 4]>(&rng).map_err(|_| UnspecifiedRandError)?;
    Ok(byteorder::BigEndian::read_u32(&random_bytes.expose()))
}

#[cfg(test)]
mod tests {

    use super::*;

    #[test]
    fn test_gen_u32() {
        assert_ne!(gen_u32(), gen_u32())
    }
}