silk.system.insecure_random.

When to use#

Require &mut InsecureRandom for simulations, games, shuffles in tests, and other uses where the same seed must give the same results. Provide InsecureRandom.seeded with a seed. Never use it for keys, nonces, tokens, passwords, or protection against hash collisions. Use silk.system.random for those.

Details#

A provider implements InsecureRandom.nextU64. InsecureRandom.nextBool, InsecureRandom.below, and InsecureRandom.fillBytes use it in a fixed way, so the results are the same on each target. InsecureRandom.seeded returns a Xoshiro256StarStar generator. It expands the seed with SplitMix64.

Gotchas#

The output is predictable. An observer who sees a few values can compute the next values.

Examples#

Get the same first value from the same seed#

import silk.core.effect { Effect }
import silk.system.insecure_random { InsecureRandom }

pub fn main() -> i32 {
  let mut provider = InsecureRandom.seeded(0)
  let first = run InsecureRandom.nextU64() |> Effect.provideMut<InsecureRandom>(&mut provider)
  if first != 0x99ec5f36cb75f2b4 {
    return 1
  }
  return 0
}

Import as InsecureRandom with import silk.system.insecure_random { InsecureRandom }.

Public declarations: 2.

InsecureRandom#

pub service InsecureRandom

The effect for a fast pseudorandom sequence that is not secure and repeats for the same seed.

When to use#

Require &mut InsecureRandom for simulations, games, shuffles in tests, and other uses where the same seed must give the same results. Provide InsecureRandom.seeded with a seed. Use silk.system.random for secrets.

Details#

A provider implements InsecureRandom.nextU64. InsecureRandom.nextBool, InsecureRandom.below, and InsecureRandom.fillBytes use it in a fixed way, so the results are the same on each target. The provider owns its state. Each call moves only the provider of the current effect forward.

Gotchas#

Do not use it for secrets, keys, nonces, tokens, passwords, or protection against hash collisions. The output is predictable: an observer who sees a few values can compute the next values.

Operation nextU64#

effect fn nextU64() -> u64 ? &mut InsecureRandom

Returns the next u64 of the sequence.

Implementation InsecureRandom#

impl InsecureRandom

Associated function seeded#

pub fn seeded(seed: u64) -> Xoshiro256StarStar

Returns a Xoshiro256StarStar generator that starts from seed.

Details#

The same seed gives the same sequence on each target. Each seed works, also 0, because the seed is expanded with four SplitMix64 steps.

Associated function nextBool#

pub effect fn nextBool() -> bool ? &mut InsecureRandom

Returns true if the highest bit of the next u64 is set.

Associated function below#

pub effect fn below(upperExclusive: u64) -> Option<u64> ? &mut InsecureRandom

Returns a value from 0 to upperExclusive - 1, with the same chance for each value. Returns an absent option if upperExclusive is 0.

Details#

It drops u64 values that would make some results more likely than others, so it can read more than one value.

Associated function fillBytes#

pub effect fn fillBytes(output: &mut [u8]) -> () ? &mut InsecureRandom

Fills output with bytes from the sequence. Each u64 gives 8 bytes, least significant byte first.

Details#

An empty slice reads nothing. If the length is not a multiple of 8, the last u64 is read in full and its extra bytes are dropped.

Xoshiro256StarStar#

pub struct Xoshiro256StarStar

A xoshiro256** generator. Make one with InsecureRandom.seeded and provide it as InsecureRandom.

Details#

The sequence is the same on each target. It is not secure: an observer who sees a few values can compute the next values.

Implementation InsecureRandom for Xoshiro256StarStar#

impl InsecureRandom for Xoshiro256StarStar

Operation nextU64#

nextU64: Xoshiro256StarStar.xoshiroNext

Category: System.

Profiles: aarch64-apple-darwin, aarch64-unknown-linux-gnu, aarch64-unknown-linux-gnu-no-libc, x86_64-unknown-linux-gnu, x86_64-unknown-linux-gnu-no-libc, wasm32-unknown-unknown, wasm32-wasip1, wasm32-wasip2.