Struct `ChaCha20Rng`

pub struct ChaCha20Rng { /* private fields */ }

A cryptographically secure random number generator that uses the ChaCha stream cipher.

See the [crate docs][crate] for more information about the underlying stream cipher.

This RNG implementation uses a 64-bit counter and 64-bit stream identifier (a.k.a nonce). A 64-bit counter over 64-byte (16 word) blocks allows 1 ZiB of output before cycling, and the stream identifier allows 2⁶⁴ unique streams of output per seed. Both counter and stream are initialized to zero but may be set via the set_word_pos and set_stream methods.

Example

use chacha20::ChaCha20Rng;
use rand_core::{SeedableRng, Rng};

let seed = [42u8; 32];
let mut rng = ChaCha20Rng::from_seed(seed);

let random_u32 = rng.next_u32();
let random_u64 = rng.next_u64();

let mut random_bytes = [0u8; 3];
rng.fill_bytes(&mut random_bytes);

See the rand crate for more advanced RNG functionality.

Implementations

`impl ChaCha20Rng`

fn get_word_pos(&self) -> u128

Get the offset from the start of the stream, in 32-bit words.

Since the generated blocks are 16 words (2⁴) long and the counter is 64-bits, the offset is a 68-bit number. Sub-word offsets are not supported, hence the result can simply be multiplied by 4 to get a byte-offset.

fn set_word_pos(&mut self, word_offset: u128)

Set the offset from the start of the stream, in 32-bit words.

This value will be erased when calling set_stream(), so call set_stream() before calling set_word_pos() if you intend on using both of them together.

As with get_word_pos, we use a 68-bit number. Since the generator simply cycles at the end of its period (1 ZiB), we ignore the upper 60 bits.

fn set_block_pos(&mut self, block_pos: u64)

Sets the block pos and resets the RNG's index.

This value will be erased when calling set_stream(), so call set_stream() before calling set_block_pos() if you intend on using both of them together.

The word pos will be equal to block_pos * 16 words per block.

fn get_block_pos(&self) -> u64

Get the block pos.

fn set_stream(&mut self, stream: u64)

Set the stream ID and reset the word_pos to 0.

fn get_stream(&self) -> u64

Get the stream number (nonce).

fn get_seed(&self) -> [u8; 32]

Get the RNG seed.

fn serialize_state(&self) -> SerializedRngState

Serialize RNG state.

Warning

Leaking serialized RNG state to an attacker defeats security properties provided by the RNG.

fn deserialize_state(state: &SerializedRngState) -> Self

Deserialize RNG state.

Trait Implementations

`impl Debug for ChaCha20Rng`

fn fmt(&self, f: &mut Formatter<'_>) -> Result

`impl Eq for ChaCha20Rng`

`impl PartialEq for ChaCha20Rng`

fn eq(&self, rhs: &ChaCha20Rng) -> bool

`impl SeedableRng for ChaCha20Rng`

type Seed = [u8; 32];
fn from_seed(seed: Self::Seed) -> Self

`impl TryCryptoRng for ChaCha20Rng`

`impl TryRng for ChaCha20Rng`

type Error = Infallible;
fn try_next_u32(&mut self) -> Result<u32, Self::Error>
fn try_next_u64(&mut self) -> Result<u64, Self::Error>
fn try_fill_bytes(&mut self, dest: &mut [u8]) -> Result<(), Self::Error>

Auto Trait Implementations

`impl Freeze for ChaCha20Rng`

`impl RefUnwindSafe for ChaCha20Rng`

`impl Send for ChaCha20Rng`

`impl Sync for ChaCha20Rng`

`impl Unpin for ChaCha20Rng`

`impl UnsafeUnpin for ChaCha20Rng`

`impl UnwindSafe for ChaCha20Rng`

Blanket Implementations

`impl<R> CryptoRng for ChaCha20Rng where R: TryCryptoRng<Error = Infallible> + ?Sized,`

`impl<R> Rng for ChaCha20Rng where R: TryRng<Error = Infallible> + ?Sized,`

fn next_u32(&mut self) -> u32
fn next_u64(&mut self) -> u64
fn fill_bytes(&mut self, dst: &mut [u8])

`impl<R> RngCore for ChaCha20Rng where R: Rng,`

`impl<R> TryRngCore for ChaCha20Rng where R: TryRng,`

type Error = <R as TryRng>::Error;

`impl<T> Any for ChaCha20Rng where T: 'static + ?Sized,`

fn type_id(&self) -> TypeId

`impl<T> Borrow<T> for ChaCha20Rng where T: ?Sized,`

fn borrow(&self) -> &T

`impl<T> BorrowMut<T> for ChaCha20Rng where T: ?Sized,`

fn borrow_mut(&mut self) -> &mut T

`impl<T> From<T> for ChaCha20Rng`

fn from(t: T) -> T: Returns the argument unchanged.

`impl<T, U> Into<U> for ChaCha20Rng where U: From<T>,`

fn into(self) -> U

Calls U::from(self).

That is, this conversion is whatever the implementation of [From]<T> for U chooses to do.

`impl<T, U> TryFrom<U> for ChaCha20Rng where U: Into<T>,`

type Error = Infallible;
fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

`impl<T, U> TryInto<U> for ChaCha20Rng where U: TryFrom<T>,`

type Error = <U as TryFrom<T>>::Error;
fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>