libzeth::chacha_rng Class Reference

#include <chacha_rng.hpp>

Public Member Functions
	chacha_rng (const void *seed, size_t seed_size)
void	random (void *output, size_t output_size)

Detailed Description

Random number generator matching the implementation used by zcash powersoftau and phase2. Usage: https://github.com/clearmatics/powersoftau (See hash_to_g2 function) Implementation is based on: https://docs.rs/rand/0.4.6/src/rand/prng/chacha.rs.html (See description comment, in particular word layout)

Definition at line 22 of file chacha_rng.hpp.

Constructor & Destructor Documentation

chacha_rng()

libzeth::chacha_rng::chacha_rng	(	const void *	seed,
		size_t	seed_size
	)

Definition at line 20 of file chacha_rng.cpp.

    : data_used(sizeof(block))
{
    // Copies behaviour of ChaChaRng::from_seed() from the referenced code.
    // Use the first 8 words of seed (padding with 0 if necessary) as the key.
    seed_size = std::min(seed_size, sizeof(key));
    memcpy(key, seed, seed_size);
    if (seed_size < sizeof(key)) {
        memset(((uint8_t *)key) + seed_size, 0, sizeof(key) - seed_size);
    }
 
    // Reset the counter to 0.
    memset(counter, 0, sizeof(counter));
}

Member Function Documentation

random()

void libzeth::chacha_rng::random	(	void *	output,
		size_t	output_size
	)

Definition at line 35 of file chacha_rng.cpp.

{
    // Iteratively take any remaining data in the current block, populating the
    // block with new data as required, until the output buffer is full.
 
    // Destination as a uint8_t pointer for easy incrementing.
    uint8_t *target = (uint8_t *)output;
    while (output_size > 0) {
        if (data_used == sizeof(block)) {
            update();
        }
 
        const size_t data_remaining = sizeof(block) - data_used;
        const size_t to_write = std::min(data_remaining, output_size);
 
        memcpy(target, &block[data_used], to_write);
        data_used += to_write;
        target += to_write;
        output_size -= to_write;
    }
}

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The documentation for this class was generated from the following files:

• /home/runner/work/zeth/zeth/libzeth/core/chacha_rng.hpp
• /home/runner/work/zeth/zeth/libzeth/core/chacha_rng.cpp