pow_sha256/README.md

PoW-SHA256

Rust crate which generates SHA256 Proofs of Work on serializable datatypes.

Any type that implements serde::Deserialize can be used.

This is a fork of the Pow library by bddap with some new additions. Primary of these being:

• PoW datatype now saves the calculation result to be used for checking proof validity given input
• is_valid_proof method to do the above mentioned

Other small changes have also been included of various importance but mostly just stylistic/ease of use improvements.

Examples

Prove we did work targeting a phrase.

use PoW::PoW;

// very easy mode
let difficulty = u128::max_value() - u128::max_value() / 2;

let phrase = b"Phrase to tag.".to_vec();
let pw = PoW::prove_work(&phrase, difficulty).unwrap();
assert!(pw.score(&phrase).unwrap() >= difficulty);

Prove more difficult work. This time targeting a time.

// more diffcult, takes around 100_000 hashes to generate proof
let difficulty = u128::max_value() - u128::max_value() / 100_000;

let now: u64 = get_unix_time_seconds();
let pw = PoW::prove_work(&now, difficulty).unwrap();
assert!(pw.score(&now).unwrap() >= difficulty);

Define a blockchain block.

struct Block<T> {
    prev: [u8; 32], // hash of last block
    payload: T,     // generic data
    proof_of_work: PoW<([u8; 32], T)>,
}

Hashing Scheme

SHA256 is calculated over the concatenation of the:

• SALT
• Serialized Input T
• Nonce

The first 16 bytes of the resulting hash are interpreted as a 128 bit unsigned integer.

A randomly generated constant, SALT, is used as prefix to prevent PoW reuse from other systems such as proof of work blockchains.

Choosing a difficulty setting.

Difficulty settings are usually best adjusted dynamically a la bitcoin.

To manually select a difficulty, choose the average number of hashes required.

fn difficulty(average: u128) -> u128 {
    debug_assert_ne!(average, 0, "It is impossible to prove work in zero attempts.");
    let m = u128::max_value();
    m - m / average
}

Conversely, to calculate probable number of hashes required to satisfy a given minimum difficulty.

fn average(difficulty: u128) -> u128 {
    let m = u128::max_value();
    if difficulty == m {
        return m;
    } 
    m / (m - difficulty)
}

License

This project is dual-licensed under Apache License Version 2.0 & MIT license.