90 lines
2.4 KiB
Markdown
90 lines
2.4 KiB
Markdown
# 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](https://github.com/bddap/pow) 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.
|
|
|
|
```rust
|
|
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.
|
|
|
|
```rust
|
|
// 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.
|
|
|
|
```rust
|
|
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.
|
|
|
|
```rust
|
|
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.
|
|
|
|
```rust
|
|
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`.
|