121 lines
3.8 KiB
Markdown
121 lines
3.8 KiB
Markdown
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<div align="center">
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<h1>PoW_SHA256</h1>
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<p>
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<strong>PoW_SHA256 - SHA256 based Proof-of-Work</strong>
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</p>
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[![Documentation](https://img.shields.io/badge/docs-master-blue)](https://mcaptcha.github.io/pow_sha256/pow_sha256/index.html)
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![CI (Linux)](<https://github.com/mcaptcha/pow_sha256/workflows/CI%20(Linux)/badge.svg>)
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[![dependency status](https://deps.rs/repo/github/mcaptcha/pow_sha256/status.svg)](https://deps.rs/repo/github/mcaptcha/pow_sha256)
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<br />
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[![codecov](https://codecov.io/gh/mcaptcha/pow_sha256/branch/master/graph/badge.svg)](https://codecov.io/gh/mcaptcha/pow_sha256)
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</div>
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> pow_sha256's copy of `pow_sha256` by
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> [robkorn](https://github.com/robkorn/pow_sha256)
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> which is a modified version of [`pow` library](https://github.com/bddap/pow).
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> All copyrights belong to the original authors.
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Rust crate which generates SHA256 Proofs of Work on serializable datatypes.
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Whether for blockchain-related projects or Hashcash-like schemes, this
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crate can be used to prove work was done on a given serializable input.
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The input merely needs to implement `serde::Deserialize` to be used.
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This is a fork of the [`pow` library](https://github.com/bddap/pow) by
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bddap with some new additions. Primary of these being:
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- PoW datatype now saves the calculation result to be used for checking
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proof validity given input
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- `is_valid_proof` method to do the above mentioned
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- PoW datatype no longer saves `u128` values as these are unsupported by
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popular serialization formats (CBOR, Msgpack, ...)
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- `is_sufficient_difficulty` method to check difficulty with new changes
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Other small changes have also been included of various importance but
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mostly just stylistic/ease of use improvements.
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# Examples
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Prove work was done, specifically targeting a phrase.
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```rust
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use pow_sha256::PoW;
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// Very easy difficulty
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let difficulty = u128::max_value() - u128::max_value() / 2;
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let phrase = b"Phrase to be used.".to_vec();
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let pw = PoW::prove_work(&phrase, difficulty).unwrap();
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// Asserting that the result is of sufficient difficulty
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assert!(pw.is_sufficient_difficulty(difficulty));
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// Asserting that the PoW was generated from the provided phrase
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assert!(pw.is_valid_proof(&phrase))
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```
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Prove more difficult work. This time targeting a time.
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```rust
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// Greater difficulty this time around. Takes around 100,000 hashes
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// to find a nonce of the correct difficulty.
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let difficulty = u128::max_value() - u128::max_value() / 100_000;
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let now: u64 = get_unix_time_seconds();
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let pw = PoW::prove_work(&now, difficulty).unwrap();
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assert!(pw.is_sufficient_difficulty(difficulty));
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assert!(pw.is_valid_proof(&phrase))
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```
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# Hashing Scheme
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A randomly generated constant, `SALT`, is used as prefix to prevent PoW
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reuse from other systems such as proof of work blockchains.
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SHA256 is calculated over the concatenation of the:
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- SALT
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- Serialized Input `T`
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- Nonce
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The first 16 bytes of the resulting hash are interpreted as a 128 bit
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unsigned integer and saved as the final result.
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# Choosing a difficulty setting.
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Depending on your use case, difficulty settings often are best set
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dynamically a la bitcoin.
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However if your use case requires manual setting then it is trivial to
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set one yourself. One way to do so is to choose the average number of
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hashes desired with a function like this:
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```rust
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fn get_difficulty(average: u128) -> u128 {
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debug_assert_ne!(average, 0, "It is impossible to prove work in zero attempts.");
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let m = u128::max_value();
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m - m / average
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}
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```
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Conversely we can use the same equation to calculate the probable number of hashes required to satisfy a given difficulty:
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```rust
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fn est_average(difficulty: u128) -> u128 {
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let m = u128::max_value();
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if difficulty == m {
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return m;
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}
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m / (m - difficulty)
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}
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```
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# License
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This project is dual-licensed under `Apache License Version 2.0` or `MIT license`.
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