Creating a Muti-Algorithm simple Proof-Of-Work library in Rust

At 09 May 2024 By Zola Gonano

I had an idea for a project that required Proof of Work as a part of it, but I couldn’t find any Rust libraries that would have Argon2id or Scrypt algorithms and were meant to provide proof of work functionality without being tied to a specific blockchain. So, I decided to develop my own. When I was doing so, I wanted to show how Rust’s data types can make such things easy and clean.

Okay, but what is PoW? Proof of Work is like solving a puzzle – an expensive task for a computer. It’s proof that your computer has done something difficult. It’s mostly used in cryptocurrency blockchains during mining, proving that the miner has completed the puzzle (equivalent to going to a mine and digging with a pickaxe for gold and silver). However, it’s not necessarily meant only for mining. Another common example of its use is for preventing spam on a network, which was the reason I needed to use it. For example, Bitmessage, which was an old (now defunct) P2P email network, used it to prevent spam on the network.

The idea is pretty straightforward. I wanted a library that is expandable, meaning multiple algorithms can be added to it without breaking everything. Secondly, I needed it to be general-purpose. I didn’t want it to be meant for one specific blockchain; I wanted it to handle any data and verify any data using it.

To start, I created a PoWAlgorithm enum, which would be expanded to include algorithms that the library is going to support. For now, I’ve used SHA2_256 for testing.

pub enum PoWAlgorithm {
    Sha2_256,
}

Next, I implemented calculate functions for it, which compute the hash of given data:

impl PoWAlgorithm {
    pub fn calculate_sha2_256(data: &[u8], nonce: usize) -> Vec<u8> {
        let mut hasher = Sha256::new();
        hasher.update(data);

        hasher.update(nonce.to_le_bytes());

        let final_hash = hasher.finalize();

        final_hash.to_vec()
    }

    pub fn calculate(&self, data: &[u8], nonce: usize) -> Vec<u8> {
        match self {
            Self::Sha2_256 => Self::calculate_sha2_256(data, nonce),
        }
    }
}

This kind of structure also allows using a trait for algorithms later, reducing some of the code and making the project cleaner as it grows.

Then I created the PoW library, meant to calculate and verify the proof of work based on the given data, difficulty, and the algorithm.

pub struct PoW {
    data: Vec<u8>,
    difficulty: usize,
    algorithm: PoWAlgorithm,
}

For the data, I decided to accept all types that implement serde’s Serialize trait and convert the data to JSON. This way, anyone could provide their own structs and data types to the PoW.

impl PoW {
    pub fn new(
        data: impl Serialize,
        difficulty: usize,
        algorithm: PoWAlgorithm,
    ) -> Result<Self, String> {
        Ok(PoW {
            data: serde_json::to_vec(&data).unwrap(),
            difficulty,
            algorithm,
        })
    }

    pub fn calculate_pow(&self, target: &[u8]) -> (Vec<u8>, usize) {
        let mut nonce = 0;

        loop {
            let hash = self.algorithm.calculate(&self.data, nonce);

            if &hash[..target.len()] == target {
                return (hash, nonce);
            }
            nonce += 1;
        }
    }

    pub fn verify_pow(&self, target: &[u8], pow_result: (Vec<u8>, usize)) -> bool {
        let (hash, nonce) = pow_result;

        let calculated_hash = self.algorithm.calculate(&self.data, nonce);

        if &calculated_hash[..target.len()] == target && calculated_hash == hash {
            return true;
        }
        false
    }
}

For the actual proof of work calculation, I followed what most cryptocurrencies do. I defined target bytes, which are the bytes that the hash should match with at the beginning. The nonce is then incremented until the hash meets this target.

---

My blog and all of its content are available under the CC by SA 4.0 License on my GitHub. If you notice any problems or have any improvements for the blog or its content, you’re always welcome to open a pull request.