sloth-permutation

Sloth permutation (modular square root) for JavaScript (TypeScript) using WebAssembly, originally from https://github.com/randomchain/pysloth

Rationale

From Subspace blockchain whitepaper:

Choice of Permutation. While any cryptographically secure
PRP [Pseudo-random Permutation] will suffice for the codec, an ideal candidate would be
both ASIC resistant and time-asymmetric, without imposing
any new security assumptions. It turns out that we may

construct such a permutation from the difficulty of comput-
ing modular square roots, using the permutation underlying

SLOTH (slow-time hash function) as a guide [14]. This has
the advantage of a near-optimal encoding time on x86-64
architecture, when using a 64-bit prime, while reducing the
decoding time by at least one order of magnitude, significantly
lowering the aggregate verification work done across the
network for each new block.

How to install

npm install @hyperhyperspace/sloth-permutation

How to build

1. Install emcc:

git clone https://github.com/emscripten-core/emsdk.git 
cd emsdk
./emsdk install 1.39.0
./emsdk activate 1.39.0
source ./emsdk_env.sh

2. Install WjCryptLib (https://github.com/WaterJuice/WjCryptLib)

3. Build:

git clone git@github.com:hyperhyperspace/sloth-permutation.git
cd sloth-permutation
yarn build

How to use

import {createHash} from "crypto";
import {SlothPermutation} from "@subspace/sloth-permutation";

(async () => {
    const blockSize = 64;
    const rounds = 5;
    const primeInput = createHash('sha512')
        .update('subspace')
        .digest();
    const dataBlock = createHash('sha512')
        .update('subspace-data')
        .digest();

    const data = Buffer.concat([dataBlock, dataBlock]);

    const encoderDecoder = await SlothPermutation.instantiate(primeInput, blockSize, rounds);

    console.log('Data:', data.toString('hex'));

    for (let i = 0; i < 5; ++i) {
        const encodedData = encoderDecoder.encode(data);
        console.log('Encoded data:', Buffer.from(encodedData).toString('hex'));

        const decodedData = encoderDecoder.decode(encodedData);
        console.log('Decoded data:', Buffer.from(decodedData).toString('hex'));
        console.log('Decoded correctly: ', data.join(',') === decodedData.join(','));
    }

    encoderDecoder.destroy();
})();

License

MIT, see license.txt