Encryption function used by FELToken

Encryption function.ts

import { encrypt } from '@metamask/eth-sig-util';
const ascii85 = require('ascii85');

function encryptData(publicKey: Buffer, data: Buffer): number[] {
  // Returned object contains 4 properties: version, ephemPublicKey, nonce, ciphertext
  // Each contains data encoded using base64, version is always the same string
  const enc = encrypt({
    publicKey: publicKey.toString('base64'),
    data: ascii85.encode(data).toString(),
    version: 'x25519-xsalsa20-poly1305',
  });

  // We want to store the data in smart contract, therefore we concatenate them
  // into single Buffer
  const buf = Buffer.concat([
    Buffer.from(enc.ephemPublicKey, 'base64'),
    Buffer.from(enc.nonce, 'base64'),
    Buffer.from(enc.ciphertext, 'base64'),
  ]);
  
  // In smart contract we are using `bytes[112]` variable (fixed size byte array)
  // you might need to use `bytes` type for dynamic sized array
  // We are also using ethers.js which requires type `number[]` when passing data
  // for argument of type `bytes` to the smart contract function
  // Next line just converts the buffer to `number[]` required by contract function
  // THIS LINE IS USED IN OUR ORIGINAL CODE:
  // return buf.toJSON().data;
  
  // Return just the Buffer to make the function directly compatible with decryptData function
  return buf;
}