How to Implement P2P Encryption with sr25519 key pair using NaCl or alternatives?

Question

I am currently working on a project that involves P2P encryption using Substrate addresses and sr25519 cryptographic keys. However, I am encountering difficulties in implementing encryption and decryption with the NaCl library.

The library doesn't work with sr25519. I tried using ed2curve, but it seems strange. Is there any other way to encrypt/decrypt with sr25519?

Answer 1

Okay, I found a way to accomplish this; I need to use a shared secret key.

The @polkadot/wasm-crypto library has a method for it. I had to conduct research on encryption to find the appropriate code because "sr25519Agree" didn't mean anything to me as a developer. :)

import { waitReady, sr25519Agree } from '@polkadot/wasm-crypto'
import { sr25519PairFromSeed, naclEncrypt, naclDecrypt, encodeAddress } from '@polkadot/util-crypto'
import { stringToU8a, u8aToString } from '@polkadot/util'

const SEED_1 = '0x8ed48adf968bfb0d712d1530442187b7a9c5ce528ae079d60c072127d5b0b924'
const SEED_2 = '0x6152353dac161f116233b73b655ee6246da278df692c5599ce108b5fef5b3a09'

(async () => {
  await waitReady()

  const pair_1 = sr25519PairFromSeed(SEED_1)
  console.log('pair_1', encodeAddress(pair_1.publicKey))

  const pair_2 = sr25519PairFromSeed(SEED_2)
  console.log('pair_2', encodeAddress(pair_2.publicKey))

  const shared_1 = sr25519Agree(pair_1.publicKey, pair_2.secretKey)
  const shared_2 = sr25519Agree(pair_2.publicKey, pair_1.secretKey)

  console.log(
    'shared_1 === shared_2',
    u8aToString(shared_1) === u8aToString(shared_2)
  )

  const message = stringToU8a('hello world')

  const {encrypted, nonce} = naclEncrypt(message, shared_1)
  const decryptedMessage = naclDecrypt(encrypted, nonce, shared_2)

  console.log('decryptedMessage', u8aToString(decryptedMessage))
})()