status-web/packages/status-core/src/topics.ts

import { BN } from 'bn.js'
import { derive } from 'ecies-geth'
import { ec } from 'elliptic'
import { bufToHex } from 'js-waku/build/main/lib/utils'

import { idToContentTopic } from './contentTopic'
import { hexToBuf } from './utils'

import { Identity } from '.'

const EC = new ec('secp256k1')
const partitionsNum = new BN(5000)

/**
 * Get the partitioned topic https://specs.status.im/spec/3#partitioned-topic
 * @param publicKey Public key of recipient
 * @returns string The Waku v2 Content Topic.
 */
export function getPartitionedTopic(publicKey: string): string {
  const key = EC.keyFromPublic(publicKey.slice(2), 'hex')
  const X = key.getPublic().getX()

  const partition = X.mod(partitionsNum)

  const partitionTopic = `contact-discovery-${partition.toString()}`

  return idToContentTopic(partitionTopic)
}

/**
 * Get the negotiated topic https://specs.status.im/spec/3#negotiated-topic
 * @param identity identity of user
 * @param publicKey Public key of recipient
 * @returns string The Waku v2 Content Topic.
 */
export async function getNegotiatedTopic(
  identity: Identity,
  publicKey: string
): Promise<string> {
  const key = EC.keyFromPublic(publicKey.slice(2), 'hex')
  const sharedSecret = await derive(
    Buffer.from(identity.privateKey),
    hexToBuf(key.getPublic('hex'))
  )
  return idToContentTopic(bufToHex(sharedSecret))
}