Decrypting payment Id of integrated address

Question

I am using monero-nodejs liberary for rpc calls. I generated an integrated address and made a payment to this address.

By splitting the integrated address, I could see the paymentId is a33582a5a77c125b.

But when I check payments of this address, I get nothing (empty object)

Wallet.getPayments(req.params.id)

Do I need any decoding on this paymentId? I can see the tx mined.

Answer 1

MyMonero provides a useful JavaScript library (mymonero-core-js) for dealing with this sort of thing.

Here is a code snippet that shows how to encrypt/decrypt a payment id using this bit of code from mymonero-core-js.

const mm = require('mymonero-core-js').monero_utils

const viewKey = mm.random_keypair()
const txKey = mm.random_keypair()
const paymentId = 'badc0ffeefabcafe'

const INTEGRATED_ID_SIZE = 8
const ENCRYPTED_PAYMENT_ID_TAIL = 0x8d

// If you have the private tx key and public view key
const pidKey = mm.cn_fast_hash(
  mm.generate_key_derivation(viewKey.pub, txKey.sec) +
  ENCRYPTED_PAYMENT_ID_TAIL.toString(16)
).slice(0, INTEGRATED_ID_SIZE * 2)

// If you have the private view key and public tx key
const pidKey2 = mm.cn_fast_hash(
  mm.generate_key_derivation(txKey.pub, viewKey.sec) +
  ENCRYPTED_PAYMENT_ID_TAIL.toString(16)
).slice(0, INTEGRATED_ID_SIZE * 2)

// Assert that the pidKeys are equal
console.log((pidKey === pidKey2)
  ? 'pidKeys are equal (expected)'
  : 'pidKeys are not equal (unexpected)')

// Encrypt Payment ID
const encryptedPaymentId = mm.hex_xor(paymentId, pidKey)
console.log('Encrypted: ' + encryptedPaymentId)

// Decrypt Payment ID
const decryptedPaymentId = mm.hex_xor(encryptedPaymentId, pidKey)
console.log('Decrypted: ' + decryptedPaymentId)

// Assert that the original and decrypted payment ids are equal
console.log((decryptedPaymentId === paymentId)
  ? 'Successful Decryption!'
  : 'Unsuccessful Decryption')

Should provide an output similar to:

pidKeys are equal (expected)
Encrypted: cfc3f2120b7db7c0
Decrypted: badc0ffeefabcafe
Successful Decryption!

Hope this helps!