Any way to encode useful information into the memo?

Question

I was trying to figure out a way to encrypt a small payload in a transaction memo to anonymize the memo id without having to store anything on the server (like a memo -> user mapping).

To achieve this I was planning to do a simple encryption/decryption:

const cryptr = new Cryptr(encryptionKey);

function getDepositToken(username, algo) {
  return cryptr.encrypt(username);
}

function getUserNameFromDepositToken(depositToken) {
   return cryptr.decrypt(username);
}

However, with usernames > 10 characters the smallest I could get it was 40 bytes using a wide range of encryption algorithms.

My end goal is to encrypt user id + nonce or timestamp so that I can completely anonymize deposits for a given user id without having to store a mapping for them all in a db.

Does anyone else have any tips to being able to fit slightly more data in it? I was hoping I could get to 15-20 characters.

Answer 1

It looks like you are doing a symmetric encryption/decryption. For the particular case you described, a crypto hash may be a better choice.

SHA256 returns exactly 32 bytes and features good collision-proof characteristics. So try to hash a username with SHA256 and store the result to memo.

Of course, it can't be "decrypted", however, the hash can be easily checked on the server side. If you need a lookup by the identifier, you can maintain one more column with hashed username in the "users" ("accounts", whatever) table.

Answer 2

If you want to use an account as database you could use manageData operations. If you want to identify transactions then the only option is the memo field or the attachments feature which is not stored on the blockchain.

Answer 3

I ended up turning this into https://github.com/stellarguard/secret-memo.

Answer 4

This is what I did to send messages between different accounts https://hmatejx.github.io/Interstellar-Whisper