Force transaction to be with memo ID

Question

Because we are exchange we use main account and we generate Id number as a memo that we send to the customer so we will know the transaction was from him. we want to force the customer to add the memo , so if he does not add it the transaction will fail. Is there a way to do it?

Answer 1

You can use a Federation server to do most of what you're asking.

If you have user user_1 and your app is hosted at a site called my-site.com, then you can host your own federated server to work a little like a DNS server whereby the exchange can call the resolveAddress method to get the address for that persons account.

So, by calling resolveAddress('user_1*my-site.com'), the exchange can expect to get a response along the lines of:

{
  "stellar_address": "user_1*my-site.com",
  "account_id": "GAIGZHHWK3REZQPLQX5DNUN4A32CSEONTU6CMDBO7GDWLPSXZDSYA4BU",
  "memo_type": "text",
  "memo": "user_1"
}

Here the account_id can be a shared custodial account or a unique account for that user. By setting the memo we can, of course, tell who the transaction was by/for.

Note: The federation server is a very simple protocol, so you can easily send a dynamic response where the memo field is a generated token.

Take for example this response:

{
  "stellar_address": "user_1*my-site.com",
  "account_id": "GAIGZHHWK3REZQPLQX5DNUN4A32CSEONTU6CMDBO7GDWLPSXZDSYA4BU",
  "memo_type": "text",
  "memo": "ABC123XYZ"
}

This second method allows you to hide the identity of the user on the ledger, as the only identifiable thing that will be recorded is ABC123XYZ. Only your systems, and the exchange performing the transaction will know the identity of the user.

The only caveat is that someone can still send a trusted asset to your account_id with a random memo, or no memo at all. I don't believe you can prevent that.

Answer 2

Method using SEP-0007 to build a payment request using either Operation TX or Operation PAY.

I have used the Operation PAY method to build a URI with a randomly generated MEMO_ID included in the URI: web+stellar:pay?destination=<DESTINATION_ADDR>&amount=[AMOUNT_CURR]&memo=<CUSTOM_MEMO_ID>

This has the added benefit of forcing the use of MEMO_ID and functionality of paying wherever the customer feels most comfortable signing a transaction; the URI can be packaged into a QR-Code or create a link that should be read by a wallet that recognizes it (for example, Keybase on phone and/or PC).

Operation TX has more functionality by allowing a Transaction Envelope to be attached to the URI.