From 668f0e42591148286504dcda243a0bfec81fd4c8 Mon Sep 17 00:00:00 2001
From: Bartek Nowotarski <bartek@nowotarski.info>
Date: Fri, 3 Aug 2018 17:16:19 +0200
Subject: [PATCH] Attachments

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+## Preamble
+
+```
+SEP: xxxx
+Title: Attachment Convention
+Author: stellar.org
+Status: Draft
+Created: 2018-08-03
+```
+
+## Simple Summary
+Sometimes there is a need to send more information about a transaction than fits in the provided memo field, for example: KYC info, an invoice, a short note. Such data shouldn't be placed in the [ledger](https://www.stellar.org/developers/guides/concepts/ledger.html) because of it's size or private nature. Instead, you should create what we call an attachment. A Stellar attachment is simply a JSON document. The `sha-256` hash of this attachment is included as a `memo_hash` in the transaction. The actual attachment document can be sent to the receiver through some other channel, most likely through the receiver's [Auth server](./sep-0003.md).
+
+## Specification
+
+The attachment has a following structure:
+
+```json
+{
+  "nonce": "<nonce>",
+  "transaction": {
+    "sender_info": {
+      "first_name": "<first_name>",
+      "middle_name": "<middle_name>",
+      "last_name": "<last_name>",
+      "address": "<address>",
+      "city": "<city>",
+      "province": "<province>",
+      "country": "<country in ISO 3166-1 alpha-2 format>",
+      "date_of_birth": "<date of birth in YYYY-MM-DD format>",
+      "company_name": "<company_name>"
+    },
+    "route": "<route>",
+    "note": "<note>"
+  },
+  "operations": [
+    {
+      "sender_info": <sender_info>,
+      "route": "<route>",
+      "note": "<note>"
+    },
+    // ...
+  ]
+}
+```
+
+Attachments can be extended with extra information however, the should contain the following fields:
+
+Name | Data Type | Description
+-----|-----------|------------
+`nonce` | string | [Nonce](https://en.wikipedia.org/wiki/Cryptographic_nonce) is a unique value. Every transaction you send should have a different value. A nonce is needed to distinguish attachments of two transactions sent with otherwise identical details. For example if you send $10 to Bob two days in a row.
+`transaction.sender_info` | JSON | JSON containing KYC info of the sender. This JSON object can be extended with more fields if needed.
+`transaction.route` | string | The route information returned by the receiving federation server (`memo` value). Tells the receiver how to get the transaction to the ultimate recipient. 
+`transaction.note` | string | A note attached to transaction.
+`operations[i]` | | `i`th operation data. Can be omitted if transaction has only one operation.
+`operations[i].sender_info` | JSON | `sender_info` for `i`th operation in the transaction. If empty, will inherit value from `transaction`.
+`operations[i].route` | string | `route` for `i`th operation in the transaction. If empty, will inherit value from `transaction`.
+`operations[i].note` | string | `note` for `i`th operation in the transaction. If empty, will inherit value from `transaction`.
+
+### Sending Attachments
+
+An attachment and its hash (in a transaction) can be sent to Auth server of a receiving organization using [Compliance protocol](./compliance-protocol.md).
+
+### Calculating Attachment hash
+
+To calculate the Attachment hash you need to stringify the JSON object and calculate `sha-256` hash. In Node.js:
+
+```js
+const crypto = require('crypto');
+const hash = crypto.createHash('sha256');
+
+hash.update(JSON.stringify(attachment));
+var memoHashHex = hash.digest('hex');
+```
+
+To add the hash to your transaction use the [`TransactionBuilder.addMemo`](http://stellar.github.io/js-stellar-base/TransactionBuilder.html#addMemo) method.
+
+#### Example
+
+```js
+var crypto = require('crypto');
+
+var nonce = crypto.randomBytes(16);
+var attachment = {
+  "nonce": nonce.toString('hex'),
+  "transaction": {
+    "sender_info": {
+      "name": "Sherlock Holmes",
+      "address": "221B Baker Street",
+      "city": "London NW1 6XE",
+      "country": "UK",
+      "date_of_birth": "1854-01-06"
+    }
+  },
+  "operations": [
+    // Operation #1: Payment for Dr. Watson
+    {
+      "route": "watson",
+      "note": "Payment for helping to solve murder case"
+    },
+    // Operation #2: Payment for Mrs. Hudson
+    {
+      "route": "hudson",
+      "note": "Rent"
+    }
+  ]
+};
+
+var hash = crypto.createHash('sha256');
+hash.update(JSON.stringify(attachment));
+var memoHashHex = hash.digest('hex');
+console.log(memoHashHex);
+```
+
+## Test Cases
+
+Use [GoStellar](https://gostellar.org/) application to check if Compliance protocol and attachments were implemented correctly.
+
+## Reference implementations
+
+* [`github.com/stellar/go/protocols/compliance` package](https://github.com/stellar/go/blob/master/protocols/compliance).