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---
terms: ["payment-ID", "payment-IDs"]
summary: "an optional flag that is added to identify transactions to merchants, consisting of 64 hexadecimal characters"
---

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### The Basics

Payment ID is an **arbitrary** and **optional** transaction attachment that consists of 32 bytes (64 hexadecimal characters) or 8 bytes (in the case of integrated addresses).

The Payment ID is usually used to identify transactions to merchants and exchanges: Given the intrinsic privacy features built into Monero, where a single public address is usually used for incoming transactions, the Payment ID is especially useful to tie incoming payments with user accounts.

### Compact Payment IDs and Integrated Addresses

Since the 0.9 Hydrogen Helix version, Payment IDs can be encrypted and embedded in a payment address. The Payment IDs of this type should be 64-bits and are encrypted with a random one-time key known only to the sender and receiver.

### Creating a Payment ID
It is recommended to use the official wallet's `integrated_address` command to automatically generate Integrated Addresses that contain Compact Payment IDs. If you want to use the command line, you can generate Payment IDs as follows:

Creating a compact Payment ID for an Integrated Address:

```# openssl rand -hex 8```

Creating an old-style Payment ID:

```# openssl rand -hex 32```