Conveying the More Instant Messaging Interoperability Message ID

In modern messaging apps (like WhatsApp, Signal, or iMessage), each platform has its own way of identifying messages and securing them with cryptographic signatures. This makes interoperability — the ability of users on different apps to communicate securely — very difficult.

The IETF More Instant Messaging Interoperability (MIMI) Working Group is trying to solve this by standardizing how messaging systems communicate. Think of it as building a shared "language" and structure so different apps can exchange messages securely and meaningfully.

The draft draft-mahy-mimi-msgid-aad defines a common format for message IDs and a standard structure for Authenticated Additional Data (AAD) that can be used when signing or encrypting messages. AAD is a part of the message that, while not encrypted, is authenticated — ensuring its integrity.

By placing the Message ID in the AAD, it becomes accessible to MIMI providers outside the immediate Messaging Layer Security (MLS) group. Including the Message ID in the AAD is crucial for interoperability because it allows different messaging services to recognize and process messages consistently. This supports features like message synchronization across platforms, consistent message threading, and accurate message delivery status updates.