Privacy by Design Comes to the fore

Enhancing Privacy and Security in Messaging with SD-JWT

In a world where our digital conversations are the new frontier of personal data, the security and privacy of our messaging applications are more critical than ever. We’ve all grown accustomed to end-to-end encryption, which is a great first step, but what happens when you need to share personal information within a conversation? SD-JWT (Selective Disclosure for JSON Web Tokens) offers a powerful solution that can take messaging privacy to a whole new level.

The Problem with Today’s Data Sharing

Even with encryption, sharing data in a messaging app often means a binary choice: either you share all of a document or none of it.

Imagine you’re chatting with a new contact and they need to verify your identity. You might send them a photo of your ID, a common but risky practice. This single action exposes a wealth of personal data—your full name, address, date of birth, and more—when all they might need is to verify a single detail, like your age or that your name matches a business record.

This all-or-nothing approach creates a significant privacy risk. Your complete personal document now exists in a new location, potentially on a third-party server, and you’ve lost control over how that information is used or stored.

SD-JWT: A Smarter Way to Share

This is where SD-JWT fundamentally changes the game for messaging. Instead of a static document or a photo, a user can hold their personal information as a set of cryptographically signed “claims” in an SD-JWT. These claims are not plain text; they are protected by a system of hashes that enable a user to prove they possess a claim without revealing the claim’s full value.

Here’s how this would work in a messaging application:

1. The Credential as a “Digital Locker”: Your digital identity is stored in your messaging app as a Verifiable Credential (VC) in the form of an SD-JWT. This VC could be an official government-issued ID, a school transcript, or a professional license.

2. The Request: When your contact needs to verify a specific piece of information (e.g., your age), they can send a “proof request” within the chat.

3. The Selective Response: Your messaging app, equipped with SD-JWT capabilities, can then selectively disclose only the specific piece of information requested. The application generates a verifiable presentation that includes the digital signature from the original issuer, the necessary disclosures, and a cryptographic proof that the data has not been tampered with. It does all of this without revealing any other claims from the original credential.

4. Verification: The contact’s messaging app receives the proof and instantly verifies it against the issuer’s public key. They can now confirm with certainty that your claim is authentic without ever seeing your full document or any other private information.

The Benefits for Messaging

• Absolute Control: You are in complete control of your data. You decide what to share, and your app handles the cryptographic heavy lifting.
• Data Minimization: Only the absolutely necessary information is ever shared, dramatically reducing the risk of oversharing and data breaches.
• Trust and Verifiability: The use of cryptographic signatures ensures that the information is authentic and hasn’t been tampered with, fostering a new level of trust in digital communication.
• Seamless User Experience: The process can be made nearly invisible to the user. From a user’s perspective, it feels as simple as tapping a button to “Verify my age,” while the technology does the complex work in the background.

By integrating SD-JWT, messaging applications can go beyond just securing the channel of communication to securing the content itself, empowering users to share data with precision and confidence. It’s an essential step in building a digital world where privacy is a built-in feature, not an optional add-on.