What is PQ3 and how does it affect message export?

In February 2024, Apple upgraded iMessage to PQ3 (Post-Quantum 3), which Apple claims provides "the strongest security properties of any at-scale messaging protocol in the world." This protocol prepares iMessage for the era of quantum computing, which threatens to break current encryption methods.

Hybrid Cryptographic Approach

PQ3 implements a hybrid system combining traditional Elliptic Curve Cryptography (ECC) with post-quantum algorithms, specifically Kyber-1024, a module-lattice-based key-encapsulation mechanism selected by NIST as a quantum-resistant standard. This means messages are encrypted using both classical and post-quantum cryptography, so even if quantum computers eventually break one layer, the other provides protection.

Security Level Progression

PQ3 represents Level 3 in messaging security hierarchy:

• Level 0: No encryption (e.g., SMS)
• Level 1: End-to-end encryption using classical cryptography (original iMessage, WhatsApp)
• Level 2: Post-quantum secure key establishment (Signal with PQXDH)
• Level 3: Post-quantum security for both key establishment and ongoing message exchange with periodic key rotation

Automatic Key Ratcheting

PQ3 automatically "ratchets" encryption keys forward with each message exchange, limiting the number of messages compromised even if a specific key is broken. This continuous key rotation provides forward secrecy—past messages remain secure even if current keys are compromised.

Impact on Message Export

The ratcheting mechanism adds complexity to message archiving. Messages encrypted under different key states would theoretically need special handling during export. However, this doesn't affect local database access—once messages are decrypted and stored in your Mac's chat.db database, tools like TextKeep can export them normally. The PQ3 encryption protects messages in transit and in cloud storage, not the local database after decryption.