Forward Secrecy

QNSP implements forward secrecy to protect past communications.

What is forward secrecy

Even if long-term keys are compromised, past session keys cannot be derived.

Implementation

TLS connections

• Ephemeral key exchange (ECDHE + Kyber)
• Session keys derived per connection
• Long-term keys only for authentication

Token signing

• Signing keys rotate regularly
• Old signing keys destroyed
• Past tokens remain valid until expiry

Data encryption

• Per-object DEKs
• DEKs wrapped with rotating KEKs
• Compromise of current KEK doesn't expose old DEKs

Key exchange

Hybrid key exchange:

1. Generate ephemeral X25519 keypair
2. Generate ephemeral Kyber keypair
3. Combine shared secrets
4. Derive session key

Session key lifecycle

1. Generated per session/connection
2. Used for session duration
3. Securely erased on session end
4. Never stored persistently

Benefits

• Past data protected from future key compromise
• Limits exposure window
• Reduces value of key theft