When to Break and When to Bend: Post-Quantum Migration Tradeoffs in Rust

Short summary

Anyhide migrated to post-quantum hybrid encryption (ML-KEM-768) to counter harvest-now-decrypt-later threats against persistent codes. The migration used two opposite strategies: additive wire-format prefixes for long-lived codes requiring backward compatibility, and a clean version break for RAM-only chat sessions with no persisted data. The never-fail decoder design enabled safe format dispatch without error-signal leakage.

• •Post-quantum migration was driven by persistent Anyhide codes vulnerable to harvest-now-decrypt-later attacks
• •Long-lived codes used additive wire-format prefixes for backward compatibility; RAM-only chat used a clean version break
• •A 5-byte magic prefix enables format detection with 1-in-4-billion collision risk, safe due to never-fail decoder design

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