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PQXDH Key Exchange

This document describes the key exchange process in the PQXDH protocol.

Key Exchange Flow​

The PQXDH key exchange involves several steps to establish a shared secret between two parties.

1. Key Generation​

Each participant generates their key pairs for both classical and post-quantum cryptography:

2. Initial Message​

The initiator creates an initial PQXDH message containing their public keys and encrypted data:

3. Response Processing​

The responder processes the initial message and generates a response with their own keys.

4. Shared Secret Derivation​

Both parties derive the same shared secret using the exchanged keys:

Security Considerations​

  • Keys should be generated using cryptographically secure random number generators
  • Ephemeral keys should be deleted after use to ensure forward secrecy
  • The protocol includes protection against replay attacks

Error Handling​

The implementation includes comprehensive error handling for:

  • Invalid key formats
  • Cryptographic failures
  • Protocol violations

For complete implementation details, refer to the Rust API documentation.