> For the complete documentation index, see [llms.txt](https://polarischain-1.gitbook.io/polarischain/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://polarischain-1.gitbook.io/polarischain/8.-network-layer-and-protocol-operations/8.2-post-quantum-transport-encryption-pqxdh.md).

# 8.2 - Post-Quantum Transport Encryption (PQXDH)

Before any application frame is exchanged, every P2P session establishes a post-quantum-secure channel via **PQXDH (Post-Quantum Extended Diffie-Hellman)**. The handshake completes in a single round-trip (1-RTT) and combines three primitives:

* **X25519** for classical elliptic-curve key exchange (defense-in-depth)
* **ML-KEM-768** for post-quantum key encapsulation
* **Dilithium2** for handshake transcript authentication

The derived session key encrypts and authenticates all subsequent traffic. Forward secrecy is guaranteed by the ephemeral nature of both X25519 and ML-KEM-768 key material; even if a validator’s long-term Dilithium key is compromised, historical sessions remain cryptographically inaccessible.PQXDH is **enabled by default** and enforced in all production deployments. Laboratory environments may explicitly disable it via environment variable, but release builds emit structured warnings when transport encryption is inactive.


---

# Agent Instructions
This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com.

## Querying This Documentation
If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter, and the optional `goal` query parameter:

```
GET https://polarischain-1.gitbook.io/polarischain/8.-network-layer-and-protocol-operations/8.2-post-quantum-transport-encryption-pqxdh.md?ask=<question>&goal=<endgoal>
```

`ask` is the immediate question: it should be specific, self-contained, and written in natural language.
`goal` is optional and describes the broader end goal you are ultimately trying to accomplish on behalf of the user. GitBook uses it to tailor the answer towards what is most useful for that goal.

The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.