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docs: add a new category of docs -> databases to explain sphinx replay #9616

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16 changes: 16 additions & 0 deletions docs/databases/sphinxreplay.md
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# Understanding Sphinx Replay Protection

Sphinx is a protocol enabling anonymous and untraceable messaging in networks, commonly used in Lightning's onion routing. To prevent replay attacks, a Sphinx replay database stores message hashes along with metadata (e.g., timestamp, sender ID).
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Can you wrap the lines at 80 characters please?


## How It Works
1. **Message Check**: When a message is received, its hash is compared against stored entries.
2. **Replay Prevention**: If the message exists, it is discarded; otherwise, it is added to the database.
3. **Network Integrity**: This ensures that previously sent messages cannot be resent maliciously.

## Onion Routing in Lightning
Sphinx follows source-based onion routing, where messages are encrypted in nested layers. Each node peels one layer, revealing only the next hop, ensuring sender anonymity and path secrecy.

Lightning’s **Sphinx Mix Format** differs from Tor, offering enhanced security tailored to payments.

For deeper insights, refer to [Chapter 10 of the Lightning Network Book](https://github.com/lnbook/lnbook/blob/develop/10_onion_routing.asciidoc).