> ## Documentation Index
> Fetch the complete documentation index at: https://docs.zas.red/llms.txt
> Use this file to discover all available pages before exploring further.

# Privacy in Zas: Encrypted and Unlinkable by Design

> Zas encrypts everything at all times. Nobody reads what you send, and no list exists of who has what. The server never sees file hashes through OPRF blind derivation.

Zas is designed so that the service cannot know who holds what. Your items are encrypted at all times. Nobody reads what you send. No queryable index links accounts to content, and no list exists of who has what.

## What the server cannot see

* **File contents**: encrypted on your device before any upload.
* **File hashes**: blind key derivation through OPRF means the server never sees content hashes.
* **Who shares what**: no queryable index connects accounts to items.

## How blind key derivation works

When you send a file, your client runs an OPRF (Oblivious Pseudo-Random Function) protocol with the server. The server helps derive a key without learning the input. This means the server cannot tell whether two users uploaded the same file, and it cannot build a map of content across accounts.

## What Zas does not do

Zas never sells storage, retention, or recovery of expired items. Once an item reaches its expiry, it is gone permanently. There is no backup for law enforcement and no data lake for analytics.

<Warning>
  Do not use the phrase "end-to-end encrypted" to describe Zas. The correct framing is: encrypted at all times; nobody reads what you send; no list exists of who has what.
</Warning>

## What to read next

* [How deduplication works](/en/concepts/dedup)
* [Anonymous sessions for untrusted devices](/en/getting-started/anonymous-sessions)
* [Enterprise identity model](/en/enterprise/identity-model)