# Building a messenger with no phone number: zk-SNARKs on the BitcoinZ blockchain

*How Z-TEXT uses zk-SNARKs, AES-256-GCM and a quantum-resistant key exchange to send messages with no phone, no email and no SIM.*

By [Z-TEXT](https://paragraph.com/@z-text), 2026-09-29

privacy, blockchain, security, cryptography, messenger, zksnarks

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Z-TEXT goes public on **October 5, 2026**. Before launch, here's how it works under the hood, and where its limits are.

**No phone. No email. No SIM. Zero metadata.**

\## Identity: a seed, not a phone number

There is no signup. Your identity is a shielded address derived from a 24-word seed. The same seed unlocks five tools: a messenger, a BTCZ wallet, an on-chain password manager, Channels (on-chain broadcast) and disposable identities.

Lose the phone, restore the seed on any device, and your messages, contacts and vault rescan from the chain.

\## The message path

1\. The message is encrypted on-device with **AES-256-GCM**.

2\. The key exchange is hybrid: **X25519 + ML-KEM-768** (NIST FIPS 203), live since version 3.7.0, so traffic recorded today resists a future quantum computer. Signatures are still classical Ed25519.

3\. The ciphertext is sent as the memo of a **Sapling shielded transaction** on BitcoinZ. zk-SNARKs prove the transaction is valid without revealing sender, recipient or amount.

4\. It is pushed through the mempool for delivery in about 1–5 seconds, then settles on-chain.

No central message server holds the conversation. What exists on-chain is an encrypted, shielded transaction, not a readable transcript.

\## Spam resistance through a micro-fee

Each message costs **0.0002 BTCZ**: a 0.0001 network fee plus 0.0001 delivered to the recipient. In a normal back-and-forth that 0.0001 comes back with each reply. Negligible for people, expensive for bots at scale.

\## Choose your trust tier

\- **Default:** connect to the official lightwalletd. It sees that a shielded transaction was submitted, not who, to whom or what.

\- **Tor:** the same, but the operator no longer sees your IP.

\- **Self-hosted:** run your own lightwalletd or full BitcoinZ node. No third party in the loop.

  
{% embed [https://www.youtube.com/watch?v=68s9hl6V-AU](https://www.youtube.com/watch?v=68s9hl6V-AU) %}  
  
\## Honest limits

\- Text only: no files, pictures or video.

\- No independent audit of the app yet. There is an active, paid bug bounty instead, but a bounty is not an audit.

\- Permanence is a feature and a responsibility: messages settle on a blockchain.

\## The chain

BitcoinZ launched on September 10, 2017, with no premine and no ICO. It is community-run and GPU-mineable. Z-TEXT does not issue or control BTCZ.

Launch day is October 5. Follow along at \[[z-text.com](http://z-text.com)\]([https://z-text.com](https://z-text.com)), and read about the chain at \[[getbtcz.com](http://getbtcz.com)\]([https://getbtcz.com](https://getbtcz.com)).

Questions about the design are welcome in the comments. 👇

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*Originally published on [Z-TEXT](https://paragraph.com/@z-text/building-a-messenger-with-no-phone-number-zk-snarks-on-the-bitcoinz-blockchain)*