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

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.

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, and read about the chain at getbtcz.com.

Questions about the design are welcome in the comments. 👇