CryptoChat

A private, end-to-end encrypted messenger for two people — no accounts, no phone number, no e-mail.

CryptoChat is a small, privacy-first Android messenger. Messages and photos are end-to-end encrypted on your phone and travel through a "dead-drop" relay server that never learns what you write, nor who is talking to whom. There are no accounts — you pair with someone by scanning a one-time invite. Tor is built into the app, so there's nothing extra to install and the server never sees your IP address.

Why it's different The server is blind. It's a dumb mailbox: it stores and hands back encrypted blobs and nothing else. No accounts, no address book, no metadata about who talks to whom. No Google push. Most messengers use push services that reveal who is messaging whom. CryptoChat instead holds its own connection over Tor — that's the price of the quiet permanent notification you'll see while it's connected. Post-quantum key exchange. Pairing uses ML-KEM-768 (NIST FIPS 203), so a future quantum computer can't retroactively break a captured handshake. You verify each other in person. After pairing you read a short code aloud; the contact is only saved if it matches on both phones. That's your protection against a man-in-the-middle. Privacy & security What the server can and cannot see Sees it? How that's ensured Message / photo content No, never End-to-end AES-256-GCM encryption happens on your phone Who is the sender / recipient No, never No accounts — only anonymous mailbox IDs That "A is talking to B" No, never Mailbox ID = HKDF of a shared key the server never saw; it also rotates daily Message length No (hidden) The app pads messages, photos and files to fixed sizes Your IP address Hidden via Tor Reached as a Tor onion service; nothing extra to install That some mailbox received something Yes Can't be fully hidden — see the threat model below The server keeps everything in memory only (nothing on disk), writes no access logs, and mailboxes have a short lifetime (TTL) and are deleted the moment they're picked up.

On top of that Automatic key rotation — keys refresh themselves as you chat (a forward-secret ratchet plus a periodic post-quantum re-key that heals after a possible leak), with no re-pairing. The contact screen shows the current state and a security code you can compare to confirm you're both on the same fresh key. Encryption at rest — keys and chat history are wrapped by a non-exportable key in the Android Keystore. App lock — optional biometric / PIN lock on every open. No cloud backup of app data, and screenshots are blocked inside the app. What it does not hide (honestly) The server can tell that some mailbox received something at a given time — otherwise it couldn't deliver. Hiding the fact that communication happens at all would need cover traffic (fake messages); that's not implemented. A global passive observer who can watch both sides of the network at once can attempt timing correlation. Tor makes this harder, not impossible. A compromised phone means the keys are on it. That's what the app lock and Keystore defend, not the relay.

Features End-to-end encrypted text, photos and files. Reactions, replies (with jump-to-original), edit and delete for everyone. Text formatting — *bold*, _italics_, ~strikethrough~, `monospace`. Day separators, a "new messages" line, jump-to-latest, and drafts that survive a restart. Reply straight from the notification, or tap Like to react. Profile photos, contact search, and unread highlights. Runs in the background — a foreground service keeps the Tor connection warm and delivers notifications while sparing the battery. Password-protected backup & restore of everything: contacts, keys, profile photos and full chat history (including photos). Update check over Tor — so checking for a new version never reveals your IP. Follows your phone's language, or force System / Čeština / English.