ZCHAT

Private messaging built on Zcash shielded transactions.

Overview

ZCHAT is a privacy-first messaging application that uses Zcash's shielded transaction memo field to send encrypted messages. Messages are stored on the Zcash blockchain, providing:

• End-to-end encryption - Messages encrypted with ECDH + AES-256-GCM
• Blockchain privacy - Shielded transactions hide sender, recipient, and content
• No central server - Messages exist only on the blockchain
• Self-destructing messages - Remote destruction via blockchain transactions

Platforms

Platform	Status	Notes
Android	Primary	Forked from Zashi wallet
iOS	Planned	After NOSTR integration
Web	Secondary	Basic messaging only

Features

Current (Android)

• Direct messaging via Zcash memos
• Group messaging with shared key encryption
• Time-locked messages (scheduled, block-height, payment-gated)
• Read receipts and reactions
• Message chunking for long content (>400 bytes)
• Remote account destruction

Planned (NOSTR Integration)

• File and image sharing (via Blossom)
• Audio messages
• Voice and video calls (WebRTC)
• Typing indicators
• Online presence

Architecture

BIP39 Seed Phrase (24 words)
         |
         +--- m/44'/133'/0'/0/0  --> Zcash unified address
         |                          (payments + private messages)
         |
         +--- m/44'/1237'/0'/0/0 --> NOSTR secp256k1 keypair
                                     (files + calls + presence)

One seed phrase provides both identities, cryptographically linked.

Project Structure

/home/yourt/zchat/           # Main monorepo
+-- apps/
|   +-- backend/             # Node.js API (port 4000)
|   +-- web/                 # Next.js frontend (port 3000)
|   +-- landing/             # Landing page (zsend.xyz)
+-- packages/
|   +-- wallet-core/         # Rust WASM wallet
+-- docs/                    # Documentation

/home/yourt/zchat-android/   # Android app (Zashi fork)

Documentation

Document	Purpose
CLAUDE.md	Project context, infrastructure, commands
PRODUCT.md	Product vision, features, roadmap
ARCHITECTURE.md	Technical architecture, protocols
ANDROID_FIX_PLAN.md	Current priorities, NOSTR integration
DEVELOPMENT_STANDARDS.md	Coding standards (TypeScript/Kotlin)
DECISIONS.md	Architectural decision log
ISSUES_TO_FIX.md	Audit findings, prioritized bugs

Quick Start

Prerequisites

• Node.js 18+
• pnpm
• Rust (for WASM wallet)
• Android Studio (for mobile development)

Backend

cd apps/backend
pnpm install
npx prisma generate
pnpm dev

Web Frontend

cd apps/web
pnpm install
pnpm dev

Android

cd /home/yourt/zchat-android
ANDROID_HOME="$HOME/android-sdk" ./gradlew assembleDebug

Public URLs

Service	URL
Landing Page	https://zsend.xyz
Web App	https://app.zsend.xyz
API	https://api.zsend.xyz

Protocol

Messages use the ZMSG protocol (v4):

ZMSG|4|<type>|<conv_id>|<sender_hash>|<payload>

Types: DM (direct), RXN (reaction), RCV (receipt), RPL (reply), REQ (request), CHK (chunk), STT (status), GRP (group)

See ARCHITECTURE.md for full protocol specification.

Security

• Seeds stored in EncryptedSharedPreferences (Android)
• E2E encryption: ECDH (secp256r1) + AES-256-GCM
• Key derivation: HKDF with HMAC-SHA256 (v2)
• No seed transmission to servers

Contributing

This is a private project. Contact the maintainer for access.

License

Proprietary. All rights reserved.

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Built with Zcash shielded transactions for true privacy.