Post Office

Encrypted mail service on Solana - Send secure messages as NFTs

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Postoffice

Decentralized encrypted messaging system based on Solana blockchain. Messages are minted as compressed NFTs with AES-256-CBC encryption, stored on IPFS, and only decryptable by the recipient wallet holder.

Architecture

  • Blockchain: Solana (Devnet)
  • NFT Standard: Compressed NFTs (Metaplex Bubblegum)
  • Encryption: AES-256-CBC, client-side
  • Storage: IPFS via Pinata
  • Access Control: Wallet-based ownership verification
  • API: Helius DAS for cNFT queries
  • Wallet: Phantom integration
  • ZKP Ready: Architecture prepared for zero-knowledge proof integration (coming soon)

File Structure

postoffice/
├── index.php                    - Landing page
├── compose.php                  - Message composition interface
├── my_letters.php              - Inbox view with cNFT list
├── view.php                    - Individual message viewer
├── pricing.php                 - Subscription plans (SOL/Token/Stripe)
├── api.php                     - API proxy to backend
├── subscription_payment.php    - Payment handler
└── init_subscriptions_db.php   - Database initialization

Database Schema

sealed_letters

Shared with notary system - stores encrypted message metadata and IPFS CID.

postoffice_subscriptions

- wallet_address: TEXT (unique)
- subscription_type: TEXT
- payment_method: TEXT (sol|token|stripe)
- amount: REAL
- transaction_id: TEXT
- start_date: TEXT
- end_date: TEXT
- status: TEXT (active|expired)

postoffice_payments

Transaction log for all subscription payments.

Message Flow

  1. Sender composes message in compose.php
  2. Client-side AES-256-CBC encryption using recipient's public key
  3. Encrypted payload uploaded to IPFS
  4. cNFT minted to recipient's wallet with IPFS CID in metadata
  5. Recipient views inbox (my_letters.php) via Helius DAS API
  6. Ownership verified via RPC before decryption
  7. Client-side decryption if ownership confirmed

Subscription Model

  • Base: 0.1 SOL/month
  • Token Discount: 50% off with $POST tokens
  • Stripe: +20% processing fee markup

Payment methods implemented in subscription_payment.php:

  • SOL transfer verification
  • Token transfer (placeholder)
  • Stripe Checkout integration

Deployment

Live at: https://postoffice.gudtek.lol

Backend shared with /notary/ system - same database, same encryption stack, different frontend.

Security Notes

  • Encryption happens client-side before transmission
  • Private keys never leave the user's wallet
  • Server only stores encrypted blobs and IPFS CIDs
  • Ownership verification required for decryption attempts
  • No central authority can decrypt messages

Development Status

Experimental protocol on Solana Devnet. Not audited. Use at own risk.

Roadmap

  • Zero-Knowledge Proofs: Implementation planned for privacy-preserving message verification without revealing content

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