SecPaste

Encrypted pastebin client with pluggable cryptography backends

SecPaste is a Python library and CLI tool for sharing encrypted content via public pastebin services. All encryption happens client-side, and the encryption key stays in the URL fragment (after #) so it never reaches the server.

Features

• Zero-knowledge architecture: Server only stores encrypted data
• Pluggable crypto backends: AES-256-GCM, ChaCha20-Poly1305, and experimental post-quantum (Kyber)
• Pluggable pastebin providers: Easy to add support for any pastebin service
• Both CLI and library: Use as a command-line tool or import in your code
• URL fragment key storage: Encryption key never sent to server (stays after #)

Security Model

┌─────────────┐         ┌──────────────┐         ┌─────────────┐
│   Client    │         │   Pastebin   │         │   Reader    │
│             │         │   Server     │         │             │
│ plaintext   │         │              │         │             │
│     ↓       │         │              │         │             │
│ encrypt     │         │              │         │             │
│     ↓       │────────▶│ [encrypted]  │────────▶│ fetch       │
│ ciphertext  │  POST   │   content    │   GET   │     ↓       │
│             │         │              │         │ decrypt     │
│ key ───────────────────────────────────────────────▶ ↓       │
│   (URL #fragment, never sent to server)      │ plaintext   │
└─────────────┘         └──────────────┘         └─────────────┘

Installation

# Basic installation
pip install cryptography requests

# For post-quantum crypto support (optional)
pip install liboqs-python

Quick Start

CLI Usage

# Paste from stdin (default: AES-256-GCM)
echo "secret message" | python -m secpaste.cli paste

# Paste a file
python -m secpaste.cli paste -f secret.txt

# Paste with ChaCha20-Poly1305
python -m secpaste.cli paste -f data.json -c chacha20-poly1305

# Paste with custom expiry and syntax highlighting
python -m secpaste.cli paste -f script.py --expiry week --syntax python

# Fetch and decrypt
python -m secpaste.cli fetch "https://dpaste.com/ABC123#aes-256-gcm:key..."

# Save fetched content to file
python -m secpaste.cli fetch "https://dpaste.com/ABC123#key..." -o output.txt

# List available options
python -m secpaste.cli list

Library Usage

from secpaste.client import SecPasteClient

# Initialize client (default: AES-256-GCM + dpaste)
client = SecPasteClient()

# Paste content
url = client.paste("secret data", expiry="week")
print(f"Share this URL: {url}")
# Output: https://dpaste.com/ABC123#aes-256-gcm:key...

# Fetch and decrypt
content = client.fetch(url)
print(content)  # "secret data"

# Use different cipher
client = SecPasteClient(cipher='chacha20-poly1305')
url = client.paste("encrypted with ChaCha20")

# Register custom cipher or provider
from secpaste.crypto.base import CipherBackend
class MyCipher(CipherBackend):
    # ... implementation ...
    pass

SecPasteClient.register_cipher('my-cipher', MyCipher)

Available Ciphers

Cipher	Description	Key Size	Quantum-Safe?
aes-256-gcm	AES-256-GCM (default)	32 bytes (~43 chars)	Symmetric: Yes
chacha20-poly1305	ChaCha20-Poly1305	32 bytes (~43 chars)	Symmetric: Yes
kyber768-aes256-gcm	Kyber-768 + AES-256 (experimental)	~1KB (~1400 chars)	Yes (PQC)

Note: Symmetric encryption (AES, ChaCha20) with 256-bit keys is already considered quantum-resistant. Post-quantum crypto (Kyber) protects against quantum attacks on key exchange, but produces much larger keys.

Post-Quantum Cryptography

The kyber768-aes256-gcm cipher uses NIST-standardized Kyber-768 for key encapsulation combined with AES-256-GCM for data encryption.

Pros:

• Future-proof against quantum computer attacks on key exchange
• NIST-standardized algorithm
• Educational/experimental

Cons:

• Much larger keys (~1KB vs 32 bytes)
• Browser URL length limits may apply (typically 2KB-8KB)
• Requires liboqs-python library
• Less mature ecosystem

Usage:

# Requires: pip install liboqs-python
from secpaste.crypto.pqc import KyberAESCipher

client = SecPasteClient(cipher='kyber768-aes256-gcm')
url = client.paste("quantum-safe secret")
# Warning: URL will be ~1.5KB longer than standard ciphers

Supported Pastebin Providers

Provider	Base URL	Notes
dpaste	https://dpaste.com	Default, supports custom expiry

Adding Custom Providers

from secpaste.providers.base import PastebinProvider
import requests

class MyPastebinProvider(PastebinProvider):
    def paste(self, content: bytes, **kwargs) -> str:
        # Upload content, return URL
        pass

    def fetch(self, paste_id: str) -> bytes:
        # Fetch content, return bytes
        pass

    def get_name(self) -> str:
        return "mypaste"

    def get_base_url(self) -> str:
        return "https://mypaste.com"

# Register it
SecPasteClient.register_provider('mypaste', MyPastebinProvider)

# Use it
client = SecPasteClient(provider='mypaste')

Project Structure

secpaste/
├── crypto/
│   ├── base.py           # Abstract cipher interface
│   ├── aes.py            # AES-256-GCM implementation
│   ├── chacha.py         # ChaCha20-Poly1305 implementation
│   └── pqc.py            # Kyber + AES (post-quantum)
├── providers/
│   ├── base.py           # Abstract provider interface
│   └── dpaste.py         # dpaste.com implementation
├── client.py             # Main SecPaste client API
└── cli.py                # Command-line interface

Security Considerations

• Server trust: The pastebin server cannot read your content (it's encrypted), but it can:

  • See paste metadata (size, IP, timing)
  • Deny service or delete pastes
  • Serve malicious JavaScript (if viewing in browser)

• URL security: The encryption key is in the URL fragment (#key):

  • Never logged in server access logs
  • Not sent in HTTP Referer headers
  • But visible in browser history and can be leaked via client-side tracking

• Key size: Larger keys (like Kyber) may hit browser URL length limits

• No authentication: Anyone with the URL can decrypt the content

Dependencies

• cryptography: For AES-256-GCM and ChaCha20-Poly1305
• requests: For HTTP API calls
• liboqs-python (optional): For post-quantum Kyber support

License

MIT License - feel free to use, modify, and distribute.

Contributing

PRs welcome! Areas for contribution:

• Additional pastebin providers (pastebin.com, termbin, privatebin, etc.)
• Additional cipher backends
• Better error handling
• Tests
• Browser extension

Similar Projects

• PrivateBin: Full web application with similar security model
• Magic Wormhole: Secure file transfer with PAKE
• Age: Modern file encryption tool

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Reminder: Never paste truly sensitive data (passwords, private keys) to public pastebins, even encrypted. Use proper secret management tools for production credentials.