Secure Spades

Secure Spades is a Rust cryptographic library providing the primitives required to build trustless card games.

The library implements cryptographic protocols developed and refined by Pascale Lafourcade and collaborators, based on the following research papers:

1. Practical Construction for Secure Trick-Taking Games Even With Cards Set Aside (2023)
2. Secure Trick-Taking Games (2019)

The goal of the library is to provide reusable, low-level cryptographic primitives while leaving the game-specific logic to the application using it.

Library Structure

cards

Defines the traits and utility functions required to implement custom card decks.

• Supports custom card representations
• Provides utilities for encoding cards as group elements
• Supports decks containing up to u16::MAX distinct cards

elgamal

Provides the structures and operations required for ElGamal encryption.

• Ciphertext representation
• Encryption and re-encryption
• Partial encryption and decryption utilities
• Card encryption helpers

group

Provides basic cryptographic group utilities.

• Ristretto group generator G
• Random scalar generation
• Group-related helper functions

keys

Defines key-related structures and utilities.

• KeyPair structure
• Secret and public key generation
• Generation of a shared/global public key from multiple participants

proof

Provides zero-knowledge proofs used by the protocols.

• Schnorr proofs
• Partial decryption proofs
• Proof generation
• Proof verification

shuffle

Provides the primitives required to securely shuffle encrypted cards.

• Encrypted deck shuffling
• Shuffle proof generation
• Shuffle proof verification
• Permutation validation

Cryptographic Properties

This implementation is based on the Ristretto group provided by curve25519-dalek.

The generator G is the RISTRETTO_BASEPOINT_POINT provided by the library.

Other cryptographic parameters and protocol details are based on the associated research papers.

Security Disclaimer

This implementation has not been externally audited and may contain bugs or security vulnerabilities.

While the library is intended as an implementation and demonstration of the protocols described in the referenced papers, no guarantee is made regarding its security or correctness.

This library should therefore not be used in security-critical or sensitive systems without a thorough independent security review and audit.

License

This project is licensed under the MIT License.

Copyright © 2026 Etienne Beard.

If you use or redistribute this project, please retain the original copyright notice and license.