C-sigma: Easy-to-use Sigma proofs in C using libsodium

Summary

Sigma Protocols Implementation in C A clean, simple C implementation of Sigma protocols with Fiat-Shamir transformation for non-interactive zero-knowledge proofs. Features Schnorr Protocol: Prove knowledge of discrete logarithm Chaum-Pedersen Protocol: Prove discrete logarithm equality (DLEQ) Non-interactive proofs: Using Fiat-Shamir transformation with SHAKE128 Minimal API: Just 6 functions for complete functionality No abstractions: Direct use of byte arrays, no wrapper types Secure: Built on libsodium's Ristretto255 group operations Quick Start #include "sigma.h" // Initialize sigma_init (); // Prove knowledge of private key uint8_t private_key [ 32 ], public_key [ 32 ], proof [ 64 ]; crypto_core_ristretto255_scalar_random ( private_key ); crypto_scalarmult_ristretto255_base ( public_key , private_key ); schnorr_prove ( proof , private_key , public_key , message , message_len ); bool valid = schnorr_verify ( proof , public_key , message , message_len ); Building Prerequisites: C compiler (clang or gcc) libsodium development libraries # Install libsodium (Ubuntu/Debian) sudo apt-get install libsodium-dev # Install libsodium (macOS) brew install libsodium # Build make # Run tests ./test # Run examples ./example API Reference Initialization int sigma_init ( void ); Initialize the library (wraps sodium_init). Schnorr Protocol Proves knowledge of x where Y = x*G (G is the generator). // Create proof int schnorr_prove ( uint8_t proof [ 64 ], // Output: 64-byte proof const uint8_t witness [ 32 ], // Secret x const uint8_t public_key [ 32 ], // Public Y = x*G const uint8_t * message , // Message to bind size_t message_len ); // Verify proof bool schnorr_verify ( const uint8_t proof [ 64 ], const uint8_t public_key [ 32 ], const uint8_t * message , size_t message_len ); Chaum-Pedersen Protocol Proves that log_g1(h1) = log_g2(h2) without revealing the exponent. // Create proof int chaum_pedersen_prove ( uint8_t proof [ 96 ], // Output: 96-byte proof const uint8_t witness [...