CROSS - Cryptographic Signature Scheme

CROSS is an asymmetric signature scheme based on the Rank Syndrome Decoding (RSD) problem, submitted to the NIST Post-Quantum Cryptography standardization process.

Original Authors

This implementation is authored by:

• Alessandro Barenghi alessandro.barenghi@polimi.it
• Marco Gianvecchio marco.gianvecchio@mail.polimi.it
• Patrick Karl patrick.karl@tum.de
• Gerardo Pelosi gerardo.pelosi@polimi.it
• Jonas Schupp jonas.schupp@tum.de

The code is hereby placed in the public domain.

Project Structure

• Reference_Implementation/ - Portable C11 reference implementation
• Optimized_Implementation/ - AVX2 optimized implementation
• Unified_Implementation/ - Runtime dispatch between ref/opt
• KAT/ - Known Answer Test vectors
• Additional_Implementations/ - Benchmarking and KAT generation tools

Quick Start

# Build everything (reference + optimized + test)
make all

# Run tests
./cross_test

# Build with custom parameters
make all CATEGORY=3 VARIANT=RSDPG TARGET=SPEED

Build Options

Parameter	Options	Default
CATEGORY	1, 3, 5	1
VARIANT	RSDP, RSDPG	RSDP
TARGET	BALANCED, SPEED, SIG_SIZE	BALANCED

Usage

# Libraries
make ref          # libcross_ref.a
make opt          # libcross_opt.a

# Test binary
make test         # uses reference by default
make test IMPL=opt  # uses optimized

# Custom build
make all CATEGORY=5 VARIANT=RSDPG TARGET=SIG_SIZE

# Clean
make clean

API

Link against libcross_ref.a or libcross_opt.a and provide:

void randombytes(unsigned char *x, unsigned long long xlen);

int crypto_sign_keypair(unsigned char *pk, unsigned char *sk);
int crypto_sign(unsigned char *sm, unsigned long long *smlen, 
                const unsigned char *m, unsigned long long mlen, 
                const unsigned char *sk);
int crypto_sign_open(unsigned char *m, unsigned long long *mlen, 
                    const unsigned char *sm, unsigned long long smlen, 
                    const unsigned char *pk);

Contributions & Fixes

This repository includes the following enhancements:

• Build System: Simplified single Makefile replacing complex CMake setup
• Documentation: Updated build instructions for easier project setup
• Fixed Include Paths: Resolved header inclusion order issues between implementations
• Unified Implementation: Runtime CPU feature detection (AVX2/SSE4.1) with automatic selection between Reference and Optimized implementations
• Namespacing: CROSS_namespace.h strategy allowing both implementations to coexist

License

Public domain. See LICENSE file.