KRONOS — Keccak RISC-V Optimized eNgine fOr haShing

Overview

Integration methodology can significantly affect the performance of dedicated hardware accelerators. This work explores this aspect using Keccak — a pivotal hashing standard in Post-Quantum Cryptography (PQC) — as a case study.

KRONOS presents three integration variants of the Keccak accelerator on the open-source 32-bit X-HEEP RISC-V SoC:

Variant	Branch	Interface	Description
Loosely coupled	loosely	Memory-mapped AXI peripheral	Accelerator accessed via load/store instructions
Tightly coupled	tightly	CV-X-IF (with extra register file)	Keccak state stored in a dedicated register file alongside the core
Coprocessor (ISE)	coprocessor	CV-X-IF (no extra register file)	Instruction Set Extension, Keccak state lives in the main register file

Results show that the tightly coupled approach is the most efficient integration method, achieving the best balance between resource consumption and throughput.

The reference publication for this work is:

Valeria Piscopo, Alessandra Dolmeta, Mattia Mirigaldi, Maurizio Martina, and Guido Masera. 2025. A Deep Dive into Integration Methodologies in RISC-V. In Proceedings of the 22nd ACM International Conference on Computing Frontiers: Workshops and Special Sessions (CF '25 Companion). Association for Computing Machinery, New York, NY, USA, 30–33. https://doi.org/10.1145/3706594.3726969

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Getting Started

Clone the repository and run the initial setup:

make mcu-gen
make x_heep-sync
make questasim-sim

Then build and run an application. The Makefile targets follow this pattern, where ACC selects the accelerator variant and VERSION selects the implementation version:

# Build the application
make app-$(ACC)-LWC-ASCON-$(VERSION) SCHEME=LWC ALG=ASCON VERSION=$(VERSION) ACC=$(ACC)

# Run the simulation
make run-$(ACC)-LWC-ASCON-$(VERSION) SCHEME=LWC ALG=ASCON VERSION=$(VERSION) ACC=$(ACC)

For example, to run the loosely coupled variant:

make app-loosely-LWC-ASCON-v1 SCHEME=LWC ALG=ASCON VERSION=v1 ACC=loosely
make run-loosely-LWC-ASCON-v1 SCHEME=LWC ALG=ASCON VERSION=v1 ACC=loosely

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Authors

• Alessandra Dolmeta
• Valeria Piscopo

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License

This project is licensed under the Apache License 2.0.

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Acknowledgement

This work is supported by the EU TRISTAN project with GA 101095947, which has received funding from the Chips Joint Undertaking and its members.