XCrypto: a cryptographic ISE for RISC-V

[coderman]

https://github.com/scarv/xcrypto

XCrypto: a cryptographic ISE for RISC-V

[Build Status](https://travis-ci.com/scarv/xcrypto) [Documentation](https://codedocs.xyz/scarv/xcrypto)

Acting as a component part of the wider [SCARV](https://www.scarv.org) project, XCrypto is a general-purpose Instruction Set Extension (ISE) for [RISC-V](https://riscv.org) that supports software-based cryptographic workloads.

Overview

A given cryptographic workload is commonly expected to satisfy a challenging and diverse range of traditional design metrics, including some combination of high-throughput, low-latency, low-footprint, power-efficiency, and high-assurance, while executing in what is potentially an adversarial environment. A large design space of options can be drawn from when developing a concrete implementation: these options span a spectrum, between those entirely based on hardware (e.g., a dedicated IP core) and those entirely based on software. ISEs can be viewed as representing a hybrid option, in the sense they alter a general-purpose processor core with special-purpose hardware and associated instructions; such targeted alterations then help to improve a software-based implementation wrt. some design metric (e.g., latency).

As an ISE, we pitch XCrypto as a solution (vs. the solution) within the wider design space of options. For example, it offers as an alternative to the solution being proposed by the RISC-V cryptography extensions group (see, e.g., their [presentation](https://www.youtube.com/watch?v=dcW6a7SO2zE): the design extends the RISC-V vector ISE). The idea is to leverage extensive existing literature and hence experience wrt. cryptographic ISEs (see, e.g., published work at the [CHES](https://dblp.uni-trier.de/db/conf/ches) conference), translating and applying it to RISC-V. Although potentially less performant than alternatives, we expect implementations using XCrypto to be more lightweight and flexible; as a result, we view it as representing an attractive solution in the context of micro-controller class cores.

Organisation

├── bin                    - scripts (e.g., environment configuration)
├── build                  - working directory for build
├── doc                    - documentation
├── extern                 - external resources (e.g., submodules)
│   ├── libscarv             - submodule: scarv/libscarv
│   ├── riscv-opcodes        - submodule: scarv/riscv-opcodes
│   ├── texmf                - submodule: scarv/texmf
│   └── wiki                 - submodule: scarv/xcrypto.wiki
├── pdf                    - PDFs, e.g., presentation slides
├── rtl                    - source code for re-usable hardware modules
└── src
    ├── docker             - source code for containers
    ├── helloworld         - source code for example program
    ├── test               - source code for test    program(s)
    └── toolchain          - source code for tool-chain

Note that:

-

[${REPO_HOME}/doc](https://github.com/scarv/xcrypto/blob/master/doc) houses the XCrypto specification: this document captures the ISE itself, acting as both a) a definition of additional architectural state (e.g., register file and CSRs) and instructions (i.e., their semantics and encoding), and b) a design document. Pre-built versions accompany each [releases](https://github.com/scarv/xcrypto/releases) of XCrypto.

-

[${REPO_HOME}/rtl](https://github.com/scarv/xcrypto/blob/master/rtl) houses a library of re-usable hardware components (e.g., for arithmetic operations), which could be used in an implementation of XCrypto.

-

Per the above, the content of this repository is non-specific to an implementation of XCrypto within any given processor core. That said, the associated repository [scarv/scarv](https://github.com/scarv/scarv) specifically houses such an implementation: the SCARV processor core (and associated SoC) offer an integrated implementation of components from the entire SCARV project, XCrypto included.

Quickstart (with more detail in the [wiki](https://github.com/scarv/xcrypto/wiki))

-

Execute

git clone
https://github.com/scarv/xcrypto.git
./xcrypto

cd

./xcrypto
git submodule update --init --recursive

source

./bin/conf.sh

to clone and initialise the repository, then configure the environment; for example, you should find that the REPO_HOME environment variable is set appropriately.

-

Use targets in the top-level Makefile to drive a set of common tasks, e.g.,

Command	Description
make build-doc
build the [LaTeX](https://www.latex-project.org)-based documentation
make clone-toolchain
clone the [tool-chain](https://github.com/scarv/xcrypto/wiki/Toolchain)

make build-toolchain
build the [tool-chain](https://github.com/scarv/xcrypto/wiki/Toolchain)

make doxygen
build the [Doxygen](http://www.doxygen.nl)-based documentation
make spotless
remove everything built in ${REPO_HOME}/build

Questions?

- read the [wiki](https://github.com/scarv/xcrypto/wiki),
- raise an [issue](https://github.com/scarv/xcrypto/issues),
- raise a [pull request](https://github.com/scarv/xcrypto/pulls),
- drop us an [email](mailto:info at scarv.org?subject=xcrypto).

Publications and presentations

- Some [slides](https://github.com/scarv/xcrypto/blob/master/pdf/riscv-meetup-bristol-slides.pdf) presented at the [RISC-V meetup](https://www.meetup.com/Bristol-RISC-V-Meetup-Group) in Bristol, April 2019.
- A [poster](https://github.com/scarv/xcrypto/blob/master/pdf/zurich-workshop-poster.pdf) presented at the [RISC-V Workshop](https://riscv.org/2019/06/risc-v-workshop-zurich-proceedings) in Zurich, June 2019.

Acknowledgements

This work has been supported in part by EPSRC via grant [EP/R012288/1](https://gow.epsrc.ukri.org/NGBOViewGrant.aspx?GrantRef=EP/R012288/1) (under the [RISE](http://www.ukrise.org) programme).
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