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README.md

User Guide

Introduction

This repository contains firmware for SPECT - Secure Processor of Elliptic Curves for Tropic. SPECT is a 256-bit processor with custom ISA and hardware accelerated arithmetic in finite fields. Algorithms like ECDSA, EdDSA and X25519 are implemented in firmware. This firmware is developed and debugged using spect_iss - Instruction Set Simulator of SPECTs ISA, available in spect_compiler repository. An executable application loads the SPECT firmware together with other configuration, like random numbers to simulate external RNG on the chip.

The spect_iss allows to write to SPECTs input memory and read from SPECTs output memory to simulate communication with host CPU (in case of Tropic01 the RISC-V CPU).

SPECTs ISA contains GRV instruction, that requests 256 bit random number from external RNG. These numbers has to be preloaded to the spect_iss before start of firmware execution by prepared hexfile. Otherwise the RNG will always return zero. The prepared flow ensures that this condition is fulfilled.

Flow

The goal of this flow is to shield the user from all implementation details of SPECTs firmware as well as the correct configuration of spect_compiler and spect_isa. It allows to configure input values of particular cryptographic algorithm as well as force mask values used for side-channel countermeasures via YAML configuration file.

Python Scripts

Python scripts are used to configure spect_iss with all operation config word, input data and random numbers and run spect_iss with prepared SPECT firmware. The input data and random numbers are configured by YAML file <sript name>_data_cfg.yml. To run the script, simply run

./<script name>.py

Configuration YAML File

To configure input data and random numbers used for masking and randomization, use the prepared <sript name>_data_cfg.yml. Structure of such YAML file is following:

input : (mandatory)
  - name : <name of input variable> (string)
    value : <value of the input variable> (string or integer)
  ...
rng : (optional)
  - name : <name of random number> (string)
    value : <value of the random number> (integer)
  ...

The rng field is used to force masks used in the particular algorithm. The name of the random number refer to particular mask, e.g. mask for group randomization of scalar. The python script then ensures that the masks are delivered to spect_iss in right order. If the rng field is not specified or some particular mask is not specified, the script then generates random number instate.

Log Files

Log files are dumped into <run dir>/logs directory.

  • iss_cmd : cmd file for iss generated by the python script
  • rng.hex : hexfile generated by the python script, that contains the random numbers to be pushed into the GRV queue of spect_iss
  • <script name>_iss.log : log file of the spect_iss run, that contains all of its actions (compilation, instruction execution details etc.)
  • <script name>_out.hex : hexfile with contents of the output memory.

Other

Some masks used for side channel hardening must not be zero (e.g. z-coordinate randomization). Firmware detects such a case and requests another random number. In such a case, the python script checks, if for the particular mask zero value is allowed, and if not, generates alternative mask for the second request from firmware. Again, the python script ensures that the masks are delivered to spect_iss in right order.