Fiat-Crypto: Synthesizing Correct-by-Construction Code for Cryptographic Primitives

Build Requirements

This repository requires:

• To build the proofs and almost-C-like outputs: Coq 8.7 (tested with 8.7.0)

To build (if your COQPATH variable is empty):

make

To build:

export COQPATH="$(pwd)/coqprime${COQPATH:+:}$COQPATH"
make

To build a representative subset, instead of make, run

    make selected-specific-display non-specific

The core library (target nonautogenerated-specific-display non-specific) is expected to build within about one hour (in serial, on a particularly fast machine), within about 3.5--4 GB of RAM, plus an additional 1-5 minutes to run coqdep on all of our files. Of the additional curves, 90% finish within 5 minutes per file, and 99% finish within 15 minutes per file (though some take upwards of 50 GB of RAM). These 99% of curves together take about 60 hours.

• To build the C outputs: Python (2 or 3)

To build:

    make c

or, for a representative subset,

    make selected-c

• To build and run the binaries, gcc (7.1.2; or 7.1.1 with -fno-peephole2) or clang of a new enough version to support the appropriate compiler intrinsics.

To build and run:

    make test bench

or, for a representative subset,

    make selected-test selected-bench

Exploring the code

Push-button synthesis

To add a new prime, add a new line to primes.txt with your prime. Then run

    ./generate_parameters.py; ./src/Specific/CurveParameters/remake_curves.sh

You will see a bunch of lines starting with git add; any .v files that show up in these lines must be added to _CoqProject. (If you are working in the git repository, you may simply run the git add lines, and then run make update-_CoqProject.) Note that the directory structure involves a textual representation of your prime, call it ${REPRESENTATION_OF_YOUR_PRIME}. To build, you can run

    make src/Specific/{montgomery,solinas}{32,64}_${REPRESENTATION_OF_YOUR_PRIME}/fibe

This will build all the necessary .vo and .c files, as well as the fibe binary, which is automatically run when you make bench or make test.

Curve Correctness Theorems

Specifications live in src/Spec, e.g., src/Spec/Ed25519.v. Some selected cuve-level proofs live in

• src/Curves/Edwards/AffineProofs.v,
• src/Curves/Edwards/XYZT/Basic.v,
• src/Curves/Montgomery/AffineProofs.v,
• src/Curves/Montgomery/XZProofs.v.

Arithmetic Core

Generic mathematical optimization strategies live in src/Arithmetic. Good examples include

• src/Arithmetic/Core.v,
• src/Arithmetic/Karatsuba.v,
• src/Arithmetic/Saturated/Core.v,
• src/Arithmetic/BarrettReduction/HAC.v,
• src/Arithmetic/MontgomeryReduction/Definition.v,
• src/Arithmetic/MontgomeryReduction/WordByWord/Abstract/Definition.v.

Demo of Synthesis

The idea of the synthesis process is demoed in src/Demo.v.

Actual Synthesis

• The curve-non-specific synthesis framework lives in src/Compilers/Z/Bounds/Pipeline.
• The API for the reflective simplification and bounds analysis pipeline is in src/Compilers/Z/Bounds/Pipeline.v.
• The definition of the pipeline and the correctness proof are in src/Compilers/Z/Bounds/Pipeline/Definition.v.
• Generic reflective syntax trees are defined in src/Compilers/Syntax.v; the specialization to the arithmetic operations on Z that we use occurs in src/Compilers/Z/Syntax.v.
• The trusted pretty-printer lives in src/Compilers/Z/CNotations.v and src/Compilers/Z/HexNotationConstants.v, which were generated by the couple-hundred-line Python scripts in a comment near the top of each file.
• The core of the bounds-analysis transformation lives in src/Compilers/Z/Bounds/Interpretation.v; the corresponding proofs live in src/Compilers/Z/Bounds/InterpretationLemmas, and the instantation of the bounds-analysis transformation with the core lives in src/Compilers/Z/Bounds/MapCastByDeBruijn.v.

The curve-specific synthesis framework lives in src/Specific/Framework.

• The input .json files live in src/Specific/CurveParameters, and the processor for those files lives in src/Specific/Framework/make_curve.py.
• The record of curve specific parameters is defined in src/Specific/Framework/RawCurveParameters.v, and defaults are filled in src/Specific/Framework/CurveParameters.v.
• The tactics that specialize the various arithmetic optimizations to specific curves live in src/Specific/Framework/ArithmeticSynthesis, e.g., src/Specific/Framework/ArithmeticSynthesis/Montgomery.v.
• The script at src/Specific/Framework/ArithmeticSynthesis/remake_packages.py processes these files to add relevant boilerplate, and gets run after significantly changing an optimization, or after adding a new optimization.
• The synthesis tactics are assembled in src/Specific/Framework/SynthesisFramework.v.
  Note that magic¹ is used to create identifiers refering to the curve-specific parameters, from tactics, so that they can be used in other curve-specific files.

Example Output

The c output lives in the various subfolders of src/Specific. For example, C-like code for X25519 multiplication on 64-bit machines lives in src/Specific/X25519/C64/femulDisplay.log, which is generated from src/Specific/X25519/C64/femulDisplay.v, which in turn uses synthesis run in src/Specific/X25519/C64/femul.v. The c target turns this into src/Specific/X25519/C64/femul.c.

Footnotes

¹ This magic comes in the form of calls to transparent_abstract, packaged up in some tactics in src/Util/Tactics/CacheTerm.v.