blst_src/

All files in this folder contain source files copied from the BLST repo https://github.com/supranational/blst, specifically from the tagged version v0.3.14.

Copyright Supranational LLC Licensed under the Apache License, Version 2.0, see LICENSE for details. SPDX-License-Identifier: Apache-2.0

While BLST exports multiple functions and tools, the implementation in Flow crypto requires access to low level BLS12-381 curve functions. Some of these tools are not exported by BLST, others we want to use without paying for the cgo cost, and therefore without using the Go bindings in BLST.

Higher level protocols are all implemented within Flow crypto and are not using BLST source. Only the BLS12-381 curve implementation from BLST is used to benfit from its high performance. All code outisde of ../blst_src and ../internal/blst is not code re-used from BLST source.

The folder contains:

• BLST LICENSE file
• all <blst>/src/*.c and <blst>/src/*.h files (C source files) but server.c.
• server.c is replaced by ./blst_src.c (which lists only the files needed by Flow crypto).
• all <blst>/build (assembly generated files).
• this README file.

To upgrade the BLST version:

• audit all BLST updates, with focus on <blst>/src: https://github.com/supranational/blst/compare/v0.3.14...<new_version>
• delete all files in this folder ./blst_src/ but blst_src.c and README.md.
• delete all files in ./internal/blst/ but non_cgo.go.
• open BLST repository on the new version.
• copy all .c and .h files from <blst>/src/ into ./blst_src/.
• delete newly copied ./blst_src/server.c.
• copy the folder <blst>/build/ into ./blst_src.
• copy <blst>/bindings/blst.h, <blst>/bindings/blst_aux.h, and <blst>/bindings/go/blst.go into ./internal/blst/..
• check that C flags in ./bls12381_utils.go still include the C flags in <blst>/bindings/go/blst.go.
• update ./blst_src/blst_src.c if needed.
• solve all breaking changes that may occur.
• update the commit version on this current file ./blst_src/README.

Note that Flow crypto is using non exported internal functions from BLST. Checking for interfaces breaking changes in BLST should be done along auditing changes between the old and new versions. This includes checking logical changes and assumptions beyond interfaces, and assessing their security and performance impact on protocols implemented in Flow crypto.