117 lines
4.1 KiB
Markdown
117 lines
4.1 KiB
Markdown
# c-kzg - work in progress
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The very beginnings of a simple implementation of [KZG commitments](https://dankradfeist.de/ethereum/2020/06/16/kate-polynomial-commitments.html) in C, using the [Blst library](https://github.com/supranational/blst) from Supranational for field and curve operations.
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Initially, at least, this largely follows the [go-kzg](https://github.com/protolambda/go-kzg) implementation.
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Done so far:
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- FFT and inverse FFT over the finite field.
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- FFTs over the G1 group
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- Polynomial single commitment and verification
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- Polynomial multi commitment and verification
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- [FK20](https://github.com/khovratovich/Kate/blob/master/Kate_amortized.pdf) single proof method (normal, and optimised for data availability)
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- FK20 multi proof method (normal, and optimised for data availability)
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- Polynomial extension for data availability sampling
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- Calculation of zero polynomials
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- Data recovery from samples
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That's basically all the necessary stuff for Eth2 use cases. Things remaining (aside from tidying up, which is never ending):
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- [ ] Document the underlying mathematics to help with checking correctness of the implementation and writing better tests
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- [ ] End-to-end tests
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- [ ] Performance tuning
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- [ ] Robustness checking (don't crash on errors; return the correct error codes; no buffer overflows)
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- [x] Java interface: see [jc-kzg](https://github.com/Nashatyrev/jc-kzg)
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- [ ] (Optional) Use alternative back-end libraries to Blst (e.g. [Herumi mcl](https://github.com/herumi/mcl))
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- [ ] Nice build process
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- [ ] Make it portable
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## Install
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Build the [Blst library](https://github.com/supranational/blst) following the instructions there. Then,
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1. Copy the resulting `libblst.a` file into the `lib/` directory here.
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2. From Blst's `bindings/` directory copy `blst.h` and `blst_aux.h` to `inc/`
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That is,
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```
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cp ../blst/libblast.a lib/
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cp ../blst/bindings/*.h inc/
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```
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## Build
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Build the `libckzg.a` library:
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```
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cd src
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make lib
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```
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Build a debug version that aborts on error conditions and attempts to print some helpful info (file, line number, condition that failed):
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```
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cd src
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make debuglib
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```
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## Run tests
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```
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cd src
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make test
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```
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Unit tests for an individual file can be built and run with `make fft_fr_test` for example. Once a test runner such as *fft_fr_test* has been built, individual unit tests can be run with `./fft_fr_test <test-name>`.
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Thanks to [Acutest](https://github.com/mity/acutest) for the unit test harness, which is used here under the MIT licence.
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## Run benchmarks
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This will run all available benchmarks, for the default one second per test size:
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```
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cd src
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make bench
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```
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You can run individual benchmarks, and optionally specify how long (in seconds) to run each test size:
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```
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make fft_fr_bench
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./fft_fr_bench 5
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```
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Doing `make clean` should resolve any weird build issues.
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## Make debug builds of the tests
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The default build is designed not to crash on errors, and will (should) return fairly coarse error codes for any issue. This is good for a utility library, but unhelpful for debugging. The `-DDEBUG` compiler flag builds a version such that any assertion failure aborts the run and outputs file and line info. This is much more useful for tracking down deeply buried errors.
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Each test suite can be compiled into its debug version. For example, as follows:
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```
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make fk20_proofs_test_debug
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./fk20_proofs_test_debug fk_single_strided
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```
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This magic is implemented via the `CHECK` and `TRY` macros in _c_kzg.h_.
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## Make documentation
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`doxygen` style comments are in place throughout, although some places need more work. Build the docs in the top directory as follows:
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```
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doxygen Doxyfile
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```
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This will produce a _doc/html_ directory. Visit the _doc/html/files.html_ file in a browser to view the documentation.
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## Prerequisites
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- Blst library (see above)
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- `clang` compiler. I'm using Clang 10.0.0. I'll likely add `gcc` options in future.
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- The Makefile is GNU make compatible.
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- I'm developing on Ubuntu 20.04. Will check portability later.
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- [Doxygen](https://www.doxygen.nl/index.html) for building the documentation. I'm using v1.8.17 right now.
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