0802d6c021
The kernel is hashed using a Keccak based sponge for now. We could switch to Poseidon later if our kernel grows too large. Note that we use simple zero-padding (pad0*) instead of the standard pad10* rule. It's simpler, and we don't care that the prover can add extra 0s at the end of the code. The program counter can never reach those bytes, and even if it could, they'd be 0 anyway given the EVM's zero-initialization rule. In one CPU row, we can do a whole Keccak hash (via the CTL), absorbing 136 bytes. But we can't actually bootstrap that many bytes of kernel code in one row, because we're also limited by memory bandwidth. Currently we can write 4 bytes of the kernel to memory in one row. So we treat the `keccak_input_limbs` columns as a buffer. We gradually fill up this buffer, 4 bytes (one `u32` word) at a time. Every `136 / 4 = 34` rows, the buffer will be full, so at that point we activate the Keccak CTL to absorb the buffer.
Plonky2
Plonky2 is a SNARK implementation based on techniques from PLONK and FRI. It is the successor of Plonky, which was based on PLONK and Halo.
Plonky2 is built for speed, and features a highly efficient recursive circuit. On a Macbook Pro, recursive proofs can be generated in about 170 ms.
Documentation
For more details about the Plonky2 argument system, see this writeup.
Building
Plonky2 requires a recent nightly toolchain, although we plan to transition to stable in the future.
To use a nightly toolchain for Plonky2 by default, you can run
rustup override set nightly
in the Plonky2 directory.
Running
To see recursion performance, one can run this bench, which generates a chain of three recursion proofs:
RUSTFLAGS=-Ctarget-cpu=native cargo run --release --example bench_recursion -- -vv
Jemalloc
Plonky2 prefers the Jemalloc memory allocator due to its superior performance. To use it, include jemallocator = "0.3.2" inCargo.tomland add the following lines
to your main.rs:
use jemallocator::Jemalloc;
#[global_allocator]
static GLOBAL: Jemalloc = Jemalloc;
Jemalloc is known to cause crashes when a binary compiled for x86 is run on an Apple silicon-based Mac under Rosetta 2. If you are experiencing crashes on your Apple silicon Mac, run rustc --print target-libdir. The output should contain aarch64-apple-darwin. If the output contains x86_64-apple-darwin, then you are running the Rust toolchain for x86; we recommend switching to the native ARM version.
Copyright
Plonky2 was developed by Polygon Zero (formerly Mir). While we plan to adopt an open source license, we haven't selected one yet, so all rights are reserved for the time being. Please reach out to us if you have thoughts on licensing.
Disclaimer
This code has not yet been audited, and should not be used in any production systems.