Keccak256
The OpenVM Keccak256 extension provides tools for using the Keccak-256 hash function.
The functional part is provided by the openvm-keccak-guest
crate, which is a guest library that can be used in any OpenVM program.
Functions for guest code
The OpenVM Keccak256 Guest extension provides two functions for using in your guest code:
keccak256(input: &[u8]) -> [u8; 32]
: Computes the Keccak-256 hash of the input data and returns it as an array of 32 bytes.set_keccak256(input: &[u8], output: &mut [u8; 32])
: Sets the output to the Keccak-256 hash of the input data into the provided output buffer.
See the full example here.
Example
use alloc::vec::Vec;
use core::hint::black_box;
use hex::FromHex;
use openvm_keccak256_guest::keccak256;
openvm::entry!(main);
pub fn main() {
let test_vectors = [
(
"",
"C5D2460186F7233C927E7DB2DCC703C0E500B653CA82273B7BFAD8045D85A470",
),
(
"CC",
"EEAD6DBFC7340A56CAEDC044696A168870549A6A7F6F56961E84A54BD9970B8A",
),
];
for (input, expected_output) in test_vectors.iter() {
let input = Vec::from_hex(input).unwrap();
let expected_output = Vec::from_hex(expected_output).unwrap();
let output = keccak256(&black_box(input));
if output != *expected_output {
panic!();
}
}
}
To be able to import the keccak256
function, add the following to your Cargo.toml
file:
openvm-keccak256-guest = { git = "https://github.com/openvm-org/openvm.git" }
hex = { version = "0.4.3", default-features = false, features = ["alloc"] }
External Linking
The keccak guest extension also provides another way to use the keccak-256 intrinsic implementation. It provides a function that is meant to be linked to other external libraries. The external libraries can use this function as a hook for the keccak-256 intrinsic. This is enabled only when the target is zkvm
.
native_keccak256(input: *const u8, len: usize, output: *mut u8)
: This function hasC
ABI. It takes in a pointer to the input, the length of the input, and a pointer to the output buffer.
In the external library, you can do the following:
#![allow(unused)] fn main() { extern "C" { fn native_keccak256(input: *const u8, len: usize, output: *mut u8); } fn keccak256(input: &[u8]) -> [u8; 32] { #[cfg(target_os = "zkvm")] { let mut output = [0u8; 32]; unsafe { native_keccak256(input.as_ptr(), input.len(), output.as_mut_ptr() as *mut u8); } output } #[cfg(not(target_os = "zkvm"))] { // Regular Keccak-256 implementation } } }
Config parameters
For the guest program to build successfully add the following to your .toml
file:
[app_vm_config.keccak]