Keccak256

The Keccak256 extension guest provides functions that are meant to be linked to other external libraries. The external libraries can use these functions as hooks for the Keccak-256 intrinsics. This is enabled only when the target is zkvm.

We provide the following functions for the low-level Keccak sponge operations:

• native_xorin(buffer: *mut u8, input: *const u8, len: usize): XORs len input bytes into a state buffer in-place. len is constrained in-circuit to be a non-negative multiple of 4 and at most 136.
• native_keccakf(buffer: *mut u8): Applies the keccak-f[1600] permutation in-place on a 200-byte state buffer.

The openvm-keccak256 guest library builds on these to provide native_keccak256, a C ABI function that implements the full Keccak-256 hash:

• native_keccak256(input: *const u8, len: usize, output: *mut u8): Computes the Keccak-256 hash of len bytes at input and writes the 32-byte digest to output.

In the external library, you can do the following:

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]