Function light_utils::truncate_to_circuit

pub fn truncate_to_circuit(bytes: &[u8; 32]) -> [u8; 32]

Truncates the given 32-byte array, replacing the least important element with 0, making it fit into Fr modulo field.

Safety

This function is used mostly for truncating hashes (i.e. SHA-256) which are not constrainted by any modulo space. At the same time, we can’t (yet) use any ZK-friendly function in one transaction. Truncating hashes to 31 should be generally safe, but please make sure that it’s appropriate in your case.

Examples

use light_utils::truncate_to_circuit;

let original: [u8; 32] = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15,
                           16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28,
                           29, 30, 31, 32];
let truncated: [u8; 32] = truncate_to_circuit(&original);
assert_eq!(truncated, [0, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17,
                       18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32]);