@nori-zk/proof-conversion/build/src/plonk/fiat-shamir/sha_to_fr.js

Verifying zkVM proofs inside o1js circuits, to generate Mina compatible proof

import { Bool, Provable } from 'o1js';
import { FrC, FrU } from '../../towers/index.js';
export function shaToFr(hashDigest) {
    let fields = hashDigest.toFields();
    const shaBitRepr = [];
    let bit255 = Bool(false);
    let bit256 = Bool(false);
    for (let i = 31; i >= 0; i--) {
        const bits = fields[i].toBits();
        for (let j = 0; j < 8; j++) {
            // we skip last 2 bits
            if (i == 0 && j == 6) {
                bit255 = bits[j];
            }
            else if (i == 0 && j == 7) {
                bit256 = bits[j];
            }
            else {
                shaBitRepr.push(bits[j]);
            }
        }
    }
    const sh254 = FrC.from(7059779437489773633646340506914701874769131765994106666166191815402473914367n); // 2^254 % r
    const sh255 = FrC.from(14119558874979547267292681013829403749538263531988213332332383630804947828734n); // 2^255 % r
    let x = FrU.fromBits(shaBitRepr);
    const a = Provable.if(bit255.equals(Bool(true)), FrC.provable, sh254, FrC.from(0n));
    const b = Provable.if(bit256.equals(Bool(true)), FrC.provable, sh255, FrC.from(0n));
    const res = x.add(a).add(b).assertCanonical();
    return res;
}
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