folding/fold-simulation.js

#!/usr/bin/env node
/**
 * Illustrative-only simulation of the IVC "folding" pattern used in
 * recursive proof systems like Nova. This is NOT real folding-scheme
 * cryptography (no algebraic relaxed-R1CS folding, no soundness proof) —
 * it exists only to show the shape of the pattern: one small accumulator
 * value that represents the validity of an arbitrarily long chain of
 * prior steps, so verification cost never grows.
 *
 * See docs/features/01-recursive-proof-folding.md for the real design
 * and honest caveats.
 */
const crypto = require("crypto");

function hash(...parts) {
  return crypto.createHash("sha256").update(parts.join("|")).digest("hex");
}

/**
 * foldStep absorbs a new compliance-check result into the running
 * accumulator. In a real folding scheme this would combine two NP
 * instances (the running instance and the new step) into one new
 * instance via random linear combination over a curve; here we just
 * hash them together to illustrate "constant-size running state."
 */
function foldStep(runningAccumulator, stepWitness) {
  return hash(runningAccumulator, stepWitness);
}

function demo() {
  let accumulator = hash("GENESIS");
  const steps = [
    "tx1:sanctions_clear+kyc_tier_1+within_limit",
    "tx2:sanctions_clear+kyc_tier_1+within_limit",
    "tx3:sanctions_clear+kyc_tier_1+within_limit",
    "tx4:sanctions_clear+kyc_tier_1+within_limit",
  ];

  for (const step of steps) {
    accumulator = foldStep(accumulator, step);
    console.log(`Folded step "${step}" -> accumulator ${accumulator.slice(0, 16)}...`);
  }

  console.log(
    `\nFinal accumulator after ${steps.length} steps: ${accumulator}`,
  );
  console.log(
    "In a real IVC/folding scheme, verifying this final value costs the",
    "same as verifying a single step, regardless of chain length — that's",
    "the property worth implementing for real with a folding-scheme library.",
  );
}

if (require.main === module) {
  demo();
}

module.exports = { foldStep };