Developer platform & API infrastructure

import crypto from "node:crypto";

const TOLERANCE_SECONDS = 300;

export function verifyNovelSignature(
  rawBody: string,
  header: string,
  secret: string,
): boolean {
  const parts = new Map(
    header.split(",").map((pair) => {
      const [key, value] = pair.split("=");
      return [key ?? "", value ?? ""] as const;
    }),
  );

  const timestamp = Number(parts.get("t"));
  const signature = parts.get("v1");
  if (!Number.isFinite(timestamp) || signature === undefined) return false;

  // Reject replays before spending any time on the digest.
  const ageSeconds = Math.abs(Date.now() / 1000 - timestamp);
  if (ageSeconds > TOLERANCE_SECONDS) return false;

  const expected = crypto
    .createHmac("sha256", secret)
    .update(`${timestamp}.${rawBody}`)
    .digest("hex");

  const a = Buffer.from(expected, "utf8");
  const b = Buffer.from(signature, "utf8");
  if (a.length !== b.length) return false;

  // timingSafeEqual, not ===. String comparison leaks the prefix length.
  return crypto.timingSafeEqual(a, b);
}

import hashlib
import hmac
import time

TOLERANCE_SECONDS = 300


def verify_novel_signature(raw_body: bytes, header: str, secret: str) -> bool:
    parts = dict(
        pair.split("=", 1) for pair in header.split(",") if "=" in pair
    )

    try:
        timestamp = int(parts["t"])
        signature = parts["v1"]
    except (KeyError, ValueError):
        return False

    # Reject replays before spending any time on the digest.
    if abs(time.time() - timestamp) > TOLERANCE_SECONDS:
        return False

    signed_payload = f"{timestamp}.".encode() + raw_body
    expected = hmac.new(
        secret.encode(), signed_payload, hashlib.sha256
    ).hexdigest()

    # compare_digest, not ==. String comparison leaks the prefix length.
    return hmac.compare_digest(expected, signature)