Google win price decrypter typescript version

decrypt_price.ts

function base64AddPadding(str: string) {
  return str + Array((4 - str.length % 4) % 4 + 1).join('=');
}

// should set your encryption, integrity key
const e_key = Buffer.from([0x00, ...]);
const i_key = Buffer.from([0x00, ...]);

// https://developers.google.com/authorized-buyers/rtb/response-guide/decrypt-price
// https://github.com/google/openrtb-doubleclick/blob/master/doubleclick-core/src/main/java/com/google/doubleclick/crypto/DoubleClickCrypto.java
const decodeWinPriceFromGoogle = (win_price: string): number => {
  if (win_price.length != 38) throw new Error('[INVALID_GOOGLE_WIN_PRICE_LENGTH] ' + win_price);

  // Base64 padding characters are omitted.
  // Add any required base64 padding (= or ==).
  const win_price_valid_base64 = base64AddPadding(win_price);

  // Web-safe decode, then base64 decode.
  const websafe_encoded = win_price_valid_base64.replace('-', '+').replace('_', '/');

  // enc_price := initVector(16 bytes) || E(payload)(8 bytes) || I(signature)(4 bytes)
  const enc_price = Buffer.from(websafe_encoded, 'base64');

  // Message is decoded but remains encrypted.
  // Split up according to fixed lengths.
  const iv = enc_price.slice(0, 16);
  const price_pad = crypto.createHmac('sha1', e_key).update(iv).digest();
  for (let i = 0; i < 8; ++i) {
    enc_price[16 + i] ^= price_pad[i];
  }

  const sig = enc_price.readUInt32BE(24);
  const conf_sig = crypto.createHmac('sha1', i_key)
    .update(enc_price.slice(16, 24))
    .update(iv)
    .digest()
    .readUInt32BE(0);

  const success = (conf_sig === sig);
  if (success) {
    // win_price is CPI https://support.google.com/authorizedbuyers/answer/3187591?hl=en
    const decoded_win_price = parseInt(enc_price.slice(16, 24).toString('hex'), 16) / 1000;
    return decoded_win_price;
  } else {
    throw new Error('[INVALID_GOOGLE_WIN_PRICE] ' + win_price);
  }
};