Function getTelegramBackupIPFromBase64

Build/lib/get-telegram-backup-ip.ts:21–110

(base64: string)

`;

export function getTelegramBackupIPFromBase64(base64: string) {
  // 1. Check base64 size
  if (base64.length !== 344) {
    throw new TypeError('Invalid base64 length');
  }

  // 2. Filter to base64 and check length
  // Not needed with base64ToUint8Array, it has built-in base64-able checking

  // 3. Decode base64 to Buffer
  const decoded = base64ToUint8Array(base64);
  if (decoded.length !== 256) {
    throw new TypeError('Decoded buffer length is not 344 bytes, received ' + decoded.length);
  }

  // 4. RSA decrypt (public key, "decrypt signature" - usually means "verify and extract")
  // In Node.js, publicDecrypt is used for signature verification (Note that no padding is needed)
  const publicKey = crypto.createPublicKey(mtptoto_public_rsa);
  const decrypted = crypto.publicDecrypt(
    {
      key: publicKey,
      padding: crypto.constants.RSA_NO_PADDING
    },
    decoded
  );

  // 5. Extract AES key/iv and encrypted payload
  const key = decrypted.subarray(0, 32);
  const iv = decrypted.subarray(16, 32);
  const dataCbc = decrypted.subarray(32); // 224 bytes

  if (dataCbc.length !== 224) {
    throw new Error(`Invalid AES payload length: ${dataCbc.length}`);
  }

  // 6. AES-CBC decrypt
  const decipher = crypto.createDecipheriv('aes-256-cbc', key, iv);
  decipher.setAutoPadding(false);

  const decryptedCbc = concatUint8Arrays([decipher.update(dataCbc), decipher.final()]);

  if (decryptedCbc.length !== 224) {
    throw new Error(`Decrypted AES payload length is not 224 bytes, received ${decryptedCbc.length}`);
  }

  // 7. SHA256 check
  const currentHash = crypto
    .createHash('sha256')
    .update(decryptedCbc.subarray(0, 208))
    .digest()
    .subarray(0, 16);

  const expectedHash = decryptedCbc.subarray(208, 224);
  // check if hash matches
  if (!currentHash.equals(expectedHash)) {
    throw new Error('SHA256 hash mismatch');
  }