encryptBytes abstract method

Future<Uint8List> encryptBytes(List<int> data, List<int> counter, int length)

Encrypt data with this AesCtrSecretKey using AES in Counter mode, as specified in NIST SP800-38A.

The operation requires a 16 bytes initial counter block counter. The length right most bits of counter are incremented for each encrypted block, the left most 128 - length bits are used as a nonce. The counter value must not be reused for subsequent messages, and the encrypted data must not exceed 2 ^ length * block-size, as this would cause counter blocks to be reused. For detailed discussion of the counter block requirements for AES-CTR, see Appendix B of NIST SP800-38A.

Example

import 'dart:convert' show utf8;
import 'dart:typed_data' show Uint8List;
import 'package:webcrypto/webcrypto.dart';

// Generate a new random AES-CTR secret key for AES-256.
final k = await AesCtrSecretKey.generate(256);

// Use a unique counter for each message.
final ctr = Uint8List(16); // always 16 bytes
fillRandomBytes(ctr);

// Length of the counter, the N'th right most bits of ctr are incremented
// for each block, the left most 128 - N bits are used as static nonce.
// Thus, messages must be less than 2^64 * 16 bytes.
final N = 64;

// Encrypt a message
final c = await k.encryptBytes(utf8.encode('hello world'), ctr, N);

// Decrypt message (requires the same counter ctr and length N)
print(utf8.decode(await k.decryptBytes(c, ctr, N))); // hello world

Remark Firefox does not implement counter rollover for AES-CTR correctly. Picking a sufficiently large length and using a counter that isn't filled with 0xff will likely avoid counter rollovers. See bug 1803105 for details.

Implementation

// Note. that if counter wraps around, then this is broken on Firefox.
Future<Uint8List> encryptBytes(
  List<int> data,
  List<int> counter,
  int length,
);