"AES engine not initialised" with pointycastle SecureRandom() - dart

Question

I want to generate a random BigInt with dynamik length Bits. I am using the pointycastle package to get a SecureRandom BigInt.
import 'package:pointycastle/pointycastle.dart';
void main(List<String> arguments) {
print(gen(500));
}
BigInt gen(int Bits) {
var n = BigInt.from(1);
var ran = SecureRandom('Fortuna');
n = ran.nextBigInteger(Bits);
return n;
}
This line throws an exception:
n = ran.nextBigInteger(Bits);
StateError (Bad state: AES engine not initialised)
This is the complete error in the console:
Unhandled exception:
Bad state: AES engine not initialised
#0 AESFastEngine.processBlock
package:pointycastle/block/aes_fast.dart:109
#1 BlockCtrRandom.nextUint8
package:pointycastle/random/block_ctr_random.dart:55
#2 SecureRandomBase._randomBits
package:pointycastle/…/impl/secure_random_base.dart:55
#3 SecureRandomBase.nextBigInteger
package:pointycastle/…/impl/secure_random_base.dart:33
#4 AutoSeedBlockCtrRandom.nextBigInteger.<anonymous closure>
package:pointycastle/random/auto_seed_block_ctr_random.dart:69
#5 AutoSeedBlockCtrRandom._autoReseedIfNeededAfter
package:pointycastle/random/auto_seed_block_ctr_random.dart:81
#6 AutoSeedBlockCtrRandom.nextBigInteger
package:pointycastle/random/auto_seed_block_ctr_random.dart:68
#7 FortunaRandom.nextBigInteger
package:pointycastle/random/fortuna_random.dart:46
#8 gen
bin\encrypt.dart:10
#9 main
bin\encrypt.dart:4
#10 _startIsolate.<anonymous closure> (dart:isolate-patch/isolate_patch.dart:299:32)
#11 _RawReceivePortImpl._handleMessage (dart:isolate-patch/isolate_patch.dart:168:12)
I can't seem to find a solution to this error message anywhere else. I hope u guys can help me. :D

Answer 1

It is not clear but if I look at the examples from the project it seems like you need to call the seed method. The following works for me:
import 'dart:math';
import 'dart:typed_data';
import 'package:pointycastle/pointycastle.dart';
void main(List<String> arguments) {
print(gen(500));
}
BigInt gen(int bits) {
final _sGen = Random.secure();
var n = BigInt.from(1);
var ran = SecureRandom('Fortuna');
ran.seed(KeyParameter(
Uint8List.fromList(List.generate(32, (_) => _sGen.nextInt(255)))));
n = ran.nextBigInteger(bits);
return n;
}
The example I was inspired by: https://github.com/PointyCastle/pointycastle/blob/master/tutorials/examples/import-demo/import-demo-1.dart

Answer 2

Welcome to Stackoverflow.
When using any part of Pointycastle you do need to instantiate the implementation objects.
In your code you are using
var ran = SecureRandom('Fortuna');
that uses the SecureRandom class.
Simply add
final rnd = new SecureRandom("AES/CTR/PRNG");
and kindly see the PointCastle SecureRandom example for further questions:
https://github.com/PointyCastle/pointycastle/blob/master/test/random/block_ctr_random_test.dart