seed method
Seed the RNG with some entropy (look at package cipher_entropy providing entropy sources).
Implementation
@override
void seed(covariant KeyParameter param) {
if (param.key.length != 32) {
throw ArgumentError('Fortuna PRNG can only be used with 256 bits keys');
}
final iv = Uint8List(16);
iv[15] = 1;
_prng.seed(ParametersWithIV(param, iv));
}