private string Shuffle(string password, KeccakNumberGenerator rng)
{
var builder = new StringBuilder(password);
for (int i = builder.Length; i > 1; --i)
{
int swapIndex = rng.NextInt(i);
var temp = builder[i - 1];
builder[i - 1] = builder[swapIndex];
builder[swapIndex] = temp;
}
return(builder.ToString());
}
private string PickUnits(KeccakNumberGenerator rng)
{
var builder = new StringBuilder();
var remainingCounts = UnitSets.ToDictionary(u => u, u => u.Bounds.Max);
// Fill in the minimum amount of each unit set.
foreach (var unitSet in UnitSets)
{
for (int i = 0; i < unitSet.Bounds.Min; ++i)
{
builder.Append(unitSet[rng.NextInt(unitSet.Count)]);
}
}
// Fill in the rest with random characters from the entire superset,
// removing sets if they reach their maximum
var availableUnitSets = UnitSets.Where(u => u.Bounds.Max > u.Bounds.Min).ToList();
int supersetCount = availableUnitSets.Sum(u => u.Count);
while (builder.Length < Length)
{
int supersetIndex = rng.NextInt(supersetCount);
for (int i = 0; i < availableUnitSets.Count; ++i)
{
if (supersetIndex < availableUnitSets[i].Count)
{
builder.Append(availableUnitSets[i][supersetIndex]);
--remainingCounts[availableUnitSets[i]];
if (remainingCounts[availableUnitSets[i]] == 0)
{
availableUnitSets.Remove(availableUnitSets[i]);
supersetCount = availableUnitSets.Sum(u => u.Count);
}
break;
}
supersetIndex -= availableUnitSets[i].Count;
}
}
return(builder.ToString());
}
public string Generate()
{
var seedBuilder = new StringBuilder();
AddSeedPart(seedBuilder, MasterPassword);
AddSeedPart(seedBuilder, Keyword);
AddSeedPart(seedBuilder, Modifier);
AddSeedPart(seedBuilder, Length);
foreach (var unitSet in UnitSets)
{
AddSeedPart(seedBuilder, unitSet);
}
var rng = new KeccakNumberGenerator(seedBuilder.ToString());
string unshuffled = PickUnits(rng);
string password = Shuffle(unshuffled, rng);
return(password);
}