/// <summary>
/// Construct a filter array.
/// </summary>
/// <param name="numberOfBitsInArray">The size of the array in bits.</param>
/// <param name="maximumBitIndexesPerElement">The maximum (and default) number of indexes (bits) in the array to associate with elements.</param>
/// <param name="initilizeBitsOfArrayAtRandom">If set to true, the bits of the filter array will be set to 0 or 1 at random (indpendently, each with probability 0.5).</param>
/// <param name="saltForHashFunctions">A salt used to generate the hash functions.
/// Any two filter arrays generated with the same salt will use the same hash functions.
/// The salt should be kept secret from attackerse who might try to manipulate the selection of elements,
/// such as to intentionally cause bit collisions with the array.</param>
public FilterArray(int numberOfBitsInArray, int maximumBitIndexesPerElement, bool initilizeBitsOfArrayAtRandom,
string saltForHashFunctions = "")
{
// Align on byte boundary to guarantee no less than numberOfBitsInArray
int capacityInBytes = (numberOfBitsInArray + 7) / 8;
// Create hash functions to map elements to indexes in the bit array.
HashFunctionsMappingElementsToBitsInTheArray = new UniversalHashFunction[maximumBitIndexesPerElement];
for (int i = 0; i < HashFunctionsMappingElementsToBitsInTheArray.Length; i++)
{
HashFunctionsMappingElementsToBitsInTheArray[i] =
new UniversalHashFunction(i + ":" + saltForHashFunctions, 64);
}
if (initilizeBitsOfArrayAtRandom)
{
// Initialize the bit array setting ~half the bits randomly to zero by using the
// cryptographic random number generator.
byte[] initialBitValues = new byte[capacityInBytes];
StrongRandomNumberGenerator.GetBytes(initialBitValues);
BitArray = new BitArray(initialBitValues);
}
else
{
// Start with all bits of the array set to zero.
BitArray = new BitArray(capacityInBytes * 8);
}
}
public async Task CookieUsedInPriorLoginAsync()
{
Init();
string username = "******";
string password = "******";
DbUserAccount account = userAccountController.Create(username, password);
string randomCookiesHash = Convert.ToBase64String(StrongRandomNumberGenerator.GetBytes(16));
bool cookieAlreadyPresentOnFirstTest = await
userAccountController.HasClientWithThisHashedCookieSuccessfullyLoggedInBeforeAsync(account, randomCookiesHash);
Assert.False(cookieAlreadyPresentOnFirstTest);
await userAccountController.RecordHashOfDeviceCookieUsedDuringSuccessfulLoginAsync(account, randomCookiesHash);
bool cookieAlreadyPresentOnSecondTest = await
userAccountController.HasClientWithThisHashedCookieSuccessfullyLoggedInBeforeAsync(account, randomCookiesHash);
Assert.True(cookieAlreadyPresentOnSecondTest);
}
public async Task AddIncorrectPhase2HashAsync()
{
Init();
string username = "******";
string password = "******";
DbUserAccount account = userAccountController.Create(username, password);
string incorrectPasswordHash = Convert.ToBase64String(StrongRandomNumberGenerator.GetBytes(16));
bool incorrectPasswordAlreadyPresentOnFirstTest = await
userAccountController.AddIncorrectPhaseTwoHashAsync(account, incorrectPasswordHash);
Assert.False(incorrectPasswordAlreadyPresentOnFirstTest);
// Since the hash is added via a background task to minimize response latency, we'll want to
// wait to be sure it's added
Thread.Sleep(1000);
bool incorrectPasswordPresentOnSecondTest = await
userAccountController.AddIncorrectPhaseTwoHashAsync(account, incorrectPasswordHash);
Assert.True(incorrectPasswordPresentOnSecondTest);
}
public FilterArray(int numberOfBitsInArray, int maximumBitIndexesPerElement, bool initilizeBitsOfArrayAtRandom,
string saltForHashFunctions = "")
{
int capacityInBytes = (numberOfBitsInArray + 7) / 8;
HashFunctionsMappingElementsToBitsInTheArray = new UniversalHashFunction[maximumBitIndexesPerElement];
for (int i = 0; i < HashFunctionsMappingElementsToBitsInTheArray.Length; i++)
{
HashFunctionsMappingElementsToBitsInTheArray[i] =
new UniversalHashFunction(i + ":" + saltForHashFunctions, 64);
}
if (initilizeBitsOfArrayAtRandom)
{
byte[] initialBitValues = new byte[capacityInBytes];
StrongRandomNumberGenerator.GetBytes(initialBitValues);
BitArray = new BitArray(initialBitValues);
}
else
{
BitArray = new BitArray(capacityInBytes * 8);
}
}
