/// <summary>
/// Creates a pair of two primes which, being multiplied one by another,
/// produce a public key of desired length for the RSA algorithm.
/// </summary>
/// <typeparam name="B">An implementation of <c>IBase</c> interface which specifies the digit base of <c>LongInt<<typeparamref name="B"/>></c> numbers.</typeparam>
/// <param name="digits">The desired number of digits in the public key.</param>
/// <param name="randomGenerator">A random generator for long integer numbers.</param>
/// <param name="primalityTest"></param>
/// <returns></returns>
public static Point <LongInt <B> > GetKey <B>(int digits, IRandomBounded <LongInt <B> > randomGenerator = null, Func <LongInt <B>, bool> primalityTest = null) where B : IBase, new()
{
Contract.Requires <ArgumentOutOfRangeException>(digits > 1, "The amount of digits in the key should be more than 1.");
/*
* Contract.Ensures(
* (Contract.Result<Point<LongInt<B>>>().X * Contract.Result<Point<LongInt<B>>>().Y)
* .Length == digits);
*/
long bits = (long)Math.Ceiling(Math.Log(LongInt <B> .BASE, 2)); // сколько бит занимает BASE
if (randomGenerator == null)
{
randomGenerator = new RandomLongIntModular <B>(new RandomMersenneTwister());
}
if (primalityTest == null)
{
primalityTest = (x => __isPrimeOptimized(x));
}
LongInt <B>
firstPrime,
secondPrime;
int half = digits / 2;
// На текущий момент длина ключа может оказаться МЕНЬШЕ
// запланированной. Сделать так, чтобы она всегда была одна.
// Нижеуказанный генератор тоже снести.
IRandomBoundedUnbounded <int> tmp = new RandomCryptographic();
do
{
firstPrime = new LongInt <B>(half, tmp, false);
}while (!primalityTest(firstPrime));
do
{
secondPrime = new LongInt <B>(digits - half, tmp, false);
}while (!primalityTest(secondPrime));
return(new Point <LongInt <B> >(firstPrime, secondPrime));
}
/// <summary>
/// Hidden method - tries the first 100 primes to test divisibility.
/// If not divisible - proceeds with Miller-Rabin.
/// </summary>
private static bool __isPrimeOptimized <B>(LongInt <B> number)
where B : IBase, new()
{
RandomMersenneTwister gen = new RandomMersenneTwister();
RandomLongIntModular <B> lgen = new RandomLongIntModular <B>(gen);
foreach (int prime in firstPrimes)
{
if (number % prime == 0)
{
return(false);
}
}
if (PrimalityTests.IsPrime_MillerRabin(number, lgen, number.LengthInBinaryPlaces) < 1)
{
return(true);
}
return(false);
}
