How can I use bigint with C#?

Question

I work to implement an RSA key algorithm. But I couldn't use a 2048-bit value. How I can use it?

I want to use big integer.

• Trisped: Usually RSA key algorithms work on 8 bits at a time. Your key would be placed in a byte array with 8 indexes.
• CompEng: not duplicate. ı do not want to use long or int64. they do not enough for me

Answer 1

You can use System.Numerics.BigInteger (add a reference to System.Numerics assembly). As mentioned in the comments this might not be the right approach though.

• Juliën: Indeed, BigInteger is the way to go. Minor note: it's only available in .NET 4.0 and higher.

Answer 2

Here's using BigInteger. This method Prints Numbers in the Fibonacci Sequence up to n.

public static void FibonacciSequence(int n)
{
 /** BigInteger easily holds the first 1000 numbers in the Fibonacci Sequence. **/
 List<BigInteger> fibonacci = new List<BigInteger>();
 fibonacci.Add(0);
 fibonacci.Add(1);
 BigInteger i = 2;
 while(i < n)
 { 
 int first = (int)i - 2;
 int second = (int) i - 1;
 BigInteger firstNumber = fibonacci[first];
 BigInteger secondNumber = fibonacci[second];
 BigInteger sum = firstNumber + secondNumber;
 fibonacci.Add(sum);
 i++;
 } 
 foreach (BigInteger f in fibonacci) { Console.WriteLine(f); }
}

Answer 3

Native support for big integers has been introduced in .NET 4.0. Just add an assembly reference to System.Numerics, add a using System.Numerics; declaration at the top of your code file, and you’re good to go. The type you’re after is BigInteger.

Answer 4

BigInteger is available in .NET 4.0 or later. There are some third-party implementations as well (In case you are using an earlier version of the framework).

Answer 5

Better use System.Numerics.BigInteger.