How can I generate cryptographically strong random strings with a given length

Question

I need to generate cryptographically strong random alphanumeric strings with a specified length, only using the following characters.

• A-Z
• a-z
• 0-9

Is there a way to accomplish this in C#?

Answer 1

You can use class RandomNumberGenerator to generate cryptographically-secure random numbers to do this, for example:

string allowed = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789";
int strlen = 10; // Or whatever
char[] randomChars = new char[strlen];

for (int i = 0; i < strlen; i++)
{
    randomChars[i] = allowed[RandomNumberGenerator.GetInt32(0, allowed.Length)];
}

string result = new string(randomChars);

Console.WriteLine(result);