Essential C# Cryptography  Suggest an edit

Cryptographically Secure Random Data

There are times when the framework’s Random() class may not be considered random enough, given that it is based on a psuedo-random number generator. The framework’s Crypto classes do, however, provide something more robust in the form of RNGCryptoServiceProvider.

The following code samples demonstrate how to generate Cryptographically Secure byte arrays, strings and numbers.

Random Byte Array

public static byte[] GenerateRandomData(int length)
{
    var rnd = new byte[length];
    using (var rng = new RNGCryptoServiceProvider())
        rng.GetBytes(rnd);
    return rnd;
}

Random Integer (with even distribution)

public static int GenerateRandomInt(int minVal=0, int maxVal=100)
{
    var rnd = new byte[4];
    using (var rng = new RNGCryptoServiceProvider())
        rng.GetBytes(rnd);
    var i = Math.Abs(BitConverter.ToInt32(rnd, 0));
    return Convert.ToInt32(i % (maxVal - minVal + 1) + minVal);
}

Random String

public static string GenerateRandomString(int length, string allowableChars=null)
{
    if (string.IsNullOrEmpty(allowableChars))
        allowableChars = @"ABCDEFGHIJKLMNOPQRSTUVWXYZ";

    // Generate random data
    var rnd = new byte[length];
    using (var rng = new RNGCryptoServiceProvider())
        rng.GetBytes(rnd);

    // Generate the output string
    var allowable = allowableChars.ToCharArray();
    var l = allowable.Length;
    var chars = new char[length];
    for (var i = 0; i < length; i++)
        chars[i] = allowable[rnd[i] % l];

    return new string(chars);
}


Table Of Contents
22 Enum
25 GUID
107 Stream
108 Timers
146 Cryptography
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