How can I generate random alphanumeric strings? [c

Question

How can I generate random 8 character alphanumeric strings in C#?

Answer 1

I heard LINQ is the new black, so here's my attempt using LINQ:

private static Random random = new Random();
public static string RandomString(int length)
{
    const string chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
    return new string(Enumerable.Repeat(chars, length)
      .Select(s => s[random.Next(s.Length)]).ToArray());
}

(Note: The use of the Random class makes this unsuitable for anything security related, such as creating passwords or tokens. Use the RNGCryptoServiceProvider class if you need a strong random number generator.)

Answer 2

The main goals of my code are:

1. The distribution of strings is almost uniform (don't care about minor deviations, as long as they're small)
2. It outputs more than a few billion strings for each argument set. Generating an 8 character string (~47 bits of entropy) is meaningless if your PRNG only generates 2 billion (31 bits of entropy) different values.
3. It's secure, since I expect people to use this for passwords or other security tokens.

The first property is achieved by taking a 64 bit value modulo the alphabet size. For small alphabets (such as the 62 characters from the question) this leads to negligible bias. The second and third property are achieved by using RNGCryptoServiceProvider instead of System.Random.

using System;
using System.Security.Cryptography;

public static string GetRandomAlphanumericString(int length)
{
    const string alphanumericCharacters =
        "ABCDEFGHIJKLMNOPQRSTUVWXYZ" +
        "abcdefghijklmnopqrstuvwxyz" +
        "0123456789";
    return GetRandomString(length, alphanumericCharacters);
}

public static string GetRandomString(int length, IEnumerable<char> characterSet)
{
    if (length < 0)
        throw new ArgumentException("length must not be negative", "length");
    if (length > int.MaxValue / 8) // 250 million chars ought to be enough for anybody
        throw new ArgumentException("length is too big", "length");
    if (characterSet == null)
        throw new ArgumentNullException("characterSet");
    var characterArray = characterSet.Distinct().ToArray();
    if (characterArray.Length == 0)
        throw new ArgumentException("characterSet must not be empty", "characterSet");

    var bytes = new byte[length * 8];
    var result = new char[length];
    using (var cryptoProvider = new RNGCryptoServiceProvider())
    {
        cryptoProvider.GetBytes(bytes);
    }
    for (int i = 0; i < length; i++)
    {
        ulong value = BitConverter.ToUInt64(bytes, i * 8);
        result[i] = characterArray[value % (uint)characterArray.Length];
    }
    return new string(result);
}

Answer 3

A slightly cleaner version of DTB's solution.

    var chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
    var random = new Random();
    var list = Enumerable.Repeat(0, 8).Select(x=>chars[random.Next(chars.Length)]);
    return string.Join("", list);

Your style preferences may vary.

Answer 4

 public static string RandomString(int length)
    {
        const string chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789";
        var random = new Random();
        return new string(Enumerable.Repeat(chars, length).Select(s => s[random.Next(s.Length)]).ToArray());
    }

Answer 5

You just use the assembly SRVTextToImage. And write below code to generate random string.

CaptchaRandomImage c1 = new CaptchaRandomImage();
            string text = c1.GetRandomString(8);

Mostly it is used to implement the Captcha. But in your case it also works. Hope it helps.

Answer 6

Now in one-liner flavour.

private string RandomName
    {
        get
        {
            return new string(
                Enumerable.Repeat("ABCDEFGHIJKLMNOPQRSTUVWXYZ", 13)
                    .Select(s =>
                    {
                        var cryptoResult = new byte[4];
                        using (var cryptoProvider = new RNGCryptoServiceProvider())
                            cryptoProvider.GetBytes(cryptoResult);
                        return s[new Random(BitConverter.ToInt32(cryptoResult, 0)).Next(s.Length)];
                    })
                    .ToArray());
        }
    }