.NET Short Unique Identifier

I need a unique identifier in .NET (cannot use GUID as it is too long for this case).

Do people think that the algorithm used here is a good candidate or do you have any other suggestions?

This one a good one - http://www.singular.co.nz/blog/archive/2007/12/20/shortguid-a-shorter-and-url-friendly-guid-in-c-sharp.aspx

and also here https://stackoverflow.com/questions/1458468/youtube-like-guid

You could use Base64:

string base64Guid = Convert.ToBase64String(Guid.NewGuid().ToByteArray());

> That generates a string like E1HKfn68Pkms5zsZsvKONw==. Since a GUID is > always 128 bits, you can omit the == that you know will always be > present at the end and that will give you a 22 character string. This > isn't as short as YouTube though.

I use a similar approach as Dor Cohen's but removing some special characters:

var uid = Regex.Replace(Convert.ToBase64String(Guid.NewGuid().ToByteArray()), "[/+=]", "");		

This will output just alphanumeric characters. The UIDs are not guaranteed to have always the same length. Here is a sample run:

vmKo0zws8k28fR4V4Hgmw 
TKbhS0G2V0KqtpHOU8e6Ug 
rfDi1RdO0aQHTosh9dVvw
3jhCD75fUWjQek8XRmMg 
CQUg1lXIXkWG8KDFy7z6Ow 
bvyxW5aj10OmKA5KMhppw
pIMK8eq5kyvLK67xtsIDg
VX4oljGWpkSQGR2OvGoOQ 
NOHBjUUHv06yIc7EvotRg
iMniAuUG9kiGLwBtBQByfg

var ticks = new DateTime(2016,1,1).Ticks;
var ans = DateTime.Now.Ticks - ticks;
var uniqueId = ans.ToString("x");

Keep a baseline date (which in this case is 1st Jan 2016) from when you will start generating these ids. This will make your ids smaller.

Generated Number: 3af3c14996e54

Simple usable package. I use it for temporal request id generator.

https://www.nuget.org/packages/shortid

https://github.com/bolorundurowb/shortid

Uses System.Random

string id = ShortId.Generate();
// id = KXTR_VzGVUoOY

(from the github page)

If you want to control the type of id generated by specifying whether you want numbers, special characters and the length, call the Generate method and pass three parameters, the first a boolean stating whether you want numbers, the second a boolean stating whether you want special characters, the last a number indicating your length preference.

string id = ShortId.Generate(true, false, 12);
// id = VvoCDPazES_w

As far as I know, just stripping off a part of a GUID isn't guaranteed to be unique - in fact, it's far from being unique.

The shortest thing that I know that guarantees global uniqueness is featured in this blog post by Jeff Atwood. In the linked post, he discusses multiple ways to shorten a GUID, and in the end gets it down to 20 bytes via Ascii85 encoding.

However, if you absolutely need a solution that's no longer than 15 bytes, I'm afraid you have no other choice than to use something which is not guaranteed to be globally unique.

For my local app I'm using this time based approach:

/// <summary>
/// Returns all ticks, milliseconds or seconds since 1970.
/// 
/// 1 tick = 100 nanoseconds
/// 
/// Samples:
/// 
/// Return unit   	value decimal           length     	value hex 		length
/// --------------------------------------------------------------------------
/// ticks           14094017407993061       17          3212786FA068F0  14
/// milliseconds    1409397614940           13          148271D0BC5     11
/// seconds         1409397492              10          5401D2AE        8
///
/// </summary>
public static string TickIdGet(bool getSecondsNotTicks, bool getMillisecondsNotTicks, bool getHexValue)
{
	string id = string.Empty;

	DateTime historicalDate = new DateTime(1970, 1, 1, 0, 0, 0);

	if (getSecondsNotTicks || getMillisecondsNotTicks)
	{
		TimeSpan spanTillNow = DateTime.UtcNow.Subtract(historicalDate);

		if (getSecondsNotTicks)
			id = String.Format("{0:0}", spanTillNow.TotalSeconds);
		else
			id = String.Format("{0:0}", spanTillNow.TotalMilliseconds);
	}
	else
	{
		long ticksTillNow = DateTime.UtcNow.Ticks - historicalDate.Ticks;
		id = ticksTillNow.ToString();
	}

	if (getHexValue)
		id = long.Parse(id).ToString("X");

	return id;
}

IDENTITY values should be unique in a database, but you should be aware of the limitations... for example, it makes bulk data inserts basically impossible which will slow you down if you're working with a very large number of records.

You may also be able to use a date/time value. I've seen several databases where they use the date/time to be the PK, and while it's not super clean - it works. If you control the inserts, you can effectively guarantee that the values will be unique in code.

here my solution, is not safe for concurrency, no more of 1000 GUID's per seconds and thread safe.

public static class Extensors
{

    private static object _lockGuidObject;

    public static string GetGuid()
    {

        if (_lockGuidObject == null)
            _lockGuidObject = new object();
        

        lock (_lockGuidObject)
        {

            Thread.Sleep(1);
            var epoch = new DateTime(1970, 1, 1, 0, 0, 0, DateTimeKind.Utc);
            var epochLong = Convert.ToInt64((DateTime.UtcNow - epoch).TotalMilliseconds);

            return epochLong.DecimalToArbitrarySystem(36);

        }

    }

    /// <summary>
    /// Converts the given decimal number to the numeral system with the
    /// specified radix (in the range [2, 36]).
    /// </summary>
    /// <param name="decimalNumber">The number to convert.</param>
    /// <param name="radix">The radix of the destination numeral system (in the range [2, 36]).</param>
    /// <returns></returns>
    public static string DecimalToArbitrarySystem(this long decimalNumber, int radix)
    {
        const int BitsInLong = 64;
        const string Digits = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";

        if (radix < 2 || radix > Digits.Length)
            throw new ArgumentException("The radix must be >= 2 and <= " + Digits.Length.ToString());

        if (decimalNumber == 0)
            return "0";

        int index = BitsInLong - 1;
        long currentNumber = Math.Abs(decimalNumber);
        char[] charArray = new char[BitsInLong];

        while (currentNumber != 0)
        {
            int remainder = (int)(currentNumber % radix);
            charArray[index--] = Digits[remainder];
            currentNumber = currentNumber / radix;
        }

        string result = new String(charArray, index + 1, BitsInLong - index - 1);
        if (decimalNumber < 0)
        {
            result = "-" + result;
        }

        return result;
    }

code not optimized, just sample!.

If your app dont have a few MILLIION people, using that generate short unique string at the SAME MILLISECOND, you can think about using below function.

private static readonly Object obj = new Object();
private static readonly Random random = new Random();
private string CreateShortUniqueString()
{
    string strDate = DateTime.Now.ToString("yyyyMMddhhmmssfff");
    string randomString ;
    lock (obj)
    {
        randomString = RandomString(3);
    }
    return strDate + randomString; // 16 charater
}
private string RandomString(int length)
{

    const string chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789abcdefghijklmnopqrstuvwxy";
    var random = new Random();
    return new string(Enumerable.Repeat(chars, length)
      .Select(s => s[random.Next(s.Length)]).ToArray());
}

change yyyy to yy if you just need to use your app in next 99 year.
Update 20160511: Correct Random function
- Add Lock object
- Move random variable out of RandomString function
Ref

Here's my small method to generate a random and short unique id. Uses a cryptographic rng for secure random number generation. Add whatever characters you need to the chars string.

using System;
using System.Security.Cryptography;

// ...

private string GenerateRandomId(int length)
{
    string charset = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";
    char[] outputChars = new char[length];
    
    using RandomNumberGenerator rng = RandomNumberGenerator.Create();
    int minIndex = 0;
    int maxIndexExclusive = charset.Length;
    int diff = maxIndexExclusive - minIndex;

    long upperBound = uint.MaxValue / diff * diff;

    byte[] randomBuffer = new byte[sizeof(int)];

    for (int i = 0; i < outputChars.Length; i++)
    {
        // Generate a fair, random number between minIndex and maxIndex
        uint randomUInt;
        do
        {
            rng.GetBytes(randomBuffer);
            randomUInt = BitConverter.ToUInt32(randomBuffer, 0);
        }
        while (randomUInt >= upperBound);
        int charIndex = (int)(randomUInt % diff);

        // Set output character based on random index
        outputChars[i] = charset[charIndex];
    }

    return new string(outputChars);
}

EDIT:

The previous version of this answer simply used modulo (%) to constrain a random byte value to the length of the array. This is not a fair way to select a random character, and produced obvious biases in the output string.

This new version properly scales a random integer down to the range of charset indices, and accounts for the edge case where the random number is the absolute upper bound by rerolling for a new integer.

This solution produces fair and evenly distributed output, tested with a 1,000,000 character long output showing no obvious biases:

string output = GenerateRandomId(1_000_000);
var tally = output.GroupBy(c => c).OrderBy(g => g.Key).Select(g => (g.Key, g.Count())).ToArray();

int average = (int)(tally.Aggregate(new BigInteger(0), (b, t) => {b += t.Item2; return b;}, b => b) / tally.Count());
int max = tally.Max(g => g.Item2);
int min = tally.Min(g => g.Item2);

Console.WriteLine($"Avg: {average}");
Console.WriteLine($"Max: {max}");
Console.WriteLine($"Min: {min}");


foreach((char key, int count) in tally) {
    Console.WriteLine($"{key}: {count}");
}

Output:

Avg: 27777
Max: 28163
Min: 27341
0: 28081
1: 27773
...
Z: 27725

I know it's quite far from posted date... :)

I have a generator which produces only 9 Hexa characters, eg: C9D6F7FF3, C9D6FB52C

public class SlimHexIdGenerator : IIdGenerator
{
    private readonly DateTime _baseDate = new DateTime(2016, 1, 1);
    private readonly IDictionary<long, IList<long>> _cache = new Dictionary<long, IList<long>>();

    public string NewId()
    {
        var now = DateTime.Now.ToString("HHmmssfff");
        var daysDiff = (DateTime.Today - _baseDate).Days;
        var current = long.Parse(string.Format("{0}{1}", daysDiff, now));
        return IdGeneratorHelper.NewId(_cache, current);
    }
}


static class IdGeneratorHelper
{
    public static string NewId(IDictionary<long, IList<long>> cache, long current)
    {
        if (cache.Any() && cache.Keys.Max() < current)
        {
            cache.Clear();
        }

        if (!cache.Any())
        {
            cache.Add(current, new List<long>());
        }

        string secondPart;
        if (cache[current].Any())
        {
            var maxValue = cache[current].Max();
            cache[current].Add(maxValue + 1);
            secondPart = maxValue.ToString(CultureInfo.InvariantCulture);
        }
        else
        {
            cache[current].Add(0);
            secondPart = string.Empty;
        }

        var nextValueFormatted = string.Format("{0}{1}", current, secondPart);
        return UInt64.Parse(nextValueFormatted).ToString("X");
    }
}

Based on some others, here is my solution which provides a different encoded guid which is URL (and Docker) safe and does not loose any information:

Convert.ToBase64String(Guid.NewGuid().ToByteArray()).Replace("=", "").Replace("+", "-").Replace("/", "_");

Example outputs are:

BcfttHA780qMdHSxSBoZFA
_4p5srPgOE2f25T_UnoGLw
H9xR_zdfm0y-zYjdR3NOig

In C# a long value has 64 bits, which if encoded with Base64, there will be 12 characters, including 1 padding =. If we trim the padding =, there will be 11 characters.

One crazy idea here is we could use a combination of Unix Epoch and a counter for one epoch value to form a long value. The Unix Epoch in C# DateTimeOffset.ToUnixEpochMilliseconds is in long format, but the first 2 bytes of the 8 bytes are always 0, because otherwise the date time value will be greater than the maximum date time value. So that gives us 2 bytes to place an ushort counter in.

So, in total, as long as the number of ID generation does not exceed 65536 per millisecond, we can have an unique ID:

// This is the counter for current epoch. Counter should reset in next millisecond
ushort currentCounter = 123;

var epoch = DateTimeOffset.UtcNow.ToUnixTimeMilliseconds();
// Because epoch is 64bit long, so we should have 8 bytes
var epochBytes = BitConverter.GetBytes(epoch);
if (BitConverter.IsLittleEndian)
{
	// Use big endian
	epochBytes = epochBytes.Reverse().ToArray();
}

// The first two bytes are always 0, because if not, the DateTime.UtcNow is greater 
// than DateTime.Max, which is not possible
var counterBytes = BitConverter.GetBytes(currentCounter);
if (BitConverter.IsLittleEndian)
{
	// Use big endian
	counterBytes = counterBytes.Reverse().ToArray();
}

// Copy counter bytes to the first 2 bytes of the epoch bytes
Array.Copy(counterBytes, 0, epochBytes, 0, 2);

// Encode the byte array and trim padding '='
// e.g. AAsBcTCCVlg
var shortUid = Convert.ToBase64String(epochBytes).TrimEnd('=');

    public static string ToTinyUuid(this Guid guid)
    {
        return Convert.ToBase64String(guid.ToByteArray())[0..^2]  // remove trailing == padding 
            .Replace('+', '-')                          // escape (for filepath)
            .Replace('/', '_');                         // escape (for filepath)
    }

Usage

Guid.NewGuid().ToTinyUuid()

It's not rocket science to convert back, so I'll leave you that much.

22 chars, url safe, and retains Guid uniqueness.

// Our url safe, base 64 alphabet:
const string alphabet = "-_0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";

// Sanitized Guid string. Preserve the last two hex chars
var guidStr = "929F7C4D4B2644E1A122A379C02D6345";
var lastTwo = guidStr.Substring(30, 2);

string shortGuid = "";

// Iterate over the ten groups of 3 hex chars: 929 F7C 4D4 B26 44E 1A1 22A 379 C02 D63
for (var i = 0; i < 10; i++)
{
	var hex = guidStr.Substring(i*3, 3);              // Get the next 3 hex chars
	var x = Convert.ToInt32(hex, 16);                 // Convert to int
	shortGuid += $"{alphabet[x/64]}{alphabet[x%64]}"; // Lookup the two-digit base64 value
}
shortGuid += lastTwo; // Don't forget the last two

Console.WriteLine(shortGuid);

Output:

yDXWhiGAfc4v6EbTK0Px45

Just in case merely removing hyphens will do for anyone:

Guid.NewGuid().ToString("n")

This generates perfectly unique strings of 32 characters:

5db4cee3bfd8436395d37fca2d48d5b3
82fac271c76148a3a0667c00a5da990d

Based on @dorcohen's answer and @pootzko's comment. You can use this. It is safe over the wire.

var errorId = System.Web.HttpServerUtility.UrlTokenEncode(Guid.NewGuid().ToByteArray());

If you dont need to type the string you could use the following:

static class GuidConverter
{
    public static string GuidToString(Guid g)
    {
        var bytes = g.ToByteArray();
        var sb = new StringBuilder();
        for (var j = 0; j < bytes.Length; j++)
        {
            var c = BitConverter.ToChar(bytes, j);
            sb.Append(c);
            j++;
        }
        return sb.ToString();
    }

    public static Guid StringToGuid(string s) 
        => new Guid(s.SelectMany(BitConverter.GetBytes).ToArray());
}

This will convert the Guid to a 8 character String like this:

{b77a49a5-182b-42fa-83a9-824ebd6ab58d} --> "䦥띺ᠫ䋺ꦃ亂檽趵"

{c5f8f7f5-8a7c-4511-b667-8ad36b446617} --> "엸詼䔑架펊䑫ᝦ"

to not lose characters (+ / -) and if you want to use your guid in an url, it must be transformed into base32

for 10 000 000 no duplicate key

    public static List<string> guids = new List<string>();
    static void Main(string[] args)
    {
        for (int i = 0; i < 10000000; i++)
        {
            var guid = Guid.NewGuid();
            string encoded = BytesToBase32(guid.ToByteArray());
            guids.Add(encoded);
            Console.Write(".");
        }
        var result = guids.GroupBy(x => x)
                    .Where(group => group.Count() > 1)
                    .Select(group => group.Key);

        foreach (var res in result)
            Console.WriteLine($"Duplicate {res}");

        Console.WriteLine($"*********** end **************");
        Console.ReadLine();
    }

    public static string BytesToBase32(byte[] bytes)
    {
        const string alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
        string output = "";
        for (int bitIndex = 0; bitIndex < bytes.Length * 8; bitIndex += 5)
        {
            int dualbyte = bytes[bitIndex / 8] << 8;
            if (bitIndex / 8 + 1 < bytes.Length)
                dualbyte |= bytes[bitIndex / 8 + 1];
            dualbyte = 0x1f & (dualbyte >> (16 - bitIndex % 8 - 5));
            output += alphabet[dualbyte];
        }

        return output;
    }

private static readonly object _getUniqueIdLock = new object();
public static string GetUniqueId()
{		
	lock(_getUniqueIdLock)
	{
		System.Threading.Thread.Sleep(1);
		return DateTime.UtcNow.Ticks.ToString("X");
	}
}

you can use

code = await UserManager.GenerateChangePhoneNumberTokenAsync(input.UserId, input.MobileNumber);

its 6 nice characters only, 599527 ,143354

and when user virify it simply

var result = await UserManager.VerifyChangePhoneNumberTokenAsync(input.UserId, input.Token, input.MobileNumber);

hope this help you

Guid.NewGuid().ToString().Split('-').First()