Calculate a MD5 hash from a string

Question

I use the following C# code to calculate a MD5 hash from a string. It works well and generates a 32-character hex string like this: 900150983cd24fb0d6963f7d28e17f72

string sSourceData;
byte[] tmpSource;
byte[] tmpHash;
sSourceData = "MySourceData";

//Create a byte array from source data.
tmpSource = ASCIIEncoding.ASCII.GetBytes(sSourceData);
tmpHash = new MD5CryptoServiceProvider().ComputeHash(tmpSource);

// and then convert tmpHash to string...

Is there a way to use code like this to generate a 16-character hex string (or 12-character string)? A 32-character hex string is good but I think it'll be boring for the customer to enter the code!

Solution 1

As per MSDN

Create MD5:

public static string CreateMD5(string input)
{
    // Use input string to calculate MD5 hash
    using (System.Security.Cryptography.MD5 md5 = System.Security.Cryptography.MD5.Create())
    {
        byte[] inputBytes = System.Text.Encoding.ASCII.GetBytes(input);
        byte[] hashBytes = md5.ComputeHash(inputBytes);

        return Convert.ToHexString(hashBytes); // .NET 5 +

        // Convert the byte array to hexadecimal string prior to .NET 5
        // StringBuilder sb = new System.Text.StringBuilder();
        // for (int i = 0; i < hashBytes.Length; i++)
        // {
        //     sb.Append(hashBytes[i].ToString("X2"));
        // }
        // return sb.ToString();
    }
}

Solution 2

// given, a password in a string
string password = @"1234abcd";

// byte array representation of that string
byte[] encodedPassword = new UTF8Encoding().GetBytes(password);

// need MD5 to calculate the hash
byte[] hash = ((HashAlgorithm) CryptoConfig.CreateFromName("MD5")).ComputeHash(encodedPassword);

// string representation (similar to UNIX format)
string encoded = BitConverter.ToString(hash)
   // without dashes
   .Replace("-", string.Empty)
   // make lowercase
   .ToLower();

// encoded contains the hash you want

Solution 3

Was trying to create a string representation of MD5 hash using LINQ, however, none of the answers were LINQ solutions, therefore adding this to the smorgasbord of available solutions.

string result;
using (MD5 hash = MD5.Create())
{
    result = String.Join
    (
        "",
        from ba in hash.ComputeHash
        (
            Encoding.UTF8.GetBytes(observedText)
        ) 
        select ba.ToString("x2")
    );
}

Solution 4

You can use Convert.ToBase64String to convert 16 byte output of MD5 to a ~24 char string. A little bit better without reducing security. (j9JIbSY8HuT89/pwdC8jlw== for your example)

Solution 5

Depends entirely on what you are trying to achieve. Technically, you could just take the first 12 characters from the result of the MD5 hash, but the specification of MD5 is to generate a 32 char one.

Reducing the size of the hash reduces the security, and increases the chance of collisions and the system being broken.

Perhaps if you let us know more about what you are trying to achieve we may be able to assist more.

View more solutions

Comments

[Danger Saints]

MD5CryptoServiceProvider instance should be disposed

[KingCronus]

A nice workaround, but I doubt he OP will want to have it case-sensitive and with special chars...

[Muhamad Jafarnejad]

thanks for your answer. and sorry about my bad explanation. I want to publish an application for windows, the user should buy the license to use my application, so my application request two fields: USERNAME: ... , and KEY: .... I want to hash the USERNAME and create the KEY, then the user should enter the specific USERNAME and KEY. my problem here is that the KEY should be 12-characters, (But in MD5 hash, I get the 32-char KEY). please help me, i really need it.

[yǝsʞǝla]

The source: msdn.microsoft.com/en-us/library/…

[Igor Gatis]

Why "similar to UNIX format"? What it is not exactly the same?

[DavidG]

You should always say where you get code from if you copy/paste from somewhere, otherwise it is classed as plagiarism.

[Paolo Iommarini]

The class MD5 implements IDisposable, remember to dispose your instance. ;)

[Oliver Bock]

In general you should hash a lossless text encoding, like UTF8.

[Monsignor]

BTW checked with the BenchmarkDotNet that the combination of Cryptography.MD5 and BitConverter (see @Michaels's answer) has the best performance.

[bh_earth0]

this gives different result from online md5 checkers. or is it just me??

[bh_earth0]

if you use UTF8, it puts bytordermark(bom). file_content and string WON'T match. to get rid of bom, i used new utf8encoding(false); when file.read/write

[Richard Schneider]

Its better to System.Text.Encoding.Utf8.GetBytesfor people outside of USA.

[Prashant Pimpale]

@Anant How to decrypt the MD5?

[Anant Dabhi]

@PrashantPimpale MD5 is a digest algorithm. Think of it as converting a cow into a steak.

[Prashant Pimpale]

Yes tried with TripleDESCryptoServiceProvider and done!

[Prashant Pimpale]

just wanted to encrypt an Email Id and then decrypt it

[eddyP23]

@bh_earth0 it seems that BitConverter doesn't work in the same fashion on windows and linux, see this question: stackoverflow.com/questions/11454004/…

[Klesun]

What does the "X2" mean?

[Anant Dabhi]

@ArturKlesun , It formats the string as two uppercase hexadecimal characters.

[Marc.2377]

One-liner, in method syntax: return string.Join( "", hash.ComputeHash( Encoding.UTF8.GetBytes(observedText) ).Select( x => x.ToString("x2") ) );

[Marc.2377]

... in which case, I propose return string.Concat( hash.ComputeHash( Encoding.UTF8.GetBytes(observedText) ).Select( x => x.ToString("x2") ) ); instead. It's a little bit shorter, possibly clearer intention, and performs marginally faster (<10% perf. increase).

[jklemmack]

@PrashantPimpale MD5 is one way - it can create a hash, but information is destroyed and cannot be recovered. It's value comes from hashing two different things then comparing the hashes. Works well for things like passwords, or comparing file contents. If you want to reverse "encryption", the look at things like AES or DES (docs.microsoft.com/en-us/dotnet/api/…). They provide the ability to "encrypt" then "decrypt"

[Detail]

This worked nicely for me when trying to convert an MD5 Hash (from Azure Blob properties) into a string. It produces exactly the same string as the Azure Storage container does.

[Jawad Zeb]

for those who are trying to calculate for Sip or an equivalent to linux md5sum don't forget to add .ToLower()

[Kurtis Jungersen]

NOTE: "Due to collision problems with MD5/SHA1, Microsoft recommends SHA256 or SHA512. Consider using the SHA256 class or the SHA512 class instead of the MD5 class. Use MD5 only for compatibility with legacy applications and data." Sources: 1) MD5 Docs linked by OP, where this notice appears, and 2) MS Docs on SHA256, with a good example

[Rey]

This does not dispose the instance of MD5

[nivs1978]

Remember a "using": using (var md5 = MD5.Create()) md5.ComputeHash(....);

[Ivandro Jao]

Using BitConverter.ToString() also gives a nice hash-string!