MD5 Class

Represents the abstract class from which all implementations of the MD5 hash algorithm inherit.

Namespace: System.Security.Cryptography
Assembly: mscorlib (in mscorlib.dll)

public abstract class MD5 : HashAlgorithm
/** @attribute ComVisibleAttribute(true) */ 
public abstract class MD5 extends HashAlgorithm
public abstract class MD5 extends HashAlgorithm
Not applicable.

Hash functions map binary strings of an arbitrary length to small binary strings of a fixed length. A cryptographic hash function has the property that it is computationally infeasible to find two distinct inputs that hash to the same value; that is, hashes of two sets of data should match if the corresponding data also matches. Small changes to the data result in large, unpredictable changes in the hash.

The hash size for the MD5 algorithm is 128 bits.

The ComputeHash methods of the MD5 class return the hash as an array of 16 bytes. Note that some MD5 implementations produce a 32-character, hexadecimal-formatted hash. To interoperate with such implementations, format the return value of the ComputeHash methods as a hexadecimal value.

The following code example computes the MD5 hash value of a string and returns the hash as a 32-character, hexadecimal-formatted string. The hash string created by this code example is compatible with any MD5 hash function (on any platform) that creates a 32-character, hexadecimal-formatted hash string.

using System;
using System.Security.Cryptography;
using System.Text;

class Example
    // Hash an input string and return the hash as
    // a 32 character hexadecimal string.
    static string getMd5Hash(string input)
        // Create a new instance of the MD5CryptoServiceProvider object.
        MD5 md5Hasher = MD5.Create();

        // Convert the input string to a byte array and compute the hash.
        byte[] data = md5Hasher.ComputeHash(Encoding.Default.GetBytes(input));

        // Create a new Stringbuilder to collect the bytes
        // and create a string.
        StringBuilder sBuilder = new StringBuilder();

        // Loop through each byte of the hashed data 
        // and format each one as a hexadecimal string.
        for (int i = 0; i < data.Length; i++)

        // Return the hexadecimal string.
        return sBuilder.ToString();

    // Verify a hash against a string.
    static bool verifyMd5Hash(string input, string hash)
        // Hash the input.
        string hashOfInput = getMd5Hash(input);

        // Create a StringComparer an comare the hashes.
        StringComparer comparer = StringComparer.OrdinalIgnoreCase;

        if (0 == comparer.Compare(hashOfInput, hash))
            return true;
            return false;

    static void Main()
        string source = "Hello World!";
        string hash = getMd5Hash(source);

        Console.WriteLine("The MD5 hash of " + source + " is: " + hash + ".");

        Console.WriteLine("Verifying the hash...");

        if (verifyMd5Hash(source, hash))
            Console.WriteLine("The hashes are the same.");
            Console.WriteLine("The hashes are not same.");
// This code example produces the following output:
// The MD5 hash of Hello World! is: ed076287532e86365e841e92bfc50d8c.
// Verifying the hash...
// The hashes are the same.

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

Windows 98, Windows Server 2000 SP4, Windows CE, Windows Millennium Edition, Windows Mobile for Pocket PC, Windows Mobile for Smartphone, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition

The Microsoft .NET Framework 3.0 is supported on Windows Vista, Microsoft Windows XP SP2, and Windows Server 2003 SP1.

.NET Framework

Supported in: 3.0, 2.0, 1.1, 1.0

.NET Compact Framework

Supported in: 2.0

Community Additions