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MD5 Class

Updated: February 2009

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

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

'Declaration
<ComVisibleAttribute(True)> _
Public MustInherit Class MD5 _
	Inherits HashAlgorithm
'Usage
Dim instance As MD5

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.

NoteNote:

Newer hash functions, such as the Secure Hash Algorithms SHA-256 and SHA-512, are available. Consider using the SHA256 class or the SHA512 class instead of the MD5 class.

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.

Imports System
Imports System.Security.Cryptography
Imports System.Text


Class Program

    Shared Sub Main(ByVal args() As String)
        Dim [source] As String = "Hello World!" 
        Using md5Hash As MD5 = MD5.Create()

            Dim hash As String = GetMd5Hash(md5Hash, source)

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

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

            If VerifyMd5Hash(md5Hash, [source], hash) Then
                Console.WriteLine("The hashes are the same.")
            Else
                Console.WriteLine("The hashes are not same.")
            End If 
        End Using 
    End Sub 'Main



    Shared Function GetMd5Hash(ByVal md5Hash As MD5, ByVal input As String) As String 

        ' Convert the input string to a byte array and compute the hash. 
        Dim data As Byte() = md5Hash.ComputeHash(Encoding.UTF8.GetBytes(input))

        ' Create a new Stringbuilder to collect the bytes 
        ' and create a string. 
        Dim sBuilder As New StringBuilder()

        ' Loop through each byte of the hashed data  
        ' and format each one as a hexadecimal string. 
        Dim i As Integer 
        For i = 0 To data.Length - 1
            sBuilder.Append(data(i).ToString("x2"))
        Next i

        ' Return the hexadecimal string. 
        Return sBuilder.ToString()

    End Function 'GetMd5Hash


    ' Verify a hash against a string. 
    Shared Function VerifyMd5Hash(ByVal md5Hash As MD5, ByVal input As String, ByVal hash As String) As Boolean 
        ' Hash the input. 
        Dim hashOfInput As String = GetMd5Hash(md5Hash, input)

        ' Create a StringComparer an compare the hashes. 
        Dim comparer As StringComparer = StringComparer.OrdinalIgnoreCase

        If 0 = comparer.Compare(hashOfInput, hash) Then 
            Return True 
        Else 
            Return False 
        End If 

    End Function 'VerifyMd5Hash
End Class 'Program 
' 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 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98, Windows CE, Windows Mobile for Smartphone, Windows Mobile for Pocket PC

The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

.NET Framework

Supported in: 3.5, 3.0, 2.0, 1.1, 1.0

.NET Compact Framework

Supported in: 3.5, 2.0

Date

History

Reason

February 2009

Added note about newer hash functions SHA-256 and SHA-512.

Information enhancement.

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