Programming Hashing Algorithms (part 3) - Hashing Data from Memory

3. Hashing Data from Memory

The simplest way to generate a hash code is to use data held in memory. The overloaded ComputeHash method is able to create a hash code from a byte array, as shown by the following signature:

# C#

public byte[] ComputeHash(
   byte[] buffer
); 

# Visual Basic .NET

Overloads Public Function ComputeHash( _
   ByVal buffer(  ) As Byte _
) As Byte(  )

The ComputeHash returns a byte array that contains the hash code for the message data. The following class demonstrates how to create a hash code for a StringSystem.Text.Encoding class to convert the string to a byte array: value; note that you should use the

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# C#

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

class StringHash {

        static void Main(string[] args) {
        
        // define the string that we will
        // create a hash code for
        String x_str = "Programming .NET Security";

        // create a byte array from the string
        byte[] x_message_data = Encoding.Default.GetBytes(x_str);

        // create an instance of the MD5 hashing algorithm
        HashAlgorithm x_hash_alg = HashAlgorithm.Create("MD5");

        // obtain the hash code from the HashAlgorithm by 
        // using the ComputeHash method
        byte[] x_hash_code = x_hash_alg.ComputeHash(x_message_data);

        // print out the hash code to the console
        foreach (byte x_byte in x_hash_code) {
            Console.Write("{0:X2} ", x_byte);
        }
        }
}

# Visual Basic .NET

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

Module StringHash 

    Sub Main(  )
        ' define the string that we will
        ' create a hash code for
        Dim x_str As String = "Programming .NET Security"

        ' create a byte array from the string
        Dim x_message_data(  ) As Byte = Encoding.Default.GetBytes(x_str)

        ' create an instance of the MD5 hashing algorithm
        Dim x_hash_alg As HashAlgorithm = HashAlgorithm.Create("MD5")

        ' obtain the hash code from the HashAlgorithm by 
        ' using the ComputeHash method
        Dim x_hash_code(  ) As Byte = x_hash_alg.ComputeHash(x_message_data)

        ' print out the hash code to the console
        Dim x_byte As Byte
        For Each x_byte In x_hash_code
            Console.Write("{0:X2} ", x_byte)
        Next
    End Sub

End Module

					  

The output from this example is:

E1 62 9F C2 96 85 C3 A4 5B 94 97 57 D8 9C 65 78

To make the hash code easier to read, convert each byte to a hexadecimal value and print a space between each one. When you used the ComputeHash method in the previous example, you wanted to process an entire byte array; however, the HashAlgorithm class includes a different version of the method, which can process a region of a byte array:

# C#

public byte[] ComputeHash(
   byte[] buffer,
   int offset,
   int count
);

# Visual Basic .NET

Overloads Public Function ComputeHash( _
   ByVal buffer(  ) As Byte, _
   ByVal offset As Integer, _
   ByVal count As Integer _
) As Byte(  )