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SECURITY

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

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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

# 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( )
Other  
 
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