Programming Hashing Algorithms (part 4) - Hashing Streamed Data

4. Hashing Streamed Data

You can also create a hash code from a stream of data; this is useful for processing datafiles or for reading data from a network connection. The HashAlgorithm class contains an overloaded version of the ComputeHash method for working with streams:

# C#

public byte[] ComputeHash(
   Stream inputStream
);

# Visual Basic .NET

Overloads Public Function ComputeHash( _
   ByVal inputStream As Stream _
) As Byte(  )

The following class demonstrates how to create a hash code using a stream, in this case streaming data from a file called myfile.txt, which contains the string "Programming .NET Security":

# C#

using System;
using System.IO;
using System.Security.Cryptography;

class StreamHash {

    static void Main(string[] args) {
        
        // create the file stream 
        Stream x_stream = new FileStream("mydata.txt", FileMode.Open);

        // 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_stream);

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

        // close the stream
        x_stream.Close(  );
    }
}

# Visual Basic .NET

Imports System
Imports System.IO
Imports System.Security.Cryptography

Module StreamHash

    Sub Main(  )
        ' create the file stream 
        Dim x_stream As Stream = New FileStream("mydata.txt", FileMode.Open)

        ' 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_stream)

        ' 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

        ' close the stream
        x_stream.Close(  )

    End Sub

End Module

					  

As you might expect, the output from the example, shown below, is the same hash code produced by our first example:

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