Section 148.3: MD5

Hash functions map binary strings of an arbitrary length to small binary strings of a fixed length.

The MD5 algorithm is a widely used hash function producing a 128-bit hash value (16 Bytes, 32 Hexdecimal characters).

The ComputeHash method of the System.Security.Cryptography.MD5 class returns the hash as an array of 16

bytes.

Example:

using System;

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

internal class Program

{

private static void Main()

{

var source = "Hello World!";

// Creates an instance of the default implementation of the MD5 hash algorithm. using (var md5Hash = MD5.Create())

{

// Byte array representation of source string

var sourceBytes = Encoding.UTF8.GetBytes(source);

//Generate hash value(Byte Array) for input data var hashBytes = md5Hash.ComputeHash(sourceBytes);

//Convert hash byte array to string

var hash = BitConverter.ToString(hashBytes).Replace("-", string.Empty);

// Output the MD5 hash

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

}

}

}

Output: The MD5 hash of Hello World! is: ED076287532E86365E841E92BFC50D8C

Security Issues:

Like most hash functions, MD5 is neither encryption nor encoding. It can be reversed by brute-force attack and su ers from extensive vulnerabilities against collision and preimage attacks.

Section 148.4: SHA1

using System;

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

namespace ConsoleApplication1

{

class Program

{

static void Main(string[] args)

{

string source = "Hello World!";

using (SHA1 sha1Hash = SHA1.Create())

{

//From String to byte array

byte[] sourceBytes = Encoding.UTF8.GetBytes(source); byte[] hashBytes = sha1Hash.ComputeHash(sourceBytes);

string hash = BitConverter.ToString(hashBytes).Replace("-",String.Empty);

Console.WriteLine("The SHA1 hash of " + source + " is: " + hash);

}

}

}

}

Output:

The SHA1 hash of Hello Word! is: 2EF7BDE608CE5404E97D5F042F95F89F1C232871

Section 148.5: SHA256

using System;

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

namespace ConsoleApplication1

{

class Program

{

static void Main(string[] args)

{

string source = "Hello World!";

using (SHA256 sha256Hash = SHA256.Create())

{

//From String to byte array

byte[] sourceBytes = Encoding.UTF8.GetBytes(source); byte[] hashBytes = sha256Hash.ComputeHash(sourceBytes);

string hash = BitConverter.ToString(hashBytes).Replace("-", String.Empty);

Console.WriteLine("The SHA256 hash of " + source + " is: " + hash);

}

}

}

}

Output:

The SHA256 hash of Hello World! is: 7F83B1657FF1FC53B92DC18148A1D65DFC2D4B1FA3D677284ADDD200126D9069

Section 148.6: SHA384

using System;

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

namespace ConsoleApplication1

{

class Program

{

static void Main(string[] args)

{

string source = "Hello World!";

using (SHA384 sha384Hash = SHA384.Create())

{

//From String to byte array

byte[] sourceBytes = Encoding.UTF8.GetBytes(source); byte[] hashBytes = sha384Hash.ComputeHash(sourceBytes);

string hash = BitConverter.ToString(hashBytes).Replace("-", String.Empty);

Console.WriteLine("The SHA384 hash of " + source + " is: " + hash);

}

}

}

}

Output:

The SHA384 hash of Hello World! is: BFD76C0EBBD006FEE583410547C1887B0292BE76D582D96C242D2A792723E3FD6FD061F9D5CFD13B8F961358E6A DBA4A

Section 148.7: SHA512

using System;

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

namespace ConsoleApplication1

{

class Program

{

static void Main(string[] args)

{

string source = "Hello World!";

using (SHA512 sha512Hash = SHA512.Create())

{

//From String to byte array

byte[] sourceBytes = Encoding.UTF8.GetBytes(source); byte[] hashBytes = sha512Hash.ComputeHash(sourceBytes);

string hash = BitConverter.ToString(hashBytes).Replace("-", String.Empty);

Console.WriteLine("The SHA512 hash of " + source + " is: " + hash);

}

}

}

}

Output: The SHA512 hash of Hello World! is: 861844D6704E8573FEC34D967E20BCFEF3D424CF48BE04E6DC08F2BD58C729743371015EAD891CC3CF1C9D34B49 264B510751B1FF9E537937BC46B5D6FF4ECC8

Chapter 149: Generating Random Numbers

in C#

Section 149.1: Generate a random int

This example generates random values between 0 and 2147483647.

Random rnd = new Random();

int randomNumber = rnd.Next();

Section 149.2: Generate a random int in a given range

Generate a random number between minValue and maxValue - 1.

Random rnd = new Random();

var randomBetween10And20 = rnd.Next(10, 20);

Section 149.3: Generating the same sequence of random numbers over and over again

When creating Random instances with the same seed, the same numbers will be generated.

int seed = 5;

for (int i = 0; i < 2; i++)

{

Console.WriteLine("Random instance " + i); Random rnd = new Random(seed);

for (int j = 0; j < 5; j++)

{

Console.Write(rnd.Next()); Console.Write(" ");

}

Console.WriteLine();

}

Output: