Encrypting and Decrypting Data in C

8/2/2019 Encrypting and Decrypting Data in C

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Encrypting and Decrypting Data in C#.NET.....

Hello Friends,

The security of the Data is most important in Softwares and our job is to protect it from the

attackers. You can use cryptography to protect the privacy and integrity of the data that yourapplication stores or transfers. Fortunately, .NET Framework provides classes for several

different types of cryptography, including symmetric and asymmetric encryption, hashing, and

digital signatures.

Encrypting and Decrypting Data with Symmetric Keys

Many people are introduced to encryption at an early age. Children protect even the most

mundane communications from imaginary spies with a secret decoder ringa toy with two rings

that translates encrypted characters to unencrypted characters. The rings on a decoder ring rotate,

and a message can be decrypted only when the two rings are lined up correctly. To exchange an

encrypted message, the children must first agree on how the rings will line up. After they haveexchanged this secret piece of information, they can freely pass encrypted messages without

worrying that someone will be able to decrypt them. Even if an imaginary spy had a decoderring, the spy would need to know how to position the rings to decrypt the message.

Because both the sender and the recipient of the message must know the same secret to encryptand decrypt a message, secret decoder rings are an example of symmetric key encryption.

Symmetric key encryption is a game for children, but it is also the foundation for most encryptedcommunications today. As children know, encryption is a fun topic. You should enjoy building it

into your application, and you'll greatly reduce the chance of private data being compromised.

What Is Symmetric Key Encryption?Symmetric key encryption, also known as secret-key encryption, is a cryptography technique that

uses a single secret key to both encrypt and decrypt data. Symmetric encryption algorithms (alsocalled ciphers) process plain text with the secret encryption key to create encrypted data called

cipher text. The cipher text cannot easily be decrypted into the plain text without possession of


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the secret key.

Symmetric Algorithm Classes in the .NET FrameworkMost of the .NET Framework's cryptography functionality is built into the

System.Security.Cryptography namespace, including the four implementations of symmetricencryption algorithms. Table 12-2 shows symmetric encryption algorithm classes.

RijndaelManagedKey Length: 128 through 256 bits, in 32-bit increments

Description: The .NET Framework implementation of the Rijndael symmetric encryption

algorithm. As a government encryption standard, this algorithm is also known as Advanced

Encryption Standard, or AES.RijndaelManaged is the only .NET Framework symmetricencryption class that is fully managed. All other encryption classes call unmanaged code.

Because of this, RijndaelManaged is the preferred choice when your application will be running

in a partially trusted environment.

RC2

Key Length: VariableDescription: An encryption standard designed to replace DES that uses variable key sizes.

DESKey Length: 56 bits

Description: The Data Encryption Standard (DES) is a symmetric encryption algorithm that usesrelatively short key lengths that are vulnerable to cracking attacks. As a result, it should be

avoided. However, it remains commonly used because it is compatible with a wide range of
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legacy platforms.

TripleDESKey Length: 156 bits, of which only 112 bits are effectively used for encryption

Description: The .NET Framework implementation of the Triple DES (3DES) symmetric

encryption algorithm, it essentially applies the DES algorithm three times.

How to Encrypt and Decrypt Messages Using Symmetric KeysAfter both the encryptor and decryptor have the same key, they can begin exchanging encrypted

messages. The .NET Framework makes this process easy. In fact, using encryption is similar to

reading and writing to standard files and streams, and it requires only a few additional lines ofcode. To encrypt or decrypt messages in your application, perform the following tasks:

1. Create a Stream object to interface with the memory or file that you will be reading from or

writing to.

2. Create a SymmetricAlgorithm object.

3. Specify the algorithm's key, the IV, or both.

4. Call SymmetricAlgorithm.CreateEncryptor() or SymmetricAlgorithm.CreateDecryptor() tocreate a ICryptoTransform object.

5. Create a CryptoStream object using the Stream object and the ICryptoTransform object.

6. Read from or write to the CryptoStream object just like any other Stream object.

The following console application demonstrates these steps by reading an unencrypted file (the

C:\Boot.ini file), encrypting it with the Rijndael algorithm, and saving the encrypted results as anew file. The application requires the System.IO and System.Security.Cryptography namespaces.

// C#

string inFileName = @"C:\Boot.ini";string outFileName = @"C:\Boot.ini.enc";

// Step 1: Create the Stream objectsFileStream inFile = new FileStream(inFileName, FileMode.Open, FileAccess.Read);

FileStream outFile = new FileStream(outFileName, FileMode.OpenOrCreate, FileAccess.Write);

// Step 2: Create the SymmetricAlgorithm objectSymmetricAlgorithm myAlg = new RijndaelManaged();

// Step 3: Specify a key (optional)myAlg.GenerateKey();

// Read the unencrypted file into fileData


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byte[] fileData = new byte[inFile.Length];

inFile.Read(fileData, 0, (int)inFile.Length);

// Step 4: Create the ICryptoTransform object

ICryptoTransform encryptor = myAlg.CreateEncryptor();

// Step 5: Create the CryptoStream object

CryptoStream encryptStream = new CryptoStream(outFile, encryptor,

CryptoStreamMode.Write);

// Step 6: Write the contents to the CryptoStream

encryptStream.Write(fileData, 0, fileData.Length);

// Close the file handles

encryptStream.Close();

inFile.Close();

outFile.Close();

Because the key is randomly generated, running the application repeatedly generates differentresults each time. Because the key is not stored, the file can never be decrypted. The key is

simply an array of bytes and can be stored by using the BinaryWriter object or by transferring

the key across a network.

The code for decrypting a file is almost identical to the code for encrypting a file, except that it

must read the encryption key that was used to encrypt the data rather than randomly generate it,

and it must call decryption methods instead of encryption methods. To reverse the process todecrypt a file, simply make the following changes to an application:

Change the code for step 3 to read the key and IV that was used to encrypt the data.

Change the code for step 4 to use the CreateDecryptor method instead of CreateEncryptor.

Change the code for step 5 to use the CryptoStreamMode.Read enumeration instead ofCryptoStreamMode.Write.

Change the code for step 6 to read from the CryptoStream object.

How to Encrypt and Decrypt Messages Using Asymmetric EncryptionTo encrypt and decrypt messages using asymmetric encryption, call the

RSACryptoServiceProvider.Encrypt and RSACryptoServiceProvider.Decrypt methods. Bothtake two parameters:

byte[] rgb An array of bytes containing the message to be encrypted or decrypted.

bool fOAEP A Boolean value. When set to true, encryption and encryption will use OAEP data

padding, which is supported only on Windows XP and later operating systems. When set to false,


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PKCS#1 v1.5 data padding will be used. Both the encryption and decryption methods must use

the same data padding.

The most challenging aspect of encryption is converting data into the byte array format. To

convert strings to byte arrays, use the System.Text.Encoding.Unicode.GetBytes and

System.Text.Encoding.Unicode.GetString methods. For example, the following consoleapplication encrypts a string using PKCS#1 v1.5 data padding, and then immediately decrypts

and displays the string:

// C#

string messageString = "Hello, World!";RSACryptoServiceProvider myRsa = new RSACryptoServiceProvider();

byte[] messageBytes = Encoding.Unicode.GetBytes(messageString);

byte[] encryptedMessage = myRsa.Encrypt(messageBytes, false);

byte[] decryptedBytes = myRsa.Decrypt(encryptedMessage, false);

Console.WriteLine(Encoding.Unicode.GetString(decryptedBytes));

Whichever encoding method you use to convert the data into a byte array, be sure you use a

matching decoding method after decrypting the data.

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Encrypting and Decrypting Data in C