Using AES encryption in C#

What is AES  ?

The Advanced Encryption Standard (AES) is a specification for the encryption of electronic data established by the U.S. National Institute of Standards and Technology (NIST) in 2001.[4]

AES is based on the Rijndael cipher[5] developed by two Belgian cryptographers, Joan Daemen and Vincent Rijmen, who submitted a proposal to NIST during the AES selection process.[6] Rijndael is a family of ciphers with different key and block sizes.

For AES, NIST selected three members of the Rijndael family, each with a block size of 128 bits, but three different key lengths: 128, 192 and 256 bits.

Using AES encryption in C#

1. Encrypting data :

The following function takes 3 parameters
    1-The first parameter is byte array of the data that has to be encrypted .
    2-The second parameter is the key that will be used to encrypt the data
    3-Third parameter is the initialization vector .
The function returns the encrypted byte array .

AesCryptoServiceProvider :

Performs symmetric encryption and decryption using the Cryptographic Application Programming Interfaces (CAPI) implementation of the Advanced Encryption Standard (AES) algorithm.

CreateEncryptor :  This function takes key and IV to create a symmetric encryptor object with the current Key property and initialization vector (IV) . If Key or IV is null the GenerateKey method is called to create a new random Key or IV .

 public byte[] encryptdata(byte[] bytearraytoencrypt, string key, string iv)  
     {  
       AesCryptoServiceProvider dataencrypt = new AesCryptoServiceProvider();  
       //Block size : Gets or sets the block size, in bits, of the cryptographic operation.  
       dataencrypt.BlockSize = 128;  
       //KeySize: Gets or sets the size, in bits, of the secret key  
       dataencrypt.KeySize = 128;  
       //Key: Gets or sets the symmetric key that is used for encryption and decryption.  
       dataencrypt.Key = System.Text.Encoding.UTF8.GetBytes(key);  
       //IV : Gets or sets the initialization vector (IV) for the symmetric algorithm  
       dataencrypt.IV = System.Text.Encoding.UTF8.GetBytes(iv);  
       //Padding: Gets or sets the padding mode used in the symmetric algorithm  
       dataencrypt.Padding = PaddingMode.PKCS7;  
       //Mode: Gets or sets the mode for operation of the symmetric algorithm  
       dataencrypt.Mode = CipherMode.CBC;  
       //Creates a symmetric AES encryptor object using the current key and initialization vector (IV).  
       ICryptoTransform crypto1 = dataencrypt.CreateEncryptor(dataencrypt.Key, dataencrypt.IV);  
       //TransformFinalBlock is a special function for transforming the last block or a partial block in the stream.   
       //It returns a new array that contains the remaining transformed bytes. A new array is returned, because the amount of   
       //information returned at the end might be larger than a single block when padding is added.  
       byte[] encrypteddata = crypto1.TransformFinalBlock(bytearraytoencrypt, 0, bytearraytoencrypt.Length);  
       crypto1.Dispose();  
       //return the encrypted data  
       return encrypteddata;  
     }  

Decrypting data :

 The following function takes 3 parameters
    1-The first parameter is byte array of the data that has to be decrypted .
    2-The second parameter is the key that will be used to decrypt the data
    3-Third parameter is the initialization vector .
The function returns the decrypted byte array .

     private byte[] decryptdata(byte[] bytearraytodecrypt, string key, string iv)  
     {  

       AesCryptoServiceProvider keydecrypt = new AesCryptoServiceProvider();  
       keydecrypt.BlockSize = 128;  
       keydecrypt.KeySize = 128;  
       keydecrypt.Key = System.Text.Encoding.UTF8.GetBytes(key);  
       keydecrypt.IV = System.Text.Encoding.UTF8.GetBytes(iv);  
       keydecrypt.Padding = PaddingMode.PKCS7;  
       keydecrypt.Mode = CipherMode.CBC;  
       ICryptoTransform crypto1 = keydecrypt.CreateDecryptor(keydecrypt.Key, keydecrypt.IV);  
      
       byte[] returnbytearray = crypto1.TransformFinalBlock(bytearraytodecrypt, 0, bytearraytodecrypt.Length);  
       crypto1.Dispose();  
       return returnbytearray;  
     }