Decrypt Utils : Encrypt Decrypt « Security « C# / C Sharp






Decrypt Utils

   

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using System;
using System.Security.Cryptography;
using System.Text;
using System.Globalization;
using System.IO;

namespace WOSI.Utilities
{
  /// <summary>
  /// Summary description for CryptoUtils.
  /// </summary>
  public class CryptoUtils
  {
    private CryptoUtils()
    {
      //
      // TODO: Add constructor logic here
      //
    }

    // Decrypt a byte array into a byte array using a key and an IV 
    public static byte[] Decrypt(byte[] cipherData, 
      byte[] Key, byte[] IV) 
    {
            try
            {
                // Create a MemoryStream that is going to accept the
                // decrypted bytes 
                MemoryStream ms = new MemoryStream();

                // Create a symmetric algorithm. 
                // We are going to use Rijndael because it is strong and
                // available on all platforms. 
                // You can use other algorithms, to do so substitute the next
                // line with something like 
                //     TripleDES alg = TripleDES.Create(); 
                Rijndael alg = Rijndael.Create();

                // Now set the key and the IV. 
                // We need the IV (Initialization Vector) because the algorithm
                // is operating in its default 
                // mode called CBC (Cipher Block Chaining). The IV is XORed with
                // the first block (8 byte) 
                // of the data after it is decrypted, and then each decrypted
                // block is XORed with the previous 
                // cipher block. This is done to make encryption more secure. 
                // There is also a mode called ECB which does not need an IV,
                // but it is much less secure. 
                alg.Key = Key;
                alg.IV = IV;

                // Create a CryptoStream through which we are going to be
                // pumping our data. 
                // CryptoStreamMode.Write means that we are going to be
                // writing data to the stream 
                // and the output will be written in the MemoryStream
                // we have provided. 
                CryptoStream cs = new CryptoStream(ms,
                    alg.CreateDecryptor(), CryptoStreamMode.Write);

                // Write the data and make it do the decryption 
                cs.Write(cipherData, 0, cipherData.Length);

                // Close the crypto stream (or do FlushFinalBlock). 
                // This will tell it that we have done our decryption
                // and there is no more data coming in, 
                // and it is now a good time to remove the padding
                // and finalize the decryption process. 
                cs.Close();

                // Now get the decrypted data from the MemoryStream. 
                // Some people make a mistake of using GetBuffer() here,
                // which is not the right way. 
                byte[] decryptedData = ms.ToArray();

                return decryptedData;
            }
            catch
            {
                return null;
            }
    }

    // Decrypt a string into a string using a password 
    //    Uses Decrypt(byte[], byte[], byte[]) 

    public static string Decrypt(string cipherText, string Password) 
    {
            try
            {
                // First we need to turn the input string into a byte array. 
                // We presume that Base64 encoding was used 
                byte[] cipherBytes = Convert.FromBase64String(cipherText);

                // Then, we need to turn the password into Key and IV 
                // We are using salt to make it harder to guess our key
                // using a dictionary attack - 
                // trying to guess a password by enumerating all possible words. 
                PasswordDeriveBytes pdb = new PasswordDeriveBytes(Password,
                    new byte[] {0x49, 0x76, 0x61, 0x6e, 0x20, 0x4d, 0x65, 
                 0x64, 0x76, 0x65, 0x64, 0x65, 0x76});

                // Now get the key/IV and do the decryption using
                // the function that accepts byte arrays. 
                // Using PasswordDeriveBytes object we are first
                // getting 32 bytes for the Key 
                // (the default Rijndael key length is 256bit = 32bytes)
                // and then 16 bytes for the IV. 
                // IV should always be the block size, which is by
                // default 16 bytes (128 bit) for Rijndael. 
                // If you are using DES/TripleDES/RC2 the block size is
                // 8 bytes and so should be the IV size. 
                // You can also read KeySize/BlockSize properties off
                // the algorithm to find out the sizes. 
                byte[] decryptedData = Decrypt(cipherBytes,
                    pdb.GetBytes(32), pdb.GetBytes(16));

                // Now we need to turn the resulting byte array into a string. 
                // A common mistake would be to use an Encoding class for that.
                // It does not work 
                // because not all byte values can be represented by characters. 
                // We are going to be using Base64 encoding that is 
                // designed exactly for what we are trying to do. 
                return System.Text.Encoding.Unicode.GetString(decryptedData);
            }
            catch
            {
                return null;
            }
    }

    // Decrypt bytes into bytes using a password 
    //    Uses Decrypt(byte[], byte[], byte[]) 

    public static byte[] Decrypt(byte[] cipherData, string Password) 
    { 
      // We need to turn the password into Key and IV. 
      // We are using salt to make it harder to guess our key
      // using a dictionary attack - 
      // trying to guess a password by enumerating all possible words. 
      PasswordDeriveBytes pdb = new PasswordDeriveBytes(Password, 
        new byte[] {0x49, 0x76, 0x61, 0x6e, 0x20, 0x4d, 
                 0x65, 0x64, 0x76, 0x65, 0x64, 0x65, 0x76}); 

      // Now get the key/IV and do the Decryption using the 
      //function that accepts byte arrays. 
      // Using PasswordDeriveBytes object we are first getting
      // 32 bytes for the Key 
      // (the default Rijndael key length is 256bit = 32bytes)
      // and then 16 bytes for the IV. 
      // IV should always be the block size, which is by default
      // 16 bytes (128 bit) for Rijndael. 
      // If you are using DES/TripleDES/RC2 the block size is
      // 8 bytes and so should be the IV size. 

      // You can also read KeySize/BlockSize properties off the
      // algorithm to find out the sizes. 
      return Decrypt(cipherData, pdb.GetBytes(32), pdb.GetBytes(16)); 
    }

    // Decrypt a file into another file using a password 
    public static void Decrypt(string fileIn, 
      string fileOut, string Password) 
    {
            try
            {
                // First we are going to open the file streams 
                FileStream fsIn = new FileStream(fileIn,
                    FileMode.Open, FileAccess.Read);
                FileStream fsOut = new FileStream(fileOut,
                    FileMode.OpenOrCreate, FileAccess.Write);

                // Then we are going to derive a Key and an IV from
                // the Password and create an algorithm 
                PasswordDeriveBytes pdb = new PasswordDeriveBytes(Password,
                    new byte[] {0x49, 0x76, 0x61, 0x6e, 0x20, 0x4d, 
                 0x65, 0x64, 0x76, 0x65, 0x64, 0x65, 0x76});
                Rijndael alg = Rijndael.Create();

                alg.Key = pdb.GetBytes(32);
                alg.IV = pdb.GetBytes(16);

                // Now create a crypto stream through which we are going
                // to be pumping data. 
                // Our fileOut is going to be receiving the Decrypted bytes. 
                CryptoStream cs = new CryptoStream(fsOut,
                    alg.CreateDecryptor(), CryptoStreamMode.Write);

                // Now will will initialize a buffer and will be 
                // processing the input file in chunks. 
                // This is done to avoid reading the whole file (which can be
                // huge) into memory. 
                int bufferLen = 4096;
                byte[] buffer = new byte[bufferLen];
                int bytesRead;

                do
                {
                    // read a chunk of data from the input file 
                    bytesRead = fsIn.Read(buffer, 0, bufferLen);

                    // Decrypt it 
                    cs.Write(buffer, 0, bytesRead);

                } while (bytesRead != 0);

                // close everything 
                cs.Close(); // this will also close the unrelying fsOut stream 
                fsIn.Close();
            }
            catch
            {
            }
    }
  }
}

   
    
    
  








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