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A Very Easy to Use Excel XML Import-Export Library

, 25 Nov 2008 CPOL
Import export library for the Excel XML format, which reduces a programmer's work to the bare minimum.
using System;
using System.Diagnostics.CodeAnalysis;
using System.IO;
using System.Security.Cryptography;

namespace Yogesh.Extensions
{
	/// <summary>
	/// Encryption and decryption methods based on a password key.
	/// </summary>
	public static class EncryptDecrypt
	{
		// Encrypt a byte array into a byte array using a key and an IV
		/// <summary>
		/// Encrypt a byte array into a byte array using a key and an IV
		/// </summary>
		/// <param name="clearData">Byte array to encrypt</param>
		/// <param name="key">Key</param>
		/// <param name="IV">IV</param>
		/// <returns>Encrypted byte array</returns>
		[SuppressMessage("Microsoft.Naming", "CA1709:IdentifiersShouldBeCasedCorrectly", MessageId = "IV")]
		public static byte[] Encrypt(byte[] clearData, byte[] key, byte[] IV)
		{
			// Create a MemoryStream that is going to accept the encrypted 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 before it is encrypted, and then each encrypted block is XORed with the
			// following block of plaintext. 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.CreateEncryptor(), CryptoStreamMode.Write);

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

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

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

			return encryptedData;
		}

		// Encrypt a string into a string using a password
		//    Uses Encrypt(byte[], byte[], byte[])
		/// <summary>
		/// Encrypt a string into a string using a password
		/// </summary>
		/// <param name="clearText">String to encrypt</param>
		/// <param name="password">Password</param>
		/// <returns>Encrypted string</returns>
		public static string Encrypt(string clearText, string password)
		{
			// First we need to turn the input string into a byte array.
			byte[] clearBytes = System.Text.Encoding.Unicode.GetBytes(clearText);

			// 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 encryption 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[] encryptedData = Encrypt(clearBytes, 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 Convert.ToBase64String(encryptedData);
		}

		// Encrypt bytes into bytes using a password
		//    Uses Encrypt(byte[], byte[], byte[])
		/// <summary>
		/// Encrypt bytes into bytes using a password
		/// </summary>
		/// <param name="clearData">Byte array to encrypt</param>
		/// <param name="password">Password</param>
		/// <returns>Encrypted byte array</returns>
		public static byte[] Encrypt(byte[] clearData, 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 encryption 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 Encrypt(clearData, pdb.GetBytes(32), pdb.GetBytes(16));
		}

		// Encrypt a file into another file using a password
		/// <summary>
		/// Encrypt a file into another file using a password
		/// </summary>
		/// <param name="fileIn">File to be encrypted</param>
		/// <param name="fileOut">Filename where encrypted data will be saved</param>
		/// <param name="password">Password</param>
		public static void Encrypt(string fileIn, string fileOut, string password)
		{
			// 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 encrypted bytes.
			CryptoStream cs = new CryptoStream(fsOut, alg.CreateEncryptor(), 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);

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

			} while (bytesRead != 0);

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

		// Decrypt a byte array into a byte array using a key and an IV
		/// <summary>
		/// Decrypt a byte array into a byte array using a key and an IV
		/// </summary>
		/// <param name="cipherData">Byte array to decrypt</param>
		/// <param name="key">Password Key</param>
		/// <param name="IV">IV</param>
		/// <returns>Returns decrypted byte array</returns>
		[SuppressMessage("Microsoft.Naming", "CA1709:IdentifiersShouldBeCasedCorrectly", MessageId = "IV")]
		public static byte[] Decrypt(byte[] cipherData, byte[] key, byte[] IV)
		{
			// 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;
		}

		// Decrypt a string into a string using a password
		//    Uses Decrypt(byte[], byte[], byte[])
		/// <summary>
		/// Decrypt a string into a string using a password
		/// </summary>
		/// <param name="cipherText">String to decrypt</param>
		/// <param name="password">password</param>
		/// <returns>Decrypted string</returns>
		public static string Decrypt(string cipherText, string password)
		{
			// 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);
		}

		// Decrypt bytes into bytes using a password
		//    Uses Decrypt(byte[], byte[], byte[])
		/// <summary>
		/// Decrypt bytes into bytes using a password
		/// </summary>
		/// <param name="cipherData">Byte array to decrypt</param>
		/// <param name="password">password</param>
		/// <returns>Returns decrypted byte array</returns>
		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
		/// <summary>
		/// Decrypt a file into another file using a password
		/// </summary>
		/// <param name="fileIn">File to decrypt</param>
		/// <param name="fileOut">Filename where decrypted data will be saved</param>
		/// <param name="password">password</param>
		public static void Decrypt(string fileIn, string fileOut, string password)
		{
			// 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();
		}
	}
}

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