form1.cs

清华大学出版社出版的 移动应用开发宝典 张大威（2008）的附书源代码

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Text;
using System.Windows.Forms;
using System.IO;
using System.Security.Cryptography;
using Microsoft.Practices.Mobile.PasswordAuthentication;

namespace Encryption
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private byte[] encryptionKey;

        private void menuItemSave_Click(object sender, EventArgs e)
        {
            // Ask user for a password from which we can derive a key
            encryptionKey = GetEncryptionKey();

            // Encrypt the data
            string encryptedData = EncryptData(encryptionKey, textBox1.Text);

            // Create the output file
            using(StreamWriter sw = new StreamWriter(@"crypt.bin", false))
            {
                sw.Write(encryptedData);
            }

            // Display
            textBox1.Text = encryptedData;
        }

        private byte[] GetEncryptionKey()
        {
            string password;
            using (GetPasswordForm frm = new GetPasswordForm())
            {
                frm.ShowDialog();
                password = frm.Password;
            }

            return DeriveKeyFromPassword(password);
        }

        private byte[] DeriveKeyFromPassword(string password)
        {
            byte[] key;
            using (RsaAesCryptographyProvider provider =
                new RsaAesCryptographyProvider("DevelopersHandbook"))
            {
                CryptNativeHelper crypto = new CryptNativeHelper(provider);
                key = crypto.GetPasswordDerivedKey(password);
            }

            return key;
        }

        /// <summary>
        /// Encrypts a string using Rijndael/AES symmetric key algorithm
        /// </summary>
        /// <param name="enckey">The encryption key</param>
        /// <param name="plainText">String to be encrypted</param>
        /// <returns>Encrypted data as a Base64 encoded string</returns>
        private string EncryptData(byte[] key, string plainText)
        {
            // Get the bytes to encrypt
            byte[] plaintextByte = System.Text.Encoding.Unicode.GetBytes(plainText);

            // Create a Rijndael instance - automatically generates symmetric key
            // and an initialization vector
            RijndaelManaged rijndael = new RijndaelManaged();

            // Set encryption mode 
            rijndael.Mode = CipherMode.ECB;
            rijndael.Padding = PaddingMode.PKCS7;

            // Create a random initialization vector
            rijndael.GenerateIV();
            byte[] iv = rijndael.IV;

            string encodedText = "";

            // Define memory stream which will be used to hold encrypted data.
            MemoryStream memStrm = new MemoryStream();

            // Write the IV length and the IV
            memStrm.Write(BitConverter.GetBytes(iv.Length), 0, 4);
            memStrm.Write(iv, 0, iv.Length);

            // Create a symmetric encryptor
            using (ICryptoTransform encryptor = rijndael.CreateEncryptor(key, iv))
            {
                // Create a CryptStream to write to the output file
                CryptoStream cryptStrm = new CryptoStream(memStrm, encryptor, CryptoStreamMode.Write);

                // Write the content to be encrypted
                cryptStrm.Write(plaintextByte, 0, plaintextByte.Length);
                cryptStrm.FlushFinalBlock();

                // Convert encrypted data from a memory stream into a byte array.
                byte[] cipherTextBytes = memStrm.ToArray();

                // Close the treams
                memStrm.Close();
                cryptStrm.Close();

                // Convert encrypted data into a base64-encoded string.
                encodedText = Convert.ToBase64String(cipherTextBytes);
            }
            return encodedText;
        }

        private void menuItemRestore_Click(object sender, EventArgs e)
        {
            // Ask user for a password from which we can derive the key
            encryptionKey = GetEncryptionKey();

            // Read encrypted data from the file
            string fileContents;
            using (StreamReader sr = new StreamReader(@"crypt.bin"))
            {
                fileContents = sr.ReadToEnd();
            }

            // Write decrypted data back into the TextBox
            textBox1.Text = DecryptData(encryptionKey, fileContents);
        }

        private string DecryptData(byte[] key, string encryptedData)
        {
            string retStr = "";

            // Create a symmetric decryptor
            RijndaelManaged rijndael = new RijndaelManaged();
            rijndael.Mode = CipherMode.ECB;
            rijndael.Padding = PaddingMode.PKCS7;

            // Convert our ciphertext into a byte array.
            byte[] cipherTextBytes = Convert.FromBase64String(encryptedData);
            // Define memory stream to use to read encrypted data.
            MemoryStream inStream = new MemoryStream(cipherTextBytes);

            // Read the IV length from the buffer
            int ivLength = BitConverter.ToInt32(cipherTextBytes, 0);
            // Reposition to after 'length' bytes in stream
            inStream.Position = 4;

            // Read the IV from the input stream 
            byte[] iv = new byte[ivLength];
            inStream.Read(iv, 0, ivLength);

            using (ICryptoTransform decryptor = rijndael.CreateDecryptor(key, iv))
            {
                // Create a CryptStream to read from the file
                CryptoStream cryptStrm = new CryptoStream(inStream, decryptor, CryptoStreamMode.Read);

                // Create another MemoryStream for the output
                MemoryStream memStrm = new MemoryStream();
                byte[] buffer = new byte[2048];
                int totalbytes = 0;
                do
                {
                    int bytesRead = cryptStrm.Read(buffer, 0, buffer.Length);
                    if (bytesRead == 0)
                        break;
                    memStrm.Write(buffer, 0, bytesRead);
                    totalbytes += bytesRead;
                } while (true);

                // Write the content to be encrypted
                memStrm.Flush();
                memStrm.Seek(0, SeekOrigin.Begin);

                // Get the string from the bytes we read 
                retStr = System.Text.Encoding.Unicode.GetString(memStrm.GetBuffer(), 0, totalbytes);
                cryptStrm.Close();
            }
            return retStr;
        }
    }
}