Silverlight 加密目录的独立存储区文件

using System;
using System.Security.Cryptography;
using System.Windows;
using System.Text;
using System.IO.IsolatedStorage;
using System.IO;

namespace Sitedirsec.Cache
{
    /// <summary>
    /// 缓存文件加密
    /// </summary>
    public class FileEncryption
    {
        private const ulong FC_TAG = 0xFC010203040506CF;

        private const int BUFFER_SIZE = 128 * 1024;
        /// <summary>
        /// 目录的独立存储区
        /// </summary>
        private static IsolatedStorageFile isoStore = IsolatedStorageFile.GetUserStoreForApplication();
        /// <summary>
        /// 创建Rijndael SymmetricAlgorithm
        /// </summary>
        /// <param name="password">密码</param>
        /// <param name="salt"></param>
        /// <returns>加密对象</returns>
        private static AesManaged CreateRijndael(string password, byte[] salt)
        {
            Rfc2898DeriveBytes pdb = new Rfc2898DeriveBytes(password, salt);
            AesManaged sma = new AesManaged();
            sma.CreateEncryptor();
            sma.KeySize = 256;
            sma.Key = pdb.GetBytes(32);
            return sma;
        }

        /// <summary>
        /// 加密文件随机数生成
        /// </summary>
        private static RandomNumberGenerator rand = new RNGCryptoServiceProvider();

        /// <summary>
        /// 生成指定长度的随机Byte数组
        /// </summary>
        /// <param name="count">Byte数组长度</param>
        /// <returns>随机Byte数组</returns>
        private static byte[] GenerateRandomBytes(int count)
        {
            byte[] bytes = new byte[count];
            rand.GetBytes(bytes);
            return bytes;
        }

        /// <summary>
        /// 加密文件
        /// </summary>
        /// <param name="str">加密的文本</param>
        /// <param name="password">加密密码</param>
        public static void EncryptFile(string str,string path, string password)
        {          
            using (IsolatedStorageFileStream fout = new IsolatedStorageFileStream(path, FileMode.Open, isoStore))
            {
                MemoryStream fin = new MemoryStream(System.Text.Encoding.UTF8.GetBytes(str));

                long lSize = fin.Length; // 输入文件长度
                int size = (int)lSize;
                byte[] bytes = new byte[BUFFER_SIZE]; // 缓存
                int read = -1; // 输入文件读取数量
                int value = 0;

                // 获取IV和salt
                byte[] IV = GenerateRandomBytes(16);
                byte[] salt = GenerateRandomBytes(16);

                // 创建加密对象
                SymmetricAlgorithm sma = CreateRijndael(password, salt);
                sma.IV = IV;

                // 在输出文件开始部分写入IV和salt
                fout.Write(IV, 0, IV.Length);
                fout.Write(salt, 0, salt.Length);

                SHA1Managed hasher = new SHA1Managed();
                using (CryptoStream cout = new CryptoStream(fout, sma.CreateEncryptor(), CryptoStreamMode.Write),
                    chash = new CryptoStream(Stream.Null, hasher, CryptoStreamMode.Write))
                {
                    BinaryWriter bw = new BinaryWriter(cout, Encoding.Unicode);
                    bw.Write(lSize);

                    bw.Write(FC_TAG);

                    // 读写字节块到加密流缓冲区
                    while ((read = fin.Read(bytes, 0, bytes.Length)) != 0)
                    {
                        cout.Write(bytes, 0, read);
                        chash.Write(bytes, 0, read);
                        value += read;
                    }
                    // 关闭加密流
                    chash.Flush();
                    chash.Close();

                    // 读取散列
                    byte[] hash = hasher.Hash;

                    // 输入文件写入散列
                    cout.Write(hash, 0, hash.Length);

                    // 关闭文件流
                    cout.Flush();
                    cout.Close();
                }
            }

        }

        /// <summary>
        /// 解密文件
        /// </summary>
        /// <param name="inFile">待解密文件</param>
        /// <param name="password">解密密码</param>
        public static string DecryptFile(string path, string password)
        {
            // 创建打开文件流
            using (IsolatedStorageFileStream fin = new IsolatedStorageFileStream(path, FileMode.Open, isoStore))
            {
                MemoryStream fout = new MemoryStream();
                int size = (int)fin.Length;
                byte[] bytes = new byte[BUFFER_SIZE];
                int read = -1;
                int value = 0;
                int outValue = 0;

                byte[] IV = new byte[16];
                fin.Read(IV, 0, 16);
                byte[] salt = new byte[16];
                fin.Read(salt, 0, 16);

                SymmetricAlgorithm sma = CreateRijndael(password, salt);
                sma.IV = IV;

                value = 32;
                long lSize = -1;

                SHA1Managed hasher = new SHA1Managed();
                CryptoStream cin = new CryptoStream(fin, sma.CreateDecryptor(), CryptoStreamMode.Read), chash = new CryptoStream(Stream.Null, hasher, CryptoStreamMode.Write);
                BinaryReader br = new BinaryReader(cin);
                lSize = br.ReadInt64();
                ulong tag = br.ReadUInt64();

                long numReads = lSize / BUFFER_SIZE;

                long slack = (long)lSize % BUFFER_SIZE;

                for (int i = 0; i < numReads; ++i)
                {
                    read = cin.Read(bytes, 0, bytes.Length);
                    fout.Write(bytes, 0, read);
                    chash.Write(bytes, 0, read);
                    value += read;
                    outValue += read;
                }

                if (slack > 0)
                {
                    read = cin.Read(bytes, 0, (int)slack);
                    fout.Write(bytes, 0, read);
                    chash.Write(bytes, 0, read);
                    value += read;
                    outValue += read;
                }

                chash.Flush();
                chash.Close();
                fout.Flush();
                fout.Close();
                cin.Flush();
                cin.Close();        
                string msg = System.Text.Encoding.UTF8.GetString(fout.ToArray(), 0, fout.ToArray().Length);               
                return  msg ;
            }
        }
    }
}
（绝大部分代码来源于网络）