Create AesUtils.cs (#6161)

新增AesUtils，替换掉DesUtils，提高安全性。
细节：
1.使用AES代替DES
2.正确使用IV调用方式
3.使用SHA256代替MD5进行密钥派生
4.使用PBKDF进行迭代生成密钥。

v2rayN/ServiceLib/Common/AesUtils.cs

@@ -0,0 +1,115 @@
+using System;
+using System.IO;
+using System.Security.Cryptography;
+using System.Text;
+
+namespace ServiceLib.Common
+{
+    public class AesUtils
+    {
+        private const int KeySize = 256; // AES-256
+        private const int IvSize = 16;   // AES block size
+        private const int Iterations = 10000;
+
+        private static readonly byte[] Salt = Encoding.ASCII.GetBytes("saltysalt".PadRight(16, ' '));//google浏览器默认盐值
+
+        /// <summary>
+        /// Encrypt
+        /// </summary>
+        /// <param name="text">Plain text</param>
+        /// <param name="password">Password for key derivation</param>
+        /// <returns>Base64 encoded cipher text with IV</returns>
+        public static string Encrypt(string text, string password)
+        {
+            if (string.IsNullOrEmpty(text))
+                return string.Empty;
+
+            if (string.IsNullOrEmpty(password))
+                throw new ArgumentNullException("Password cannot be null.");
+
+            byte[] plaintext = Encoding.UTF8.GetBytes(text);
+            byte[] key = GetDefaultKey(password);
+            byte[] iv = GenerateIv();
+
+            using (Aes aes = Aes.Create())
+            {
+                aes.Key = key;
+                aes.IV = iv;
+
+                using (MemoryStream ms = new MemoryStream())
+                {
+                    ms.Write(iv, 0, iv.Length);
+
+                    using (CryptoStream cs = new CryptoStream(ms, aes.CreateEncryptor(), CryptoStreamMode.Write))
+                    {
+                        cs.Write(plaintext, 0, plaintext.Length);
+                        cs.FlushFinalBlock();
+                    }
+
+                    byte[] cipherTextWithIv = ms.ToArray();
+                    return Convert.ToBase64String(cipherTextWithIv);
+                }
+            }
+        }
+
+        /// <summary>
+        /// Decrypt
+        /// </summary>
+        /// <param name="cipherTextWithIv">Base64 encoded cipher text with IV</param>
+        /// <param name="password">Password for key derivation</param>
+        /// <returns>Plain text</returns>
+        public static string Decrypt(string cipherTextWithIv, string password)
+        {
+            if (string.IsNullOrEmpty(cipherTextWithIv))
+                return string.Empty;
+
+            if (string.IsNullOrEmpty(password))
+                throw new ArgumentNullException("Password cannot be null.");
+
+            byte[] cipherTextWithIvBytes = Convert.FromBase64String(cipherTextWithIv);
+            byte[] key = GetDefaultKey(password);
+
+            byte[] iv = new byte[IvSize];
+            Buffer.BlockCopy(cipherTextWithIvBytes, 0, iv, 0, IvSize);
+
+            byte[] cipherText = new byte[cipherTextWithIvBytes.Length - IvSize];
+            Buffer.BlockCopy(cipherTextWithIvBytes, IvSize, cipherText, 0, cipherText.Length - IvSize);
+
+            using (Aes aes = Aes.Create())
+            {
+                aes.Key = key;
+                aes.IV = iv;
+
+                using (MemoryStream ms = new MemoryStream())
+                {
+                    using (CryptoStream cs = new CryptoStream(ms, aes.CreateDecryptor(), CryptoStreamMode.Write))
+                    {
+                        cs.Write(cipherText, 0, cipherText.Length);
+                        cs.FlushFinalBlock();
+                    }
+
+                    byte[] plainText = ms.ToArray();
+                    return Encoding.UTF8.GetString(plainText);
+                }
+            }
+        }
+
+        private static byte[] GetDefaultKey(string password)
+        {
+            using (Rfc2898DeriveBytes pbkdf2 = new Rfc2898DeriveBytes(password, Salt, Iterations, HashAlgorithmName.SHA256))
+            {
+                return pbkdf2.GetBytes(KeySize / 8);
+            }
+        }
+
+        private static byte[] GenerateIv()
+        {
+            using (RNGCryptoServiceProvider rng = new RNGCryptoServiceProvider())
+            {
+                byte[] iv = new byte[IvSize];
+                rng.GetBytes(iv);
+                return iv;
+            }
+        }
+    }
+}