C# AES CFB加解密模式兼容JAVA

C# AES CFB加解密模式兼容JAVA代码片段

最近在和java做对接的时候老是遇到加密使用java写的，需要我们使用C#来解密相关数据，AES加解密平常也在用，但是这种跨语言的应用还是比较少，因为对方不知道使用的是哪些参数进行的加密，调试起来就比较耗时耗力，做个记录方便后期查漏补缺。

using System.Security.Cryptography;

       static void Example(int i)
        {
            Console.WriteLine(i+">>>>>>");
            //
            // Encrypt a small sample of data
            //
            String Plain = "2121050";
            byte[] plainBytes = Encoding.ASCII.GetBytes(Plain);
            Console.WriteLine("plaintext length is" + plainBytes.Length);
            Console.WriteLine("Plaintext is" + BitConverter.ToString(plainBytes));

            

            byte[] savedKey = Convert.FromBase64String("5S1I25wtR6vdJrlPwF4E1Q==");

            var d = BitConverter.ToString(savedKey).Replace("-"," ");

            byte[] savedIV = new byte[16] {0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0};
            byte[] cipherBytes;
            using (RijndaelManaged Aes128 = new RijndaelManaged())
            {
                //
                // Specify a blocksize of 128, and a key size of 128, which make this
                // instance of RijndaelManaged an instance of AES 128.
                //
                Aes128.BlockSize = 128;
                Aes128.KeySize = 128;
                
                //
                // Specify CFB8 mode
                //
                Aes128.Mode = CipherMode.CFB;
                Aes128.FeedbackSize = 8*i;
                Aes128.Padding = PaddingMode.Zeros;
                //
                // Generate and save random key and IV.
                //
                //Aes128.GenerateKey();
                //Aes128.GenerateIV();
                Aes128.Key = savedKey;
                Aes128.IV = savedIV;
                

                //Aes128.Key.CopyTo(savedKey, 0);
                //Aes128.IV.CopyTo(savedIV, 0);

                using (var encryptor = Aes128.CreateEncryptor())
                using (var msEncrypt = new MemoryStream())
                using (var csEncrypt = new CryptoStream(msEncrypt, encryptor, CryptoStreamMode.Write))
                using (var bw = new BinaryWriter(csEncrypt, Encoding.UTF8))
                {
                    bw.Write(plainBytes);
                    bw.Close();

                    cipherBytes = msEncrypt.ToArray();
                    Console.WriteLine("Cipher length is" + cipherBytes.Length);
                    Console.WriteLine("Cipher text is" + BitConverter.ToString(cipherBytes));
                    Console.WriteLine("AES Base64:" + Convert.ToBase64String(cipherBytes));
                }
            }

            //
            // Now decrypt the cipher back to plaintext
            //

            using (RijndaelManaged Aes128 = new RijndaelManaged())
            {
                Aes128.BlockSize = 128;
                Aes128.KeySize = 128;
                Aes128.Mode = CipherMode.CFB;
                Aes128.FeedbackSize = 8*i;
                Aes128.Padding = PaddingMode.Zeros;

                Aes128.Key = savedKey;
                Aes128.IV = savedIV;

                using (var decryptor = Aes128.CreateDecryptor())
                using (var msEncrypt = new MemoryStream(cipherBytes))
                using (var csEncrypt = new CryptoStream(msEncrypt, decryptor, CryptoStreamMode.Read))
                using (var br = new BinaryReader(csEncrypt, Encoding.UTF8))
                {
                    //csEncrypt.FlushFinalBlock();
                    plainBytes = br.ReadBytes(cipherBytes.Length);

                    Console.WriteLine("Decrypted plain length is" + plainBytes.Length);
                    Console.WriteLine("Decrypted plain text bytes is" + BitConverter.ToString(plainBytes));
                    Console.WriteLine("Decrypted plain text is" + Encoding.UTF8.GetString(plainBytes));
                }
            }
        }

1. 重点调试的参数就FeedbackSize，这个是CFB模式下特有的，常用的有8,64,128,这个现场恰恰用的是56这个模式。
2. Aes128.Padding = PaddingMode.Zeros; 设置Padding为0，这个也是要根据实际情况去调的。
3. 还有要注意的就是byte[] savedKey = Convert.FromBase64String("5S1I25wtR6vdJrlPwF4E1Q==");,Key的编码方式，这边Java用的是Base64模式，刚开始我没注意，使用的是UTF8模式进行转换，调试过程中各种问题，最后发现了这个隐蔽问题。

        static void Main(string[] args)
        {
            Example(7);
            Console.ReadLine();
        }

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