加密和解密时出错.无法找到异常的原因

Question

我有以下两种方法.

第一种方法

  //SymmetricEncryting 
 private byte[] SymmetricEncrypt()
  {
  try
      {
        //Get Byte Value 
        byte[] x= Encoding.Default.GetBytes("Test");

        byte [] y;

        //Create Symmetric Key Encription
        RijndaelManaged rijndaelManaged = new RijndaelManaged();

        //GetSymmetricPublicKey
        _symmetricPublicKey = rijndaelManaged.Key;

        //Get Symmetric Public IV
        _symmetricPublicIv = rijndaelManaged.IV;

        using (MemoryStream memoryStream = new MemoryStream(x))
        {
            //Start EncriptionProcess
            var cryptoStream = new CryptoStream(memoryStream,
                                                rijndaelManaged.CreateEncryptor
                                                 (_symmetricPublicKey,
                                                 _symmetricPublicIv),
                                                CryptoStreamMode.Write);

            cryptoStream.Write(x, 0, x.Length);

            // Complete the encryption process
            //cryptoStream.FlushFinalBlock();

            y= memoryStream.ToArray();


        }

        return y;
    }
    catch (Exception)
    {
        throw;
    }
}

第二种方法

private string Decrypt(
    byte[] y,
    byte[] symmetricPublicKey,
    byte[] symmtricPublicIv)
{
    try
    {
        //Create the Key Container
        CspParameters cspParameters = new CspParameters();

        //Get the AsyPrivate and Public key from the Container
        cspParameters.KeyContainerName = "Keys";


        var rsaCryptoServiceProvider = new RSACryptoServiceProvider(cspParameters);

        //Decrypt and get the Symmetric Public key
        var decryptedSymmetricPubk = rsaCryptoServiceProvider.Decrypt(symmetricPublicKey, false);

        //Decrypt and get the Symmetric Public IV
        var decryptedSymmetricPubIv = rsaCryptoServiceProvider.Decrypt(symmtricPublicIv, false);

        //Create RijndaelManaged object to do the Symmtric dycrption
        RijndaelManaged rijndaelManaged = new RijndaelManaged();

        //Create cryptostream using decrypted symmetric Public Key and IV
        ICryptoTransform iCryptoTransform = rijndaelManaged.CreateDecryptor(decryptedSymmetricPubk,
                                                                            decryptedSymmetricPubIv);
        //Create a memory stream 
        using (MemoryStream memoryStream = new MemoryStream(y))
        {

            var cryptoStream = new CryptoStream(memoryStream, iCryptoTransform, CryptoStreamMode.Read);

            byte[] z= new byte[y.Length];

            cryptoStream.Read(z, 0, z.Length);

            //cryptoStream.FlushFinalBlock();

            //Convert byte array to string
            var x= System.Text.Encoding.Default.GetString(z);

            return x;
        }
    }
    catch (Exception)
    {
        throw;
    }

正如您在代码中看到的那样,我正在尝试使用对称加密来加密字符串.我使用我已经创建的非对称公钥来加密对称公钥和Iv.然后我尝试解密加密的字符串.

问题1cryptoStream.FlushFinalBlock();加密和解密 的目的是什么.我从msdn那里了解到它将结束在cyptostream上运行的进程

问题2 如果我取消注释该行,cryptoStream.FlushFinalBlock();则会抛出异常 "Memory stream is not expandable.".但是,如果我对该行进行注释,它将正常工作并返回一个字节数组.

问题3 然而,第二种方法"system.security.cryptography.cryptographicexception length of the data to decrypt is invalid在执行行cryptoStream.Read(z,0,z.Length)时抛出异常;

我在调试时找不到这些错误的实际原因.我也在Google上进行了一些搜索.但遗憾的是我找不到任何解决方案.任何人都可以解释一下答案吗？

Answer 1

您正在使用PKCS填充进行加密(这是默认设置).AES/Rijndael是一个块密码,这意味着它一次只能加密16个字节的块.为了允许块密码加密任意大小的数据,我们使用填充算法.PKCS填充的工作原理是在加密时加入1-16个字节,并在解密时删除它们.填充的长度在填充本身中编码.

你需要FlushFinalBlock加密时让CryptoStream知道没有更多的传入数据,它应该添加填充.在Read-mode中使用CryptoStream时,没有必要也不应该使用它.

第一个例外是因为您使用明文数组作为MemoryStream的后备存储.由于填充,加密将大于明文.

第二个例外是因为您删除了该FlushFinalBlock语句,并且因为不允许MemoryStream调整大小以使数组具有正确的长度.加密数据应始终是16个字节的倍数,但由于MemoryStream将重用x,y因此长度与长度相同x,并不总是有效长度.

解决方案是:

1. FlushFinalBlock在SymmetricEncrypt中使用.
2. 更换using (MemoryStream memoryStream = new MemoryStream(x))和using (MemoryStream memoryStream = new MemoryStream(y))使用using (MemoryStream memoryStream = new MemoryStream()).这将允许MemoryStreams自由调整大小.