Reusing ICryptoTransform Objects

I have a class that is used to encrypt text data. I am trying to reuse ICryptoTransform objects where possible. However, the second time when I try to use the same object, I get partially incorrectly decrypted data. I think the first block is wrong, but it seems to be okay (tested it with longer texts).

I split the class into the following:

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Security.Cryptography;
using System.Text;

namespace Sample.Crypto
{
    public class EncryptedStreamResolver : IDisposable
    {
        private AesCryptoServiceProvider _cryptoProvider;
        private ICryptoTransform _encryptorTransform;
        private ICryptoTransform _decryptorTransform;

        private ICryptoTransform EncryptorTransform
        {
            get
            {
                if (null == _encryptorTransform || !_encryptorTransform.CanReuseTransform)
                {
                    _encryptorTransform?.Dispose();
                    _encryptorTransform = _cryptoProvider.CreateEncryptor();
                }
                return _encryptorTransform;
            }
        }

        private ICryptoTransform DecryptorTransform
        {
            get
            {
                if (null == _decryptorTransform || !_decryptorTransform.CanReuseTransform)
                {
                    _decryptorTransform?.Dispose();
                    _decryptorTransform = _cryptoProvider.CreateDecryptor();
                }
                return _decryptorTransform;
            }
        }

        public EncryptedStreamResolver()
        {
            GenerateCryptoProvider();
        }

        public Stream OpenRead(string rawPath)
        {
            return new CryptoStream(File.OpenRead(rawPath + ".crypto"), DecryptorTransform, CryptoStreamMode.Read);
        }

        public Stream OpenWrite(string rawPath)
        {
            return new CryptoStream(File.OpenWrite(rawPath + ".crypto"), EncryptorTransform, CryptoStreamMode.Write);
        }

        private void GenerateCryptoProvider(string password = "totallysafepassword")
        {
            _cryptoProvider = new AesCryptoServiceProvider();
            _cryptoProvider.BlockSize = _cryptoProvider.LegalBlockSizes.Select(ks => ks.MaxSize).Max();
            _cryptoProvider.KeySize = _cryptoProvider.LegalKeySizes.Select(ks => ks.MaxSize).Max();
            _cryptoProvider.IV = new byte[_cryptoProvider.BlockSize / 8];
            _cryptoProvider.Key = new byte[_cryptoProvider.KeySize / 8];

            var pwBytes = Encoding.UTF8.GetBytes(password);
            for (var i = 0; i < _cryptoProvider.IV.Length; i++)
                _cryptoProvider.IV[i] = pwBytes[i % pwBytes.Length];
            for (var i = 0; i < _cryptoProvider.Key.Length; i++)
                _cryptoProvider.Key[i] = pwBytes[i % pwBytes.Length];
        }

        public void Dispose()
        {
            _encryptorTransform?.Dispose();
            _decryptorTransform?.Dispose();
            _cryptoProvider?.Dispose();
        }
    }
}

      

        
        
        
      

    

I wrote a sample usage test to demonstrate the problem:

public void Can_reuse_encryptor()
{
    const string message = "Secret corporate information here.";
    const string testFilePath1 = "Foo1.xml";
    const string testFilePath2 = "Foo2.xml";
    var sr = new EncryptedStreamResolver();

    // Write secret data to file
    using (var writer = new StreamWriter(sr.OpenWrite(testFilePath1)))
        writer.Write(message);

    // Read it back and compare with original message
    using (var reader = new StreamReader(sr.OpenRead(testFilePath1)))
        if (!message.Equals(reader.ReadToEnd()))
            throw new Exception("This should never happend :(");

    // Write the same data again to a different file
    using (var writer = new StreamWriter(sr.OpenWrite(testFilePath2)))
        writer.Write(message);

    // Read that back and compare
    using (var reader = new StreamReader(sr.OpenRead(testFilePath2)))
        if (!message.Equals(reader.ReadToEnd()))
            throw new Exception("This should never happend :(");
}

      

        
        
        
      

    

What am I missing? The documentation suggests that these objects can be reused, but I can't figure out how to do this. Can anyone help me?

EDIT:

As @bartonjs pointed out, if I migrate my project containing the codes above to .NET 4.6 (or higher), I can use System.AppContext.TryGetSwitch like this:

var reuseTransform = false;
if (null == _decryptorTransform ||
    !(AppContext.TryGetSwitch("Switch.System.Security.Cryptography.AesCryptoServiceProvider.DontCorrectlyResetDecryptor", out reuseTransform) && reuseTransform && _decryptorTransform.CanReuseTransform))
{
    _decryptorTransform?.Dispose();
    _decryptorTransform = _cryptoProvider.Createdecryptor();
}

      

        
        
        
      

    

Then I can set this switch to the main app.config as in @ bartonjs answer.