c# - Can a CryptoStream leave the base Stream open?

Question

I create a MemoryStream, pass it to CryptoStream for writing. I want the CryptoStream to encrypt, and leave the MemoryStream open for me to then read into something else. But as soon as CryptoStream is disposed, it disposes of MemoryStream too.

Can CryptoStream leave the base MemoryStream open somehow?

using (MemoryStream scratch = new MemoryStream())
{
    using (AesManaged aes = new AesManaged())
    {
        // <snip>
        // Set some aes parameters, including Key, IV, etc.
        // </snip>
        ICryptoTransform encryptor = aes.CreateEncryptor();
        using (CryptoStream myCryptoStream = new CryptoStream(scratch, encryptor, CryptoStreamMode.Write))
        {
            myCryptoStream.Write(someByteArray, 0, someByteArray.Length);
        }
    }
    // Here, I'm still within the MemoryStream block, so I expect
    // MemoryStream to still be usable.
    scratch.Position = 0;    // Throws ObjectDisposedException
    byte[] scratchBytes = new byte[scratch.Length];
    scratch.Read(scratchBytes,0,scratchBytes.Length);
    return Convert.ToBase64String(scratchBytes);
}

Answer 1

As of .NET 4.7.2, there is a second constructor with an added bool parameter called leaveOpen. If this is set to true then the CryptoStream's dispose method will not call dispose on the underlying stream.

Additionally, the other constructor without the leaveOpen parameter simply forwards the parameters to the new constructor with leaveOpen set to false.

MSDN
CryptoStream.Dispose(bool disposing)