> I pass a literal string into the CryptoStream to encrypt the data into a MemoryStream. And then decrypt the MemoryStream back. But I am getting CryptographicException with Bad Data.

> Another info I found is that the encrypted file is 16 bytes, and if I encrypt it to MemoryStream, the stream is in length 8.
> [snip] but I didn't specify the encoding.

> if so, which encoding should I use?

On Wed, 13 Feb 2008 21:09:36 -0800, Gasnic <gasnic@gmail.com> wrote:

> I pass a literal string into the CryptoStream to encrypt the data into a
> MemoryStream. And then decrypt the MemoryStream back. But I am getting
> CryptographicException with Bad Data.
>
> When I tried to encryption the same data into a FileStream and then
> decrypt the file, it works.
>
> [...]
> I used StreamWriter to write data into the CryptoStream but I didn't
> specify the encoding.
> Should I specify an encoding? if so, which encoding should I use?

"Marc Gravell" <marc.gravell@gmail.com> wrote in message
news:d5da9766-f9d5-4f8b-ac76-b2e8ccaf102a@d70g2000hsb.googlegroups.com...
>> I pass a literal string into the CryptoStream to encrypt the data into a
>> MemoryStream. And then decrypt the MemoryStream back. But I am getting
>> CryptographicException with Bad Data.
>
> Did you rewind the stream? Should have something like:
>
> using(MemoryStream memStream = new MemoryStream()) {
> // write the values
> using([whatever] foo = new [whatever](memStream)) {
> // some code to write to foo
> foo.Close();
> }
> // rewind the stream
> memStream.Position = 0;
> // read the stream to verify
> using([wossit] bar = new [wossit](memStream)) {
> // some code to read from bar
> bar.Close();
> }
> }
>
>> Another info I found is that the encrypted file is 16 bytes, and if I
>> encrypt it to MemoryStream, the stream is in length 8.
>> [snip] but I didn't specify the encoding.
> That *could* be encoding related (as you mention), but I would expect
> it to use the same encoding in both directions; but it wouldn't hurt
> to be explicit.
>
>> if so, which encoding should I use?
> UTF8 is a good all-rounder; supports full unicode, and has the
> advantage of single-byte for ASCII chars. A bit more expensive if you
> are using a lot of "interesting" characters, i.e. a non-latin
> language.
>
> Marc

"Peter Duniho" <NpOeStPeAdM@nnowslpianmk.com> wrote in message
news:op.t6h161n58jd0ej@petes-computer.local...
> On Wed, 13 Feb 2008 21:09:36 -0800, Gasnic <gasnic@gmail.com> wrote:
>
>> I pass a literal string into the CryptoStream to encrypt the data into a
>> MemoryStream. And then decrypt the MemoryStream back. But I am getting
>> CryptographicException with Bad Data.
>>
>> When I tried to encryption the same data into a FileStream and then
>> decrypt the file, it works.
>>
>> [...]
>> I used StreamWriter to write data into the CryptoStream but I didn't
>> specify the encoding.
>> Should I specify an encoding? if so, which encoding should I use?
>
> I would not expect how you stream data to the CryptoStream to affect the
> encryption. You could very well run into an encoding issue when trying to
> reconstitute the text data from the _unencrypted_ stream but a) unless
> you're changing the encoding I would expect the default encoding to apply
> in both directions, and b) the encoding shouldn't have any effect on the
> data after it's encrypted, nor should it affect the decryption of the
> previously encrypted data. You might get an exception thrown by a
> StreamReader or something trying to read the unencrypted stream, but it
> shouldn't affect the encryption itself.
>
> This all assumes, of course, that when you write "I used StreamWriter to
> write data into the CryptoStream", you are talking about the encryption
> stage and that your data flow looks something like:
>
> StreamWriter --> CryptoStream --> FileStream
> and
> StreamWriter --> CryptoStream --> MemoryStream
>
> for encryption, and basically the inverse for decryption (with the
> appropriate stream classes replaced as necessary of course).
>
> If you're using StreamWriter post-encryption, then yes...that'd be a
> problem. :)
>
> Generally speaking, what you're trying to do (if I understand the post
> correctly) should work. You should be able to use a MemoryStream and
> FileStream essentially interchangeably here and they should work the
> same. Since they are not working the same, I suspect that you've got some
> sort of simple typographical error or you're not treating the two exactly
> the same somehow.
>
> You should look through the code carefully to make sure you're not
> treating the two different. You may even want to make sure that the code
> doing the encryption only ever uses a Stream that you pass to it for
> output and input, and just make the caller aware of the MemoryStream
> versus FileStream. That will guarantee that at least the encryption part
> isn't depending on the type of the stream used to store the encrypted
> data.
>
> If after checking all that you still have a problem, you should post a
> concise-but-complete code sample that reliably demonstrates the problem.
> The exception you describe seems to imply that the data isn't making the
> round-trip post-encryption/pre-decryption safely, but if you're really
> treating both storage streams the same, it's hard to see how that might
> happen.
>
> One final thought (now that I've written all of the above, this occurs to
> me :) ): are you sure that in the MemoryStream case, you have reset the
> stream position back to the beginning before trying to decrypt the data?
>
> Pete