Re: Encryption/Decryption Changes File Size

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The following line sets fromEncypt to the same size as data length (actually
data length + 1)
so you have 9 extra (0) bytes at the end. I think the 8 bytes are the
encryption key.

' Create buffer to hold the decrypted data.

Dim fromEncrypt(Data.Length ) As Byte



you could do this:

' Create buffer to hold the decrypted data.

Dim fromEncrypt(Data.Length - 9) As Byte

or

I think the right way is something like this (NOTE: in DecryptBytes that
"CryptoStreamMode.Write" is Write NOT Read - This is NOT a mistype, it needs
to be this way, the same is true for csDecrypt.Write, then change Return to
msDecrypt.ToArray , you will also be writing directly from Data, no need for
fromEncrypt) . For more information on this go to:

http://blogs.gotdotnet.com/ivanmed/PermaLink.aspx/01380bfa-caf5-40b9-ace6-5973106935a4



Friend Function DecryptBytes(ByVal Data() As Byte, ByVal APassphrase
As String) As Byte()
Try
' Create a new MemoryStream using the passed
' array of encrypted data.
Dim msDecrypt As New MemoryStream(Data)

' Create a CryptoStream using the MemoryStream
' and the passed key and initialization vector (IV).
Dim csDecrypt As New CryptoStream(msDecrypt, New
TripleDESCryptoServiceProvider().CreateDecryptor(GetKey(APassphrase),
GetIV(APassphrase)), CryptoStreamMode.Write) <=== Changed this line

' Create buffer to hold the decrypted data.
Dim fromEncrypt(Data.Length) As Byte

' Read the decrypted data out of the crypto stream
' and place it into the temporary buffer.
csDecrypt.Write(Data, 0, Data.Length -1) <=== Changed this line

'Convert the buffer into a string and return it.
Return msDecrypt.ToArray <==== Changed this line.


Catch e As CryptographicException
Console.WriteLine("A Cryptographic error occurred: " & e.Message)
Return Nothing
End Try
End Function


"Phillip Ian" <phlian@xxxxxxxxxxx> wrote in message
news:1128717854.429905.187360@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
> Version: VS 2005
>
> I took the sample code from help about encrypting and decrypting
> strings, and changed it to work directly with byte arrays and get the
> key and IV values from functions I've written to privide them. No
> other changes were made...
>
> Friend Function EncryptBytes(ByVal Data() As Byte, ByVal APassphrase
> As String) As Byte()
> Try
> ' Create a MemoryStream.
> Dim mStream As New MemoryStream
>
> ' Create a CryptoStream using the MemoryStream
> ' and the passed key and initialization vector (IV).
> Dim cStream As New CryptoStream(mStream, New
> TripleDESCryptoServiceProvider().CreateEncryptor(GetKey(APassphrase),
> GetIV(APassphrase)), CryptoStreamMode.Write)
>
> ' Write the byte array to the crypto stream and flush it.
> cStream.Write(Data, 0, Data.Length)
> cStream.FlushFinalBlock()
>
> ' Get an array of bytes from the
> ' MemoryStream that holds the
> ' encrypted data.
> Dim ret As Byte() = mStream.ToArray()
>
> ' Close the streams.
> cStream.Close()
> mStream.Close()
>
> ' Return the encrypted buffer.
> Return ret
> Catch e As CryptographicException
> Console.WriteLine("A Cryptographic error occurred: " & e.Message)
> Return Nothing
> End Try
> End Function
>
> Friend Function DecryptBytes(ByVal Data() As Byte, ByVal APassphrase
> As String) As Byte()
> Try
> ' Create a new MemoryStream using the passed
> ' array of encrypted data.
> Dim msDecrypt As New MemoryStream(Data)
>
> ' Create a CryptoStream using the MemoryStream
> ' and the passed key and initialization vector (IV).
> Dim csDecrypt As New CryptoStream(msDecrypt, New
> TripleDESCryptoServiceProvider().CreateDecryptor(GetKey(APassphrase),
> GetIV(APassphrase)), CryptoStreamMode.Read)
>
> ' Create buffer to hold the decrypted data.
> Dim fromEncrypt(Data.Length) As Byte
>
> ' Read the decrypted data out of the crypto stream
> ' and place it into the temporary buffer.
> csDecrypt.Read(fromEncrypt, 0, fromEncrypt.Length)
>
> 'Convert the buffer into a string and return it.
> Return fromEncrypt
> Catch e As CryptographicException
> Console.WriteLine("A Cryptographic error occurred: " & e.Message)
> Return Nothing
> End Try
> End Function
>
> When I encrypt and decrypt a file, the file ends up with extra blank
> bytes on the end of it. My encrypt/decrypt routine is as follows:
>
> Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As
> System.EventArgs) Handles Button1.Click
> Dim fin As New FileStream("test.jpg", FileMode.Open)
> Dim mugshot(fin.Length) As Byte
> fin.Read(mugshot, 0, fin.Length)
> fin.Close()
> MessageBox.Show(mugshot.Length)
>
> Dim encrypted() As Byte
> encrypted = EncryptBytes(mugshot, "This is a test...")
> MessageBox.Show(encrypted.Length)
>
> Dim decrypted() As Byte
> decrypted = DecryptBytes(encrypted, "This is a test...")
> MessageBox.Show(decrypted.Length)
>
> Dim fout As New FileStream("testout.jpg", FileMode.Create)
> fout.Write(decrypted, 0, decrypted.Length)
> fout.Close()
> End Sub
>
> This doesn't seem to bother the jpeg files...they read just fine. But
> what if it WASN'T a jpeg? Is it the encrypt/decrypt routine or the
> file IO stuff that's adding the extra bytes?
>
> Any help appreciated.
>


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