Re: Encryption/Decryption Changes File Size

P.S. I was able to get rid of the extra bytes in the encryption by changing
the code as shown below.
I have noticed Memory Streams work differently then File streams. As I am
just learning Cryptography and am actually encrypting differently then you
are, I am not sure of the impact of this.

I would (and am going to) play with this to find out the answers. Another
article that would be worth going through is
http://www.dotnetdevs.com/articles/UsingEncryption.aspx

If you want things to look like they are secure you can short cut it, but if
you want things to be secure, it looks like there is a bit more work to do.
That is where I am with it now.

HTH

' Write the byte array to the crypto stream and flush it.
'cStream.Write(Data, 0, Data.Length)

'cStream.FlushFinalBlock()

' Initialize a buffer

Dim bufferLen As Integer = 4096

Dim buffer(bufferLen) As Byte

Dim bytesRead As Integer

' Create buffer to hold the decrypted data.

Dim toEncrypt As New MemoryStream

Dim s As Stream

toEncrypt.Write(Data, 0, Data.Length)

toEncrypt.Position = 0



Do

' Read a chunk of data from the MemoryStream

bytesRead = toEncrypt.Read(buffer, 0, bufferLen)

' Decrypt it

cStream.Write(buffer, 0, bytesRead)

Loop While bytesRead <> 0





"DazedAndConfused" <AceMagoo61@xxxxxxxxx> wrote in message
news:%23SPN6g7yFHA.2540@xxxxxxxxxxxxxxxxxxxxxxx
> 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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