Reading/Writing bytes help.

[tassa]

Hello...

I'm trying to read 5 bytes from a file and then do something according to what has been read. This is my code (I'll explain in a bit what's wrong):

cStream = New CryptoStream(input, _
                           RijndaelAlg.CreateDecryptor(_key, IV), _
                           CryptoStreamMode.Read)
 
                    Dim HeaderBuffer(4) As Byte
                    cStream.Read(HeaderBuffer, 0, 5)
 
                    If encoding.GetString(HeaderBuffer) <> HeaderString Then
                        RaiseEvent ReturnType(ActionReturnType.InvalidPassword)
                        cStream.Clear()
                        Exit Try
                    End If
 
                    Do While BytesProcessed < SourceLength
                        CurrentBytes = cStream.Read(Buffer, 0, 4096)
                        output.Write(Buffer, 0, CurrentBytes)
                        BytesProcessed += CLng(CurrentBytes)
                        PercentDone = CInt((BytesProcessed / SourceLength) * 100)
                        RaiseEvent Progress(PercentDone)
                    Loop

It reads the 5 bytes I added to the encrypted file, but I want the CryptoStream to start from the sixth value and then copy the original bytes into the decrypted file, but it gives me an error:

Padding is invalid and cannot be removed.

That's why I'm trying to make it read from the sixth value and then continue copying normally, but I'm stuck.

Any help will be greatly appreciated!

Thanks .

[tassa]

I have tested it and have taken a better look at the code. It reads the header and then, when inside the loop, it starts reading at the sixth byte. The problem that I've noticed is that the loop exits when the file reaches 99.90% of its completion, why is this happening?

This is my whole code... In case it helps.

Public Shared Function RijndaelEncryptDecrypt(ByVal source As String, ByVal destination As String, _
                                                ByVal key As String, _
                                                ByVal action As RijndaelCryptographicAction) _
                                                As Boolean
        RijndaelAlg.BlockSize = 256
 
        GenerateOutput(source, destination, action)
        Dim input As New FileStream(source, FileMode.Open, FileAccess.Read)
        Dim output As New FileStream(destination, FileMode.OpenOrCreate)
        Dim cStream As CryptoStream = Nothing
 
        Dim Buffer(4096) As Byte
        Dim CurrentBytes As Integer = 0
        Dim BytesProcessed As Long = 0
        Dim SourceLength As Long = input.Length
        Dim PercentDone As Integer = 0
 
        Dim _key As Byte() = CheckKey(key)
        Dim IV As Byte() = GenerateIV(key)
 
        Try
            Select Case action
                Case RijndaelCryptographicAction.Encrypt
                    If source.EndsWith(".encx") Then
                        output.Close()
                        input.Close()
 
                        File.Delete(destination)
 
                        RaiseEvent ReturnType(ActionReturnType.EncryptInvalidFileType)
                        Exit Try
                    End If
 
                    cStream = New CryptoStream(output, _
                                               RijndaelAlg.CreateEncryptor(_key, IV), _
                                               CryptoStreamMode.Write)
 
                    cStream.Write(HeaderBytes, 0, 5)
 
                    Do While BytesProcessed < SourceLength
                        CurrentBytes = input.Read(Buffer, 0, 4096)
                        cStream.Write(Buffer, 0, CurrentBytes)
                        BytesProcessed += CLng(CurrentBytes)
                        PercentDone = CInt((BytesProcessed / SourceLength) * 100)
                        RaiseEvent Progress(PercentDone)
                    Loop
 
                Case RijndaelCryptographicAction.Decrypt
                    If Not source.EndsWith(".encx") Then
                        output.Close()
                        input.Close()
 
                        File.Delete(destination)
 
                        RaiseEvent ReturnType(ActionReturnType.DecryptInvalidFileType)
                        Exit Try
                    End If
 
                    cStream = New CryptoStream(input, _
                                               RijndaelAlg.CreateDecryptor(_key, IV), _
                                               CryptoStreamMode.Read)
 
                    Dim HeaderBuffer(4) As Byte
                    cStream.Read(HeaderBuffer, 0, 5)
 
                    If encoding.GetString(HeaderBuffer) <> HeaderString Then
                        RaiseEvent ReturnType(ActionReturnType.InvalidPassword)
                        cStream.Clear()
                        Exit Try
                    End If
 
                    Do While BytesProcessed < SourceLength
                        CurrentBytes = cStream.Read(Buffer, 0, 4096)
                        output.Write(Buffer, 0, CurrentBytes)
                        BytesProcessed += CLng(CurrentBytes)
                        PercentDone = CInt((BytesProcessed / SourceLength) * 100)
                        RaiseEvent Progress(PercentDone)
                    Loop
 
            End Select
 
 
            output.Close()
            input.Close()
 
            File.Delete(source)
 
            RaiseEvent ReturnType(ActionReturnType.Good)
            Return True
 
        Catch ex As Exception
 
            output.Close()
            input.Close()
 
            RaiseEvent ReturnType(ActionReturnType.Bad)
            Return False
        End Try
 
    End Function