A first chance exception of type 'System.ArgumentNullException' occurred in mscorlib.dll

Question

I a building a program that can ecnrypt and decrypt files using rijndael algorithm. But if i debug i get the following error:

A first chance exception of type 'System.ArgumentNullException' occurred in mscorlib.dll

this is my code:

    Imports crypter.crypter
Public Class Form1

  Private Sub btnEncrypt_Click(sender As System.Object, e As System.EventArgs) Handles btnEncrypt.Click
    Dim objCrypter As New crypter.crypter
    Dim strPass As String = txtPass.Text
    Dim bytkey As Byte()
    Dim bytIV As Byte()

    bytkey = objCrypter.CreateKey(strPass)
    bytIV = objCrypter.CreateIV(strPass)

    objCrypter.EncryptOrDecryptFile(txtSource.Text, txtDestination.Text, bytkey, bytIV, CryptoAction.ActionEncrypt)


  End Sub


  Private Sub btnDecrypt_Click(sender As Object, e As System.EventArgs) Handles btnDecrypt.Click
    Dim objCrypter As New crypter.crypter
    Dim strPass As String = txtPass.Text
    Dim bytkey As Byte()
    Dim bytIV As Byte()

    bytkey = objCrypter.CreateKey(strPass)
    bytIV = objCrypter.CreateIV(strPass)

    objCrypter.EncryptOrDecryptFile(txtSource.Text, txtDestination.Text, bytkey, bytIV, crypter.crypter.CryptoAction.ActionDecrypt)

  End Sub
End Class

and this is my code from my class crypter

Imports System
Imports System.IO
Imports System.Security
Imports System.Security.Cryptography

Public Class crypter
#Region "1. Global Variables "

    '*************************
    '** Global Variables
    '*************************

    Dim strFileToEncrypt As String
    Dim strFileToDecrypt As String
    Dim strOutputEncrypt As String
    Dim strOutputDecrypt As String
    Dim fsInput As System.IO.FileStream
    Dim fsOutput As System.IO.FileStream

#End Region


#Region "2. Create A Key "

    '*************************
    '** Create A Key
    '*************************

    Private Function CreateKey(ByVal strPassword As String) As Byte()
        'Convert strPassword to an array and store in chrData.
        Dim chrData() As Char = strPassword.ToCharArray
        'Use intLength to get strPassword size.
        Dim intLength As Integer = chrData.GetUpperBound(0)
        'Declare bytDataToHash and make it the same size as chrData.
        Dim bytDataToHash(intLength) As Byte

        'Use For Next to convert and store chrData into bytDataToHash.
        For i As Integer = 0 To chrData.GetUpperBound(0)
            bytDataToHash(i) = CByte(Asc(chrData(i)))
        Next

        'Declare what hash to use.
        Dim SHA512 As New System.Security.Cryptography.SHA512Managed
        'Declare bytResult, Hash bytDataToHash and store it in bytResult.
        Dim bytResult As Byte() = SHA512.ComputeHash(bytDataToHash)
        'Declare bytKey(31).  It will hold 256 bits.
        Dim bytKey(31) As Byte

        'Use For Next to put a specific size (256 bits) of 
        'bytResult into bytKey. The 0 To 31 will put the first 256 bits
        'of 512 bits into bytKey.
        For i As Integer = 0 To 31
            bytKey(i) = bytResult(i)
        Next

        Return bytKey 'Return the key.
    End Function

#End Region


#Region "3. Create An IV "

    '*************************
    '** Create An IV
    '*************************

    Private Function CreateIV(ByVal strPassword As String) As Byte()
        'Convert strPassword to an array and store in chrData.
        Dim chrData() As Char = strPassword.ToCharArray
        'Use intLength to get strPassword size.
        Dim intLength As Integer = chrData.GetUpperBound(0)
        'Declare bytDataToHash and make it the same size as chrData.
        Dim bytDataToHash(intLength) As Byte

        'Use For Next to convert and store chrData into bytDataToHash.
        For i As Integer = 0 To chrData.GetUpperBound(0)
            bytDataToHash(i) = CByte(Asc(chrData(i)))
        Next

        'Declare what hash to use.
        Dim SHA512 As New System.Security.Cryptography.SHA512Managed
        'Declare bytResult, Hash bytDataToHash and store it in bytResult.
        Dim bytResult As Byte() = SHA512.ComputeHash(bytDataToHash)
        'Declare bytIV(15).  It will hold 128 bits.
        Dim bytIV(15) As Byte

        'Use For Next to put a specific size (128 bits) of 
        'bytResult into bytIV. The 0 To 30 for bytKey used the first 256 bits.
        'of the hashed password. The 32 To 47 will put the next 128 bits into bytIV.
        For i As Integer = 32 To 47
            bytIV(i - 32) = bytResult(i)
        Next

        Return bytIV 'return the IV
    End Function

#End Region


#Region "4. Encrypt / Decrypt File "

    '****************************
    '** Encrypt/Decrypt File
    '****************************

    Private Enum CryptoAction
        'Define the enumeration for CryptoAction.
        ActionEncrypt = 1
        ActionDecrypt = 2
    End Enum

    Private Sub EncryptOrDecryptFile(ByVal strInputFile As String, _
                                     ByVal strOutputFile As String, _
                                     ByVal bytKey() As Byte, _
                                     ByVal bytIV() As Byte, _
                                     ByVal Direction As CryptoAction)
        Try 'In case of errors.

            'Setup file streams to handle input and output.
            fsInput = New System.IO.FileStream(strInputFile, FileMode.Open, _
                                               FileAccess.Read)
            fsOutput = New System.IO.FileStream(strOutputFile, FileMode.OpenOrCreate, _
                                                FileAccess.Write)
            fsOutput.SetLength(0) 'make sure fsOutput is empty

            'Declare variables for encrypt/decrypt process.
            Dim bytBuffer(4096) As Byte 'holds a block of bytes for processing
            Dim lngBytesProcessed As Long = 0 'running count of bytes processed
            Dim lngFileLength As Long = fsInput.Length 'the input file's length
            Dim intBytesInCurrentBlock As Integer 'current bytes being processed
      Dim csCryptoStream As CryptoStream
            'Declare your CryptoServiceProvider.
            Dim cspRijndael As New System.Security.Cryptography.RijndaelManaged


            'Determine if ecryption or decryption and setup CryptoStream.
            Select Case Direction
                Case CryptoAction.ActionEncrypt
                    csCryptoStream = New CryptoStream(fsOutput, _
                    cspRijndael.CreateEncryptor(bytKey, bytIV), _
                    CryptoStreamMode.Write)

                Case CryptoAction.ActionDecrypt
                    csCryptoStream = New CryptoStream(fsOutput, _
                    cspRijndael.CreateDecryptor(bytKey, bytIV), _
                    CryptoStreamMode.Write)
            End Select

            'Use While to loop until all of the file is processed.
            While lngBytesProcessed < lngFileLength
                'Read file with the input filestream.
                intBytesInCurrentBlock = fsInput.Read(bytBuffer, 0, 4096)
                'Write output file with the cryptostream.
                csCryptoStream.Write(bytBuffer, 0, intBytesInCurrentBlock)
                'Update lngBytesProcessed
                lngBytesProcessed = lngBytesProcessed + CLng(intBytesInCurrentBlock)
            End While

            'Close FileStreams and CryptoStream.
            csCryptoStream.Close()
            fsInput.Close()
            fsOutput.Close()

            'If encrypting then delete the original unencrypted file.
            If Direction = CryptoAction.ActionEncrypt Then
                Dim fileOriginal As New FileInfo(strFileToEncrypt)
                fileOriginal.Delete()
            End If

            'If decrypting then delete the encrypted file.
            If Direction = CryptoAction.ActionDecrypt Then
                Dim fileEncrypted As New FileInfo(strFileToDecrypt)
                fileEncrypted.Delete()
            End If

        Catch
            fsInput.Close()
            fsOutput.Close()

            If Direction = CryptoAction.ActionDecrypt Then
                Dim fileDelete As New FileInfo(strOutputFile)
                fileDelete.Delete()

            Else
                Dim fileDelete As New FileInfo(strOutputFile)
                fileDelete.Delete()


            End If

        End Try
    End Sub

#End Region

End Class

Does anybody have an idea about what might be my mistake?

Thanks in advance,

Answer 1

While I do not know the particular problem, the way I find the causes of first chance exceptions is to go to the Visual Studio Debug menu-> choose the Exceptions entry, check both boxes for Common Language Runtime Exceptions.

Now when you debug, the IDE will break for all exceptions even if they are caught.

Rerun your code and you should see the line that calls into mscorlib and causes the null exception.

Good luck!