Re: How do I get this to work ?

From: Per Vestergaard-Laustsen (pvl_at_capto.dk)
Date: 04/30/03 

Date: Wed, 30 Apr 2003 13:02:11 +0200

Thanks, but unfortunately it didn't work. I tried to just change the method from CreateEncryptor to CreateDecryptot in the encrypt function, and got the exact same error. What does 'Bad data' really mean, what is wrong when I get that kind of message ? Is it the length of the argument to be decrypted that is wrong, or is it the bytes in the argument that can only assume certain values ? I do not understand how data can be 'bad' since anything should go, because the user can choose Key, IV and value to en-/decrypt quite freely. I feel that I need more information about the error, in order to shoot it down.

Best regards

Per Vestergaard-Laustsen, Denmark
  "Ivan Medvedev [MS]" <ivanmed@online.microsoft.com> skrev i en meddelelse news:evABrqmDDHA.2288@TK2MSFTNGP12.phx.gbl...
  Per -
  I would recommend using the same method in your Decrypt function as you used in the Encrypt - that is create a CryptoStream with CryptoStreamMode.Write and a decrytor object and write encrypted bytes to it. Then in the same manner you can grab the decrypted bytes from the MemoryStream.ToArray().
  If for some reason you have to stay with the current model, don't use BinaryReader - you can read bytes directly off the CryptoStream.
  Hope this helps.
  --Ivan

  This posting is provided "AS IS" with no warranties, and confers no rights.

    "Per Vestergaard-Laustsen" <pvl@capto.dk> wrote in message news:uRxqzUYDDHA.1604@TK2MSFTNGP10.phx.gbl...
    Well it gets worse.

    I have done some tidying up in the code and tried to implement your suggestions, so now I at least get another errormessage, but I am not sure wether it is a step forward or back.

    The errormessage now reads 'Stream does not support seeking', when I issue the statement :
    "decryptStreamReader.ReadBytes(CInt(decryptStream.Length))".
    Can you please help me out.

    This is what the code looks like now :

    Public Function encrypt(ByRef textPIN As String, ByRef textKey As String, ByRef textInitialValue As String) As String

    On Error GoTo ErrorHandler

    errPosition = "In encrypt function"

    Dim cryptPIN As New MemoryStream()

    Dim cryptPINReadBinary As New BinaryReader(cryptPIN)

    Dim PIN() As Byte

    Dim Key() As Byte

    Dim InitialValue() As Byte

    PIN = GetEncryptKeyByteArray(textPIN)

    Key = GetEncryptKeyByteArray(textKey)

    InitialValue = GetEncryptKeyByteArray(textInitialValue)

    Dim buffer(128) As Byte

    Dim transformation As ICryptoTransform

    Dim cryptoService As New System.Security.Cryptography.DESCryptoServiceProvider()

    transformation = cryptoService.CreateEncryptor(Key, InitialValue)

    Dim encryptStream As New System.Security.Cryptography.CryptoStream(cryptPIN, _

    transformation, _

    CryptoStreamMode.Write)

    encryptStream.Write(PIN, 0, CInt(PIN.Length)) 'encrypt writing to the encryptionstream

    encryptStream.FlushFinalBlock() 'empty the temporary stream-buffer by force

    encrypt = byte2str(cryptPIN.ToArray())

    'close the streams that has been opened

    encryptStream.Close()

    cryptPIN.Close()

    'destroy the objects that has been created and used

    cryptPIN = Nothing

    cryptPINReadBinary = Nothing

    transformation = Nothing

    cryptoService = Nothing

    encryptStream = Nothing

    Return encrypt

    ErrorHandler:

    textPIN = Err.Description

    textKey = errPosition

    End Function

    Public Function decrypt(ByRef textPIN As String, ByRef textKey As String, ByRef textInitialValue As String) As String

    'On Error GoTo ErrorHandler

    errPosition = "In decrypt function"

    Dim globalException As CryptographicException

    Dim i As Integer

    Dim cryptPIN As New MemoryStream()

    Dim cryptPINWriteBinary As New BinaryWriter(cryptPIN)

    Dim PIN(15) As Byte

    Dim Key(7) As Byte

    Dim InitialValue(7) As Byte

    PIN = GetDecryptKeyByteArray(textPIN)

    Key = GetEncryptKeyByteArray(textKey)

    InitialValue = GetEncryptKeyByteArray(textInitialValue)

    Dim buffer(1024) As Byte

    Dim decryption As ICryptoTransform

    Dim cryptoService As New DESCryptoServiceProvider()

    cryptPINWriteBinary.Write(PIN, 0, CInt(PIN.Length))

    cryptPINWriteBinary.Flush() 'empty the temporary stream-buffer by force

    decryption = cryptoService.CreateDecryptor(Key, InitialValue)

    cryptPIN.Seek(0, SeekOrigin.Begin)

    'the decryption takes place here

    Dim decryptStream As New CryptoStream(cryptPIN, _

    decryption, _

    CryptoStreamMode.Read)

    'definition of a reader in order to be able to read the decrypted PIN from the stream

    Dim decryptStreamReader As New BinaryReader(decryptStream)

    'reading the decrypted PIN into a textstring

    Try

    buffer = decryptStreamReader.ReadBytes(CInt(decryptStream.Length))

    decryptStream.FlushFinalBlock()

    Catch exception As CryptographicException

    globalException = exception

    GoTo ErrorHandler

    End Try

    'close the streams that has been opened

    cryptPIN.Close()

    decryptStream.Close()

    'destroy all objects used

    cryptPINWriteBinary = Nothing

    decryption = Nothing

    globalException = Nothing

    cryptoService = Nothing

    Return decrypt

    ErrorHandler:

    If globalException.Message = "" Then

    textPIN = Err.Description

    textKey = errPosition

    Else

    Dim inner As Exception

    textPIN = globalException.Message

    inner = globalException.InnerException()

    If Not inner Is Nothing Then

    textKey = inner.Message

    End If

    textInitialValue = globalException.Source

    End If

    End Function

    Private Function GetEncryptKeyByteArray(ByVal sPassword As String) As Byte()

    Dim byteTemp(7) As Byte

    sPassword = sPassword.PadRight(8) ' make sure we have 8 chars

    Dim iCharIndex As Integer

    For iCharIndex = 0 To sPassword.Length - 1

    byteTemp(iCharIndex) = Asc(Mid$(sPassword, iCharIndex + 1, 1))

    Next

    Return byteTemp

    End Function

    Private Function GetDecryptKeyByteArray(ByVal sPassword As String) As Byte()

    Dim byteTemp(15) As Byte

    Dim iCharIndex As Integer

    For iCharIndex = 0 To sPassword.Length - 1

    byteTemp(iCharIndex) = Asc(Mid$(sPassword, iCharIndex + 1, 1))

    Next

    Return byteTemp

    End Function

    Private Function byte2str(ByRef bytes() As Byte) As String

    errPosition = "In byte2str"

    Dim i As Integer

    Dim tmpString As String

    Dim tmpStringOneChar As String

    tmpString = ""

    errPosition = "Before for loop in byte2str"

    For i = 1 To bytes.Length - 1

    tmpStringOneChar = Chr(bytes(i))

    tmpString = tmpString + tmpStringOneChar

    errPosition = "In for loop in byte2str"

    Next

    errPosition = "After for loop in byte2str"

    byte2str = tmpString

    errPosition = "Before return from byte2str"

    Return byte2str

    End Function

    "Ivan Medvedev [MS]" <ivanmed@online.microsoft.com> skrev i en meddelelse news:OEPI523CDHA.3040@TK2MSFTNGP11.phx.gbl...
> Per -
> I think the problem is that your are not accounting for the changed length
> of the encrypted data. When you encrypt 8 bytes if data the resulting
> cyphertext is usually 16 bytes because of the padding added. In your code
> however you use a 8 byte long buffer to store enciphered bytes, that is why
> you are having problems decrypting. I would recommend using
> MemoryStream.ToArray() method, it is simpler then reading from the stream in
> a conventional way, and it gives you an array of the right size.
> Hope this helps.
> --Ivan
>
> This posting is provided "AS IS" with no warranties, and confers no rights.
>
>
> "Per Vestergaard-Laustsen" <pvl@capto.dk> wrote in message
> news:etI1N8vCDHA.28568@TK2MSFTNGP10.phx.gbl...
> > When trying to decrypt I get a bad data error.
> > Public Function encrypt(ByRef textPIN As String, ByRef textKey As String,
> > ByRef textInitialValue As String) As String
> >
> > On Error GoTo ErrorHandler
> >
> > errPosition = "In encrypt function"
> >
> > Dim cryptPIN As New MemoryStream()
> >
> > Dim cryptPINReadBinary As New BinaryReader(cryptPIN)
> >
> > Dim PIN() As Byte
> >
> > Dim Key() As Byte
> >
> > Dim InitialValue() As Byte
> >
> > PIN = GetKeyByteArray(textPIN)
> >
> > Key = GetKeyByteArray(textKey)
> >
> > InitialValue = GetKeyByteArray(textInitialValue)
> >
> > Dim buffer(8) As Byte
> >
> > Dim transformation As ICryptoTransform
> >
> > Dim cryptoService As New
> > System.Security.Cryptography.DESCryptoServiceProvider()
> >
> > transformation = cryptoService.CreateEncryptor(Key, InitialValue)
> >
> > Dim encryptStream As New
> System.Security.Cryptography.CryptoStream(cryptPIN,
> > _
> >
> > transformation, _
> >
> > CryptoStreamMode.Write)
> >
> > encryptStream.Write(PIN, 0, CInt(PIN.Length)) 'encrypt writing to the
> > encryptionstream
> >
> > encryptStream.FlushFinalBlock() 'empty the temporary stream-buffer by
> force
> >
> > cryptPIN.Seek(0, SeekOrigin.Begin)
> >
> > cryptPINReadBinary.Read(buffer, 0, cryptPIN.Length) 'read back into the
> > buffer the encrypted PIN from the memorystream
> >
> > errPosition = "Before call to byte2str"
> >
> > encrypt = byte2str(buffer)
> >
> > errPosition = "After call to byte2str"
> >
> > 'close the streams that has been opened
> >
> > encryptStream.Close()
> >
> > cryptPIN.Close()
> >
> > 'destroy the objects that has been created and used
> >
> > cryptPIN = Nothing
> >
> > cryptPINReadBinary = Nothing
> >
> > transformation = Nothing
> >
> > cryptoService = Nothing
> >
> > encryptStream = Nothing
> >
> > Return encrypt
> >
> > ErrorHandler:
> >
> > textPIN = Err.Description
> >
> > textKey = errPosition
> >
> > End Function
> >
> > Public Function decrypt(ByRef textPIN As String, ByRef textKey As String,
> > ByRef textInitialValue As String) As String
> >
> > 'On Error GoTo ErrorHandler
> >
> > errPosition = "In decrypt function"
> >
> > Dim globalException As CryptographicException
> >
> > Dim i As Integer
> >
> > Dim cryptPIN As New MemoryStream()
> >
> > Dim cryptPINWriteBinary As New BinaryWriter(cryptPIN)
> >
> > Dim PIN() As Byte
> >
> > Dim Key() As Byte
> >
> > Dim InitialValue() As Byte
> >
> > PIN = GetKeyByteArray(textPIN)
> >
> > Key = GetKeyByteArray(textKey)
> >
> > InitialValue = GetKeyByteArray(textInitialValue)
> >
> > Dim buffer(1024) As Byte
> >
> > Dim decryption As ICryptoTransform
> >
> > Dim cryptoService As New DESCryptoServiceProvider()
> >
> > cryptPINWriteBinary.Write(PIN, 0, CInt(PIN.Length))
> >
> > cryptPINWriteBinary.Flush() 'empty the temporary stream-buffer by force
> >
> > decryption = cryptoService.CreateDecryptor(Key, InitialValue)
> >
> > cryptPIN.Seek(0, SeekOrigin.Begin)
> >
> > 'the decryption takes place here
> >
> > Dim decryptStream As New CryptoStream(cryptPIN, _
> >
> > decryption, _
> >
> > CryptoStreamMode.Read)
> >
> > 'definition of a reader in order to be able to read the decrypted PIN from
> > the stream
> >
> > Dim decryptStreamReader As New BinaryReader(decryptStream)
> >
> > 'readtoend delivers a string, so we need a temporary string to store it in
> >
> > Dim txtString As String
> >
> > 'reading the decrypted PIN into a textstring
> >
> > Try
> >
> > decryptStream.Read(buffer, 0, PIN.Length)
> >
> > buffer = decryptStreamReader.ReadBytes(CInt(PIN.Length))
> >
> > Catch exception As CryptographicException
> >
> > globalException = exception
> >
> > GoTo ErrorHandler
> >
> > End Try
> >
> > 'close the streams that has been opened
> >
> > cryptPIN.Close()
> >
> > decryptStream.Close()
> >
> > 'destroy all objects used
> >
> > cryptPIN = Nothing
> >
> > cryptPINWriteBinary = Nothing
> >
> > decryption = Nothing
> >
> > decryptStream = Nothing
> >
> > globalException = Nothing
> >
> > cryptoService = Nothing
> >
> > Return decrypt
> >
> > ErrorHandler:
> >
> > If globalException.Message = "" Then
> >
> > textPIN = Err.Description
> >
> > textKey = errPosition
> >
> > Else
> >
> > Dim inner As Exception
> >
> > textPIN = globalException.Message
> >
> > inner = globalException.InnerException()
> >
> > If Not inner Is Nothing Then
> >
> > textKey = inner.Message
> >
> > End If
> >
> > textInitialValue = globalException.Source
> >
> > End If
> >
> > End Function
> >
> > How do I avoid that ?
> >
> > Best regards Per Vestergaard-Laustsen, Denmark
> >
> >
>
>