DES ECB Encryption cannot decrypt

From: Per Vestergaard-Laustsen (pvl_at_capto.dk)
Date: 05/08/03 

Date: Thu, 8 May 2003 11:54:22 +0200

I am making an ActiveX component, and the application supposed to use it
only supports passing arguments as strings. Internally that particular
application only uses ASCII format for strings. I need to pass binary values
to and from the ActiveX component, where each byte can assume all values
from 0 to 255 (unsigned char).

By the way the crypto API still will not work.

I use DES, Mode=ECB. If I have the value to encrypt =
'01-47-11-00-00-00-00-00', the Key = 'EE-B7-55-E0-E7-35-B1-74' and IV =
'00-00-00-00-00-00-00-00'(since it should not be used when mode=ECB), then
when encrypting I get 'C0-30-76-FF-4D-2C-3C-C5-8B-03-5A-A1-96-FB-9C-3C'.

So far so good. But now when I try and decrypt that value, with the same Key
and IV, I get a bad data error. The Exception thrown has Hresult =
&HFFFFFFFF80131430 and _xcode = &HFFFFFFFFE0434F4D.

Best regards Per Vestergaard-Laustsen, Denmark

Code used :

Imports System

Imports System.Security.Cryptography 'in order to be able to en- / de- crypt

Imports System.IO 'in order to use streams or memorystreams

Imports System.Object 'in order to be able to create a BinaryReader

Imports System.NotSupportedException 'in order to troubleshoot not supported
exceptions

Imports System.Text.UTF8Encoding 'in order to be able to convert between
texts and bytearrays

<ComClass(Crypto.ClassId, Crypto.InterfaceId, Crypto.EventsId)> _

Public Class Crypto

#Region "COM GUIDs"

' These GUIDs provide the COM identity for this class

' and its COM interfaces. If you change them, existing

' clients will no longer be able to access the class.

Public Const ClassId As String = "E283E523-DDF6-41E5-99FD-D49BEA927F6B"

Public Const InterfaceId As String = "63468760-BECB-43D0-B001-D656E7D83519"

Public Const EventsId As String = "E42A8155-7740-4BE8-BB53-A845E0286A12"

#End Region

' A creatable COM class must have a Public Sub New()

' with no parameters, otherwise, the class will not be

' registered in the COM registry and cannot be created

' via CreateObject.

Public Sub New()

MyBase.New()

End Sub

Protected Overrides Sub Finalize()

MyBase.Finalize()

End Sub

Dim errPosition As String

Dim globalexception As CryptographicException

Public Sub test()

If "0655" <> decrypt(encrypt("0655", "09689036", "80682702"), "09689036",
"80682702") Then

Console.WriteLine("Decrypted : " + decrypt(encrypt("0655", "09689036",
"80682702"), "09689036", "80682702"))

Console.WriteLine("Unencrypted : " + "0655")

End If

End Sub

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 PIN() As Byte

Dim Key() As Byte

Dim InitialValue() As Byte

PIN = GetEncryptKeyByteArray(textPIN)

Key = GetEncryptKeyByteArray(textKey)

InitialValue = GetEncryptKeyByteArray(textInitialValue)

Dim cryptPIN As MemoryStream

cryptPIN = New MemoryStream()

Dim encryption As ICryptoTransform

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

'cryptoService.Mode = CipherMode.ECB

encryption = cryptoService.CreateEncryptor(Key, InitialValue)

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

encryption, _

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

encryption = 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 i As Integer

Dim cryptPIN As MemoryStream

Dim PIN(15) As Byte

Dim Key(7) As Byte

Dim InitialValue(7) As Byte

PIN = GetDecryptKeyByteArray(textPIN)

Key = GetEncryptKeyByteArray(textKey)

InitialValue = GetEncryptKeyByteArray(textInitialValue)

cryptPIN = New MemoryStream()

Dim buffer(1024) As Byte

Dim decryption As ICryptoTransform

Dim cryptoService As New DESCryptoServiceProvider()

'cryptoService.Mode = CipherMode.ECB

decryption = cryptoService.CreateDecryptor(Key, InitialValue)

'the decryption takes place here

Dim decryptStream As New CryptoStream(cryptPIN, _

decryption, _

CryptoStreamMode.Write)

'temp TEST

Dim tempArrayOfByte(7) As Byte

For i = 0 To 7

tempArrayOfByte(i) = PIN(i)

Next

Try

decryptStream.Write(tempArrayOfByte, 0, CInt(tempArrayOfByte.Length))
'encrypt writing to the decryptionstream

Catch exception As CryptographicUnexpectedOperationException

globalexception = exception

GoTo errorhandler

End Try

Try

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

Catch exception As CryptographicException

globalexception = exception

GoTo ErrorHandler

End Try

'end temp TEST

Try

decryptStream.Write(PIN, 0, CInt(PIN.Length)) 'encrypt writing to the
decryptionstream

Catch exception As CryptographicUnexpectedOperationException

globalexception = exception

GoTo errorhandler

End Try

Try

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

Catch exception As CryptographicException

globalexception = exception

GoTo ErrorHandler

End Try

decrypt = byte2str(cryptPIN.ToArray())

'close the streams that has been opened

cryptPIN.Close()

decryptStream.Close()

'destroy all objects used

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

Public Function calcXOR(ByVal Arg1 As Integer, ByVal Arg2 As Integer) As
Integer

calcXOR = Arg1 Xor Arg2

Return calcXOR

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 a, b As String

Dim i, n As Integer

Dim bPW(7) As Byte

n = 0

For i = 1 To 22 Step 3

a = Asc(Mid(sPassword, i, 1)) - Asc("0")

If a > 9 Then a = a - 7

If a < 0 Or a > 15 Then

Err.Raise(vbObjectError + 513)

End If

b = Asc(Mid(sPassword, i + 1, 1)) - Asc("0")

If b > 9 Then b = b - 7

If b < 0 Or b > 15 Then

Err.Raise(vbObjectError + 513)

End If

bPW(n) = a * 16 + b

n += 1

Next i

'Dim iCharIndex As Integer

'For iCharIndex = 0 To sPassword.Length - 1

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

'Next

'byteTemp = UTF8.GetBytes(sPassword)

Return bPW

End Function

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

Dim byteTemp(15) As Byte

' sPassword = sPassword.PadRight(16) ' make sure we have 16 chars

Dim a, b As String

Dim i, n As Integer

Dim bPW(15) As Byte

n = 0

For i = 1 To 46 Step 3

a = Asc(Mid(sPassword, i, 1)) - Asc("0")

If a > 9 Then a = a - 7

If a < 0 Or a > 15 Then

Err.Raise(vbObjectError + 513)

End If

b = Asc(Mid(sPassword, i + 1, 1)) - Asc("0")

If b > 9 Then b = b - 7

If b < 0 Or b > 15 Then

Err.Raise(vbObjectError + 513)

End If

bPW(n) = a * 16 + b

n += 1

Next i

'Dim iCharIndex As Integer

'For iCharIndex = 0 To sPassword.Length - 1

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

'Next

'byteTemp = UTF8.GetBytes(sPassword)

Return bPW

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

byte2str = BitConverter.ToString(bytes)

errPosition = "Before return from byte2str"

Return byte2str

End Function

Public Function argtest(ByRef bytes As Byte()) As Object

Return bytes

End Function

End Class

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