Re: DES Encryption and Decryption using different keys gives 'Bad Data' exception

From: dean (abc_at_def.com)
Date: 06/04/03

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In reply to: Ivan Medvedev [MS]: "Re: DES Encryption and Decryption using different keys gives 'Bad Data' exception"
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Date: Wed, 4 Jun 2003 12:27:11 +0200

Thanks Ivan, I have attached the comments I recd from MS support on this.

**********************
301070.KB.EN-US HOW TO: Encrypt and Decrypt a File by Using Visual Basic
.NET

(http://support.microsoft.com/?id=301070)

It contains the following about the Keys:

The DESCryptoServiceProvider is based on Symmetric encryption algorithm. The
symmetric encryption require a key and a initialization vector (IV) to
encrypt data. To decrypt the data the user must possess the same key and IV
and use the same encryption algorithm.

************************

However I find this odd. If the DES algorithm merely transforms an input
string to an output using a Key and IV etc, then how will it be able to
determine what input key the cipher text was created with. I accept that to
get the original plain text you need to use the same key (hence the name
symmetric encryption) to decrypt. What do you think of the above statement?

I have read that the process indicated is effectively triple des with a
128bit key (112 without parity) but I can't confirm this because DES gives a
bad data exception using different encrypt and decrypt keys (ie the 128
split into 2) and using a 128 bit key that has the same first half and
second half causes Triple DES to raise an exception becuase that is a weak
key.

I have attached the test harness code I am using to try this out. It
contains a form and class. Hopefully this will highlight any errors.
essentially I have to get the value stored in KCV1 by encrypting the string
value of zero using the KEK component split into two and using DES.

Thanks for the help

Dean

********************************
'The form code
********************************
Imports System.Text

Imports System.Security

Imports System.Security.Cryptography

Public Class Form1

Inherits System.Windows.Forms.Form

#Region " Windows Form Designer generated code "

Public Sub New()

MyBase.New()

'This call is required by the Windows Form Designer.

InitializeComponent()

'Add any initialization after the InitializeComponent() call

PerformStartup()

End Sub

'Form overrides dispose to clean up the component list.

Protected Overloads Overrides Sub Dispose(ByVal disposing As Boolean)

If disposing Then

If Not (components Is Nothing) Then

components.Dispose()

End If

MyBase.Dispose(disposing)

End Sub

'Required by the Windows Form Designer

Private components As System.ComponentModel.IContainer

'NOTE: The following procedure is required by the Windows Form Designer

'It can be modified using the Windows Form Designer.

'Do not modify it using the code editor.

Friend WithEvents Button1 As System.Windows.Forms.Button

Friend WithEvents Button2 As System.Windows.Forms.Button

Friend WithEvents lstOutput As System.Windows.Forms.ListBox

<System.Diagnostics.DebuggerStepThrough()> Private Sub InitializeComponent()

Me.Button1 = New System.Windows.Forms.Button()

Me.Button2 = New System.Windows.Forms.Button()

Me.lstOutput = New System.Windows.Forms.ListBox()

Me.SuspendLayout()

'Button1

Me.Button1.Location = New System.Drawing.Point(16, 16)

Me.Button1.Name = "Button1"

Me.Button1.Size = New System.Drawing.Size(152, 24)

Me.Button1.TabIndex = 0

Me.Button1.Text = "Calc KCV Using DES"

'Button2

Me.Button2.Location = New System.Drawing.Point(176, 16)

Me.Button2.Name = "Button2"

Me.Button2.Size = New System.Drawing.Size(152, 24)

Me.Button2.TabIndex = 1

Me.Button2.Text = "Calc Using Triple DES"

'lstOutput

Me.lstOutput.Anchor = (((System.Windows.Forms.AnchorStyles.Top Or
System.Windows.Forms.AnchorStyles.Bottom) _

Or System.Windows.Forms.AnchorStyles.Left) _

Or System.Windows.Forms.AnchorStyles.Right)

Me.lstOutput.Location = New System.Drawing.Point(0, 48)

Me.lstOutput.Name = "lstOutput"

Me.lstOutput.Size = New System.Drawing.Size(336, 277)

Me.lstOutput.TabIndex = 2

'Form1

Me.AutoScaleBaseSize = New System.Drawing.Size(5, 13)

Me.ClientSize = New System.Drawing.Size(336, 325)

Me.Controls.AddRange(New System.Windows.Forms.Control() {Me.lstOutput,
Me.Button2, Me.Button1})

Me.Name = "Form1"

Me.Text = "Form1"

Me.ResumeLayout(False)

End Sub

#End Region

'Friend Const KEK1 As String = "8F5E-6EBA-BC0E-2F92-49E5-C201-0708-C834"

'Friend Const KCV1 As String = "94-F5-F0-D8-43-46-E7-7D"

Friend Const KEK1 As String = "1111-1111-1111-1111-1111-1111-1111-1111"

Friend Const KCV1 As String = "82-E1-36-65-B4-62-4D-F5"

Private btTempStore(7) As Byte

Private Sub PerformStartup()

AddHandler Button1.Click, AddressOf CalcKCV1DESClick

AddHandler Button2.Click, AddressOf CalcKCV1TDESClick

End Sub

'Generate a Key Check Value for Key Value 1 using DES so verify correct
entry

Private Sub CalcKCV1DESClick(ByVal sender As System.Object, ByVal e As
System.EventArgs)

Try

Dim btKEK1() As Byte

Dim btKL(7) As Byte

Dim btKR(7) As Byte

Dim sKEK1Converted As String

Dim btBytesReturned2() As Byte

Dim btBytesReturned3() As Byte

Dim btBytesReturned4() As Byte

Dim btInitVector(7) As Byte

Dim sInitVector As String

Dim oEncryptDecrypt As clsEncryptDecrypt

oEncryptDecrypt = New clsEncryptDecrypt(CipherMode.CBC, PaddingMode.PKCS7)

'Following on from the Guidance note methodology

'STEP 1 - get the Byte array version of this string

btKEK1 = ConvertKEKFromHexToByteArray(KEK1)

'Break it into two 64 bit sub keys - Key left (KL) and Key Right (KR)

Array.Copy(btKEK1, 0, btKL, 0, 8)

Array.Copy(btKEK1, 8, btKR, 0, 8)

'Get the Init Vector

btInitVector = Encoding.UTF8.GetBytes("00000000")

'STEP2 - encrypt 0 with a key = KL

btBytesReturned2 = oEncryptDecrypt.DESEncrypt("0", btKL, btInitVector)

btTempStore = btBytesReturned2

lstOutput.Items.Add("KCV 1 calculation Step 1")

lstOutput.Items.Add("DES Encrypted CipherText: " &
BitConverter.ToString(btBytesReturned2))

lstOutput.Items.Add("DES Encrypted Text: " &
Encoding.UTF8.GetString(btBytesReturned2))

'STEP3 - decrypt with a key = KR

btBytesReturned3 = oEncryptDecrypt.DESDecrypt(btBytesReturned2, btKR,
btInitVector)

lstOutput.Items.Add("Step 3")

lstOutput.Items.Add("DES Encrypted CipherText: " &
BitConverter.ToString(btBytesReturned3))

lstOutput.Items.Add("DES Encrypted Text: " &
Encoding.UTF8.GetString(btBytesReturned3))

'STEP2 - encrypt 0 with a key = KEK1

btBytesReturned4 = oEncryptDecrypt.DESEncrypt(btBytesReturned3, btKL,
btInitVector)

lstOutput.Items.Add("Step 4")

lstOutput.Items.Add("DES Encrypted CipherText: " &
BitConverter.ToString(btBytesReturned4))

lstOutput.Items.Add("DES Encrypted Text: " &
Encoding.UTF8.GetString(btBytesReturned4))

lstOutput.Items.Add("KCV Returned : " &
BitConverter.ToString(btBytesReturned4))

Catch exp As Exception

HandleException(exp)

End Try

End Sub

'Generate a Key Check Value for Key Value 1 using Triple DES so verify
correct entry

Private Sub CalcKCV1TDESClick(ByVal sender As System.Object, ByVal e As
System.EventArgs)

Try

Dim btKEK1() As Byte

Dim sKEK1Converted As String

Dim btBytesReturned() As Byte

Dim btInitVector() As Byte

Dim sInitVector As String

Dim oEncryptDecrypt As clsEncryptDecrypt

oEncryptDecrypt = New clsEncryptDecrypt(CipherMode.CBC, PaddingMode.PKCS7)

'Following on from the Guidance note methodology

'STEP 1 - get the Byte array version of this string

btKEK1 = ConvertKEKFromHexToByteArray(KEK1)

'Get the Init Vector

btInitVector = Encoding.UTF8.GetBytes("00000000")

'STEP2 - encrypt 0 with a key = KEK1

btBytesReturned = oEncryptDecrypt.TripleDESEncrypt("0", btKEK1,
btInitVector)

lstOutput.Items.Add("KCV 1 calculation")

lstOutput.Items.Add("3DES Encrypted CipherText: " &
BitConverter.ToString(btBytesReturned))

lstOutput.Items.Add("3DES Encrypted Text: " &
Encoding.UTF8.GetString(btBytesReturned))

'Test that this can be decrypted

Dim btBytesDecrypted() As Byte

btBytesDecrypted = oEncryptDecrypt.TripleDESDecrypt(btBytesReturned, btKEK1,
btInitVector)

lstOutput.Items.Add("KCV 1 Decryption")

lstOutput.Items.Add("3DES Decrypted CipherText: " &
BitConverter.ToString(btBytesDecrypted))

lstOutput.Items.Add("3DES Decrypted Text: " &
Encoding.UTF8.GetString(btBytesDecrypted))

lstOutput.Items.Add("KCV Returned : " &
BitConverter.ToString(btBytesReturned))

Catch exp As Exception

HandleException(exp)

End Try

End Sub

'Convert HEX to Byte Array

Friend Function ConvertKEKFromHexToByteArray(ByVal sKEK As String) As Byte()

'The Hex string needs to be broken into groups of two and then converted to
ASCII

Dim iHexLeft As Integer

Dim iHexRight As Integer

Dim sTempCharString As String

Dim iCounter As Integer

Dim iNoOfHexChars As Integer

Dim btConvertedHex() As Byte

Dim iArrayCounter As Integer

'Extract all the "-" if they exist

sKEK = sKEK.Replace("-", "")

'Check that the string is in multiples of two

If ((sKEK.Length Mod 2) = 0) Then

iNoOfHexChars = CInt(sKEK.Length / 2)

ReDim btConvertedHex(iNoOfHexChars - 1)

Else

Throw New ApplicationException("Invalid length of string")

End If

'Becasue the loop increments by 2 each time use another counter

iArrayCounter = 0

'Try reading the hex from left to right!

For iCounter = 0 To (sKEK.Length - 1) Step 2

sTempCharString = sKEK.Substring(iCounter, 2)

iHexLeft = Uri.FromHex(CChar(sTempCharString.Substring(0, 1))) * 16

iHexRight = Uri.FromHex(CChar(sTempCharString.Substring(1, 1)))

Debug.WriteLine("Converted " & sTempCharString & " to int yields : " &
iHexLeft + iHexRight)

btConvertedHex(iArrayCounter) = iHexLeft + iHexRight

iArrayCounter += 1

Return btConvertedHex

End Function

Public Sub HandleException(ByVal exp As Exception)

MsgBox("Exception Occurred" & vbCrLf & exp.Message & _

vbCrLf & exp.GetType.ToString & vbCrLf & exp.Source & _

vbCrLf & exp.StackTrace)

End Sub

End Class

********************************
The class code
********************************
Imports System

Imports System.IO

Imports System.Text

Imports System.Security.Cryptography

Friend Class clsEncryptDecrypt

Private m_eCipherMode As CipherMode

Private m_ePaddingMode As PaddingMode

Public Sub New(ByVal eCipherMode As CipherMode, ByVal ePaddingMode As
PaddingMode)

m_eCipherMode = eCipherMode

m_ePaddingMode = ePaddingMode

End Sub

'Overload that accepts the String to encrypt, the encryption key

'and Init Vector as byte arrays

Public Function DESEncrypt(ByVal btStringToEncrypt() As Byte, _

ByVal btEncryptionKey() As Byte, ByVal btInitVector() As Byte) As Byte()

Dim msEncrypt As New MemoryStream()

Dim oTransformation As ICryptoTransform

Dim oCryptoService As DESCryptoServiceProvider

Dim oEncryptStream As CryptoStream

'Create the DEs service provider

oCryptoService = New DESCryptoServiceProvider()

oCryptoService.Key = btEncryptionKey

oCryptoService.IV = btInitVector

'Set the Crypto provider mode

oCryptoService.Mode = m_eCipherMode

oCryptoService.Padding = m_ePaddingMode

'Create the Transformation using the input key and Init Vector

oTransformation = oCryptoService.CreateEncryptor(btEncryptionKey,
btInitVector)

'Create the encryption stream using the memory stream and the

'create encryptor transformation

oEncryptStream = New CryptoStream(msEncrypt, _

oTransformation, CryptoStreamMode.Write)

'encrypt writing to the encryptionstream which is the memory stream

oEncryptStream.Write(btStringToEncrypt, 0, CInt(btStringToEncrypt.Length))

'close the streams that has been opened

oEncryptStream.Close()

'Write out some useful info

Debug.WriteLine("DES Encrypt called")

Debug.WriteLine("Entered Text : " &
BitConverter.ToString(btStringToEncrypt))

Debug.WriteLine("Encrypted Cipher Text : " &
BitConverter.ToString(msEncrypt.ToArray))

'Return the byte array

Return msEncrypt.ToArray()

End Function

'Overload that accepts the encryption key and Init Vector as byte arrays

Public Function DESEncrypt(ByVal sStringToEncrypt As String, _

ByVal btEncryptionKey() As Byte, ByVal btInitVector() As Byte) As Byte()

Dim msEncrypt As New MemoryStream()

Dim btStringToEncrypt() As Byte

Dim oTransformation As ICryptoTransform

Dim oCryptoService As DESCryptoServiceProvider

Dim oEncryptStream As CryptoStream

btStringToEncrypt = System.Text.Encoding.UTF8.GetBytes(sStringToEncrypt)

'Create the DES service provider

oCryptoService = New DESCryptoServiceProvider()

oCryptoService.Key = btEncryptionKey

oCryptoService.IV = btInitVector

'Set the Crypto provider mode

oCryptoService.Mode = m_eCipherMode

oCryptoService.Padding = m_ePaddingMode

'Create the Transformation using the input key and Init Vector

oTransformation = oCryptoService.CreateEncryptor(btEncryptionKey,
btInitVector)

'Create the encryption stream using the memory stream and the

'create encryptor transformation

oEncryptStream = New CryptoStream(msEncrypt, _

oTransformation, CryptoStreamMode.Write)

'encrypt writing to the encryptionstream which is the memory stream

oEncryptStream.Write(btStringToEncrypt, 0, CInt(btStringToEncrypt.Length))

'Finish encoding the last block

oEncryptStream.Flush()

oEncryptStream.FlushFinalBlock()

'close the streams that has been opened

oEncryptStream.Close()

'Write out some useful info

Debug.WriteLine("DES Encrypt called")

Debug.WriteLine("Entered Text : " &
BitConverter.ToString(btStringToEncrypt))

Debug.WriteLine("Encrypted Cipher Text : " &
BitConverter.ToString(msEncrypt.ToArray))

'Return the byte array

Return msEncrypt.ToArray()

End Function

'Overload that accepts the encryption key and Init Vector as strings

Public Function DESEncrypt(ByVal sStringToEncrypt As String, _

ByVal sEncryptionKey As String, ByVal sInitVector As String) As Byte()

Dim msEncrypt As New MemoryStream()

Dim btStringToEncrypt() As Byte

Dim btEncryptionKey() As Byte

Dim btInitVector() As Byte

Dim oTransformation As ICryptoTransform

Dim oCryptoService As DESCryptoServiceProvider

Dim oEncryptStream As CryptoStream

btStringToEncrypt = System.Text.Encoding.UTF8.GetBytes(sStringToEncrypt)

'Create the DEs service provider

oCryptoService = New DESCryptoServiceProvider()

'Set the Crypto provider mode

oCryptoService.Mode = m_eCipherMode

oCryptoService.Padding = m_ePaddingMode

'Create the Transformation using the input key and Init Vector

btEncryptionKey = System.Text.Encoding.UTF8.GetBytes(sEncryptionKey)

btInitVector = System.Text.Encoding.UTF8.GetBytes(sInitVector)

oTransformation = oCryptoService.CreateEncryptor(btEncryptionKey,
btInitVector)

'Create the encryption stream using the memory stream and the

'create encryptor transformation

oEncryptStream = New CryptoStream(msEncrypt, _

oTransformation, CryptoStreamMode.Write)

'encrypt writing to the encryptionstream which is the memory stream

oEncryptStream.Write(btStringToEncrypt, 0, CInt(btStringToEncrypt.Length))

'close the streams that has been opened

oEncryptStream.Close()

'Write out some useful info

Debug.WriteLine("DES Encrypt called")

Debug.WriteLine("Entered Text : " &
BitConverter.ToString(btStringToEncrypt))

Debug.WriteLine("Encrypted Cipher Text : " &
BitConverter.ToString(msEncrypt.ToArray))

'Return the byte array

Return msEncrypt.ToArray()

End Function

'Overload that accepts the encryption key and Init Vector as byte arrays

Public Function DESDecrypt(ByVal btByteArrayToDecrypt As Byte(), _

ByVal sEncryptionKey As String, ByVal sInitVector As String) As Byte()

Dim msDecrypt As New MemoryStream()

Dim btEncryptionKey() As Byte

Dim btInitVector() As Byte

Dim oTransformation As ICryptoTransform

Dim oCryptoService As DESCryptoServiceProvider

Dim oDecryptStream As CryptoStream

'Create the DEs service provider

oCryptoService = New DESCryptoServiceProvider()

'Set the Crypto provider mode

oCryptoService.Mode = m_eCipherMode

oCryptoService.Padding = m_ePaddingMode

'Create the Transformation using the input key and Init Vector

btEncryptionKey = System.Text.Encoding.UTF8.GetBytes(sEncryptionKey)

btInitVector = System.Text.Encoding.UTF8.GetBytes(sInitVector)

oTransformation = oCryptoService.CreateDecryptor(btEncryptionKey,
btInitVector)

'Create the encryption stream using the memory stream and the

'create DECRYPTOR transformation

oDecryptStream = New CryptoStream(msDecrypt, _

oTransformation, CryptoStreamMode.Write)

'Decrypt writing to the encryptionstream which is the underlying memory
stream

oDecryptStream.Write(btByteArrayToDecrypt, 0,
CInt(btByteArrayToDecrypt.Length))

'close the streams that has been opened

oDecryptStream.Close()

'Write out some useful info

Debug.WriteLine("DES Decrypt called")

Debug.WriteLine("Cipher Text : " &
BitConverter.ToString(btByteArrayToDecrypt))

Debug.WriteLine("Decrypted Text : " &
BitConverter.ToString(msDecrypt.ToArray()))

'return the memory stream to a byte array

Return msDecrypt.ToArray()

End Function

'Overload that accepts the encryption key and Init Vector as byte arrays

Public Function DESDecrypt(ByVal btByteArrayToDecrypt As Byte(), _

ByVal btEncryptionKey() As Byte, ByVal btInitVector() As Byte) As Byte()

Dim msDecrypt As New MemoryStream()

Dim oTransformation As ICryptoTransform

Dim oCryptoService As DESCryptoServiceProvider

Dim oDecryptStream As CryptoStream

'Create the DEs service provider

oCryptoService = New DESCryptoServiceProvider()

'Set the Crypto provider mode

oCryptoService.Mode = m_eCipherMode

oCryptoService.Padding = m_ePaddingMode

'Create the Transformation using the input key and Init Vector

oTransformation = oCryptoService.CreateDecryptor(btEncryptionKey,
btInitVector)

'Create the encryption stream using the memory stream and the

'create DECRYPTOR transformation

oDecryptStream = New CryptoStream(msDecrypt, _

oTransformation, CryptoStreamMode.Write)

'Decrypt writing to the encryptionstream which is the underlying memory
stream

oDecryptStream.Write(btByteArrayToDecrypt, 0,
CInt(btByteArrayToDecrypt.Length))

'Finish encoding the last block

oDecryptStream.Flush()

oDecryptStream.FlushFinalBlock()

'close the streams that has been opened

oDecryptStream.Close()

'Write out some useful info

Debug.WriteLine("DES Decrypt called")

Debug.WriteLine("Cipher Text : " &
BitConverter.ToString(btByteArrayToDecrypt))

Debug.WriteLine("Decrypted Text : " &
BitConverter.ToString(msDecrypt.ToArray()))

'return the memory stream to a byte array

Return msDecrypt.ToArray()

End Function

'Overload that accepts the encryption key and Init Vector as byte arrays

Public Function TripleDESEncrypt(ByVal sStringToEncrypt As String, _

ByVal btEncryptionKey() As Byte, ByVal btInitVector() As Byte) As Byte()

Dim msEncrypt As New MemoryStream()

Dim btStringToEncrypt() As Byte

Dim oTransformation As ICryptoTransform

Dim oCryptoService As TripleDESCryptoServiceProvider

Dim oEncryptStream As CryptoStream

btStringToEncrypt = System.Text.Encoding.UTF8.GetBytes(sStringToEncrypt)

'Create the Triple DES service provider

oCryptoService = New TripleDESCryptoServiceProvider()

'Set the Crypto provider mode

oCryptoService.Mode = m_eCipherMode

oCryptoService.Padding = m_ePaddingMode

'Create the Transformation using the input key and Init Vector

oTransformation = oCryptoService.CreateEncryptor(btEncryptionKey,
btInitVector)

'Create the encryption stream using the memory stream and the

'create encryptor transformation

oEncryptStream = New CryptoStream(msEncrypt, _

oTransformation, CryptoStreamMode.Write)

'encrypt writing to the encryptionstream which is the memory stream

oEncryptStream.Write(btStringToEncrypt, 0, CInt(btStringToEncrypt.Length))

'close the streams that has been opened

oEncryptStream.Close()

'Write out some useful info

Debug.WriteLine("3DES Encrypt called")

Debug.WriteLine("Text Input : " & BitConverter.ToString(btStringToEncrypt))

Debug.WriteLine("Encrypted Cipher Text : " &
BitConverter.ToString(msEncrypt.ToArray))

'Return the byte array

Return msEncrypt.ToArray()

End Function

'Overload that accepts the encryption key and Init Vector as byte arrays

Public Function TripleDESEncrypt(ByVal sStringToEncrypt As String, _

ByVal sEncryptionKey As String, ByVal sInitVector As String) As Byte()

Dim msEncrypt As New MemoryStream()

Dim btStringToEncrypt() As Byte

Dim btEncryptionKey() As Byte

Dim btInitVector() As Byte

Dim oTransformation As ICryptoTransform

Dim oCryptoService As TripleDESCryptoServiceProvider

Dim oEncryptStream As CryptoStream

btStringToEncrypt = System.Text.Encoding.UTF8.GetBytes(sStringToEncrypt)

'Create the DEs service provider

oCryptoService = New TripleDESCryptoServiceProvider()

'Set the Crypto provider mode

oCryptoService.Mode = m_eCipherMode

oCryptoService.Padding = m_ePaddingMode

'Create the Transformation using the input key and Init Vector

btEncryptionKey = System.Text.Encoding.UTF8.GetBytes(sEncryptionKey)

btInitVector = System.Text.Encoding.UTF8.GetBytes(sInitVector)

oTransformation = oCryptoService.CreateEncryptor(btEncryptionKey,
btInitVector)

'Create the encryption stream using the memory stream and the

'create encryptor transformation

oEncryptStream = New CryptoStream(msEncrypt, _

oTransformation, CryptoStreamMode.Write)

'encrypt writing to the encryptionstream which is the memory stream

oEncryptStream.Write(btStringToEncrypt, 0, CInt(btStringToEncrypt.Length))

'close the streams that has been opened

oEncryptStream.Close()

'Write out some useful info

Debug.WriteLine("3DES Encrypt called")

Debug.WriteLine("Entered Text : " &
BitConverter.ToString(btStringToEncrypt))

Debug.WriteLine("Encrypted Cipher Text : " &
BitConverter.ToString(msEncrypt.ToArray))

'Return the byte array

Return msEncrypt.ToArray()

End Function

'Overload that accepts the encryption key and Init Vector as byte arrays

Public Function TripleDESDecrypt(ByVal btByteArrayToDecrypt As Byte(), _

ByVal btEncryptionKey() As Byte, ByVal btInitVector() As Byte) As Byte()

Dim msDecrypt As New MemoryStream()

Dim oTransformation As ICryptoTransform

Dim oCryptoService As TripleDESCryptoServiceProvider

Dim oDecryptStream As CryptoStream

'Create the DEs service provider

oCryptoService = New TripleDESCryptoServiceProvider()

'Set the Crypto provider mode

oCryptoService.Mode = m_eCipherMode

oCryptoService.Padding = m_ePaddingMode

'Create the Transformation using the input key and Init Vector

oTransformation = oCryptoService.CreateDecryptor(btEncryptionKey,
btInitVector)

'Create the encryption stream using the memory stream and the

'create DECRYPTOR transformation

oDecryptStream = New CryptoStream(msDecrypt, _

oTransformation, CryptoStreamMode.Write)

'Decrypt writing to the encryptionstream which is the underlying memory
stream

oDecryptStream.Write(btByteArrayToDecrypt, 0,
CInt(btByteArrayToDecrypt.Length))

'close the streams that has been opened

oDecryptStream.Close()

'Write out some useful info

Debug.WriteLine("Triple DES Decrypt called")

Debug.WriteLine("Cipher Text : " &
BitConverter.ToString(btByteArrayToDecrypt))

Debug.WriteLine("Decrypted Text : " &
BitConverter.ToString(msDecrypt.ToArray()))

'return the memory stream to a byte array

Return msDecrypt.ToArray()

End Function

Public Sub TestThisCode(ByVal lstRefToListBox As
System.Windows.Forms.ListBox, _

ByVal sStringToencrypt As String, ByVal sEncryptionKey As String, _

ByVal sInitVector As String)

Dim btEncryptedString() As Byte

Dim btDecryptedString() As Byte

btEncryptedString = DESEncrypt(sStringToencrypt, sEncryptionKey,
sInitVector)

btDecryptedString = DESDecrypt(btEncryptedString, sEncryptionKey,
sInitVector)

'Display the hex values of the byte array

lstRefToListBox.Items.Add("Start values")

lstRefToListBox.Items.Add(vbTab & "String to Encrypt - " & sStringToencrypt)

lstRefToListBox.Items.Add(vbTab & "Encryption key - " & sEncryptionKey)

lstRefToListBox.Items.Add(vbTab & "Init Vector - " & sInitVector)

lstRefToListBox.Items.Add("Encrypted data: " +
BitConverter.ToString(btEncryptedString))

lstRefToListBox.Items.Add("Decrypted data: " +
BitConverter.ToString(btDecryptedString))

lstRefToListBox.Items.Add("Decrypted text: " +
System.Text.Encoding.UTF8.GetString(btDecryptedString))

End Sub

End Class

********************************

"Ivan Medvedev [MS]" <ivanmed@online.microsoft.com> wrote in message
news:#laC6zgKDHA.1612@TK2MSFTNGP11.phx.gbl...
> Dean -
> please check that you are feeding to the decryptor all the data you have
> received on the encryption phase. Normally a cipher text is skightly
longer
> that the plain text and it is a very common mistake when people are
feeding
> the number of bytes the plaintext had to the decryptor. If this is not the
> case in your implementation please post some code.
> Thanks,
> --Ivan
> This posting is provided "AS IS" with no warranties, and confers no
rights.
>
>
> "dean" <abc@def.com> wrote in message
> news:eL%23H1ZFJDHA.1732@TK2MSFTNGP11.phx.gbl...
> > Hi all,
> >
> > Is anyone familiar with the AnsiX9.19 document which handles the
> generation
> > of Key Encryption Keys (KEK) and Key Check Vaues (KCV). A rough overview
> of
> > the process is as follows:
> >
> > Step 1 : Take a given 128bit key, and divide it into 2 - to generate key
> > parts KL equals the left 64 bits and KR the right.
> > Step 2 : Then encrypt the number zero "0" using the left hand key part
> (KL)
> > and DES.
> > Step 3 : The output of step 2 is then decrypted using the right hand key
> > part (KR).
> > Step 4 : The final step is to re-encrypt this output using the left hand
> key
> > part once again.
> >
> > According to the ANSI doc this yields a Key Check Value which can be
used
> > for message authentication.
> >
> > The Step 1 encryption part works fine but Step 2 decrypting using the
> right
> > hand key part fails with the infamous 'Bad Data' cryptographic
exception.
> > When I reran the process using the the left hand key part (KL) for both
> > encryption, decryption and the re-encryption it works fine. This leads
me
> to
> > beleive that the code is ok but the decryption process doesn't like a
> > different key.
> >
> > Does any one have any ideas on this. Help would be greatly appreciated.
> >
> > Best regards
> >
> > Dean
> >
> > PS I can attach some code samples if that would help.
> >
> >
>
>

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