Secure Query String using Symmetric Cryptography

It is important to secure information on the web specially when transferring data from one page to another. Some information you may not want to make it readable by end user. Microsoft .NET provides Cryptography namespace which can be easily utilized for this purpose. The following example contains a simple class containing Encryption and Decryption method. It supports 2 types – DESC and Rijndael. Symmetric type and encryption key can be configured easily through .config file.

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Imports System

Imports System.IO

Imports System.Text

Imports System.Security.Cryptography

Imports System.Configuration

 

''' <summary>

''' Custom Encryption Class

''' Author: Vishwa

''' Date :05/28/08

''' Purpose: To Encrypt and Decrypt the Data

''' Design Pattern : Singleton

''' </summary>

''' <remarks>

''' This class implements a Base 64 encryption and decryption Using Symetric

''' IMPT: Config File will contain 2 keys and its value - SymmetricType and SymmetricKey

''' </remarks>

 

Public NotInheritable Class RegCryptographer

    Private Shared _instance As New RegCryptographer

 

#Region "Constructor"

    Private Sub New()

 

    End Sub

#End Region

 

#Region "Public Methods"

 

    Public Shared Function DecryptQueryString(ByVal stringToDecrypt As String) As String

        Return DecryptSymmetric(stringToDecrypt.Replace(" ", "+"))

    End Function

 

    Public Shared Function EncryptQueryString(ByVal stringToEncrypt As String) As String

        Return EncryptSymmetric(stringToEncrypt)

    End Function

 

#End Region

 

#Region "Custom Cryptography"

    Private Shared _key() As Byte = {}

    Private Shared _IV() As Byte = {}

    Private Shared _symmetricKey As String = String.Empty

 

#Region "Rijndael Encryption/Decryption"

    Public Shared Function DecryptSymmetric(ByVal stringToDecrypt As String) As String

        If SymmetricType = "Rijndael" Then

            Return DecryptSymmetricRijndael(stringToDecrypt)

        Else

            Return DecryptSymmetricDESC(stringToDecrypt)

        End If

    End Function

 

    Public Shared Function EncryptSymmetric(ByVal stringToEncrypt As String) As String

        If SymmetricType = "Rijndael" Then

            Return EncryptSymmetricRijndael(stringToEncrypt)

        Else

            Return EncryptSymmetricDESC(stringToEncrypt)

        End If

    End Function

 

    Private Shared Function DecryptSymmetricRijndael(ByVal stringToDecrypt As String) As String

        Try

            Dim inputByteArray(stringToDecrypt.Length) As Byte

            Dim rijndael As New RijndaelManaged()

            rijndael.GenerateIV()

            'rijndael.GenerateKey()

            '_key = rijndael.Key

            _IV = rijndael.IV

 

            rijndael.KeySize = 128

            rijndael.BlockSize = 128

            rijndael.Mode = CipherMode.ECB

            rijndael.Padding = PaddingMode.PKCS7

            _key = System.Text.Encoding.UTF32.GetBytes(SymmetricKey)

            inputByteArray = Convert.FromBase64String(stringToDecrypt)

 

            Dim decryptor As ICryptoTransform = rijndael.CreateDecryptor(_key, _IV)

            Dim msDecrypt As New MemoryStream()

            Dim csDecrypt As New CryptoStream(msDecrypt, decryptor, CryptoStreamMode.Write)

            csDecrypt.Write(inputByteArray, 0, inputByteArray.Length)

            csDecrypt.FlushFinalBlock()

            Dim encoding As System.Text.Encoding = System.Text.Encoding.UTF8

            Return encoding.GetString(msDecrypt.ToArray())

        Catch e As Exception

            Return e.Message

        End Try

    End Function

 

    Private Shared Function EncryptSymmetricRijndael(ByVal stringToEncrypt As String) As String

        Try

            Dim rijndael As New RijndaelManaged()

            rijndael.GenerateIV()

            'rijndael.GenerateKey()

            '_key = rijndael.Key

            _IV = rijndael.IV

            _key = System.Text.Encoding.UTF32.GetBytes(SymmetricKey)

 

            rijndael.KeySize = 128

            rijndael.BlockSize = 128

            rijndael.Mode = CipherMode.ECB

            rijndael.Padding = PaddingMode.PKCS7

            Dim encryptor As ICryptoTransform = rijndael.CreateEncryptor(_key, _IV)

            Dim inputByteArray() As Byte = Encoding.UTF8.GetBytes(stringToEncrypt)

            Dim msEncrypt As New MemoryStream()

            Dim csEncrypt As New CryptoStream(msEncrypt, encryptor, CryptoStreamMode.Write)

            csEncrypt.Write(inputByteArray, 0, inputByteArray.Length)

            csEncrypt.FlushFinalBlock()

            Return Convert.ToBase64String(msEncrypt.ToArray())

        Catch e As Exception

            Return e.Message

        End Try

    End Function

 

#End Region

 

#Region "DESC Encryption/DeCryption"

    Private Shared _symmetricType As String = String.Empty

    Private Shared Function DecryptSymmetricDESC(ByVal stringToDecrypt As String) As String

        Dim inputByteArray(stringToDecrypt.Length) As Byte

        Try

            inputByteArray = Convert.FromBase64String(stringToDecrypt)

            Dim des As New DESCryptoServiceProvider()

            des.GenerateIV()

            _IV = des.IV

            _key = System.Text.Encoding.UTF8.GetBytes(SymmetricKey)

 

            Dim ms As New MemoryStream()

            Dim cs As New CryptoStream(ms, des.CreateDecryptor(_key, _IV), CryptoStreamMode.Write)

            cs.Write(inputByteArray, 0, inputByteArray.Length)

            cs.FlushFinalBlock()

            Dim encoding As System.Text.Encoding = System.Text.Encoding.UTF8

            Return encoding.GetString(ms.ToArray())

        Catch e As Exception

            Return e.Message

        End Try

    End Function

 

    Private Shared Function EncryptSymmetricDESC(ByVal stringToEncrypt As String) As String

        Try

            Dim des As New DESCryptoServiceProvider()

            des.GenerateIV()

            _IV = des.IV

            _key = System.Text.Encoding.UTF8.GetBytes(SymmetricKey)

 

            Dim inputByteArray() As Byte = Encoding.UTF8.GetBytes(stringToEncrypt)

            Dim ms As New MemoryStream()

            Dim cs As New CryptoStream(ms, des.CreateEncryptor(_key, _IV), CryptoStreamMode.Write)

            cs.Write(inputByteArray, 0, inputByteArray.Length)

            cs.FlushFinalBlock()

            Return Convert.ToBase64String(ms.ToArray())

        Catch e As Exception

            Return e.Message

        End Try

    End Function

 

 

#End Region

 

#Region "Properties"

   

    Private Shared ReadOnly Property SymmetricType() As String

        Get

            If String.IsNullOrEmpty(_symmetricType) Then

                Try

                   _symmetricType = ConfigurationManager.AppSettings.Item("SymmetricType")

                Catch ex As Exception

                    _symmetricType = "Rijndael"

                End Try

                If String.IsNullOrEmpty(_symmetricType) Then _symmetricType = "Rijndael"

            End If

            Return _symmetricType

        End Get

    End Property

 

 

    Private Shared ReadOnly Property SymmetricKey() As String

        Get

            If String.IsNullOrEmpty(_symmetricKey) Then

                Try

                    _symmetricKey = ConfigurationManager.AppSettings.Item("SymmetricKey")

                Catch ex As Exception

                    _symmetricKey = "DIffTkey"

                End Try

                If String.IsNullOrEmpty(_symmetricKey) Then _symmetricKey = "DIffTkey"

            End If

            Return Left(_symmetricKey, 8)

        End Get

    End Property

 

#End Region

 

#End Region

 

End Class