An Encrypted String Data Type for Visual Studio LightSwitch: Listing 2

EncryptedString.vb

Imports System.IO
Imports System.Reflection
Imports System.Security.Cryptography
Imports System.Text

Public Class EncryptString
  Private Key As Byte()
  Private IV As Byte()

  Public Sub New()
    Dim mPassword = 
      Assembly.GetExecutingAssembly().GetType().GUID.ToString().Replace("-", "")
    SetKeyAndIV(mPassword)
  End Sub

  Private Sub SetKeyAndIV(pw As String)
    Try
      Dim Salt = pw.Substring(pw.Length - 16)
      Dim bytPassword = UTF8Encoding.UTF8.GetBytes(pw)
      Dim bytSalt = UTF8Encoding.UTF8.GetBytes(Salt)
      Dim rfc2898 = New Rfc2898DeriveBytes(bytPassword, bytSalt, 10000)
      Key = rfc2898.GetBytes(32)
      IV = rfc2898.GetBytes(16)
    Catch ex As Exception
      Throw New Exception("Set Key and IV String Error", ex)
    End Try
  End Sub

  Public Function DecryptString(EncryptedText As String) As String
    Dim Result = String.Empty
    Dim bytEncryptedText = Convert.FromBase64String(EncryptedText)
    Try
      Using aes As New AesManaged
            aes.Key = Key
            aes.IV = IV
            Dim decryptor = aes.CreateDecryptor(aes.Key, aes.IV)
            Using msDecrypt As New MemoryStream(bytEncryptedText)
              Using csDecrypt As New CryptoStream(
                msDecrypt, decryptor, CryptoStreamMode.Read)
                Using srDecrypt As New StreamReader(csDecrypt)
                  Result = srDecrypt.ReadToEnd
                End Using
              End Using
              Return Result
            End Using
          End Using
        Catch ex As Exception
          Throw New Exception("Decrypt String Error", ex)
        End Try
        Return Result
    End Function

    Public Function EncryptString(UnencryptedText As String) As String
      Dim result = String.Empty
      Dim bytEncrypted As Byte()

      Try
        Using aes As New AesManaged()
              aes.Key = Key
              aes.IV = IV
              Dim encryptor = aes.CreateEncryptor(aes.Key, aes.IV)
              Using msEncrypt As New MemoryStream()
                Using csEncrypt As New CryptoStream(
                  msEncrypt, encryptor, CryptoStreamMode.Write)
                  Using swEncrypt As New StreamWriter(csEncrypt)
                swEncrypt.Write(UnencryptedText)
              End Using
              bytEncrypted = msEncrypt.ToArray()
              result = Convert.ToBase64String(bytEncrypted)
            End Using
          End Using
        End Using
      Catch ex As Exception
        Throw New Exception("Encrypt String Error", ex)
      End Try
      Return result
    End Function
  End Class

About the Author

Joe Kunk is a Microsoft MVP in Visual Basic, three-time president of the Greater Lansing User Group for .NET, and developer for Dart Container Corporation of Mason, Michigan. He's been developing software for over 30 years and has worked in the education, government, financial and manufacturing industries. Kunk's co-authored the book "Professional DevExpress ASP.NET Controls" (Wrox Programmer to Programmer, 2009). He can be reached via email at joekunk@ajboggs.com.