This example will show you how to use public and private keys to encrypt data.

First off lets create a class and call it CryptoService:

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

Public Class CryptoService

Now we are going to add a two properties and two methods to our class. The properties will hold the public and private keys and the methods will encrypt and decrypt the data we pass. Lets start with the properties first:

We will first add two private variables to our class to store the property data:

Private bytKey() As Byte
Private strKey As String

Now lets add our two properties:

Public Property Key() As Byte()
    Get
      Return bytKey
    End Get

    Set(ByVal KeyIn() As Byte)

      If KeyIn.Length < 8 Or KeyIn.Length > 8 Then
        Exit Property
      End If

      bytKey = KeyIn

    End Set

End Property

Public Property KeyString() As String
    Get
      Return strKey
    End Get

    Set(ByVal KeyStringIn As Byte)

      If KeyStringIn.Length < 8 Or KeyString.Length > 8 Then
        Exit Property
      End If

      strKey = KeyStringIn

    End Set

End Property

Notice that we will only except 8 numbers for our Key and 8 chars for our KeyString.

Now we will add the heart of the class with the two methods Encrypt and Decrypt:

Public Function Encrypt(ByVal Data As String) As String

    If Data = "" Then
      Exit Function
    End If

    If Key.Length = 0 Or KeyString = "" Then
      Exit Function
    End If

    Dim bytKeys() As Byte = Encoding.UTF8.GetBytes(KeyString)
    Dim bytIn() As Byte = Encoding.UTF8.GetBytes(Data)
    Dim objMs As New MemoryStream
    Dim objDes As New DESCryptoServiceProvider

    Dim objCs As New CryptoStream(objMs, objDes.CreateEncryptor(bytKeys, Key), CryptoStreamMode.Write)

    objCs.Write(bytIn, 0, bytIn.Length)
    objCs.FlushFinalBlock()

    Return Convert.ToBase64String(objMs.ToArray())

End Function

Public Function Decrypt(ByVal Data As String) As String

    If Data = "" Then
      Exit Function
    End If

    If Key.Length = 0 Or KeyString = "" Then
      Exit Function
    End If

    Dim bytKeys() As Byte = Encoding.UTF8.GetBytes(KeyString)
    Dim bytIn(Data.Length) As Byte
    Dim objMs As New MemoryStream
    Dim objDes As New DESCryptoServiceProvider

    bytIn = Convert.FromBase64String(Data)

    Dim objCs As New CryptoStream(objMs, objDes.CreateDecryptor(bytKeys, Key), CryptoStreamMode.Write)

    objCs.Write(bytIn, 0, bytIn.Length)
    objCs.FlushFinalBlock()

    Return Encoding.UTF8.GetString(objMs.ToArray)

End Function

This class is now ready to be used to encrypt and decrypt data based upon the keys we submit to the class, for example:

    Dim objCrypto As New CryptoService
    objCrypto.Key = New Byte() {100, 20, 32, 77, 65, 89, 44, 2}
    objCrypto.KeyString = "!#e^*h&="

    Dim strEnc As String = objCrypto.Encrypt("my string")
    Dim strDec As String = objCrypto.Decrypt(strEnc)

    MessageBox.Show("Encrypted Data: " & strEnc & vbCrLf & "Decrypted Data: " & strDec)

I'll be posting more examples as I have time. If you would like me to make an example of something specific, just let me know.

Originally posted 6/8/2004 by pre