form1.vb

清华大学出版社出版的 移动应用开发宝典 张大威（2008）的附书源代码

Imports System.IO
Imports System.Security.Cryptography
Imports Microsoft.Practices.Mobile.PasswordAuthentication

Public Class Form1

    Private encryptionKey() As Byte

    Private Sub menuItemSave_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles menuItemSave.Click
        ' Ask user for a password from which we can derive a key
        encryptionKey = GetEncryptionKey()

        ' Encrypt the data
        Dim encryptedData As String = EncryptData(encryptionKey, textBox1.Text)

        ' Create the output file
        Using sw As StreamWriter = New StreamWriter("crypt.bin", False)
            sw.Write(encryptedData)
        End Using

        ' Display
        textBox1.Text = encryptedData
    End Sub

    Private Function GetEncryptionKey() As Byte()
        Dim password As String
        Using frm As GetPasswordForm = New GetPasswordForm()
            frm.ShowDialog()
            password = frm.Password

            ' Save the password encrypted with the public key
            Dim rsa As New EncryptPasswordRSA()
            rsa.SavePassword(password)

        End Using

        Return DeriveKeyFromPassword(password)
    End Function

    Private Function DeriveKeyFromPassword(ByVal password As String) As Byte()
        Dim key() As Byte
        Using provider As RsaAesCryptographyProvider = New RsaAesCryptographyProvider("DevelopersHandbook")
            Dim crypto As CryptNativeHelper = New CryptNativeHelper(provider)
            key = crypto.GetPasswordDerivedKey(password)
        End Using
        Return key
    End Function

    Private Function EncryptData(ByVal key() As Byte, ByVal plainText As String) As String
        ' Get the bytes to encrypt
        Dim plaintextByte() As Byte = System.Text.Encoding.Unicode.GetBytes(plainText)

        ' Create a Rijndael instance - automatically generates symmetric key
        ' and an initialization vector
        Dim rijndael As RijndaelManaged = New RijndaelManaged()

        ' Set encryption mode 
        rijndael.Mode = CipherMode.ECB
        rijndael.Padding = PaddingMode.PKCS7

        ' Create a random initialization vector
        rijndael.GenerateIV()
        Dim iv() As Byte = rijndael.IV

        Dim encodedText As String = ""

        ' Define memory stream which will be used to hold encrypted data.
        Dim memStrm As MemoryStream = New MemoryStream()

        ' Write the IV length and the IV
        memStrm.Write(BitConverter.GetBytes(iv.Length), 0, 4)
        memStrm.Write(iv, 0, iv.Length)

        ' Create a symmetric encryptor
        Using encryptor As ICryptoTransform = rijndael.CreateEncryptor(key, iv)
            ' Create a CryptStream to write to the output file
            Dim cryptStrm As CryptoStream = New CryptoStream(memStrm, encryptor, CryptoStreamMode.Write)

            ' Write the content to be encrypted
            cryptStrm.Write(plaintextByte, 0, plaintextByte.Length)
            cryptStrm.FlushFinalBlock()

            ' Convert encrypted data from a memory stream into a byte array.
            Dim cipherTextBytes() As Byte = memStrm.ToArray()

            ' Close the treams
            memStrm.Close()
            cryptStrm.Close()

            ' Convert encrypted data into a base64-encoded string.
            encodedText = Convert.ToBase64String(cipherTextBytes)
        End Using

        Return encodedText
    End Function

    Private Function DecryptData(ByVal key() As Byte, ByVal encryptedData As String) As String
        Dim retStr As String = ""

        ' Create a symmetric decryptor
        Dim rijndael As RijndaelManaged = New RijndaelManaged()
        rijndael.Mode = CipherMode.ECB
        rijndael.Padding = PaddingMode.PKCS7

        ' Convert our ciphertext into a byte array.
        Dim cipherTextBytes() As Byte = Convert.FromBase64String(encryptedData)
        ' Define memory stream to use to read encrypted data.
        Dim inStream As MemoryStream = New MemoryStream(cipherTextBytes)

        ' Read the IV length from the buffer
        Dim ivLength As Integer = BitConverter.ToInt32(cipherTextBytes, 0)
        ' Reposition to after 'length' bytes in stream
        inStream.Position = 4

        ' Read the IV from the input stream 
        Dim iv() As Byte = New Byte(ivLength) {}
        inStream.Read(iv, 0, ivLength)

        Using decryptor As ICryptoTransform = rijndael.CreateDecryptor(key, iv)
            ' Create a CryptStream to read from the file
            Dim cryptStrm As CryptoStream = New CryptoStream(inStream, decryptor, CryptoStreamMode.Read)

            ' Create another MemoryStream for the output
            Dim memStrm As MemoryStream = New MemoryStream()
            Dim buffer() As Byte = New Byte(2048) {}
            Dim totalbytes As Integer = 0
            Do
                Dim bytesRead As Integer = cryptStrm.Read(buffer, 0, buffer.Length)
                If bytesRead = 0 Then
                    Exit Do
                End If
                memStrm.Write(buffer, 0, bytesRead)
                totalbytes += bytesRead
            Loop

            ' Write the content to be encrypted
            memStrm.Flush()
            memStrm.Seek(0, SeekOrigin.Begin)

            ' Get the string from the bytes we read 
            retStr = System.Text.Encoding.Unicode.GetString(memStrm.GetBuffer(), 0, totalbytes)
            cryptStrm.Close()
        End Using

        Return retStr
    End Function


    Private Sub menuItemRestore_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles menuItemRestore.Click
        ' Ask user for a password from which we can derive the key
        encryptionKey = GetEncryptionKey()

        ' Read encrypted data from the file
        Dim fileContents As String
        Using sr As StreamReader = New StreamReader("crypt.bin")
            fileContents = sr.ReadToEnd()
        End Using

        ' Write decrypted data back into the TextBox
        textBox1.Text = DecryptData(encryptionKey, fileContents)
    End Sub

    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        System.Diagnostics.Debug.Assert(False, "Have you run the DeskTopKeyUnlocker program first, and copied the public key details into the PublicKey.xml file in this project? When you have, comment out this Assert in Form1_Load.")
    End Sub
End Class