简单加解密算法 - vb.net

Public Class Form1
    Dim charAarray() As Char

    '加密
    Private Sub Btn_En_Click(sender As System.Object, e As System.EventArgs) Handles Btn_En.Click
        Dim s As String
        Dim result As Boolean
        result = EncryptOrDecrypt(Txt_PlainText_1.Text, Txt_Secrect_Key.Text, 1, s)
        Txt_Text_1.Text = s

        MessageBox.Show(IIf(result, "Success", "Failure"))
    End Sub

    '解密
    Private Sub Btn_De_Click(sender As System.Object, e As System.EventArgs) Handles Btn_De.Click
        Dim s As String
        Dim result As Boolean
        result = EncryptOrDecrypt(Txt_Text_2.Text, Txt_Secrect_Key.Text, -1, s)
        Txt_PlainText_2.Text = s

        MessageBox.Show(IIf(result, "Success", "Failure"))
    End Sub

    '加解密字符串
    'str为待加密的字符串
    'secretKey为秘钥
    'f为加解密标示，f=1标示加密，f=-1标示解密
    'outputStr为加解密之后的字符串
    '返回操作结果
    Function EncryptOrDecrypt(ByVal str As String, ByVal secretKey As Integer, ByVal f As Integer, ByRef outputStr As String) As Boolean
        outputStr = ""

        If (String.IsNullOrWhiteSpace(str)) Then
            Return False
        End If

        Dim c As Char
        For i As Integer = 0 To str.Length - 1
            c = str(i)
            c = EncryptChar(c, secretKey, f)
            outputStr &= c
        Next i

        Return True
    End Function

    Private Sub Form1_Load(sender As System.Object, e As System.EventArgs) Handles MyBase.Load
        charAarray = CreateCharArray()
        MessageBox.Show("OK")
    End Sub

    Function CreateCharArray() As System.Array
        Dim s As String = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789_"
        Dim rnd As New Random
        Dim cArray(s.Length - 1) As Char
        Dim index As Integer
        Dim i As Integer

        i = 0
        Do
            index = rnd.Next(s.Length)
            If Not cArray.Contains(s(index)) Then
                cArray(i) = s(index)
                i += 1
            End If
        Loop While (i < s.Length)

        Return cArray
    End Function

    '加密单个字符
    'c为要加密的字符
    'secretKey为秘钥
    'f为加解密标示，f=1标示加密，f=-1标示解密
    '返回加密之后的字符
    Function EncryptChar(ByVal c As Char, ByVal secretKey As Integer, ByVal f As Integer) As Char
        Dim cIndex As Integer
        Dim len As Integer
        len = charAarray.Length

        cIndex = Array.IndexOf(charAarray, c)
        If f = 1 Then
            cIndex += secretKey
        Else
            cIndex -= secretKey
        End If

        If (cIndex >= len) Then
            Math.DivRem(cIndex, len, cIndex)
        End If

        If (cIndex < 0) Then
            Do
                cIndex += len
            Loop While (cIndex < 0)
        End If

        Return charAarray(cIndex)
    End Function
End Class