加密解密字元串

Option Explicit

' Encipher the text using the pasword.

Private Sub Cipher(ByVal password As String, ByVal from_text As String, to_text As String)

Const MIN_ASC = 32  ' Space.

Const MAX_ASC = 126 ' ~.

Const NUM_ASC = MAX_ASC - MIN_ASC + 1

Dim offset As Long

Dim str_len As Integer

Dim i As Integer

Dim ch As Integer

    ' Initialize the random number generator.

    offset = NumericPassword(password)

    Rnd -1

    Randomize offset

    ' Encipher the string.

    str_len = Len(from_text)

    For i = 1 To str_len

        ch = Asc(Mid$(from_text, i, 1))

        If ch >= MIN_ASC And ch <= MAX_ASC Then

            ch = ch - MIN_ASC

            offset = Int((NUM_ASC + 1) * Rnd)

            ch = ((ch + offset) Mod NUM_ASC)

            ch = ch + MIN_ASC

            to_text = to_text & Chr$(ch)

        End If

    Next i

End Sub

' Encipher the text using the pasword.

Private Sub Decipher(ByVal password As String, ByVal from_text As String, to_text As String)

Const MIN_ASC = 32  ' Space.

Const MAX_ASC = 126 ' ~.

Const NUM_ASC = MAX_ASC - MIN_ASC + 1

Dim offset As Long

Dim str_len As Integer

Dim i As Integer

Dim ch As Integer

    ' Initialize the random number generator.

    offset = NumericPassword(password)

    Rnd -1

    Randomize offset

    ' Encipher the string.

    str_len = Len(from_text)

    For i = 1 To str_len

        ch = Asc(Mid$(from_text, i, 1))

        If ch >= MIN_ASC And ch <= MAX_ASC Then

            ch = ch - MIN_ASC

            offset = Int((NUM_ASC + 1) * Rnd)

            ch = ((ch - offset) Mod NUM_ASC)

            If ch < 0 Then ch = ch + NUM_ASC

            ch = ch + MIN_ASC

            to_text = to_text & Chr$(ch)

        End If

    Next i

End Sub

' Translate a password into an offset value.

Private Function NumericPassword(ByVal password As String) As Long

Dim value As Long

Dim ch As Long

Dim shift1 As Long

Dim shift2 As Long

Dim i As Integer

Dim str_len As Integer

    str_len = Len(password)

    For i = 1 To str_len

        ' Add the next letter.

        ch = Asc(Mid$(password, i, 1))

        value = value Xor (ch * 2 ^ shift1)

        value = value Xor (ch * 2 ^ shift2)

        ' Change the shift offsets.

        shift1 = (shift1 + 7) Mod 19

        shift2 = (shift2 + 13) Mod 23

    Next i

    NumericPassword = value

End Function

Private Sub cmdCipher_Click()

Dim cipher_text As String

    Cipher txtPassword.Text, txtPlain.Text, cipher_text

    txtCipher.Text = cipher_text

End Sub

Private Sub cmdDecipher_Click()

Dim plain_text As String

    Decipher txtPassword.Text, txtCipher.Text, plain_text

    txtPlain.Text = plain_text

End Sub

Private Sub Form_Load()

End Sub

Private Sub txtPassword_Change()

    If Len(txtPassword.Text) > 0 Then

        cmdCipher.Enabled = True

        cmdDecipher.Enabled = True

    Else

        cmdCipher.Enabled = False

        cmdDecipher.Enabled = False

    End If

End Sub