Simple Encryption

[Bjørn Erik Tveiten]

Can anyone help me?
a) I must write a program that encrypts a meesage using rot13
b) Then i must decrypt the skrambled message using 13 as the key.

My code looks like this now:
Option Explicit
Dim mAlfabet As String


Private Sub cmdDeKrypter_Click()
Dim Melding As String
Dim Tegn As String
Dim teller As Single
Dim foran As String
Dim bak As String
Dim antallTegn As Integer
Dim temp As Integer
Dim res As String

Melding = txtMelding.Text
For teller = 1 To Len(Melding)
bak = Right(Melding, Len(Melding) + teller)
Melding = foran & Tegn & bak
txtOutputKrypter.Text = txtOutputKrypter.Text
txtOutputKrypter.Text = ""
Next teller


MsgBox Melding







End Sub



Private Sub cmdKrypter_Click()
Dim Melding As String
Dim Tegn As String
Dim teller As Single
Dim foran As String
Dim bak As String
Dim antallTegn As Integer
Dim temp As Integer
Dim res As String

Melding = txtMelding.Text
For teller = 1 To Len(Melding)
Tegn = Mid$(Melding, teller, 1)
temp = InStr(1, mAlfabet, Tegn, vbBinaryCompare)
Tegn = Mid$(mAlfabet, temp + 13, 1)
foran = Left(Melding, teller - 1)
bak = Right(Melding, Len(Melding) - teller)
Melding = foran & Tegn & bak
txtOutputKrypter.Text = txtOutputKrypter.Text
txtOutputKrypter.Text = ""

Next teller


MsgBox Melding






End Sub

Private Sub Form_Load()
mAlfabet = "abcdefghijklmnopqrstuvwxyzabcdefghijklmn"






End Sub

Private Sub mnuAvslutt_Click()
End

End Sub

Thank you!

[Jerry Grant]

Try the following

Should explain the process in the coments

'/////////////////////////////////////////////////////////////////////////
'//                                                                     //
'// Purpose: To encrypt/decrypt passwords or other short text.          //
'// ___________________________________________________________________ //
'//                                                                     //
'// Inputs:  strText:        as the text to encrypt/decrypt.            //
'//          strCipherText:  scrambler code for encryption/decryption.  //
'//          intAction:      switch for encrypt/decrypt                 //
'//                          K_DECRYPT = 0                              //
'//                          K_ENCRYPT = 1                              //
'// ___________________________________________________________________ //
'//                                                                     //
'// Returns: Encryped [strPlainText] or decypted [strCipherText].       //
'//                                                                     //
'// ___________________________________________________________________ //
'// Author:  Jerry Grant Touch-base 2000 : 22/02/2000                   //
'/////////////////////////////////////////////////////////////////////////
Public Function F_SimpleCrypt( _
                              ByVal strText As String, _
                              ByVal strCipherText As String, _
                              ByVal intAction As Integer _
                              ) As String
    
    Dim lngLoop            As Long
    Dim intPrev            As Integer
    Dim intChar            As Integer
    Dim intKeyIndex        As Integer
    Dim intKeyLen          As Integer
    Dim strTextValue       As String
    Dim strResultCode      As String
    Dim intNewChar         As Integer
    Dim intEncrypting      As Integer
    ReDim intAKeyChar(255) As Integer
    
    '//'Magic values' used for en/decryption. DO NOT CHANGE THESE.  //
    Const K_MAGIC1 = 42
    Const K_MAGIC2 = 3
    
    '//Determine if we're encrypting or decrypting                  //
    If intAction = K_DECRYPT Then
        intEncrypting = False
    Else
        intEncrypting = True
    End If

    strTextValue = strText
    
    '//Initialize 'previous character' value, index into            //
    '//key string and length of key                                 //
    intPrev = K_MAGIC1: intKeyIndex = 1
    intKeyLen = Len(strCipherText)
    
    '//Convert key string to array                                  //
    For lngLoop = 1 To Len(strCipherText)
        intAKeyChar(lngLoop) = Asc(Mid(strCipherText, lngLoop, 1))
    Next lngLoop
    
    '//Actual en/decryption loop                                    //
    For lngLoop = 1 To Len(strTextValue)
         intChar = Asc(Mid(strTextValue, lngLoop, 1))
         intNewChar = intChar Xor intAKeyChar(intKeyIndex) _
                    Xor intPrev _
                    Xor ((lngLoop / K_MAGIC2) Mod 255)
                    
         strResultCode = strResultCode & Chr(intNewChar)
         If intEncrypting Then
            intPrev = intChar
         Else
            intPrev = intNewChar
         End If
         intKeyIndex = intKeyIndex + 1
         If intKeyIndex > intKeyLen Then intKeyIndex = 1
    Next lngLoop
    
    '//Return strResultCode to caller                               //
    
    F_SimpleCrypt = strResultCode

End Function

[Edited by Jerry Grant on 10-04-2000 at 08:04 AM]