[2005] String Conversions / BASIC encryption

Hello...

I'm creating my own encryption-of-sorts on my application. The application is VERY simplistic so I don't need any hugely complicated encryption.

Basically,

I want my program to automatically convert characters in a string. I already know the conversion method that I'm going to use I just need help with the syntax.

So, in plain english, what i need is code that will

For each letter in STRING.

Replace A with B (case statement?)

Until the end of the string.

Here's a basic example. Say I want to use the following encryption (we'll just use numbers for now, since there's only 10 of them).

User enters "1234567890" into a textbox and presses encrypt.
My application goes through the string, one character at a time and checks for the 'switching' rule. In this example i'll use
1 becomes 2
2 becomes 3
...etc...
9 becomes 0
0 becomes 1

So, in textbox two the "encrypted" string would be: 234567890

Can someone help me with code on this please? I"m a newbie and I think my theory works for what I want to do, just not sure the most efficient way to do this.

do you want to encrypt numbers, letters or both? what kind of string characters your string will contain?

I've created a conversion chart for all possible character entries. So, to answer your question... I'm going to be converting both/everything.... all letters, numbers, special characters.

I already know what conversions I'm going to use... just need to know how to do it.

Because I've got conversions for every possible character, this should be a simple "for each character, if it's THIS, make it THAT, move to the next character, until there are no more characters". And i'll use the reverse for my decryption.

Does this make sense?

Use Select Case statements if the encryption keys are not random. I mean for all 0, it is 1, for all 1 is 2 and so on.

VB Code:

Dim chr() As Char
        chr = TextBox1.Text
        Dim i As Int16
        For i = 0 To chr.Length() - 1
            Select Case chr(i)
                Case "0" : chr(i) = "1"
                Case "1" : chr(i) = "2"
                Case "2" : chr(i) = "3"
                Case "3" : chr(i) = "4"
                Case "4" : chr(i) = "5"
                Case "5" : chr(i) = "6"
                Case "6" : chr(i) = "7"
                Case "7" : chr(i) = "8"
                Case "8" : chr(i) = "9"
                Case "9" : chr(i) = "0"
            End Select
        Next
        TextBox2.Text = chr

Not very pretty, but nicer than using a bunch of Case statements.

VB Code:

Public Class Crypto
 
    Public Function Cypher(ByVal msg As String) As String
        Dim ALPHA As String = "abcdefghijklmnopqrstuvwxyz "
        Dim CODE As String = "fstyzudeqrvwghijabcklmnopx "
        Dim ch As Char = Nothing
        Dim pos As Integer = 0
        Dim sReturn As String = Nothing
 
        For i As Integer = 0 To msg.Length - 1
            ch = CChar(msg.Substring(i, 1).ToLower)
            pos = ALPHA.IndexOf(ch)
            If (pos >= 0 And (pos <= 26)) Then
                sReturn = sReturn & CODE.Substring(pos, 1)
            End If
        Next i
        Return sReturn
    End Function
 
 
    Public Function UnCypher(ByVal msg As String) As String
        Dim ALPHA As String = "fstyzudeqrvwghijabcklmnopx "
        Dim CODE As String = "abcdefghijklmnopqrstuvwxyz "
        Dim ch As Char = Nothing
        Dim pos As Integer = 0
        Dim sReturn As String = Nothing
 
        For i As Integer = 0 To msg.Length - 1
            ch = CChar(msg.Substring(i, 1).ToLower)
            pos = ALPHA.IndexOf(ch)
            If (pos >= 0 And (pos <= 26)) Then
                sReturn = sReturn & CODE.Substring(pos, 1)
            End If
        Next i
        Return sReturn
    End Function
End Class

thanks both. looks like i'm on the right track!

Edited: I put some code together too. You just need to use the same string key to encrypt and decrypt the string. Make the key at least with six chars including letters and numbers for more security. It is simple and very hard to break. :D

VB Code:

Public Function Encrypt(ByVal _string As String, ByVal key As String) As String
        Dim encryptString As String = ""
        Dim i, i1, ascii As Integer
 
        If _string <> "" AndAlso key <> "" Then
            i1 = key.Length - 1
            For Each ch As Char In _string
                While i <= i1
                    ascii = AscW(ch) Xor AscW(key.Substring(i))
                    ch = ChrW(ascii)
                    i += 1
                End While
                i = 0
                i1 -= 1
                If i1 < 0 Then
                    i1 = key.Length - 1
                End If
                encryptString &= ChrW(ascii)
            Next
        End If
        Return encryptString
    End Function
 
    Public Function Decrypt(ByVal _string As String, ByVal key As String) As String
        Dim decryptString As String = ""
        Dim i, i1, ascii As Integer
 
        If _string <> "" AndAlso key <> "" Then
            For Each ch As Char In _string
                i = key.Length - 1
                While i - i1 >= 0
                    ascii = AscW(ch) Xor AscW(key.Substring(i - i1))
                    ch = ChrW(ascii)
                    i -= 1
                End While
                i1 += 1
                If i1 > key.Length - 1 Then
                    i1 = 0
                End If
                decryptString &= ChrW(ascii)
            Next
        End If
        Return decryptString
    End Function

OK, I'm being VERY N00B right now.

I want to take a combination of ALL of these.

If I create a class for Encryption and then two Functions : Encrypt and Decrypt.

How would I then go about passing my textbox elements TO the encryptor and from the encryptor back... I haven't worked with classes at all...

you juct declar the class variable and use it. for example

VB Code:

Public Class Form1
    Dim cryption As New ARGHendeCrypt
 
    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Dim myString As String = TextBox2.Text
        Dim ent, dc As String
        ent = cryption.Encrypt(myString, TextBox1.Text)
        dc = cryption.Decrypt(ent, TextBox5.Text)
 
        TextBox3.Text = ent
        TextBox4.Text = dc
    End Sub
End Class

and this is the class

VB Code:

'Author: Arman G.
'Created date: 10/04/2006
Public Class ARGHendeCrypt
    ''' <summary>
    ''' Encrypts a string expression (Unicode also) and returns the encrypted string.
    ''' </summary>
    ''' <param name="_string">A string expression that will be encrypted.</param>
    ''' <param name="key">A string key for encryption.</param>
    Public Function Encrypt(ByVal _string As String, ByVal key As String) As String
        Dim encryptString As String = ""
        Dim i, i1, ascii As Integer
 
        If _string <> "" AndAlso key <> "" Then
            i1 = key.Length - 1
            For Each ch As Char In _string
                While i <= i1
                    ascii = AscW(ch) Xor AscW(key.Substring(i))
                    ch = ChrW(ascii)
                    i += 1
                End While
                i = 0
                i1 -= 1
                If i1 < 0 Then
                    i1 = key.Length - 1
                End If
                encryptString &= ChrW(ascii)
            Next
        End If
        Return encryptString
    End Function
 
    ''' <summary>
    ''' Decrypts an encrypted string expression (Unicode also) and returns the decrypted string.
    ''' </summary>
    ''' <param name="_string">An encrypted string that will be decrypted.</param>
    ''' <param name="key">A string key for decryption.</param>
    Public Function Decrypt(ByVal _string As String, ByVal key As String) As String
        Dim decryptString As String = ""
        Dim i, i1, ascii As Integer
 
        If _string <> "" AndAlso key <> "" Then
            For Each ch As Char In _string
                i = key.Length - 1
                While i - i1 >= 0
                    ascii = AscW(ch) Xor AscW(key.Substring(i - i1))
                    ch = ChrW(ascii)
                    i -= 1
                End While
                i1 += 1
                If i1 > key.Length - 1 Then
                    i1 = 0
                End If
                decryptString &= ChrW(ascii)
            Next
        End If
        Return decryptString
    End Function
End Class

If you will use this class then you need to save or hold the encrypted text in a variable or in the text file.