Encryption? How?

Hi i have made a simple IM client server app and was wondering
how i could encrypt the data the encryption doesn't need to be very strong

Code would be nice but just the theroy explination is what im looking for since im confused
:confused:

Sam Lad

well, how simple is simple? your could just replace a with z, b with y, c with x, etc.. that's extremely simple. or you could use whatever letters you wanted. there's way better than that, but that's pretty simple.

too simple?

Hehe my old "simple" encryption method was take the asc value of the character and add 20 to it :)

It was good enough for what it was doing.. on a small business app that no one there knew how to use a computer to even look at non encrypted files anyway. They just knew how to enter the data haha.

thank you people


but how do i get the key ascii values for a string varible?

for example

VB Code:

dim msg as string
dim username as string
 
username = "bob"
 
  msg = username & " says... " & txtmsg.txt
     msg 'encrypt here????
        Winsockout.sendData msg

VB Code:

dim msg as string
dim username as string
dim i as long
dim nmsg as string
 
username = "bob"
 
  msg = username & " says... " & txtmsg.txt
  nmsg = ""
  for i = 1 to len(msg)
     nmsg = nmsg & (asc(mid(msg,i,1)) + 20)
  next
  msg = nmsg
        Winsockout.sendData msg

That would perform the encryption method I spoke of.

would this work for the decrpyting?

VB Code:

Dim strData As String
    ' get the data and add it to the listbox
    Winsock1.GetData strData
for i = 1 to len(strData)
     nmsg = nmsg & (asc(mid(strData,i,1)) - 20)
  next
  msg = nmsg
 
lstconvo.add item msg

would that work???

thanks for the code i greatly appricate it thanks mate
thanks all :)

I have a litte function to do this

VB Code:

Public Function EncryptText(ByVal sMessage As String, Optional ByVal nCode As Long = -1) As String
Dim i As Long, sRet As String, nAscii As Long
 
    If Len(sMessage) = 0 Then
        EncryptText = ""
        Exit Function
    End If
    
    If nCode < 0 Then
        nCode = G_Shift_Char
    End If
    
    sRet = ""
    For i = 1 To Len(sMessage)
        nAscii = Asc(Mid$(sMessage, i, 1)) + nCode
        If nAscii >= 255 Then nAscii = nAscii - 223
        sRet = sRet & Chr(nAscii)
    Next i
    
    EncryptText = sRet
 
End Function
 
Public Function DecryptText(ByVal sCode As String, Optional ByVal nCode As Long = -1) As String
Dim i As Long, sRet As String, nAscii As Long
 
    If Len(sCode) = 0 Then
        DecryptText = ""
        Exit Function
    End If
    
    If nCode < 0 Then
        nCode = G_Shift_Char
    End If
        
    sRet = ""
    For i = 1 To Len(sCode)
        nAscii = Asc(Mid$(sCode, i, 1)) - nCode
        If nAscii < 32 Then nAscii = nAscii + 223
        sRet = sRet & Chr(nAscii)
    Next i
    
    DecryptText = sRet
 
End Function

This will shift ASCII code by specific value

thanks csar but my code works ok

thanks for all ya help people

Hi my winsock set up will only allow one user at a time could someone explain to me how i could ammend this so that many users can use the server at once

code not nessacary just a explanation


thanks all
Sam Lad

I'm not an expert on winsock.. heck I probably just a beginner with it but to my understanding the easiest way to allow multiple users is to create the winsock as a control array.

Have one watching a port for connections then after that create a new array for each user that connects. Or have it setup so it tries connecting and the client changes ports until it finds an open port on the server and just stay there. Send input through the connection for what port the user is assigned to and change the winsock controls there to connect through that port. Keep up via a database or something what user is on what control array or port and then you can send messages between the ports server side to get the messages from user to another.

This would work for a simple program like your doing. Not sure if there is a more complex way of doing it or not.

hey for encryption there are a lot of options :

1. simplest : make a mapping list like a= 2, b=c and change each character like this.this is easy to decrypt

2. find th acsii value and then add a number to it and store it.be careful when the value after adding becomes more than 255.

3. like 2 but donnt add a fixed number , rather generate a random number and store it in the file itself at some particular position.this is a bit diff. to hack

4. there are some standard encryption alogos available also.

best a luck

I use and stand by RC4 encryption, it is very secure.

if you want to start from nil in encription techniques, try this:

instead of doing a=1, b=2 try:

convert each letter of your message to it's decimal number, and then convert the number to an binary number and then apply:

bynary number XOR key

key, is the password for encryption.


E.g.(with ficticious numbers):

Message => P
Password (in this case just one letter) = G

P -> 76 -> 01100010

Do: (01100010) XOR (bynary number of G)

and there you have an encription method for the message P.


Did you get it ?

For multipe winsock connections, I have the same thing that StevenHickerson refers to...

VB Code:

'1st WinSock control = tcpServer
'2nd WinSock control = Link() [a control array]
 
Private Sub tcpServer_ConnectionRequest(ByVal requestID As Long)
 
    Dim lIndex As Long
    Dim lCount1 As Long
    
    'Part 1 : Check for available links (not loaded/connected)
    lIndex = -1
    For lCount1 = 1 To MAX_LINKS
        If Me.Link.UBound < lCount1 Then Load Me.Link(lCount1)
        If Not LinkConnected(lCount1) Then
            lIndex = lCount1
            Exit For
        End If
    Next lCount1
 
    'Part 2 : Connect the client to Link(lIndex) instead of the tcpServer that they originally contacted.
    If lIndex = -1 Then
        MsgBox("No more connections available")
    Else
        Me.Link(lIndex).Close
        Me.Link(lIndex).Accept requestID
    End If
End Sub
 
Private Sub link_DataArrival(iIndex As Integer, ByVal lTotalBytes As Long)
    Dim sReceiveString As String
    
    Me.Link(iIndex).GetData sReceiveString, vbString
    'Process (iIndex indicates the client that connected)
End Sub

Spajeoly

Please tell me more about the RC 4 encrytion.... :eek:

here is part of an encryption I devised that uses text hashing for any ascii values < 128

Any comments??

VB Code:

Private sData As String
 
 
Public Function Encrypt(Data As String, Key As String) As String
    Dim byt() As Byte
    Dim l As Long
    Dim m As Long
    Dim s As String
    Dim s1 As String
    
    'convert to byte array
    For l = 0 To Len(Data) - 1
        ReDim Preserve byt(l)
        byt(l) = Asc(Mid(Data, l + 1, 1))
    Next
    
    'byt = Data
    
    'hash the key with the data.
    For l = 0 To UBound(byt)
        m = m + 1
        If m > Len(Key) Then m = 1
        If byt(l) < 128 Then
            byt(l) = byt(l) + Asc(Mid(Key, m, 1))
        End If
        'l = l + 1
    Next
    
    For l = 0 To UBound(byt)
        s = s & Chr(byt(l))
    Next
    
    Encrypt = s
    sData = s
    Debug.Print s
End Function
 
Public Function Decrypt(ByVal Encrypted As String, Key As String) As String
    Dim byt() As Byte
    Dim l As Long
    Dim m As Long
    Dim s As String
    Dim s1 As String
 
    s = Encrypted
    
    ReDim byt(Len(s) - 1)
    m = 0
    For l = 1 To Len(s)
        m = m + 1
        If m > Len(Key) Then m = 1
        byt(l - 1) = Asc(Mid(s, l, 1))
        byt(l - 1) = byt(l - 1) - Asc(Mid(Key, m, 1))
        s1 = s1 & Chr(byt(l - 1))
    Next
    
    Debug.Print s1
    Decrypt = s1
    sData = s1
End Function
 
 
Public Sub SaveToFile(FileName As String)
    Dim l  As Long
    l = FreeFile
    Open FileName For Binary Access Write As #l
    Put #l, 1, sData
    Close #l
End Sub

for encryption, everyone seems to have done something similair to what I did:
http://acid.freewebpage.org/VB/0007.zip

What I want to know is, how do you encrypt a file? like for instance a .jpg file.

Quote:

---

Originally posted by Spajeoly
I use and stand by RC4 encryption, it is very secure.

---

RC4 is a good algorithm, i personally prefer AES(Advanced Encription Standard), thought its a bit slow encrypting large volume of data.

I wrote a application which encrypts message using AES and sends throug MSN Messenger, works pretty well for me. You can use the Msn Messenger API to send and receive the messages. Just simply decrypt it before displaying and encrypt them before sending.

You could find vb implementation of AES on the Net, if you cant i have one in my libray if you interested i can dig it out.


Hope this helps.

Danial