B4J Question Diffie-Hellman

[schimanski]

I try to make a deffie-hellman-sub to exchange secret keys between two devices. Does anybody know, if the syntax for the following calculation is correct? It builds the foundation for the calculations..

y=Power(g,x) mod p

Thanks for help..

 

[Erel]

Looks correct however I don't recommend you to implement the algorithm yourself. How are the two devices connected? What are these devices?

 

[schimanski]

I have tried something and the following code is able to create two same keys. Bit it doesn't work for all prime numbers:

Sub Process_Globals
    Dim p As Int = 11    'Primzahl'
    Dim g As Int = 7    'Ganze Zahl < Primzahl'
   
    Dim A As Long
    Dim B As Long
End Sub

Sub AppStart (Form1 As Form, Args() As String)
    Dim xAlice As Int = Rnd(1, p-1)      'Zufallszahl Alice < Primzahl
    Dim xBop As Int = Rnd(1,p-1)        'Zufallszahl Bop < Primzahl'
    Log("xAlice:" & xAlice)
    Log("xBop:" & xBop)
   
    A=Power(g,xAlice) mod p
    Log("A:" & A)
    B=Power(g,xBop) mod p
    Log("B:" & B)
   
    Dim sA As Long
    sA=Power(B,xAlice) mod p            'Gemeinsamer Schlüssel'
    Log("Key Alice:" & sA)
   
    Dim sB As Long
    sB=Power(A,xBop) mod p
    Log("Key Bop: " & sB)            'Gemeinsamer Schlüssel'
End Sub

Perhaps there is someone who is expert in cryptography.

 

[schimanski]

@Erel: I use a server-solution to connect the devices for an instant messenger-system. The algorithm seems to be simple, but they are only save, if the prime-numbers and numbers are big enough. Don't know, how to do it, without implementing it by myself...

 

[Erel]

Configure your server to work over SSL.

 

[schimanski]

The server works over SSL, but it seems, that it is for some experts not enough..

 

[Erel]

Your solution will not be safer than SSL. SSL already implements this algorithm.