# Diffie-Hellman Example

Diffie-Hellman is a standard method of Alice and Bob being able to communicate, and end up with the same secret encryption key. It is used in many applications. Initially the values of G and N are defined:

G:

N:

Next Bob and Allice will calculate an X value and a Y value, respectively:

 Bob X Value Alice's Y value Next ... Bob's A value Alice's B value A=G^x mod N B=G^y mod N

and Bob will send his A value to Alice, and Alice will send her B value to Bob, and they now re-calculate the values to generate the same shared key:

 Finally ... Bob's Key Alice's Key Key=B^x mod N Key=A^y mod N

Then, as if by magic Bob and Alice have the same secret key. Obviously this example uses small 64-bit integers, but it shows the principle.

protected void Button3_Click(object sender, EventArgs e)
{
Random val = new Random();

X.Text = Convert.ToString(val.Next(10));
Y.Text = Convert.ToString(val.Next(10));
G.Text=Convert.ToString(val.Next(50));
N.Text=Convert.ToString(val.Next(200)+10);
}

protected void Button1_Click(object sender, EventArgs e)
{
double g, n, x, y;
long a, b;

g = Convert.ToDouble(G.Text);
n = Convert.ToDouble(N.Text);
x = Convert.ToDouble(X.Text);
y = Convert.ToDouble(Y.Text);

a = Convert.ToInt64(Math.Pow(g, x)) % Convert.ToInt64(n);
b = Convert.ToInt64(Math.Pow(g, y)) % Convert.ToInt64(n);

A.Text = Convert.ToString(a);
B.Text = Convert.ToString(b);
}

protected void Button2_Click(object sender, EventArgs e)
{

double g, n, x, y;
long a, b;

g = Convert.ToDouble(G.Text);
n = Convert.ToDouble(N.Text);
x = Convert.ToDouble(X.Text);
y = Convert.ToDouble(Y.Text);
a = Convert.ToInt64(A.Text);
b = Convert.ToInt64(B.Text);

this.BobKey.Text = Convert.ToString(Convert.ToInt64(Math.Pow(b, x)) % Convert.ToInt64(n));
this.AliceKey.Text = Convert.ToString(Convert.ToInt64(Math.Pow(a, y)) % Convert.ToInt64(n));

} and an example: Other related .NET articles I've written include: - Design Tip 298. [.NET] HMAC-SHA1. - Design Tip 243. [.NET] Base-64 or Hex hash values. - Design Tip 242. [.NET] Digital Certificates. - Design Tip 241. [.NET] Public-key Encryption. - Design Tip 240. [.NET] Diffie-Hellman Method. - Design Tip 239. [.NET] Symmetric Encryption (Private-key). - Design Tip 238. [.NET] Obfuscation Part II. - Design Tip 237. [.NET] Obfuscation Part I - Design Tip 236. [.NET] Data packet capture (filters: IP, TCP, and so on). - Design Tip 235. [.NET] Data packet capture. - Design Tip 234. [.NET] Interface to network adapter. - Design Tip 232. [.NET] Creating an SSH client. - Design Tip 231. [.NET] Creating an SNMP client. - Design Tip 216. [.NET] Client/server communications. - Design Tip 210. [XML/.NET] XML and .NET. - Design Tip 207. [.NET] Treeviews for interest. - Design Tip 206. [.NET/Design] Design, evaluate, design, ..... - Design Tip 205. [.NET] Treeviews. - Design Tip 203. [.NET] Replacing menus with Treeviews. - Design Tip 202. [.NET/Flash] .NET and Flash - the perfect pair.