add diffie hellman exchange

Author: Pl4tt

python/cryptography/diffie_hellman.py

@@ -0,0 +1,74 @@
+import random
+
+
+class Network:
+    def __init__(self) -> None:
+        self.users = []
+        self.base = 13
+        self.mod = random.getrandbits(4000)
+
+    def _rotate_users(self):
+        self.users = self.users[1:] + [self.users[0]]
+    
+    def key_exchange(self) -> None:
+        for _ in range(len(self.users)):
+            curr_base = self.base
+
+            for user in self.users:
+                store_key = user is self.users[-1]
+                
+                key = user.sign_key(curr_base, store_key)
+                curr_base = key
+            
+            self._rotate_users()
+
+
+class User:
+    def __init__(self, network: Network) -> None:
+        self.network = network
+        self.network.users.append(self)
+
+        self.network_key = None
+        self.private_key = random.randint(self.network.mod//2, self.network.mod-1)
+    
+    def sign_key(self, key: int, store_key: bool) -> int:
+        network_key = pow(key, self.private_key, self.network.mod)
+        
+        if store_key:
+            self.network_key = network_key
+
+        return network_key
+
+
+
+
+if __name__ == "__main__":
+    # TEST
+    network1 = Network()
+
+    user1 = User(network1)
+    user2 = User(network1)
+    user3 = User(network1)
+    user4 = User(network1)
+    user5 = User(network1)
+    user6 = User(network1)
+    user7 = User(network1)
+
+    network1.key_exchange()
+
+    check_key = pow(
+        network1.base,
+        user1.private_key*
+        user2.private_key*
+        user3.private_key*
+        user4.private_key*
+        user5.private_key*
+        user6.private_key*
+        user7.private_key,
+        network1.mod
+    )
+
+    for user in network1.users:
+        assert user.network_key == check_key
+    
+    print(check_key)