Create 05_Implement_Diffie_Hellman_Key_Exchange.md

crypto/challenges/05_Implement_Diffie_Hellman_Key_Exchange.md

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+# Challenge 5: Implement Diffie-Hellman Key Exchange
+
+**Level:** Intermediate
+
+**Description:**
+Simulate the Diffie-Hellman key exchange algorithm to securely share a symmetric key between two parties.
+
+**Challenge Text:**
+```
+Given prime p = 23, base g = 5
+Party A's private key: 6
+Party B's private key: 15
+```
+
+**Instructions:**
+1. Compute Party A's and Party B's public keys.
+2. Compute the shared secret key for both parties.
+3. Validate that both parties have the same shared secret key.
+
+
+**Answer:**
+Shared secret key: 2
+
+**Code:**
+```python
+p = 23
+g = 5
+a_private = 6
+b_private = 15
+
+# Compute public keys
+A_public = (g ** a_private) % p
+B_public = (g ** b_private) % p
+
+# Compute shared secret key
+shared_secret_A = (B_public ** a_private) % p
+shared_secret_B = (A_public ** b_private) % p
+
+print("Shared secret key (Party A):", shared_secret_A)
+print("Shared secret key (Party B):", shared_secret_B)
+```
+