updated IS codes

IS/Lab/Lab6/dh_basic.py

@@ -0,0 +1,63 @@
+from typing import Tuple
+
+from Crypto.Hash import SHA256
+from Crypto.Protocol.KDF import HKDF
+
+
+def rfc3526_group14() -> Tuple[int, int]:
+    p_hex = (
+        "FFFFFFFFFFFFFFFFC90FDAA22168C234C4C6628B80DC1CD1"
+        "29024E088A67CC74020BBEA63B139B22514A08798E3404DD"
+        "EF9519B3CD3A431B302B0A6DF25F14374FE1356D6D51C245"
+        "E485B576625E7EC6F44C42E9A637ED6B0BFF5CB6F406B7ED"
+        "EE386BFB5A899FA5AE9F24117C4B1FE649286651ECE45B3D"
+        "C2007CB8A163BF0598DA48361C55D39A69163FA8FD24CF5F"
+        "83655D23DCA3AD961C62F356208552BB9ED529077096966D"
+        "670C354E4ABC9804F1746C08CA18217C32905E462E36CE3B"
+        "E39E772C180E86039B2783A2EC07A28FB5C55DF06F4C52C9"
+        "DE2BCBF6955817183995497CEA956AE515D2261898FA0510"
+        "15728E5A8AACAA68FFFFFFFFFFFFFFFF"
+    )
+    return int(p_hex, 16), 2
+
+
+def int_to_fixed_length_bytes(value: int, length_bits: int) -> bytes:
+    length_bytes = (length_bits + 7) // 8
+    return value.to_bytes(length_bytes, byteorder="big")
+
+
+def dh_keypair(p: int, g: int, private_bits: int = 256) -> Tuple[int, int]:
+    from Crypto.Util import number
+
+    a = 0
+    while a < 2:
+        a = number.getRandomNBitInteger(private_bits)
+    A = pow(g, a, p)
+    return a, A
+
+
+def main() -> None:
+    p, g = rfc3526_group14()
+    a_priv, a_pub = dh_keypair(p, g)
+    b_priv, b_pub = dh_keypair(p, g)
+
+    a_shared = pow(b_pub, a_priv, p)
+    b_shared = pow(a_pub, b_priv, p)
+    same = (a_shared == b_shared)
+
+    print("Lab6: Basic Diffie-Hellman (no symmetric cipher)")
+    print(f"- Group: p({p.bit_length()} bits), g={g}")
+    print(f"- A public: {hex(a_pub)[:18]}...")
+    print(f"- B public: {hex(b_pub)[:18]}...")
+    print(f"- Shared equal: {same}")
+
+    # Optionally derive a fixed-length key material to show post-processing (not used to encrypt)
+    shared_bytes = int_to_fixed_length_bytes(a_shared, p.bit_length())
+    key_material = HKDF(shared_bytes, 32, salt=None, hashmod=SHA256, context=b"demo")
+    print(f"- Derived key material (SHA256/HKDF) prefix: {key_material.hex()[:16]}...")
+
+
+if __name__ == "__main__":
+    main()
+
+