From 00c58d5d17b253acdba6326d0c8d3c3872c1b2f3 Mon Sep 17 00:00:00 2001
From: aadit <aadit@noreply.localhost>
Date: Tue, 2 Sep 2025 02:29:05 +0530
Subject: [PATCH] Update IS/Lab/Lab4/q1.py

---
 IS/Lab/Lab4/q1.py | 37 ++++++++++++++++++++++++++-----------
 1 file changed, 26 insertions(+), 11 deletions(-)

diff --git a/IS/Lab/Lab4/q1.py b/IS/Lab/Lab4/q1.py
index 08ba7fb..2cfa2fc 100644
--- a/IS/Lab/Lab4/q1.py
+++ b/IS/Lab/Lab4/q1.py
@@ -7,40 +7,55 @@ from Crypto.Random import get_random_bytes as rb
 
 def gen_role(n):
     r = RSA.generate(2048)
+    print(f"[keygen] role={n} RSA-2048")
     return {"name": n, "priv": r.export_key(), "pub": r.publickey().export_key()}
 
 def ecdh_key():
     a, b = ECC.generate(curve="P-256"), ECC.generate(curve="P-256")
-    s = a._multiply(b.pointQ, a.d).x.to_bytes()
-    return SHA256.new(s).digest()
+    s1 = (b.pointQ * a.d).x.to_bytes(32, "big")
+    s2 = (a.pointQ * b.d).x.to_bytes(32, "big")
+    assert s1 == s2
+    k = SHA256.new(s1).digest()
+    print(f"[ecdh] P-256 shared -> AES key {len(k)*8} bits")
+    return k
 
 def enc(k, m, aad=b""):
     n = rb(12); c = AES.new(k, AES.MODE_GCM, nonce=n); c.update(aad)
-    t = c.encrypt_and_digest(m)[1]
-    return n, c.encrypt(b""), t  # ciphertext unused; keeping API tiny
+    ct, t = c.encrypt_and_digest(m)
+    print(f"[enc] nonce={n.hex()} tag={t.hex()}")
+    return n, ct, t
 
 def dec(k, n, ct, t, aad=b""):
     c = AES.new(k, AES.MODE_GCM, nonce=n); c.update(aad)
-    c.decrypt(b""); c.verify(t)
+    pt = c.decrypt_and_verify(ct, t)
+    print(f"[dec] ok len={len(pt)}")
+    return pt
 
 def sign(role, msg):
     h = SHA256.new(msg)
-    return pkcs1_15.new(RSA.import_key(role["priv"])).sign(h)
+    sig = pkcs1_15.new(RSA.import_key(role["priv"])).sign(h)
+    print(f"[sign] by {role['name']} siglen={len(sig)}")
+    return sig
 
 def verify(pub, msg, sig):
     try:
-        pkcs1_15.new(RSA.import_key(pub)).verify(SHA256.new(msg), sig); return True
-    except: return False
+        pkcs1_15.new(RSA.import_key(pub)).verify(SHA256.new(msg), sig)
+        print("[verify] signature OK")
+        return True
+    except:
+        print("[verify] signature FAIL")
+        return False
 
 def demo(s, r, msg):
+    print(f"[demo] {s['name']} -> {r['name']}: {msg}")
     k = ecdh_key()
     hdr = f"{s['name']}->{r['name']}".encode()
     sig = sign(s, hdr)
     n, ct, t = enc(k, msg.encode(), hdr)
     assert verify(s["pub"], hdr, sig)
-    dec(k, n, ct, t, hdr)
-    print("OK:", msg)
+    pt = dec(k, n, ct, t, hdr).decode()
+    print(f"[result] {pt}")
 
 if __name__ == "__main__":
     a, b = gen_role("A"), gen_role("B")
-    demo(a, b, "secret")
\ No newline at end of file
+    demo(a, b, "secret message")
\ No newline at end of file