Added Lab2/Lab3 IS

IS/Lab/Lab3/ECC.py

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+from Crypto.PublicKey import ECC
+from Crypto.Cipher import AES
+from Crypto.Hash import SHA256
+import binascii
+
+
+def ecc_keygen(curve: str = 'P-256') -> ECC.EccKey:
+    return ECC.generate(curve=curve)
+
+
+def ecc_encrypt(plaintext: str, recipient_public_key: ECC.EccKey):
+    eph_private = ECC.generate(curve=recipient_public_key.curve)
+    shared_point = recipient_public_key.pointQ * eph_private.d
+    shared_x = int(shared_point.x)
+    aes_key = SHA256.new(shared_x.to_bytes(32, 'big')).digest()
+
+    cipher = AES.new(aes_key, AES.MODE_GCM)
+    ciphertext, tag = cipher.encrypt_and_digest(plaintext.encode('utf-8'))
+
+    return {
+        'ephemeral_pub_der': eph_private.public_key().export_key(format='DER'),
+        'nonce': cipher.nonce,
+        'tag': tag,
+        'ciphertext': ciphertext,
+    }
+
+
+def ecc_decrypt(enc: dict, recipient_private_key: ECC.EccKey) -> str:
+    eph_public = ECC.import_key(enc['ephemeral_pub_der'])
+    shared_point = eph_public.pointQ * recipient_private_key.d
+    shared_x = int(shared_point.x)
+    aes_key = SHA256.new(shared_x.to_bytes(32, 'big')).digest()
+
+    cipher = AES.new(aes_key, AES.MODE_GCM, nonce=enc['nonce'])
+    plaintext = cipher.decrypt_and_verify(enc['ciphertext'], enc['tag'])
+    return plaintext.decode('utf-8')
+
+
+def main():
+    print('Welcome to ECC (ECIES-style)')
+    ptext = input('Enter plaintext: ')
+
+    priv_key = ecc_keygen()
+    pub_key = priv_key.public_key()
+
+    print('\nPublic Key (Qx, Qy):')
+    print('Qx =', hex(int(pub_key.pointQ.x)))
+    print('Qy =', hex(int(pub_key.pointQ.y)))
+
+    enc = ecc_encrypt(ptext, pub_key)
+    print("\nYour ciphertext (hex):", binascii.hexlify(enc['ciphertext']).decode())
+
+    decrypted = ecc_decrypt(enc, priv_key)
+    print('Your decrypted plaintext:', decrypted)
+
+
+if __name__ == '__main__':
+    main()