+ File structure re-design

+ Moved ECC functions to a dedicated Crypto class

pyplayready/crypto/elgamal.py

@@ -0,0 +1,42 @@
+from typing import Tuple
+
+from ecpy.curves import Curve, Point
+import secrets
+
+
+class ElGamal:
+    """ElGamal ECC utility using ecpy"""
+
+    def __init__(self, curve: Curve):
+        """Initialize the utility with a given curve type ('secp256r1' for PlayReady)"""
+        self.curve = curve
+
+    @staticmethod
+    def to_bytes(n: int) -> bytes:
+        byte_len = (n.bit_length() + 7) // 8
+        if byte_len % 2 != 0:
+            byte_len += 1
+        return n.to_bytes(byte_len, 'big')
+
+    def encrypt(self, message_point: Point, public_key: Point) -> Tuple[Point, Point]:
+        """
+        Encrypt a single point with a given public key
+
+        Returns an encrypted point pair
+        """
+        ephemeral_key = secrets.randbelow(self.curve.order)
+        point1 = ephemeral_key * self.curve.generator
+        point2 = message_point + (ephemeral_key * public_key)
+        return point1, point2
+
+    @staticmethod
+    def decrypt(encrypted: Tuple[Point, Point], private_key: int) -> Point:
+        """
+        Decrypt and encrypted point pair with a given private key
+
+        Returns a single decrypted point
+        """
+        point1, point2 = encrypted
+        shared_secret = private_key * point1
+        decrypted_message = point2 - shared_secret
+        return decrypted_message