[test/crypto] Add ECDH

Co-authored-by: Pieter Wuille <pieter.wuille@gmail.com>

test/functional/test_framework/v2_p2p.py

@@ -0,0 +1,20 @@
+#!/usr/bin/env python3
+# Copyright (c) 2022 The Bitcoin Core developers
+# Distributed under the MIT software license, see the accompanying
+# file COPYING or http://www.opensource.org/licenses/mit-license.php.
+"""Class for v2 P2P protocol (see BIP 324)"""
+
+from .crypto.ellswift import ellswift_ecdh_xonly
+from .key import TaggedHash
+
+class EncryptedP2PState:
+    @staticmethod
+    def v2_ecdh(priv, ellswift_theirs, ellswift_ours, initiating):
+        """Compute BIP324 shared secret."""
+        ecdh_point_x32 = ellswift_ecdh_xonly(ellswift_theirs, priv)
+        if initiating:
+            # Initiating, place our public key encoding first.
+            return TaggedHash("bip324_ellswift_xonly_ecdh", ellswift_ours + ellswift_theirs + ecdh_point_x32)
+        else:
+            # Responding, place their public key encoding first.
+            return TaggedHash("bip324_ellswift_xonly_ecdh", ellswift_theirs + ellswift_ours + ecdh_point_x32)