From da752536ab390f4561d7e8949044a10fd6fbf155 Mon Sep 17 00:00:00 2001
From: Lennart Jongeneel <lennart@1200wd.com>
Date: Sun, 19 Nov 2023 20:19:02 +0100
Subject: [PATCH] [ADD] Inverse method, allow to inverse public keys

---
 bitcoinlib/keys.py | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/bitcoinlib/keys.py b/bitcoinlib/keys.py
index 2eb24c78..cc17b70a 100644
--- a/bitcoinlib/keys.py
+++ b/bitcoinlib/keys.py
@@ -978,8 +978,7 @@ def __rmul__(self, other):
         return self * other
 
     def __neg__(self):
-        assert self.secret
-        return HDKey(secp256k1_n - self.secret)
+        return self.inverse()
 
     def __len__(self):
         return len(self.public_byte)
@@ -1004,6 +1003,13 @@ def __int__(self):
         else:
             return None
 
+    def inverse(self):
+        if self.is_private:
+            return HDKey(secp256k1_n - self.secret)
+        else:
+            # Inverse y in init: self._y = secp256k1_p - self._y
+            return Key(('02' if self._y % 2 else '03') + self.x_hex)
+
     @property
     def x(self):
         if not self._x and self.x_hex: