From 0d41c23c2146c9d392856e9ae9282a2a6aa42da1 Mon Sep 17 00:00:00 2001
From: Andrew Poelstra <apoelstra@wpsoftware.net>
Date: Wed, 22 Aug 2018 20:18:25 +0000
Subject: [PATCH] Revert "remove PublicKey::combine"

This reverts commit 17450e91fd83f396198dd9c14a2bd2b5c2d058bc.
---
 CHANGELOG.md |  4 ++++
 src/key.rs   | 39 +++++++++++++++++++++++++++++++++++++++
 2 files changed, 43 insertions(+)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 0a47b34..6d0d716 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,4 +1,8 @@
 
+# 0.11.1 - 2018-08-22
+
+* Put `PublicKey::combine` back because it is currently needed to implement Lightning BOLT 3
+
 # 0.11.0 - 2018-08-22
 
 * Update `rand` to 0.4 and `gcc` 0.3 to `cc` 1.0. (`rand` 0.5 exists but has a lot of breaking changes and no longer compiles with 1.14.0.)
diff --git a/src/key.rs b/src/key.rs
index 5bab047..463353c 100644
--- a/src/key.rs
+++ b/src/key.rs
@@ -273,6 +273,21 @@ impl PublicKey {
             }
         }
     }
+
+    /// Adds a second key to this one, returning the sum. Returns an error if
+    /// the result would be the point at infinity, i.e. we are adding this point
+    /// to its own negation
+    pub fn combine<C>(&self, secp: &Secp256k1<C>, other: &PublicKey) -> Result<PublicKey, Error> {
+        unsafe {
+            let mut ret = mem::uninitialized();
+            let ptrs = [self.as_ptr(), other.as_ptr()];
+            if ffi::secp256k1_ec_pubkey_combine(secp.ctx, &mut ret, ptrs.as_ptr(), 2) == 1 {
+                Ok(PublicKey(ret))
+            } else {
+                Err(InvalidPublicKey)
+            }
+        }
+    }
 }
 
 /// Creates a new public key from a FFI public key
@@ -551,6 +566,30 @@ mod test {
         assert_eq!(count, COUNT);
     }
 
+    #[test]
+    fn pubkey_combine() {
+        let s = Secp256k1::without_caps();
+        let compressed1 = PublicKey::from_slice(
+            &s,
+            &hex!("0241cc121c419921942add6db6482fb36243faf83317c866d2a28d8c6d7089f7ba"),
+        ).unwrap();
+        let compressed2 = PublicKey::from_slice(
+            &s,
+            &hex!("02e6642fd69bd211f93f7f1f36ca51a26a5290eb2dd1b0d8279a87bb0d480c8443"),
+        ).unwrap();
+        let exp_sum = PublicKey::from_slice(
+            &s,
+            &hex!("0384526253c27c7aef56c7b71a5cd25bebb66dddda437826defc5b2568bde81f07"),
+        ).unwrap();
+
+        let sum1 = compressed1.combine(&s, &compressed2);
+        assert!(sum1.is_ok());
+        let sum2 = compressed2.combine(&s, &compressed1);
+        assert!(sum2.is_ok());
+        assert_eq!(sum1, sum2);
+        assert_eq!(sum1.unwrap(), exp_sum);
+    }
+
     #[test]
     fn pubkey_equal() {
         let s = Secp256k1::new();