add PublicKey::recover

3 files changed, 24 insertions, 0 deletions

diff --git a/include/bls.hpp b/include/bls.hpp
index 2ba7ef5..82378be 100644
--- a/include/bls.hpp
+++ b/include/bls.hpp
@@ -67,6 +67,10 @@ public:
 	friend std::ostream& operator<<(std::ostream& os, const PublicKey& pub);
 	friend std::istream& operator>>(std::istream& is, PublicKey& pub);
 	bool verify(const Sign& sign, const std::string& m) const;
+	/*
+		recover publicKey from k pubVec
+	*/
+	void recover(const std::vector<PublicKey>& pubVec);
 };
 
 class PrivateKey {
diff --git a/src/bls.cpp b/src/bls.cpp
index 8c6ff4a..8577c95 100644
--- a/src/bls.cpp
+++ b/src/bls.cpp
@@ -152,6 +152,7 @@ struct PublicKey {
 		BN::pairing(e2, sQ, Hm); // e(sQ, Hm)
 		return e1 == e2;
 	}
+	const G2& get() const { return sQ; }
 };
 
 struct PrivateKey {
@@ -292,6 +293,14 @@ bool PublicKey::verify(const Sign& sign, const std::string& m) const
 	return self_->verify(*sign.self_, m);
 }
 
+void PublicKey::recover(const std::vector<PublicKey>& pubVec)
+{
+	G2 sQ;
+	LagrangeInterpolation(sQ, pubVec);
+	self_->sQ = sQ;
+	id_ = 0;
+}
+
 PrivateKey::PrivateKey()
 	: self_(new impl::PrivateKey())
 	, id_(0)
diff --git a/test/bls_test.cpp b/test/bls_test.cpp
index 074117f..59924d9 100644
--- a/test/bls_test.cpp
+++ b/test/bls_test.cpp
@@ -158,4 +158,15 @@ CYBOZU_TEST_AUTO(k_of_n)
 			CYBOZU_TEST_ASSERT(s != s0);
 		}
 	}
+	// share and recover publicKey
+	{
+		std::vector<bls::PublicKey> pubVec(k);
+		// select [0, k) publicKey
+		for (int i = 0; i < k; i++) {
+			allPrvVec[i].getPublicKey(pubVec[i]);
+		}
+		bls::PublicKey pub;
+		pub.recover(pubVec);
+		CYBOZU_TEST_EQUAL(pub, pub0);
+	}
 }