diff --git a/include/mcl/fp.hpp b/include/mcl/fp.hpp
index 403bcf1..894d939 100644
--- a/include/mcl/fp.hpp
+++ b/include/mcl/fp.hpp
@@ -74,6 +74,7 @@ uint32_t sha256(void *out, uint32_t maxOutSize, const void *msg, uint32_t msgSiz
 uint32_t sha512(void *out, uint32_t maxOutSize, const void *msg, uint32_t msgSize);
 
 void hkdf_extract_addZeroByte(uint8_t hmac[32], const uint8_t *salt, size_t saltSize, const uint8_t *msg, size_t msgSize);
+void hkdf_extract(uint8_t hmac[32], const uint8_t *salt, size_t saltSize, const uint8_t *msg, size_t msgSize);
 void hkdf_expand(uint8_t out[64], const uint8_t prk[32], char info[6]);
 
 namespace local {
diff --git a/include/mcl/mapto_wb19.hpp b/include/mcl/mapto_wb19.hpp
index 37c184e..ba6662b 100644
--- a/include/mcl/mapto_wb19.hpp
+++ b/include/mcl/mapto_wb19.hpp
@@ -9,14 +9,18 @@
 */
 
 // ctr = 0 or 1 or 2
-inline void hashToFp2(Fp2& out, const void *msg, size_t msgSize, uint8_t ctr, const void *dst, size_t dstSize)
+inline void hashToFp2(Fp2& out, const void *msg, size_t msgSize, uint8_t ctr, const void *dst, size_t dstSize, bool addZero = true)
 {
 	assert(ctr <= 2);
 	const size_t degree = 2;
 	uint8_t msg_prime[32];
 	// add '\0' at the end of dst
 	// see. 5.3. Implementation of https://datatracker.ietf.org/doc/draft-irtf-cfrg-hash-to-curve
-	fp::hkdf_extract_addZeroByte(msg_prime, reinterpret_cast<const uint8_t*>(dst), dstSize, reinterpret_cast<const uint8_t*>(msg), msgSize);
+	if (addZero) {
+		fp::hkdf_extract_addZeroByte(msg_prime, reinterpret_cast<const uint8_t*>(dst), dstSize, reinterpret_cast<const uint8_t*>(msg), msgSize);
+	} else {
+		fp::hkdf_extract(msg_prime, reinterpret_cast<const uint8_t*>(dst), dstSize, reinterpret_cast<const uint8_t*>(msg), msgSize);
+	}
 	char info_pfx[] = "H2C000";
 	info_pfx[3] = ctr;
 	for (size_t i = 0; i < degree; i++) {
@@ -480,13 +484,17 @@ struct MapToG2_WB19 {
 		iso3(P, Pp);
 		clear_h2(P, P);
 	}
-	void map2curve_osswu2(G2& out, const void *msg, size_t msgSize, const void *dst, size_t dstSize) const
+	void map2curve_osswu2(G2& out, const void *msg, size_t msgSize, const void *dst, size_t dstSize, bool addZero = true) const
 	{
 		Fp2 t1, t2;
-		hashToFp2(t1, msg, msgSize, 0, dst, dstSize);
-		hashToFp2(t2, msg, msgSize, 1, dst, dstSize);
+		hashToFp2(t1, msg, msgSize, 0, dst, dstSize, addZero);
+		hashToFp2(t2, msg, msgSize, 1, dst, dstSize, addZero);
 		opt_swu2_map(out, t1, &t2);
 	}
-
+	void msgToG2(G2& out, const void *msg, size_t msgSize) const
+	{
+		const char *dst = "BLS_SIG_BLS12381G2-SHA256-SSWU-RO-_POP_";
+		map2curve_osswu2(out, msg, msgSize, dst, strlen(dst), false);
+	}
 };
 
diff --git a/src/fp.cpp b/src/fp.cpp
index 4dce66d..64dc4a1 100644
--- a/src/fp.cpp
+++ b/src/fp.cpp
@@ -139,6 +139,17 @@ void hkdf_extract_addZeroByte(uint8_t hmac[32], const uint8_t *salt, size_t salt
 	cybozu::hmac256addZeroByte(hmac, salt, saltSize, msg, msgSize);
 }
 
+void hkdf_extract(uint8_t hmac[32], const uint8_t *salt, size_t saltSize, const uint8_t *msg, size_t msgSize)
+{
+	uint8_t saltZero[32];
+	if (salt == 0 || saltSize == 0) {
+		memset(saltZero, 0, sizeof(saltZero));
+		salt = saltZero;
+		saltSize = sizeof(saltZero);
+	}
+	cybozu::hmac256(hmac, salt, saltSize, msg, msgSize);
+}
+
 void hkdf_expand(uint8_t out[64], const uint8_t prk[32], char info[6])
 {
 	info[5] = 1;