diff --git a/include/mcl/she.h b/include/mcl/she.h
index d474216..84a25a7 100644
--- a/include/mcl/she.h
+++ b/include/mcl/she.h
@@ -74,6 +74,10 @@ typedef struct {
 typedef struct {
 	mclBnFr d[7];
 } sheZkpBinEq;
+
+typedef struct {
+	mclBnFr d[7];
+} sheZkpDec;
 /*
 	initialize this library
 	call this once before using the other functions
@@ -96,6 +100,7 @@ MCLSHE_DLL_API mclSize sheCipherTextGTSerialize(void *buf, mclSize maxBufSize, c
 MCLSHE_DLL_API mclSize sheZkpBinSerialize(void *buf, mclSize maxBufSize, const sheZkpBin *zkp);
 MCLSHE_DLL_API mclSize sheZkpEqSerialize(void *buf, mclSize maxBufSize, const sheZkpEq *zkp);
 MCLSHE_DLL_API mclSize sheZkpBinEqSerialize(void *buf, mclSize maxBufSize, const sheZkpBinEq *zkp);
+MCLSHE_DLL_API mclSize sheZkpDecSerialize(void *buf, mclSize maxBufSize, const sheZkpDec *zkp);
 
 // return read byte size if sucess else 0
 MCLSHE_DLL_API mclSize sheSecretKeyDeserialize(sheSecretKey* sec, const void *buf, mclSize bufSize);
@@ -106,6 +111,7 @@ MCLSHE_DLL_API mclSize sheCipherTextGTDeserialize(sheCipherTextGT* c, const void
 MCLSHE_DLL_API mclSize sheZkpBinDeserialize(sheZkpBin* zkp, const void *buf, mclSize bufSize);
 MCLSHE_DLL_API mclSize sheZkpEqDeserialize(sheZkpEq* zkp, const void *buf, mclSize bufSize);
 MCLSHE_DLL_API mclSize sheZkpBinEqDeserialize(sheZkpBinEq* zkp, const void *buf, mclSize bufSize);
+MCLSHE_DLL_API mclSize sheZkpDecDeserialize(sheZkpDec* zkp, const void *buf, mclSize bufSize);
 
 /*
 	set secretKey if system has /dev/urandom or CryptGenRandom
@@ -192,6 +198,12 @@ MCLSHE_DLL_API int shePrecomputedPublicKeyEncWithZkpBinEq(sheCipherTextG1 *c1, s
 MCLSHE_DLL_API int sheEncWithZkpEq(sheCipherTextG1 *c1, sheCipherTextG2 *c2, sheZkpEq *zkp, const shePublicKey *pub, mclInt m);
 MCLSHE_DLL_API int shePrecomputedPublicKeyEncWithZkpEq(sheCipherTextG1 *c1, sheCipherTextG2 *c2, sheZkpEq *zkp, const shePrecomputedPublicKey *ppub, mclInt m);
 
+/*
+	Zkp s.t. Dec(c) = m
+	return 0 if success
+*/
+MCLSHE_DLL_API int sheDecWithZkpDecG1(mclInt *m, sheZkpDec *zkp, const sheSecretKey *sec, const sheCipherTextG1 *c, const shePublicKey *pub);
+
 /*
 	decode c and set m
 	return 0 if success
@@ -211,6 +223,7 @@ MCLSHE_DLL_API int shePrecomputedPublicKeyVerifyZkpBinG1(const shePrecomputedPub
 MCLSHE_DLL_API int shePrecomputedPublicKeyVerifyZkpBinG2(const shePrecomputedPublicKey *ppub, const sheCipherTextG2 *c, const sheZkpBin *zkp);
 MCLSHE_DLL_API int shePrecomputedPublicKeyVerifyZkpEq(const shePrecomputedPublicKey *ppub, const sheCipherTextG1 *c1, const sheCipherTextG2 *c2, const sheZkpEq *zkp);
 MCLSHE_DLL_API int shePrecomputedPublicKeyVerifyZkpBinEq(const shePrecomputedPublicKey *ppub, const sheCipherTextG1 *c1, const sheCipherTextG2 *c2, const sheZkpBinEq *zkp);
+MCLSHE_DLL_API int sheVerifyZkpDecG1(const shePublicKey *pub, const sheCipherTextG1 *c1, mclInt m, const sheZkpDec *zkp);
 /*
 	decode c via GT and set m
 	return 0 if success
diff --git a/src/she_c_impl.hpp b/src/she_c_impl.hpp
index 8dd0a54..6fcb2d3 100644
--- a/src/she_c_impl.hpp
+++ b/src/she_c_impl.hpp
@@ -41,6 +41,9 @@ static const ZkpEq *cast(const sheZkpEq *p) { return reinterpret_cast<const ZkpE
 static ZkpBinEq *cast(sheZkpBinEq *p) { return reinterpret_cast<ZkpBinEq*>(p); }
 static const ZkpBinEq *cast(const sheZkpBinEq *p) { return reinterpret_cast<const ZkpBinEq*>(p); }
 
+static ZkpDec *cast(sheZkpDec *p) { return reinterpret_cast<ZkpDec*>(p); }
+static const ZkpDec *cast(const sheZkpDec *p) { return reinterpret_cast<const ZkpDec*>(p); }
+
 int sheInit(int curve, int compiledTimeVar)
 	try
 {
@@ -116,6 +119,11 @@ mclSize sheZkpBinEqSerialize(void *buf, mclSize maxBufSize, const sheZkpBinEq *z
 	return (mclSize)cast(zkp)->serialize(buf, maxBufSize);
 }
 
+mclSize sheZkpDecSerialize(void *buf, mclSize maxBufSize, const sheZkpDec *zkp)
+{
+	return (mclSize)cast(zkp)->serialize(buf, maxBufSize);
+}
+
 mclSize sheSecretKeyDeserialize(sheSecretKey* sec, const void *buf, mclSize bufSize)
 {
 	return (mclSize)cast(sec)->deserialize(buf, bufSize);
@@ -156,6 +164,11 @@ mclSize sheZkpBinEqDeserialize(sheZkpBinEq* zkp, const void *buf, mclSize bufSiz
 	return (mclSize)cast(zkp)->deserialize(buf, bufSize);
 }
 
+mclSize sheZkpDecDeserialize(sheZkpDec* zkp, const void *buf, mclSize bufSize)
+{
+	return (mclSize)cast(zkp)->deserialize(buf, bufSize);
+}
+
 int sheSecretKeySetByCSPRNG(sheSecretKey *sec)
 {
 	cast(sec)->setByCSPRNG();
@@ -768,3 +781,15 @@ int shePrecomputedPublicKeyVerifyZkpBinEq(const shePrecomputedPublicKey *ppub, c
 	return verifyT(*cast(ppub), *cast(c1), *cast(c2), *cast(zkp));
 }
 
+int sheDecWithZkpDecG1(mclInt *m, sheZkpDec *zkp, const sheSecretKey *sec, const sheCipherTextG1 *c, const shePublicKey *pub)
+{
+	bool b;
+	*m = cast(sec)->decWithZkpDec(&b, *cast(zkp), *cast(c), *cast(pub));
+	return b ? 0 : -1;
+}
+
+int sheVerifyZkpDecG1(const shePublicKey *pub, const sheCipherTextG1 *c1, mclInt m, const sheZkpDec *zkp)
+{
+	return cast(pub)->verify(*cast(c1), m, *cast(zkp));
+}
+
diff --git a/test/she_c_test.hpp b/test/she_c_test.hpp
index 58139f0..b00b6a2 100644
--- a/test/she_c_test.hpp
+++ b/test/she_c_test.hpp
@@ -443,6 +443,28 @@ void ZkpEqTest(const sheSecretKey *sec, const PK *pub, encWithZkpFunc encWithZkp
 }
 
 CYBOZU_TEST_AUTO(ZkpEq)
+{
+	sheSecretKey sec;
+	sheSecretKeySetByCSPRNG(&sec);
+	shePublicKey pub;
+	sheGetPublicKey(&pub, &sec);
+	int m = 123;
+	sheCipherTextG1 c1;
+	sheEncG1(&c1, &pub, m);
+	sheZkpDec zkp;
+	int64_t dec;
+	CYBOZU_TEST_EQUAL(sheDecWithZkpDecG1(&dec, &zkp, &sec, &c1, &pub), 0);
+	CYBOZU_TEST_EQUAL(m, dec);
+	CYBOZU_TEST_EQUAL(sheVerifyZkpDecG1(&pub, &c1, m, &zkp), 1);
+	CYBOZU_TEST_EQUAL(sheVerifyZkpDecG1(&pub, &c1, m + 1, &zkp), 0);
+	sheCipherTextG1 c2;
+	sheEncG1(&c2, &pub, m);
+	CYBOZU_TEST_EQUAL(sheVerifyZkpDecG1(&pub, &c2, m, &zkp), 0);
+	zkp.d[0].d[0]++;
+	CYBOZU_TEST_EQUAL(sheVerifyZkpDecG1(&pub, &c1, m, &zkp), 0);
+}
+
+CYBOZU_TEST_AUTO(ZkpDec)
 {
 	sheSecretKey sec;
 	sheSecretKeySetByCSPRNG(&sec);