diff --git a/hc128.cpp b/hc128.cpp
index 19b4a3db..ec90a1bc 100644
--- a/hc128.cpp
+++ b/hc128.cpp
@@ -193,7 +193,7 @@ void HC128Policy::CipherSetKey(const NameValuePairs &params, const byte *userKey
 {
 	CRYPTOPP_UNUSED(params);
 
-	GetUserKey(LITTLE_ENDIAN_ORDER, m_key, 4, userKey, keylen);
+	GetUserKey(LITTLE_ENDIAN_ORDER, m_key.begin(), 4, userKey, keylen);
 	for (unsigned int i = 4; i < 8; i++)
 		m_key[i] = m_key[i - 4];
 }
@@ -238,7 +238,7 @@ void HC128Policy::CipherResynchronize(byte *keystreamBuffer, const byte *iv, siz
 {
 	CRYPTOPP_UNUSED(keystreamBuffer);
 
-	GetUserKey(LITTLE_ENDIAN_ORDER, m_iv, 4, iv, length);
+	GetUserKey(LITTLE_ENDIAN_ORDER, m_iv.begin(), 4, iv, length);
 	for (unsigned int i = 4; i < 8; i++)
 		m_iv[i] = m_iv[i - 4];
 
diff --git a/hc128.h b/hc128.h
index 205f6b08..6c2c5b0d 100644
--- a/hc128.h
+++ b/hc128.h
@@ -41,12 +41,12 @@ protected:
 	void SetupUpdate();
 
 private:
-	word32 m_T[1024];       /* P[i] = T[i]; Q[i] = T[1024+i];*/
-	word32 m_X[16];
-	word32 m_Y[16];
-	word32 m_key[8];
-	word32 m_iv[8];
-	word32 m_ctr;   /*counter1024 = i mod 1024 at the i-th step */
+	FixedSizeSecBlock<word32, 16> m_X;
+	FixedSizeSecBlock<word32, 16> m_Y;
+	FixedSizeSecBlock<word32, 8> m_key;
+	FixedSizeSecBlock<word32, 8> m_iv;
+	word32 m_T[1024];
+	word32 m_ctr;
 };
 
 /// \brief HC-128 stream cipher
diff --git a/hc256.h b/hc256.h
index 360999e7..e6271b1a 100644
--- a/hc256.h
+++ b/hc256.h
@@ -42,10 +42,10 @@ protected:
 	word32 Generate();
 
 private:
+	FixedSizeSecBlock<word32, 8> m_key;
+	FixedSizeSecBlock<word32, 8> m_iv;
 	word32 m_P[1024];
 	word32 m_Q[1024];
-	word32 m_key[8];
-	word32 m_iv[8];
 	word32 m_ctr;
 };