diff --git a/core/MySigning.cpp b/core/MySigning.cpp
index 59590d5..3302363 100644
--- a/core/MySigning.cpp
+++ b/core/MySigning.cpp
@@ -284,12 +284,10 @@ bool signerVerifyMsg(MyMessage &msg)
 	return verificationResult;
 }
 
-static uint8_t sha256_hash[32];
 Sha256Class _soft_sha256;
 
 void signerSha256Init(void)
 {
-	memset(sha256_hash, 0, 32);
 	_soft_sha256.init();
 }
 
@@ -302,8 +300,7 @@ void signerSha256Update(const uint8_t* data, size_t sz)
 
 uint8_t* signerSha256Final(void)
 {
-	memcpy(sha256_hash, _soft_sha256.result(), 32);
-	return sha256_hash;
+	return _soft_sha256.result();
 }
 
 int signerMemcmp(const void* a, const void* b, size_t sz)
diff --git a/core/MySigningAtsha204Soft.cpp b/core/MySigningAtsha204Soft.cpp
index fe19d59..2f25f4d 100644
--- a/core/MySigningAtsha204Soft.cpp
+++ b/core/MySigningAtsha204Soft.cpp
@@ -63,7 +63,7 @@ static void buf2str(const uint8_t* buf, size_t sz)
 #define SIGN_DEBUG(x,...)
 #endif
 
-Sha256Class _signing_sha256;
+HmacClass _signing_sha256;
 static unsigned long _signing_timestamp;
 static bool _signing_verification_ongoing = false;
 static uint8_t _signing_verifying_nonce[32+9+1];
diff --git a/drivers/ATSHA204/sha256.cpp b/drivers/ATSHA204/sha256.cpp
index 7d60def..97b034e 100644
--- a/drivers/ATSHA204/sha256.cpp
+++ b/drivers/ATSHA204/sha256.cpp
@@ -19,8 +19,6 @@ const uint32_t sha256K[] PROGMEM = {
 	0x748f82ee,0x78a5636f,0x84c87814,0x8cc70208,0x90befffa,0xa4506ceb,0xbef9a3f7,0xc67178f2
 };
 
-#define BUFFER_SIZE 64
-
 const uint8_t sha256InitState[] PROGMEM = {
 	0x67,0xe6,0x09,0x6a, // H0
 	0x85,0xae,0x67,0xbb, // H1
@@ -110,7 +108,7 @@ void Sha256Class::addUncounted(uint8_t data)
 {
 	buffer.b[bufferOffset ^ 3] = data;
 	bufferOffset++;
-	if (bufferOffset == BUFFER_SIZE) {
+	if (bufferOffset == BLOCK_LENGTH) {
 		hashBlock();
 		bufferOffset = 0;
 	}
@@ -167,10 +165,7 @@ uint8_t* Sha256Class::result(void)
 #define HMAC_IPAD 0x36
 #define HMAC_OPAD 0x5c
 
-uint8_t keyBuffer[BLOCK_LENGTH]; // K0 in FIPS-198a
-uint8_t innerHash[HASH_LENGTH];
-
-void Sha256Class::initHmac(const uint8_t* key, int keyLength)
+void HmacClass::initHmac(const uint8_t* key, int keyLength)
 {
 	uint8_t i;
 	memset(keyBuffer,0,BLOCK_LENGTH);
@@ -192,7 +187,7 @@ void Sha256Class::initHmac(const uint8_t* key, int keyLength)
 	}
 }
 
-uint8_t* Sha256Class::resultHmac(void)
+uint8_t* HmacClass::resultHmac(void)
 {
 	uint8_t i;
 	// Complete inner hash
diff --git a/drivers/ATSHA204/sha256.h b/drivers/ATSHA204/sha256.h
index 115b368..25bb4b6 100644
--- a/drivers/ATSHA204/sha256.h
+++ b/drivers/ATSHA204/sha256.h
@@ -21,9 +21,7 @@ class Sha256Class
 public:
 	Sha256Class(); // Constructor
 	void init(void);
-	void initHmac(const uint8_t* secret, int secretLength);
 	uint8_t* result(void);
-	uint8_t* resultHmac(void);
 	void write(uint8_t);
 private:
 	void pad();
@@ -34,6 +32,14 @@ private:
 	uint8_t bufferOffset;
 	_state state;
 	uint32_t byteCount;
+};
+
+class HmacClass : public Sha256Class
+{
+public:
+	void initHmac(const uint8_t* secret, int secretLength);
+	uint8_t* resultHmac(void);
+private:
 	uint8_t keyBuffer[BLOCK_LENGTH];
 	uint8_t innerHash[HASH_LENGTH];
 };