diff --git a/Serializer.cpp b/Serializer.cpp
index 9dea65629e..68f4cef54a 100644
--- a/Serializer.cpp
+++ b/Serializer.cpp
@@ -125,22 +125,27 @@ std::vector<unsigned char> Serializer::getRaw(int offset, int length) const
 uint160 Serializer::getRIPEMD160(int size) const
 {
 	uint160 ret;
-	if((size==0)||(size>mData.size())) size=mData.size();
+	if((size<0)||(size>mData.size())) size=mData.size();
 	RIPEMD160(&(mData.front()), size, (unsigned char *) &ret);
 }
 
 uint256 Serializer::getSHA256(int size) const
 {
 	uint256 ret;
-	if((size==0)||(size>mData.size())) size=mData.size();
+	if((size<0)||(size>mData.size())) size=mData.size();
 	SHA256(&(mData.front()), size, (unsigned char *) &ret);
 }
 
 uint256 Serializer::getSHA512Half(int size) const
+{
+	return getSHA512Half(mData, size);
+}
+
+uint256 Serializer::getSHA512Half(const std::vector<unsigned char>& data, int size)
 {
 	char buf[64];
-	if((size==0)||(size>mData.size())) size=mData.size();
-	SHA512(&(mData.front()), size, (unsigned char *) buf);
+	if((size<0)||(size>data.size())) size=data.size();
+	SHA512(&(data.front()), size, (unsigned char *) buf);
 	return * (uint256 *) buf;
 }
 
diff --git a/Serializer.h b/Serializer.h
index 0d5688d7e1..bcf62dfe80 100644
--- a/Serializer.h
+++ b/Serializer.h
@@ -39,9 +39,10 @@ class Serializer
 	std::vector<unsigned char> getRaw(int offset, int length) const;
 	
 	// hash functions
-	uint160 getRIPEMD160(int size=0) const;
-	uint256 getSHA256(int size=0) const;
-	uint256 getSHA512Half(int size=0) const;
+	uint160 getRIPEMD160(int size=-1) const;
+	uint256 getSHA256(int size=-1) const;
+	uint256 getSHA512Half(int size=-1) const;
+	static uint256 getSHA512Half(const std::vector<unsigned char>& data, int size=-1);
 
 	// totality functions
 	int getLength() const { return mData.size(); }