1 files changed, 48 insertions, 0 deletions
diff --git a/CryptoPP/trunhash.h b/CryptoPP/trunhash.h
new file mode 100644
index 000000000..c1c4e9b64
--- /dev/null
+++ b/CryptoPP/trunhash.h
@@ -0,0 +1,48 @@
+#ifndef CRYPTOPP_TRUNHASH_H
+#define CRYPTOPP_TRUNHASH_H
+
+#include "cryptlib.h"
+
+NAMESPACE_BEGIN(CryptoPP)
+
+class NullHash : public HashTransformation
+{
+public:
+	void Update(const byte *input, size_t length) {}
+	unsigned int DigestSize() const {return 0;}
+	void TruncatedFinal(byte *digest, size_t digestSize) {}
+	bool TruncatedVerify(const byte *digest, size_t digestLength) {return true;}
+};
+
+//! construct new HashModule with smaller DigestSize() from existing one
+template <class T>
+class TruncatedHashTemplate : public HashTransformation
+{
+public:
+	TruncatedHashTemplate(T hm, unsigned int digestSize)
+		: m_hm(hm), m_digestSize(digestSize) {}
+	TruncatedHashTemplate(const byte *key, size_t keyLength, unsigned int digestSize)
+		: m_hm(key, keyLength), m_digestSize(digestSize) {}
+	TruncatedHashTemplate(size_t digestSize)
+		: m_digestSize(digestSize) {}
+
+	void Restart()
+		{m_hm.Restart();}
+	void Update(const byte *input, size_t length)
+		{m_hm.Update(input, length);}
+	unsigned int DigestSize() const {return m_digestSize;}
+	void TruncatedFinal(byte *digest, size_t digestSize)
+		{m_hm.TruncatedFinal(digest, digestSize);}
+	bool TruncatedVerify(const byte *digest, size_t digestLength)
+		{return m_hm.TruncatedVerify(digest, digestLength);}
+
+private:
+	T m_hm;
+	unsigned int m_digestSize;
+};
+
+typedef TruncatedHashTemplate<HashTransformation &> TruncatedHashModule;
+
+NAMESPACE_END
+
+#endif