trunhash.h

#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)
        {CRYPTOPP_UNUSED(input);CRYPTOPP_UNUSED(length);}
    unsigned int DigestSize() const
        {return 0;}
    void TruncatedFinal(byte *digest, size_t digestSize)
        {CRYPTOPP_UNUSED(digest);CRYPTOPP_UNUSED(digestSize);}
    bool TruncatedVerify(const byte *digest, size_t digestLength)
        {CRYPTOPP_UNUSED(digest);CRYPTOPP_UNUSED(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