source: git/src-cryptopp/hmac.cpp

// hmac.cpp - written and placed in the public domain by Wei Dai

#include "pch.h"

#ifndef CRYPTOPP_IMPORTS

#include "hmac.h"

NAMESPACE_BEGIN(CryptoPP)

void HMAC_Base::UncheckedSetKey(const byte *userKey, unsigned int keylength, const NameValuePairs &)
{
        AssertValidKeyLength(keylength);

        Restart();

        HashTransformation &hash = AccessHash();
        unsigned int blockSize = hash.BlockSize();

        if (!blockSize)
                throw InvalidArgument("HMAC: can only be used with a block-based hash function");

        m_buf.resize(2*AccessHash().BlockSize() + AccessHash().DigestSize());

        if (keylength <= blockSize)
                memcpy(AccessIpad(), userKey, keylength);
        else
        {
                AccessHash().CalculateDigest(AccessIpad(), userKey, keylength);
                keylength = hash.DigestSize();
        }

        CRYPTOPP_ASSERT(keylength <= blockSize);
        memset(AccessIpad()+keylength, 0, blockSize-keylength);

        for (unsigned int i=0; i<blockSize; i++)
        {
                AccessOpad()[i] = AccessIpad()[i] ^ 0x5c;
                AccessIpad()[i] ^= 0x36;
        }
}

void HMAC_Base::KeyInnerHash()
{
        CRYPTOPP_ASSERT(!m_innerHashKeyed);
        HashTransformation &hash = AccessHash();
        hash.Update(AccessIpad(), hash.BlockSize());
        m_innerHashKeyed = true;
}

void HMAC_Base::Restart()
{
        if (m_innerHashKeyed)
        {
                AccessHash().Restart();
                m_innerHashKeyed = false;
        }
}

void HMAC_Base::Update(const byte *input, size_t length)
{
        if (!m_innerHashKeyed)
                KeyInnerHash();
        AccessHash().Update(input, length);
}

void HMAC_Base::TruncatedFinal(byte *mac, size_t size)
{
        ThrowIfInvalidTruncatedSize(size);

        HashTransformation &hash = AccessHash();

        if (!m_innerHashKeyed)
                KeyInnerHash();
        hash.Final(AccessInnerHash());

        hash.Update(AccessOpad(), hash.BlockSize());
        hash.Update(AccessInnerHash(), hash.DigestSize());
        hash.TruncatedFinal(mac, size);

        m_innerHashKeyed = false;
}

NAMESPACE_END

#endif