HMAC_MD5.hpp

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/*
    Copyright (c) 2009-2010 Christopher A. Taylor.  All rights reserved.

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/*
    HMAC-MD5 is still secure despite the ease of producing collisions in MD5.
    See Mihir Bellare paper "New Proofs for NMAC and HMAC: Security without Collision-Resistance" (June 2006)

    Using HMAC construction:
        HMAC(x) = h(k || p1 || h(k || p2 || x))
        h() = MD5 hash
        p1,p2 = distinct padding to bring k up to the block size
        p1 = 0x36 repeated, p2 = 0x5c repeated

    Diverges from usual implementation by using little-endian rather than big-endian input
*/

#ifndef HMAC_MD5_HPP
#define HMAC_MD5_HPP

#include <cat/crypt/hash/ICryptHash.hpp>

namespace cat {


class HMAC_MD5 : public ICryptHash
{
protected:
    static const int DIGEST_BYTES = 16;
    static const int WORK_BYTES = 64; // bytes in one block
    static const int WORK_WORDS = WORK_BYTES / sizeof(u32);

    u32 CachedInitialState[4]; // Cached state for H(K||inner padding)
    u32 CachedFinalState[4];   // Cached state for H(K||outer padding)

    u64 byte_counter;
    u32 State[4];
    u8 Work[WORK_BYTES];
    int used_bytes;

    void HashComputation(const void *message, int blocks, u32 *NextState);

    // Unsupported modes
    bool BeginKey(int /*bits*/) { return false; }
    bool BeginKDF() { return false; }
    bool BeginPRNG() { return false; }

public:
    ~HMAC_MD5();
    bool SetKey(ICryptHash *parent);
    void RekeyFromMD5(HMAC_MD5 *parent);
    bool BeginMAC();
    void Crunch(const void *message, int bytes);
    void End();

    // TODO: Strengthening is not supported right now
    void Generate(void *out, int bytes, int strengthening_rounds = 0);
};


} // namespace cat

#endif // HMAC_MD5_HPP