emsha/hmac.cc

/*
 * The MIT License (MIT)
 *
 * Copyright (c) 2015 K. Isom <coder@kyleisom.net>
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * copy of this  software and associated documentation  files (the "Software"),
 * to deal  in the Software  without restriction, including  without limitation
 * the rights  to use,  copy, modify,  merge, publish,  distribute, sublicense,
 * and/or  sell copies  of the  Software,  and to  permit persons  to whom  the
 * Software is furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS  PROVIDED "AS IS", WITHOUT WARRANTY OF  ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING  BUT NOT  LIMITED TO  THE WARRANTIES  OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND  NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS  OR COPYRIGHT  HOLDERS BE  LIABLE FOR  ANY CLAIM,  DAMAGES OR  OTHER
 * LIABILITY,  WHETHER IN  AN ACTION  OF CONTRACT,  TORT OR  OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
 * IN THE SOFTWARE.
 */


#include <algorithm>
#include <cassert>
#include <cstdint>


#include <emsha/emsha.h>
#include <emsha/sha256.h>
#include <emsha/hmac.h>


namespace emsha {


// These constants are used to keep track of the state of the HMAC.

// HMAC is in a clean-slate state following a call to Reset().
constexpr uint8_t HMAC_INIT = 0;

// The ipad constants have been XOR'd into the key and written to the
// SHA-256 context.
constexpr uint8_t HMAC_IPAD = 1;

// The opad constants have been XOR'd into the key and written to the
// SHA-256 context.
constexpr uint8_t HMAC_OPAD = 2;

// HMAC has been finalised
constexpr uint8_t HMAC_FIN = 3;

// HMAC is in an invalid state.
constexpr uint8_t HMAC_INVALID = 4;


static constexpr uint8_t ipad = 0x36;
static constexpr uint8_t opad = 0x5c;


HMAC::HMAC(const uint8_t *ik, uint32_t ikl)
    : hstate(HMAC_INIT), k{0}, buf{0}
{
	std::fill(this->k, this->k+HMAC_KEY_LENGTH, 0);

	if (ikl < HMAC_KEY_LENGTH) {
		for (uint32_t i = 0; i < ikl; i++) {
			this->k[i] = ik[i];
		}
		while (ikl < HMAC_KEY_LENGTH) {
			this->k[ikl++] = 0;
		}
	} else if (ikl > HMAC_KEY_LENGTH) {
		this->ctx.Update(ik, ikl);
		this->ctx.Result(this->k);
		this->ctx.Reset();
	} else {
		for (uint32_t i = 0; i < ikl; i++) {
			this->k[i] = ik[i];
		}
	}

	this->reset();
}


/*
 * A custom destructor is needed to ensure that the key material is wiped.
 */
HMAC::~HMAC()
{
	this->reset();
	std::fill(this->k, this->k + HMAC_KEY_LENGTH, 0);
}


EMSHAResult
HMAC::Reset()
{
	return this->reset();
}


EMSHAResult
HMAC::reset()
{
	EMSHAResult res;

	// Following a reset, both SHA-256 contexts and result buffer should be
	// zero'd out for a clean slate. The HMAC state should be reset
	// accordingly.
	this->ctx.Reset();
	std::fill(this->buf, this->buf + SHA256_HASH_SIZE, 0);

	// Set up the k0 ⊕ ipad construction, and write it into the
	// SHA-256 context.
	uint8_t       key[HMAC_KEY_LENGTH];
	for (uint32_t i = 0; i < HMAC_KEY_LENGTH; i++) {
		key[i] = this->k[i] ^ ipad;
	}

	res = this->ctx.Update(key, HMAC_KEY_LENGTH);
	if (EMSHAResult::OK != res) {
		this->hstate = HMAC_INVALID;
		return res;
	}

	// This key is considered sensitive material and should be wiped.
	std::fill(key, key + HMAC_KEY_LENGTH, 0);

	this->hstate = HMAC_IPAD;
	return EMSHAResult::OK;
}


EMSHAResult
HMAC::Update(const std::uint8_t *message, std::uint32_t messageLength)
{
	EMSHAResult res;
	SHA256      &hctx = this->ctx;

	EMSHA_CHECK(message != nullptr, EMSHAResult::NullPointer);
	EMSHA_CHECK(HMAC_IPAD == this->hstate, EMSHAResult::InvalidState);

	// Write the message to the SHA-256 context.
	res = hctx.Update(message, messageLength);
	if (EMSHAResult::OK != res) {
		this->hstate = HMAC_INVALID;
		return res;
	}
	assert(HMAC_IPAD == this->hstate);

	return EMSHAResult::OK;
}


inline EMSHAResult
HMAC::finalResult(uint8_t *d)
{
	if (nullptr == d) {
		return EMSHAResult::NullPointer;
	}

	// If the HMAC has already been finalised, skip straight to
	// copying the result.
	if (this->hstate == HMAC_FIN) {
		std::copy(this->buf, this->buf+SHA256_HASH_SIZE, d);

		return EMSHAResult::OK;
	}

	EMSHA_CHECK(HMAC_IPAD == this->hstate, EMSHAResult::InvalidState);

	EMSHAResult res;

	// Use the result buffer as an intermediate buffer to store the result
	// of the inner hash.
	res = this->ctx.Result(this->buf);
	if (EMSHAResult::OK != res) {
		this->hstate = HMAC_INVALID;
		return EMSHAResult::InvalidState;
	}
	assert(HMAC_IPAD == this->hstate);

	// The SHA-256 context needs to be reset so that it may be
	// re-used for the outer digest.
	this->ctx.Reset();

	// Set up the k0 ⊕ opad construction, and write it into the
	// SHA-256 context.
	uint8_t       key[HMAC_KEY_LENGTH];
	for (uint32_t i = 0; i < HMAC_KEY_LENGTH; i++) {
		key[i] = this->k[i] ^ opad;
	}

	res          = this->ctx.Update(key, HMAC_KEY_LENGTH);
	if (EMSHAResult::OK != res) {
		this->hstate = HMAC_INVALID;
		return res;
	}
	this->hstate = HMAC_OPAD;

	// This key is considered sensitive material and should be wiped.
	std::fill(key, key + HMAC_KEY_LENGTH, 0);

	// Write the inner hash result into the outer hash.
	res = this->ctx.Update(this->buf, SHA256_HASH_SIZE);
	if (EMSHAResult::OK != res) {
		this->hstate = HMAC_INVALID;
		return res;
	}

	// Write the outer hash result into the working buffer.
	res = this->ctx.Finalise(this->buf);
	if (EMSHAResult::OK != res) {
		this->hstate = HMAC_INVALID;
		return res;
	}
	assert(HMAC_OPAD == this->hstate);

	std::copy(this->buf, this->buf + SHA256_HASH_SIZE, d);
	this->hstate = HMAC_FIN;
	return EMSHAResult::OK;
}


EMSHAResult
HMAC::Finalise(std::uint8_t *digest)
{
	return this->finalResult(digest);
}


EMSHAResult
HMAC::Result(std::uint8_t *digest)
{
	return this->finalResult(digest);
}


std::uint32_t
HMAC::Size()
{
	return SHA256_HASH_SIZE;
}


EMSHAResult
ComputeHMAC(const uint8_t *k, const uint32_t kl,
	    const uint8_t *m, const uint32_t ml,
	    uint8_t *d)
{
	EMSHAResult res;
	HMAC        h(k, kl);

	res = h.Update(m, ml);
	if (res == EMSHAResult::OK) {
		res = h.Result(d);
	}

	return res;
}


} // end of namespace emsha