lora-irrigation/comms.c

/*-
 * Copyright 2021 John-Mark Gurney.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 */

#include <comms.h>
#include <strobe_rng_init.h>

static const size_t MAC_LEN = 8;
static const size_t CHALLENGE_LEN = 16;
static const uint8_t domain[] = "com.funkthat.lora.irrigation.shared.v0.0.1";

static int comms_pktbuf_equal(struct pktbuf a, struct pktbuf b);

/* returns 1 if equal, 0 if not equal */
static int
comms_pktbuf_equal(struct pktbuf a, struct pktbuf b)
{

	if (a.pktlen != b.pktlen)
		return 0;

	return memcmp(a.pkt, b.pkt, a.pktlen) == 0;
}

size_t
_strobe_state_size()
{

	return sizeof(strobe_s);
}

void
comms_init(struct comms_state *cs, process_msgfunc_t pmf, struct pktbuf *shared)
{

	*cs = (struct comms_state){
		.cs_comm_state = COMMS_WAIT_REQUEST,
		.cs_procmsg = pmf,
	};

	strobe_init(&cs->cs_start, domain, sizeof domain - 1);

	if (shared != NULL)
		strobe_key(&cs->cs_start, SYM_KEY, shared->pkt, shared->pktlen);

	/* copy starting state over to initial state */
	cs->cs_state = cs->cs_start;
}

#define CONFIRMED_STR_BASE	"confirmed"
#define CONFIRMED_STR		((const uint8_t *)CONFIRMED_STR_BASE)
#define CONFIRMED_STR_LEN	(sizeof(CONFIRMED_STR_BASE) - 1)

/*
 * encrypted data to be processed is passed in via pbin.
 *
 * The pktbuf pointed to by pbout contains the buffer that a [encrypted]
 * response will be written to.  The length needs to be updated, where 0
 * means no reply.
 */
void
comms_process(struct comms_state *cs, struct pktbuf pbin, struct pktbuf *pbout)
{
	uint8_t buf[64] = {};
	struct pktbuf pbmsg, pbrep;
	ssize_t cnt, ret, msglen;

	/* if the current msg matches the previous */
	if (comms_pktbuf_equal(pbin, cs->cs_prevmsg)) {
		/* send the previous response */
		pbout->pktlen = cs->cs_prevmsgresp.pktlen;
		memcpy(pbout->pkt, cs->cs_prevmsgresp.pkt, pbout->pktlen);
		return;
	}

	strobe_attach_buffer(&cs->cs_state, pbin.pkt, pbin.pktlen);

	cnt = strobe_get(&cs->cs_state, APP_CIPHERTEXT, buf, pbin.pktlen -
	    MAC_LEN);
	msglen = cnt;

	cnt = strobe_get(&cs->cs_state, MAC, pbin.pkt +
	    (pbin.pktlen - MAC_LEN), MAC_LEN);

	/* XXX - cnt != MAC_LEN test case */

	/*
	 * if we have arrived here, MAC has been verified, and buf now
	 * contains the data to operate upon.
	 */

	/* attach the buffer for output */
	strobe_attach_buffer(&cs->cs_state, pbout->pkt, pbout->pktlen);

	ret = 0;
	switch (cs->cs_comm_state) {
	case COMMS_WAIT_REQUEST:
		/* XXX - reqreset check */

		bare_strobe_randomize(buf, CHALLENGE_LEN);
		ret = strobe_put(&cs->cs_state, APP_CIPHERTEXT, buf,
		    CHALLENGE_LEN);
		ret += strobe_put(&cs->cs_state, MAC, NULL, MAC_LEN);

		strobe_operate(&cs->cs_state, RATCHET, NULL, 32);

		cs->cs_comm_state = COMMS_WAIT_CONFIRM;
		break;

	case COMMS_WAIT_CONFIRM:
		/* XXX - confirm check */
		ret = strobe_put(&cs->cs_state, APP_CIPHERTEXT, CONFIRMED_STR,
		    CONFIRMED_STR_LEN);
		ret += strobe_put(&cs->cs_state, MAC, NULL, MAC_LEN);
		cs->cs_comm_state = COMMS_PROCESS_MSGS;
		break;

	case COMMS_PROCESS_MSGS: {
		uint8_t repbuf[pbout->pktlen - MAC_LEN];

		memset(repbuf, '\x00', sizeof repbuf);

		pbmsg.pkt = buf;
		pbmsg.pktlen = msglen;

		pbrep.pkt = repbuf;
		pbrep.pktlen = sizeof repbuf;

		cs->cs_procmsg(pbmsg, &pbrep);

		ret = strobe_put(&cs->cs_state, APP_CIPHERTEXT, repbuf,
		    pbrep.pktlen);
		ret += strobe_put(&cs->cs_state, MAC, NULL, MAC_LEN);

		break;
		}
	}

	/* set the output buffer length */
	pbout->pktlen = ret;

	if (ret != 0) {
		/* we accepted a new message store it */

		/* store the req */
		cs->cs_prevmsg.pkt = cs->cs_prevmsgbuf;
		cs->cs_prevmsg.pktlen = pbin.pktlen;
		memcpy(cs->cs_prevmsg.pkt, pbin.pkt, pbin.pktlen);

		/* store the response */
		cs->cs_prevmsgresp.pkt = cs->cs_prevmsgrespbuf;
		cs->cs_prevmsgresp.pktlen = pbout->pktlen;
		memcpy(cs->cs_prevmsgresp.pkt, pbout->pkt, pbout->pktlen);
	}
}