/*	$NetBSD$	*/

/*-
 * Copyright (c) 2015 The NetBSD Foundation, Inc.
 * All rights reserved.
 *
 * This code is derived from software contributed to The NetBSD Foundation
 * by Taylor R. Campbell.
 *
 * 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 NETBSD FOUNDATION, INC. 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 FOUNDATION 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 <sys/cdefs.h>
__KERNEL_RCSID(0, "$NetBSD$");

#include <sys/types.h>
#include <sys/entpool.h>
#include <sys/systm.h>

#include <lib/libkern/keccakf1600.h>

/*
 * entpool_enter: Enter len bytes of data from buf into the entropy
 * pool ep, permuting the state as necessary when the internal buffer
 * fills up.
 */
void
entpool_enter(struct entpool *ep, const void *buf, size_t len)
{
	const uint8_t *p = buf;
	size_t n = len;

	/* If we don't have any room, stir.  */
	if (ep->ep_inleft == 0)
		entpool_stir(ep);

	/* Enter the data.  */
	while (0 < n) {
		/* Provide framing for the sample.  */
		KASSERT(0 < ep->ep_inleft);
		CTASSERT(ENTPOOL_INRATE_BYTES < 0x100);
		KASSERT(ep->ep_inleft <= ENTPOOL_INRATE_BYTES);
		--ep->ep_inleft;
		ep->ep_state.u8[rate - ep->ep_inleft] ^=
		    MIN(n, ep->ep_inleft) + 1;

		/* Don't let anyone see output now without stirring first.  */
		ep->ep_outleft = 0;

		/* Enter as many bytes as we can into the buffer.  */
		while (0 < MIN(n, ep->ep_nleft)) {
			ep->ep_state.u8[rate - --ep->ep_inleft] ^= *p++;
			n--;
		}

		/* If we filled the buffer, stir now.  */
		if (ep->ep_nleft == 0)
			entpool_stir(ep);
	}
}

/*
 * entpool_enter_nostir: Enter up to len bytes from buf into the
 * entropy pool without stirring it.  Return the number of bytes
 * actually used.
 *
 * Stirring takes about 2300 cycles on Intel Ivy Bridge, which is a bit
 * much for an interrupt handler.
 */
size_t
entpool_enter_nostir(struct entpool *ep, const void *buf, size_t len)
{
	const uint8_t *p = buf;
	size_t n = len;

	if (ep->ep_inleft == 0)
		return 0;

	/* Provide framing for the sample.  */
	CTASSERT(ENTPOOL_INRATE_BYTES < 0x100);
	KASSERT(ep->ep_inleft <= ENTPOOL_INRATE_BYTES);
	--ep->ep_inleft;
	ep->ep_state.u8[rate - ep->ep_inleft] ^= MIN(n, ep->ep_inleft) + 1;

	/* Don't let anyone see output now without stirring first.  */
	ep->ep_outleft = 0;

	/* Xor as much of the sample into the state as we can.  */
	while (0 < MIN(n, ep->ep_inleft)) {
		ep->ep_state.u8[rate - --ep->ep_inleft] ^= *p++;
		n--;
	}

	/* n is number of bytes left; return number of bytes used.  */
	return len - n;
}

/*
 * entpool_stir: Permute the Keccak state and mark the input buffer
 * empty and the output buffer full.  Since keccakf1600 is a
 * permutation, applying it never loses information.
 */
void
entpool_stir(struct entpool *ep)
{

	keccakf1600(ep->ep_state.u64);
	ep->ep_inleft = ENTPOOL_INRATE_BYTES;
	ep->ep_outleft = ENTPOOL_OUTRATE_BYTES;
}

/*
 * entpool_extract: Extract len bytes of data into buf from the entropy
 * pool ep, permuting the state as necessary when the internal buffer
 * empties, and permuting after filling buf.
 */
void
entpool_extract(struct entpool *ep, void *buf, size_t len)
{
	const unsigned rate = ENTPOOL_OUTRATE_BYTES;
	uint8_t *p = buf;
	size_t n = len;

	KASSERT(len <= ENTPOOL_OUTRATE_BYTES);
	KASSERT(ep->ep_outleft <= ENTPOOL_OUTRATE_BYTES);

	/* Extract byte by byte, stirring if we run out.  */
	while (0 < n) {
		if (ep->ep_outleft == 0)
			entpool_stir(ep);
		*p++ = ep->ep_state.u8[rate - --ep->ep_outleft];
		n--;
	}

	/*
	 * Stir once more for key erasure / forward secrecy /
	 * backtracking resistance.
	 */
	entpool_stir(ep);
}