xref: /openbsd-src/sys/net80211/ieee80211_crypto_tkip.c (revision 678831be5eff0bcb5217b54d0dcfb6698acf8411)

/*	$OpenBSD: ieee80211_crypto_tkip.c,v 1.33 2021/03/10 10:21:48 jsg Exp $	*/

/*-
 * Copyright (c) 2008 Damien Bergamini <damien.bergamini@free.fr>
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */

/*
 * This code implements the Temporal Key Integrity Protocol (TKIP) defined
 * in IEEE Std 802.11-2007 section 8.3.2.
 */

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/mbuf.h>
#include <sys/malloc.h>
#include <sys/kernel.h>
#include <sys/socket.h>
#include <sys/endian.h>
#include <sys/syslog.h>

#include <net/if.h>
#include <net/if_dl.h>
#include <net/if_media.h>

#include <netinet/in.h>
#include <netinet/if_ether.h>

#include <net80211/ieee80211_var.h>
#include <net80211/ieee80211_crypto.h>

#include <crypto/arc4.h>
#include <crypto/michael.h>

typedef u_int8_t  byte;	/* 8-bit byte (octet) */
typedef u_int16_t u16b;	/* 16-bit unsigned word */
typedef u_int32_t u32b;	/* 32-bit unsigned word */

static void	Phase1(u16b *, const byte *, const byte *, u32b);
static void	Phase2(byte *, const byte *, const u16b *, u16b);

/* TKIP software crypto context */
struct ieee80211_tkip_ctx {
	struct rc4_ctx	rc4;
	const u_int8_t	*txmic;
	const u_int8_t	*rxmic;
	u_int16_t	txttak[5];
	u_int16_t	rxttak[5];
	u_int8_t	txttak_ok;
	u_int8_t	rxttak_ok;
};

/*
 * Initialize software crypto context.  This function can be overridden
 * by drivers doing hardware crypto.
 */
int
ieee80211_tkip_set_key(struct ieee80211com *ic, struct ieee80211_key *k)
{
	struct ieee80211_tkip_ctx *ctx;

	ctx = malloc(sizeof(*ctx), M_DEVBUF, M_NOWAIT | M_ZERO);
	if (ctx == NULL)
		return ENOMEM;
	/*
	 * Use bits 128-191 as the Michael key for AA->SPA and bits
	 * 192-255 as the Michael key for SPA->AA.
	 */
#ifndef IEEE80211_STA_ONLY
	if (ic->ic_opmode == IEEE80211_M_HOSTAP) {
		ctx->txmic = &k->k_key[16];
		ctx->rxmic = &k->k_key[24];
	} else
#endif
	{
		ctx->rxmic = &k->k_key[16];
		ctx->txmic = &k->k_key[24];
	}
	k->k_priv = ctx;
	return 0;
}

void
ieee80211_tkip_delete_key(struct ieee80211com *ic, struct ieee80211_key *k)
{
	if (k->k_priv != NULL) {
		explicit_bzero(k->k_priv, sizeof(struct ieee80211_tkip_ctx));
		free(k->k_priv, M_DEVBUF, sizeof(struct ieee80211_tkip_ctx));
	}
	k->k_priv = NULL;
}

/* pseudo-header used for TKIP MIC computation */
struct ieee80211_tkip_frame {
	u_int8_t	i_da[IEEE80211_ADDR_LEN];
	u_int8_t	i_sa[IEEE80211_ADDR_LEN];
	u_int8_t	i_pri;
	u_int8_t	i_pad[3];
} __packed;

/*
 * Compute TKIP MIC over an mbuf chain starting "off" bytes from the
 * beginning.  This function should be kept independent from the software
 * TKIP crypto code so that drivers doing hardware crypto but not MIC can
 * call it without a software crypto context.
 */
void
ieee80211_tkip_mic(struct mbuf *m0, int off, const u_int8_t *key,
    u_int8_t mic[IEEE80211_TKIP_MICLEN])
{
	const struct ieee80211_frame *wh;
	struct ieee80211_tkip_frame wht;
	MICHAEL_CTX ctx;	/* small enough */
	struct mbuf *m;
	caddr_t pos;
	int len;

	/* assumes 802.11 header is contiguous */
	wh = mtod(m0, struct ieee80211_frame *);

	/* construct pseudo-header for TKIP MIC computation */
	switch (wh->i_fc[1] & IEEE80211_FC1_DIR_MASK) {
	case IEEE80211_FC1_DIR_NODS:
		IEEE80211_ADDR_COPY(wht.i_da, wh->i_addr1);
		IEEE80211_ADDR_COPY(wht.i_sa, wh->i_addr2);
		break;
	case IEEE80211_FC1_DIR_TODS:
		IEEE80211_ADDR_COPY(wht.i_da, wh->i_addr3);
		IEEE80211_ADDR_COPY(wht.i_sa, wh->i_addr2);
		break;
	case IEEE80211_FC1_DIR_FROMDS:
		IEEE80211_ADDR_COPY(wht.i_da, wh->i_addr1);
		IEEE80211_ADDR_COPY(wht.i_sa, wh->i_addr3);
		break;
	case IEEE80211_FC1_DIR_DSTODS:
		IEEE80211_ADDR_COPY(wht.i_da, wh->i_addr3);
		IEEE80211_ADDR_COPY(wht.i_sa,
		    ((const struct ieee80211_frame_addr4 *)wh)->i_addr4);
		break;
	}
	if (ieee80211_has_qos(wh))
		wht.i_pri = ieee80211_get_qos(wh) & IEEE80211_QOS_TID;
	else
		wht.i_pri = 0;
	wht.i_pad[0] = wht.i_pad[1] = wht.i_pad[2] = 0;

	michael_init(&ctx);
	michael_key(key, &ctx);

	michael_update(&ctx, (caddr_t)&wht, sizeof(wht));

	m = m0;
	/* assumes the first "off" bytes are contiguous */
	pos = mtod(m, caddr_t) + off;
	len = m->m_len - off;
	for (;;) {
		michael_update(&ctx, pos, len);
		if ((m = m->m_next) == NULL)
			break;
		pos = mtod(m, caddr_t);
		len = m->m_len;
	}

	michael_final(mic, &ctx);
}

/* shortcuts */
#define IEEE80211_TKIP_TAILLEN	\
	(IEEE80211_TKIP_MICLEN + IEEE80211_WEP_CRCLEN)
#define IEEE80211_TKIP_OVHD	\
	(IEEE80211_TKIP_HDRLEN + IEEE80211_TKIP_TAILLEN)

struct mbuf *
ieee80211_tkip_encrypt(struct ieee80211com *ic, struct mbuf *m0,
    struct ieee80211_key *k)
{
	struct ieee80211_tkip_ctx *ctx = k->k_priv;
	u_int16_t wepseed[8];	/* needs to be 16-bit aligned for Phase2 */
	const struct ieee80211_frame *wh;
	u_int8_t *ivp, *mic, *icvp;
	struct mbuf *n0, *m, *n;
	u_int32_t crc;
	int left, moff, noff, len, hdrlen;

	MGET(n0, M_DONTWAIT, m0->m_type);
	if (n0 == NULL)
		goto nospace;
	if (m_dup_pkthdr(n0, m0, M_DONTWAIT))
		goto nospace;
	n0->m_pkthdr.len += IEEE80211_TKIP_HDRLEN;
	n0->m_len = MHLEN;
	if (n0->m_pkthdr.len >= MINCLSIZE - IEEE80211_TKIP_TAILLEN) {
		MCLGET(n0, M_DONTWAIT);
		if (n0->m_flags & M_EXT)
			n0->m_len = n0->m_ext.ext_size;
	}
	if (n0->m_len > n0->m_pkthdr.len)
		n0->m_len = n0->m_pkthdr.len;

	/* copy 802.11 header */
	wh = mtod(m0, struct ieee80211_frame *);
	hdrlen = ieee80211_get_hdrlen(wh);
	memcpy(mtod(n0, caddr_t), wh, hdrlen);

	k->k_tsc++;	/* increment the 48-bit TSC */

	/* construct TKIP header */
	ivp = mtod(n0, u_int8_t *) + hdrlen;
	ivp[0] = k->k_tsc >> 8;		/* TSC1 */
	/* WEP Seed = (TSC1 | 0x20) & 0x7f (see 8.3.2.2) */
	ivp[1] = (ivp[0] | 0x20) & 0x7f;
	ivp[2] = k->k_tsc;		/* TSC0 */
	ivp[3] = k->k_id << 6 | IEEE80211_WEP_EXTIV;	/* KeyID | ExtIV */
	ivp[4] = k->k_tsc >> 16;	/* TSC2 */
	ivp[5] = k->k_tsc >> 24;	/* TSC3 */
	ivp[6] = k->k_tsc >> 32;	/* TSC4 */
	ivp[7] = k->k_tsc >> 40;	/* TSC5 */

	/* compute WEP seed */
	if (!ctx->txttak_ok || (k->k_tsc & 0xffff) == 0) {
		Phase1(ctx->txttak, k->k_key, wh->i_addr2, k->k_tsc >> 16);
		ctx->txttak_ok = 1;
	}
	Phase2((u_int8_t *)wepseed, k->k_key, ctx->txttak, k->k_tsc & 0xffff);
	rc4_keysetup(&ctx->rc4, (u_int8_t *)wepseed, 16);
	explicit_bzero(wepseed, sizeof(wepseed));

	/* encrypt frame body and compute WEP ICV */
	m = m0;
	n = n0;
	moff = hdrlen;
	noff = hdrlen + IEEE80211_TKIP_HDRLEN;
	left = m0->m_pkthdr.len - moff;
	crc = ~0;
	while (left > 0) {
		if (moff == m->m_len) {
			/* nothing left to copy from m */
			m = m->m_next;
			moff = 0;
		}
		if (noff == n->m_len) {
			/* n is full and there's more data to copy */
			MGET(n->m_next, M_DONTWAIT, n->m_type);
			if (n->m_next == NULL)
				goto nospace;
			n = n->m_next;
			n->m_len = MLEN;
			if (left >= MINCLSIZE - IEEE80211_TKIP_TAILLEN) {
				MCLGET(n, M_DONTWAIT);
				if (n->m_flags & M_EXT)
					n->m_len = n->m_ext.ext_size;
			}
			if (n->m_len > left)
				n->m_len = left;
			noff = 0;
		}
		len = min(m->m_len - moff, n->m_len - noff);

		crc = ether_crc32_le_update(crc, mtod(m, caddr_t) + moff, len);
		rc4_crypt(&ctx->rc4, mtod(m, caddr_t) + moff,
		    mtod(n, caddr_t) + noff, len);

		moff += len;
		noff += len;
		left -= len;
	}

	/* reserve trailing space for TKIP MIC and WEP ICV */
	if (m_trailingspace(n) < IEEE80211_TKIP_TAILLEN) {
		MGET(n->m_next, M_DONTWAIT, n->m_type);
		if (n->m_next == NULL)
			goto nospace;
		n = n->m_next;
		n->m_len = 0;
	}

	/* compute TKIP MIC over clear text */
	mic = mtod(n, caddr_t) + n->m_len;
	ieee80211_tkip_mic(m0, hdrlen, ctx->txmic, mic);
	crc = ether_crc32_le_update(crc, mic, IEEE80211_TKIP_MICLEN);
	rc4_crypt(&ctx->rc4, mic, mic, IEEE80211_TKIP_MICLEN);
	n->m_len += IEEE80211_TKIP_MICLEN;

	/* finalize WEP ICV */
	icvp = mtod(n, caddr_t) + n->m_len;
	crc = ~crc;
	icvp[0] = crc;
	icvp[1] = crc >> 8;
	icvp[2] = crc >> 16;
	icvp[3] = crc >> 24;
	rc4_crypt(&ctx->rc4, icvp, icvp, IEEE80211_WEP_CRCLEN);
	n->m_len += IEEE80211_WEP_CRCLEN;

	n0->m_pkthdr.len += IEEE80211_TKIP_TAILLEN;

	m_freem(m0);
	return n0;
 nospace:
	ic->ic_stats.is_tx_nombuf++;
	m_freem(m0);
	m_freem(n0);
	return NULL;
}

int
ieee80211_tkip_get_tsc(uint64_t *tsc, uint64_t **prsc, struct mbuf *m,
    struct ieee80211_key *k)
{
	struct ieee80211_frame *wh;
	int hdrlen;
	u_int8_t tid;
	const u_int8_t *ivp;

	wh = mtod(m, struct ieee80211_frame *);
	hdrlen = ieee80211_get_hdrlen(wh);

	if (m->m_pkthdr.len < hdrlen + IEEE80211_TKIP_HDRLEN)
		return EINVAL;

	ivp = (u_int8_t *)wh + hdrlen;
	/* check that ExtIV bit is set */
	if (!(ivp[3] & IEEE80211_WEP_EXTIV))
		return EINVAL;

	/* Retrieve last seen packet number for this frame priority. */
	tid = ieee80211_has_qos(wh) ?
	    ieee80211_get_qos(wh) & IEEE80211_QOS_TID : 0;
	*prsc = &k->k_rsc[tid];

	/* extract the 48-bit TSC from the TKIP header */
	*tsc = (u_int64_t)ivp[2]      |
	      (u_int64_t)ivp[0] <<  8 |
	      (u_int64_t)ivp[4] << 16 |
	      (u_int64_t)ivp[5] << 24 |
	      (u_int64_t)ivp[6] << 32 |
	      (u_int64_t)ivp[7] << 40;

	return 0;
}

struct mbuf *
ieee80211_tkip_decrypt(struct ieee80211com *ic, struct mbuf *m0,
    struct ieee80211_key *k)
{
	struct ieee80211_tkip_ctx *ctx = k->k_priv;
	struct ieee80211_frame *wh;
	u_int16_t wepseed[8];	/* needs to be 16-bit aligned for Phase2 */
	u_int8_t buf[IEEE80211_TKIP_MICLEN + IEEE80211_WEP_CRCLEN];
	u_int8_t mic[IEEE80211_TKIP_MICLEN];
	u_int64_t tsc, *prsc;
	u_int32_t crc, crc0;
	u_int8_t *mic0;
	struct mbuf *n0, *m, *n;
	int hdrlen, left, moff, noff, len;

	wh = mtod(m0, struct ieee80211_frame *);
	hdrlen = ieee80211_get_hdrlen(wh);

	if (m0->m_pkthdr.len < hdrlen + IEEE80211_TKIP_OVHD) {
		m_freem(m0);
		return NULL;
	}

	/*
	 * Get the frame's Transmit Sequence Counter (TSC), and a pointer to
	 * our last-seen Receive Sequence Counter (RSC) with which we can
	 * detect replays.
	 */
	if (ieee80211_tkip_get_tsc(&tsc, &prsc, m0, k) != 0) {
		m_freem(m0);
		return NULL;
	}
	if (tsc <= *prsc) {
		/* replayed frame, discard */
		ic->ic_stats.is_tkip_replays++;
		m_freem(m0);
		return NULL;
	}

	MGET(n0, M_DONTWAIT, m0->m_type);
	if (n0 == NULL)
		goto nospace;
	if (m_dup_pkthdr(n0, m0, M_DONTWAIT))
		goto nospace;
	n0->m_pkthdr.len -= IEEE80211_TKIP_OVHD;
	n0->m_len = MHLEN;
	if (n0->m_pkthdr.len >= MINCLSIZE) {
		MCLGET(n0, M_DONTWAIT);
		if (n0->m_flags & M_EXT)
			n0->m_len = n0->m_ext.ext_size;
	}
	if (n0->m_len > n0->m_pkthdr.len)
		n0->m_len = n0->m_pkthdr.len;

	/* copy 802.11 header and clear protected bit */
	memcpy(mtod(n0, caddr_t), wh, hdrlen);
	wh = mtod(n0, struct ieee80211_frame *);
	wh->i_fc[1] &= ~IEEE80211_FC1_PROTECTED;

	/* compute WEP seed */
	if (!ctx->rxttak_ok || (tsc >> 16) != (*prsc >> 16)) {
		ctx->rxttak_ok = 0;	/* invalidate cached TTAK (if any) */
		Phase1(ctx->rxttak, k->k_key, wh->i_addr2, tsc >> 16);
	}
	Phase2((u_int8_t *)wepseed, k->k_key, ctx->rxttak, tsc & 0xffff);
	rc4_keysetup(&ctx->rc4, (u_int8_t *)wepseed, 16);
	explicit_bzero(wepseed, sizeof(wepseed));

	/* decrypt frame body and compute WEP ICV */
	m = m0;
	n = n0;
	moff = hdrlen + IEEE80211_TKIP_HDRLEN;
	noff = hdrlen;
	left = n0->m_pkthdr.len - noff;
	crc = ~0;
	while (left > 0) {
		if (moff == m->m_len) {
			/* nothing left to copy from m */
			m = m->m_next;
			moff = 0;
		}
		if (noff == n->m_len) {
			/* n is full and there's more data to copy */
			MGET(n->m_next, M_DONTWAIT, n->m_type);
			if (n->m_next == NULL)
				goto nospace;
			n = n->m_next;
			n->m_len = MLEN;
			if (left >= MINCLSIZE) {
				MCLGET(n, M_DONTWAIT);
				if (n->m_flags & M_EXT)
					n->m_len = n->m_ext.ext_size;
			}
			if (n->m_len > left)
				n->m_len = left;
			noff = 0;
		}
		len = min(m->m_len - moff, n->m_len - noff);

		rc4_crypt(&ctx->rc4, mtod(m, caddr_t) + moff,
		    mtod(n, caddr_t) + noff, len);
		crc = ether_crc32_le_update(crc, mtod(n, caddr_t) + noff, len);

		moff += len;
		noff += len;
		left -= len;
	}

	/* extract and decrypt TKIP MIC and WEP ICV from m0's tail */
	m_copydata(m, moff, IEEE80211_TKIP_TAILLEN, buf);
	rc4_crypt(&ctx->rc4, buf, buf, IEEE80211_TKIP_TAILLEN);

	/* include TKIP MIC in WEP ICV */
	mic0 = buf;
	crc = ether_crc32_le_update(crc, mic0, IEEE80211_TKIP_MICLEN);
	crc = ~crc;

	/* decrypt ICV and compare it with calculated ICV */
	crc0 = *(u_int32_t *)(buf + IEEE80211_TKIP_MICLEN);
	if (crc != letoh32(crc0)) {
		ic->ic_stats.is_tkip_icv_errs++;
		m_freem(m0);
		m_freem(n0);
		return NULL;
	}

	/* compute TKIP MIC over decrypted message */
	ieee80211_tkip_mic(n0, hdrlen, ctx->rxmic, mic);
	/* check that it matches the MIC in received frame */
	if (timingsafe_bcmp(mic0, mic, IEEE80211_TKIP_MICLEN) != 0) {
		m_freem(m0);
		m_freem(n0);
		ic->ic_stats.is_rx_locmicfail++;
		ieee80211_michael_mic_failure(ic, tsc);
		return NULL;
	}

	/* update last seen packet number (MIC is validated) */
	*prsc = tsc;
	/* mark cached TTAK as valid */
	ctx->rxttak_ok = 1;

	m_freem(m0);
	return n0;
 nospace:
	ic->ic_stats.is_rx_nombuf++;
	m_freem(m0);
	m_freem(n0);
	return NULL;
}

#ifndef IEEE80211_STA_ONLY
/*
 * This function is called in HostAP mode to deauthenticate all STAs using
 * TKIP as their pairwise or group cipher (as part of TKIP countermeasures).
 */
static void
ieee80211_tkip_deauth(void *arg, struct ieee80211_node *ni)
{
	struct ieee80211com *ic = arg;

	if (ni->ni_state == IEEE80211_STA_ASSOC &&
	    (ic->ic_bss->ni_rsngroupcipher == IEEE80211_CIPHER_TKIP ||
	     ni->ni_rsncipher == IEEE80211_CIPHER_TKIP)) {
		/* deauthenticate STA */
		IEEE80211_SEND_MGMT(ic, ni, IEEE80211_FC0_SUBTYPE_DEAUTH,
		    IEEE80211_REASON_MIC_FAILURE);
		ieee80211_node_leave(ic, ni);
	}
}

void
ieee80211_michael_mic_failure_timeout(void *arg)
{
	struct ieee80211com *ic = arg;

	/* Disable TKIP countermeasures. */
	ic->ic_flags &= ~IEEE80211_F_COUNTERM;
}
#endif	/* IEEE80211_STA_ONLY */

/*
 * This function can be called by the software TKIP crypto code or by the
 * drivers when their hardware crypto engines detect a Michael MIC failure.
 */
void
ieee80211_michael_mic_failure(struct ieee80211com *ic, u_int64_t tsc)
{
	time_t now;
#ifndef IEEE80211_STA_ONLY
	int sec;
#endif

	if (ic->ic_flags & IEEE80211_F_COUNTERM)
		return;	/* countermeasures already active */

	log(LOG_WARNING, "%s: Michael MIC failure\n", ic->ic_if.if_xname);

	/*
	 * NB. do not send Michael MIC Failure reports as recommended since
	 * these may be used as an oracle to verify CRC guesses as described
	 * in Beck, M. and Tews S. "Practical attacks against WEP and WPA"
	 * http://dl.aircrack-ng.org/breakingwepandwpa.pdf
	 */

	/*
	 * Activate TKIP countermeasures (see 802.11-2012 11.4.2.4) if less than
	 * 60 seconds have passed since the most recent previous MIC failure.
	 */
	now = getuptime();
	if (ic->ic_tkip_micfail == 0 || ic->ic_tkip_micfail + 60 >= now) {
		ic->ic_tkip_micfail = now;
		ic->ic_tkip_micfail_last_tsc = tsc;
		return;
	}

	switch (ic->ic_opmode) {
#ifndef IEEE80211_STA_ONLY
	case IEEE80211_M_HOSTAP:
		/* refuse new TKIP associations for at least 60 seconds */
		ic->ic_flags |= IEEE80211_F_COUNTERM;
		sec = 60 + arc4random_uniform(30);
		log(LOG_WARNING, "%s: HostAP will be disabled for %d seconds "
		    "as a countermeasure against TKIP key cracking attempts\n",
		    ic->ic_if.if_xname, sec);
		timeout_add_sec(&ic->ic_tkip_micfail_timeout, sec);

		/* deauthenticate all currently associated STAs using TKIP */
		ieee80211_iterate_nodes(ic, ieee80211_tkip_deauth, ic);

		/* schedule a GTK change */
		timeout_add_sec(&ic->ic_rsn_timeout, 1);
		break;
#endif
	case IEEE80211_M_STA:
		/*
		 * Notify the AP of MIC failures: send two Michael
		 * MIC Failure Report frames back-to-back to trigger
		 * countermeasures at the AP end.
		 */
		(void)ieee80211_send_eapol_key_req(ic, ic->ic_bss,
		    EAPOL_KEY_KEYMIC | EAPOL_KEY_ERROR | EAPOL_KEY_SECURE,
		    ic->ic_tkip_micfail_last_tsc);
		(void)ieee80211_send_eapol_key_req(ic, ic->ic_bss,
		    EAPOL_KEY_KEYMIC | EAPOL_KEY_ERROR | EAPOL_KEY_SECURE,
		    tsc);

		/* deauthenticate from the AP.. */
		IEEE80211_SEND_MGMT(ic, ic->ic_bss,
		    IEEE80211_FC0_SUBTYPE_DEAUTH,
		    IEEE80211_REASON_MIC_FAILURE);
		/* ..and find another one */
		(void)ieee80211_new_state(ic, IEEE80211_S_SCAN, -1);
		break;
	default:
		break;
	}

	ic->ic_tkip_micfail = now;
	ic->ic_tkip_micfail_last_tsc = tsc;
}

/***********************************************************************
   Contents:    Generate IEEE 802.11 per-frame RC4 key hash test vectors
   Date:        April 19, 2002
   Notes:
   This code is written for pedagogical purposes, NOT for performance.
************************************************************************/

/* macros for extraction/creation of byte/u16b values */
#define RotR1(v16)	((((v16) >> 1) & 0x7FFF) ^ (((v16) & 1) << 15))
#define   Lo8(v16)	((byte)( (v16)       & 0x00FF))
#define   Hi8(v16)	((byte)(((v16) >> 8) & 0x00FF))
#define Lo16(v32)	((u16b)( (v32)       & 0xFFFF))
#define Hi16(v32)	((u16b)(((v32) >>16) & 0xFFFF))
#define Mk16(hi,lo)	((lo) ^ (((u16b)(hi)) << 8))

/* select the Nth 16-bit word of the Temporal Key byte array TK[] */
#define TK16(N)		Mk16(TK[2 * (N) + 1], TK[2 * (N)])

/* S-box lookup: 16 bits --> 16 bits */
#define _S_(v16)	(Sbox[Lo8(v16)] ^ swap16(Sbox[Hi8(v16)]))

/* fixed algorithm "parameters" */
#define PHASE1_LOOP_CNT	 8	/* this needs to be "big enough"     */
#define TA_SIZE		 6	/* 48-bit transmitter address        */
#define TK_SIZE		16	/* 128-bit Temporal Key              */
#define P1K_SIZE	10	/* 80-bit Phase1 key                 */
#define RC4_KEY_SIZE	16	/* 128-bit RC4KEY (104 bits unknown) */

/* 2-byte by 2-byte subset of the full AES S-box table */
static const u16b Sbox[256]=	/* Sbox for hash */
{
	0xC6A5, 0xF884, 0xEE99, 0xF68D, 0xFF0D, 0xD6BD, 0xDEB1, 0x9154,
	0x6050, 0x0203, 0xCEA9, 0x567D, 0xE719, 0xB562, 0x4DE6, 0xEC9A,
	0x8F45, 0x1F9D, 0x8940, 0xFA87, 0xEF15, 0xB2EB, 0x8EC9, 0xFB0B,
	0x41EC, 0xB367, 0x5FFD, 0x45EA, 0x23BF, 0x53F7, 0xE496, 0x9B5B,
	0x75C2, 0xE11C, 0x3DAE, 0x4C6A, 0x6C5A, 0x7E41, 0xF502, 0x834F,
	0x685C, 0x51F4, 0xD134, 0xF908, 0xE293, 0xAB73, 0x6253, 0x2A3F,
	0x080C, 0x9552, 0x4665, 0x9D5E, 0x3028, 0x37A1, 0x0A0F, 0x2FB5,
	0x0E09, 0x2436, 0x1B9B, 0xDF3D, 0xCD26, 0x4E69, 0x7FCD, 0xEA9F,
	0x121B, 0x1D9E, 0x5874, 0x342E, 0x362D, 0xDCB2, 0xB4EE, 0x5BFB,
	0xA4F6, 0x764D, 0xB761, 0x7DCE, 0x527B, 0xDD3E, 0x5E71, 0x1397,
	0xA6F5, 0xB968, 0x0000, 0xC12C, 0x4060, 0xE31F, 0x79C8, 0xB6ED,
	0xD4BE, 0x8D46, 0x67D9, 0x724B, 0x94DE, 0x98D4, 0xB0E8, 0x854A,
	0xBB6B, 0xC52A, 0x4FE5, 0xED16, 0x86C5, 0x9AD7, 0x6655, 0x1194,
	0x8ACF, 0xE910, 0x0406, 0xFE81, 0xA0F0, 0x7844, 0x25BA, 0x4BE3,
	0xA2F3, 0x5DFE, 0x80C0, 0x058A, 0x3FAD, 0x21BC, 0x7048, 0xF104,
	0x63DF, 0x77C1, 0xAF75, 0x4263, 0x2030, 0xE51A, 0xFD0E, 0xBF6D,
	0x814C, 0x1814, 0x2635, 0xC32F, 0xBEE1, 0x35A2, 0x88CC, 0x2E39,
	0x9357, 0x55F2, 0xFC82, 0x7A47, 0xC8AC, 0xBAE7, 0x322B, 0xE695,
	0xC0A0, 0x1998, 0x9ED1, 0xA37F, 0x4466, 0x547E, 0x3BAB, 0x0B83,
	0x8CCA, 0xC729, 0x6BD3, 0x283C, 0xA779, 0xBCE2, 0x161D, 0xAD76,
	0xDB3B, 0x6456, 0x744E, 0x141E, 0x92DB, 0x0C0A, 0x486C, 0xB8E4,
	0x9F5D, 0xBD6E, 0x43EF, 0xC4A6, 0x39A8, 0x31A4, 0xD337, 0xF28B,
	0xD532, 0x8B43, 0x6E59, 0xDAB7, 0x018C, 0xB164, 0x9CD2, 0x49E0,
	0xD8B4, 0xACFA, 0xF307, 0xCF25, 0xCAAF, 0xF48E, 0x47E9, 0x1018,
	0x6FD5, 0xF088, 0x4A6F, 0x5C72, 0x3824, 0x57F1, 0x73C7, 0x9751,
	0xCB23, 0xA17C, 0xE89C, 0x3E21, 0x96DD, 0x61DC, 0x0D86, 0x0F85,
	0xE090, 0x7C42, 0x71C4, 0xCCAA, 0x90D8, 0x0605, 0xF701, 0x1C12,
	0xC2A3, 0x6A5F, 0xAEF9, 0x69D0, 0x1791, 0x9958, 0x3A27, 0x27B9,
	0xD938, 0xEB13, 0x2BB3, 0x2233, 0xD2BB, 0xA970, 0x0789, 0x33A7,
	0x2DB6, 0x3C22, 0x1592, 0xC920, 0x8749, 0xAAFF, 0x5078, 0xA57A,
	0x038F, 0x59F8, 0x0980, 0x1A17, 0x65DA, 0xD731, 0x84C6, 0xD0B8,
	0x82C3, 0x29B0, 0x5A77, 0x1E11, 0x7BCB, 0xA8FC, 0x6DD6, 0x2C3A
};

/*
 **********************************************************************
 * Routine: Phase 1 -- generate P1K, given TA, TK, IV32
 *
 * Inputs:
 *     TK[]      = Temporal Key                         [128 bits]
 *     TA[]      = transmitter's MAC address            [ 48 bits]
 *     IV32      = upper 32 bits of IV                  [ 32 bits]
 * Output:
 *     P1K[]     = Phase 1 key                          [ 80 bits]
 *
 * Note:
 *     This function only needs to be called every 2**16 frames,
 *     although in theory it could be called every frame.
 *
 **********************************************************************
 */
static void
Phase1(u16b *P1K, const byte *TK, const byte *TA, u32b IV32)
{
	int i;

	/* Initialize the 80 bits of P1K[] from IV32 and TA[0..5] */
	P1K[0] = Lo16(IV32);
	P1K[1] = Hi16(IV32);
	P1K[2] = Mk16(TA[1], TA[0]);	/* use TA[] as little-endian */
	P1K[3] = Mk16(TA[3], TA[2]);
	P1K[4] = Mk16(TA[5], TA[4]);

	/* Now compute an unbalanced Feistel cipher with 80-bit block */
	/* size on the 80-bit block P1K[], using the 128-bit key TK[] */
	for (i = 0; i < PHASE1_LOOP_CNT; i++) {
		/* Each add operation here is mod 2**16 */
		P1K[0] += _S_(P1K[4] ^ TK16((i & 1) + 0));
		P1K[1] += _S_(P1K[0] ^ TK16((i & 1) + 2));
		P1K[2] += _S_(P1K[1] ^ TK16((i & 1) + 4));
		P1K[3] += _S_(P1K[2] ^ TK16((i & 1) + 6));
		P1K[4] += _S_(P1K[3] ^ TK16((i & 1) + 0));
		P1K[4] += i;	/* avoid "slide attacks" */
	}
}

/*
 **********************************************************************
 * Routine: Phase 2 -- generate RC4KEY, given TK, P1K, IV16
 *
 * Inputs:
 *     TK[]      = Temporal Key                         [128 bits]
 *     P1K[]     = Phase 1 output key                   [ 80 bits]
 *     IV16      = low 16 bits of IV counter            [ 16 bits]
 * Output:
 *     RC4KEY[] = the key used to encrypt the frame     [128 bits]
 *
 * Note:
 *     The value {TA,IV32,IV16} for Phase1/Phase2 must be unique
 *     across all frames using the same key TK value. Then, for a
 *     given value of TK[], this TKIP48 construction guarantees that
 *     the final RC4KEY value is unique across all frames.
 *
 **********************************************************************
 */
static void
Phase2(byte *RC4KEY, const byte *TK, const u16b *P1K, u16b IV16)
{
	u16b *PPK;	/* temporary key for mixing */
	int i;

	/*
	 * Suggested implementation optimization: if PPK[] is "overlaid"
	 * appropriately on RC4KEY[], there is no need for the final for
	 * loop that copies the PPK[] result into RC4KEY[].
	 */
	PPK = (u16b *)&RC4KEY[4];

	/* all adds in the PPK[] equations below are mod 2**16 */
	for (i = 0; i < 5; i++)
		PPK[i] = P1K[i];	/* first, copy P1K to PPK */
	PPK[5] = P1K[4] + IV16;		/* next, add in IV16 */

	/* Bijective non-linear mixing of the 96 bits of PPK[0..5] */
	PPK[0] += _S_(PPK[5] ^ TK16(0)); /* Mix key in each "round" */
	PPK[1] += _S_(PPK[0] ^ TK16(1));
	PPK[2] += _S_(PPK[1] ^ TK16(2));
	PPK[3] += _S_(PPK[2] ^ TK16(3));
	PPK[4] += _S_(PPK[3] ^ TK16(4));
	PPK[5] += _S_(PPK[4] ^ TK16(5)); /* Total # S-box lookups == 6 */

	/* Final sweep: bijective, linear. Rotates kill LSB correlations */
	PPK[0] += RotR1(PPK[5] ^ TK16(6));
	PPK[1] += RotR1(PPK[0] ^ TK16(7)); /* Use all of TK[] in Phase2 */
	PPK[2] += RotR1(PPK[1]);
	PPK[3] += RotR1(PPK[2]);
	PPK[4] += RotR1(PPK[3]);
	PPK[5] += RotR1(PPK[4]);

	/* At this point, for a given key TK[0..15], the 96-bit output */
	/* value PPK[0..5] is guaranteed to be unique, as a function */
	/* of the 96-bit "input" value   {TA,IV32,IV16}. That is, P1K */
	/* is now a keyed permutation of {TA,IV32,IV16}. */
	/* Set RC4KEY[0..3], which includes cleartext portion of RC4 key  */
	RC4KEY[0] = Hi8(IV16);	/* RC4KEY[0..2] is the WEP IV */
	RC4KEY[1] =(Hi8(IV16) | 0x20) & 0x7F; /* Help avoid FMS weak keys */
	RC4KEY[2] = Lo8(IV16);
	RC4KEY[3] = Lo8((PPK[5] ^ TK16(0)) >> 1);

#if BYTE_ORDER == BIG_ENDIAN
	/* Copy 96 bits of PPK[0..5] to RC4KEY[4..15] (little-endian) */
	for (i = 0; i < 6; i++)
		PPK[i] = swap16(PPK[i]);
#endif
}