Date: Sat, 06 Feb 2010 13:56:15 -0800 From: Sam Leffler <sam@errno.com> To: Bernhard Schmidt <bschmidt@techwires.net> Cc: freebsd-net@freebsd.org Subject: Re: Software TKIP group rekeying and phase1 issue Message-ID: <4B6DE57F.7060104@errno.com> In-Reply-To: <201002040915.04470.bschmidt@techwires.net> References: <201002040915.04470.bschmidt@techwires.net>
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Bernhard Schmidt wrote:
> Hi,
>
> When hostapd triggers rekeying of the group key, wpa_supplicant successfully
> sets the correct new key. On first use of the new key tkip_mixing_phase1()
> should be applied before decrypting any frames, tkip_decrypt() does this as
>
> if (iv32 != (u32)(key->wk_keyrsc[tid] >> 16) || !ctx->rx_phase1_done) {
> tkip_mixing_phase1(ctx->rx_ttak, key->wk_key,
> wh->i_addr2, iv32);
> ctx->rx_phase1_done = 1;
> }
>
> But, after a rekeying event, neither of this condition match, especially as
> rx_phase1_done is no longer zero, therefore tkip_mixing_phase1() isn't called
> which leads to dropped frames with "TKIP ICV mismatch on decrypt" messages.
>
> A working solution for that is to set rx_phase1_done to zero inside
> tkip_setkey(). I'm not sure whether that is the best solution or if it is
> better to set/reset the wk_keyrsc sequence, at least this diff works for me
> and few other over at the Forums.
>
> Index: sys/net80211/ieee80211_crypto_tkip.c
> ===================================================================
> --- sys/net80211/ieee80211_crypto_tkip.c (revision 203242)
> +++ sys/net80211/ieee80211_crypto_tkip.c (working copy)
> @@ -144,6 +144,8 @@ tkip_setkey(struct ieee80211_key *k)
> return 0;
> }
> k->wk_keytsc = 1; /* TSC starts at 1 */
> + if (k->wk_flags & IEEE80211_KEY_GROUP)
> + ctx->rx_phase1_done = 0;
> return 1;
> }
>
Reseting this flag in setkey looks right but why only for group keys? I
don't think you want to reset the keyrsc unless instructed; if I recall
a new RSC may be sent down by the authenticator when plumbing a key--but
it's been a while since I looked at this.
Have you looked at other implementations?
Sam
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