michael.c

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/*
 * Michael MIC implementation - optimized for TKIP MIC operations
 * Copyright 2002-2003, Instant802 Networks, Inc.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 */
#include <linux/types.h>
#include <linux/bitops.h>
#include <linux/ieee80211.h>
#include <asm/unaligned.h>

#include "michael.h"

static void michael_block(struct michael_mic_ctx *mctx, u32 val)
{
        mctx->l ^= val;
        mctx->r ^= rol32(mctx->l, 17);
        mctx->l += mctx->r;
        mctx->r ^= ((mctx->l & 0xff00ff00) >> 8) |
                   ((mctx->l & 0x00ff00ff) << 8);
        mctx->l += mctx->r;
        mctx->r ^= rol32(mctx->l, 3);
        mctx->l += mctx->r;
        mctx->r ^= ror32(mctx->l, 2);
        mctx->l += mctx->r;
}

static void michael_mic_hdr(struct michael_mic_ctx *mctx, const u8 *key,
                            struct ieee80211_hdr *hdr)
{
        u8 *da, *sa, tid;

        da = ieee80211_get_DA(hdr);
        sa = ieee80211_get_SA(hdr);
        if (ieee80211_is_data_qos(hdr->frame_control))
                tid = *ieee80211_get_qos_ctl(hdr) & IEEE80211_QOS_CTL_TID_MASK;
        else
                tid = 0;

        mctx->l = get_unaligned_le32(key);
        mctx->r = get_unaligned_le32(key + 4);

        /*
         * A pseudo header (DA, SA, Priority, 0, 0, 0) is used in Michael MIC
         * calculation, but it is _not_ transmitted
         */
        michael_block(mctx, get_unaligned_le32(da));
        michael_block(mctx, get_unaligned_le16(&da[4]) |
                            (get_unaligned_le16(sa) << 16));
        michael_block(mctx, get_unaligned_le32(&sa[2]));
        michael_block(mctx, tid);
}

void michael_mic(const u8 *key, struct ieee80211_hdr *hdr,
                 const u8 *data, size_t data_len, u8 *mic)
{
        u32 val;
        size_t block, blocks, left;
        struct michael_mic_ctx mctx;

        michael_mic_hdr(&mctx, key, hdr);

        /* Real data */
        blocks = data_len / 4;
        left = data_len % 4;

        for (block = 0; block < blocks; block++)
                michael_block(&mctx, get_unaligned_le32(&data[block * 4]));

        /* Partial block of 0..3 bytes and padding: 0x5a + 4..7 zeros to make
         * total length a multiple of 4. */
        val = 0x5a;
        while (left > 0) {
                val <<= 8;
                left--;
                val |= data[blocks * 4 + left];
        }

        michael_block(&mctx, val);
        michael_block(&mctx, 0);

        put_unaligned_le32(mctx.l, mic);
        put_unaligned_le32(mctx.r, mic + 4);
}