wpa_ccmp.c

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/*
 * Copyright (c) 2009 Joshua Oreman <oremanj@rwcr.net>.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License as
 * published by the Free Software Foundation; either version 2 of the
 * License, or any later version.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 */

FILE_LICENCE ( GPL2_OR_LATER );

#include <gpxe/net80211.h>
#include <gpxe/crypto.h>
#include <gpxe/hmac.h>
#include <gpxe/sha1.h>
#include <gpxe/aes.h>
#include <gpxe/wpa.h>
#include <byteswap.h>
#include <errno.h>

/** @file
 *
 * Backend for WPA using the CCMP encryption method
 */

/** Context for CCMP encryption and decryption */
struct ccmp_ctx
{
        /** AES context - only ever used for encryption */
        u8 aes_ctx[AES_CTX_SIZE];

        /** Most recently sent packet number */
        u64 tx_seq;

        /** Most recently received packet number */
        u64 rx_seq;
};

/** Header structure at the beginning of CCMP frame data */
struct ccmp_head
{
        u8 pn_lo[2];            /**< Bytes 0 and 1 of packet number */
        u8 _rsvd;               /**< Reserved byte */
        u8 kid;                 /**< Key ID and ExtIV byte */
        u8 pn_hi[4];            /**< Bytes 2-5 (2 first) of packet number */
} __attribute__ (( packed ));


/** CCMP header overhead */
#define CCMP_HEAD_LEN   8

/** CCMP MIC trailer overhead */
#define CCMP_MIC_LEN    8

/** CCMP nonce length */
#define CCMP_NONCE_LEN  13

/** CCMP nonce structure */
struct ccmp_nonce
{
        u8 prio;                /**< Packet priority, 0 for non-QoS */
        u8 a2[ETH_ALEN];        /**< Address 2 from packet header (sender) */
        u8 pn[6];               /**< Packet number */
} __attribute__ (( packed ));

/** CCMP additional authentication data length (for non-QoS, non-WDS frames) */
#define CCMP_AAD_LEN    22

/** CCMP additional authentication data structure */
struct ccmp_aad
{
        u16 fc;                 /**< Frame Control field */
        u8 a1[6];               /**< Address 1 */
        u8 a2[6];               /**< Address 2 */
        u8 a3[6];               /**< Address 3 */
        u16 seq;                /**< Sequence Control field */
        /* Address 4 and QoS Control are included if present */
} __attribute__ (( packed ));

/** Mask for Frame Control field in AAD */
#define CCMP_AAD_FC_MASK        0xC38F

/** Mask for Sequence Control field in AAD */
#define CCMP_AAD_SEQ_MASK       0x000F


/**
 * Convert 6-byte LSB packet number to 64-bit integer
 *
 * @v pn        Pointer to 6-byte packet number
 * @ret v       64-bit integer value of @a pn
 */
static u64 pn_to_u64 ( const u8 *pn )
{
        int i;
        u64 ret = 0;

        for ( i = 5; i >= 0; i-- ) {
                ret <<= 8;
                ret |= pn[i];
        }

        return ret;
}

/**
 * Convert 64-bit integer to 6-byte packet number
 *
 * @v v         64-bit integer
 * @v msb       If TRUE, reverse the output PN to be in MSB order
 * @ret pn      6-byte packet number
 *
 * The PN is stored in LSB order in the packet header and in MSB order
 * in the nonce. WHYYYYY?
 */
static void u64_to_pn ( u64 v, u8 *pn, int msb )
{
        int i;
        u8 *pnp = pn + ( msb ? 5 : 0 );
        int delta = ( msb ? -1 : +1 );

        for ( i = 0; i < 6; i++ ) {
                *pnp = v & 0xFF;
                pnp += delta;
                v >>= 8;
        }
}

/** Value for @a msb argument of u64_to_pn() for MSB output */
#define PN_MSB  1

/** Value for @a msb argument of u64_to_pn() for LSB output */
#define PN_LSB  0



/**
 * Initialise CCMP state and install key
 *
 * @v crypto    CCMP cryptosystem structure
 * @v key       Pointer to 16-byte temporal key to install
 * @v keylen    Length of key (16 bytes)
 * @v rsc       Initial receive sequence counter
 */
static int ccmp_init ( struct net80211_crypto *crypto, const void *key,
                       int keylen, const void *rsc )
{
        struct ccmp_ctx *ctx = crypto->priv;

        if ( keylen != 16 )
                return -EINVAL;

        if ( rsc )
                ctx->rx_seq = pn_to_u64 ( rsc );

        cipher_setkey ( &aes_algorithm, ctx->aes_ctx, key, keylen );

        return 0;
}


/**
 * Encrypt or decrypt data stream using AES in Counter mode
 *
 * @v ctx       CCMP cryptosystem context
 * @v nonce     Nonce value, 13 bytes
 * @v srcv      Data to encrypt or decrypt
 * @v len       Number of bytes pointed to by @a src
 * @v msrcv     MIC value to encrypt or decrypt (may be NULL)
 * @ret destv   Encrypted or decrypted data
 * @ret mdestv  Encrypted or decrypted MIC value
 *
 * This assumes CCMP parameters of L=2 and M=8. The algorithm is
 * defined in RFC 3610.
 */
static void ccmp_ctr_xor ( struct ccmp_ctx *ctx, const void *nonce,
                           const void *srcv, void *destv, int len,
                           const void *msrcv, void *mdestv )
{
        u8 A[16], S[16];
        u16 ctr;
        int i;
        const u8 *src = srcv, *msrc = msrcv;
        u8 *dest = destv, *mdest = mdestv;

        A[0] = 0x01;            /* flags, L' = L - 1 = 1, other bits rsvd */
        memcpy ( A + 1, nonce, CCMP_NONCE_LEN );

        if ( msrcv ) {
                A[14] = A[15] = 0;

                cipher_encrypt ( &aes_algorithm, ctx->aes_ctx, A, S, 16 );

                for ( i = 0; i < 8; i++ ) {
                        *mdest++ = *msrc++ ^ S[i];
                }
        }

        for ( ctr = 1 ;; ctr++ ) {
                A[14] = ctr >> 8;
                A[15] = ctr & 0xFF;

                cipher_encrypt ( &aes_algorithm, ctx->aes_ctx, A, S, 16 );

                for ( i = 0; i < len && i < 16; i++ )
                        *dest++ = *src++ ^ S[i];

                if ( len <= 16 )
                        break;  /* we're done */

                len -= 16;
        }
}


/**
 * Advance one block in CBC-MAC calculation
 *
 * @v aes_ctx   AES encryption context with key set
 * @v B         Cleartext block to incorporate (16 bytes)
 * @v X         Previous ciphertext block (16 bytes)
 * @ret B       Clobbered
 * @ret X       New ciphertext block (16 bytes)
 *
 * This function does X := E[key] ( X ^ B ).
 */
static void ccmp_feed_cbc_mac ( void *aes_ctx, u8 *B, u8 *X )
{
        int i;
        for ( i = 0; i < 16; i++ )
                B[i] ^= X[i];
        cipher_encrypt ( &aes_algorithm, aes_ctx, B, X, 16 );
}


/**
 * Calculate MIC on plaintext data using CBC-MAC
 *
 * @v ctx       CCMP cryptosystem context
 * @v nonce     Nonce value, 13 bytes
 * @v data      Data to calculate MIC over
 * @v datalen   Length of @a data
 * @v aad       Additional authentication data, for MIC but not encryption
 * @ret mic     MIC value (unencrypted), 8 bytes
 *
 * @a aadlen is assumed to be 22 bytes long, as it always is for
 * 802.11 use when transmitting non-QoS, not-between-APs frames (the
 * only type we deal with).
 */
static void ccmp_cbc_mac ( struct ccmp_ctx *ctx, const void *nonce,
                           const void *data, u16 datalen,
                           const void *aad, void *mic )
{
        u8 X[16], B[16];

        /* Zeroth block: flags, nonce, length */

        /* Rsv AAD - M'-  - L'-
         *  0   1  0 1 1  0 0 1   for an 8-byte MAC and 2-byte message length
         */
        B[0] = 0x59;
        memcpy ( B + 1, nonce, CCMP_NONCE_LEN );
        B[14] = datalen >> 8;
        B[15] = datalen & 0xFF;

        cipher_encrypt ( &aes_algorithm, ctx->aes_ctx, B, X, 16 );

        /* First block: AAD length field and 14 bytes of AAD */
        B[0] = 0;
        B[1] = CCMP_AAD_LEN;
        memcpy ( B + 2, aad, 14 );

        ccmp_feed_cbc_mac ( ctx->aes_ctx, B, X );

        /* Second block: Remaining 8 bytes of AAD, 8 bytes zero pad */
        memcpy ( B, aad + 14, 8 );
        memset ( B + 8, 0, 8 );

        ccmp_feed_cbc_mac ( ctx->aes_ctx, B, X );

        /* Message blocks */
        while ( datalen ) {
                if ( datalen >= 16 ) {
                        memcpy ( B, data, 16 );
                        datalen -= 16;
                } else {
                        memcpy ( B, data, datalen );
                        memset ( B + datalen, 0, 16 - datalen );
                        datalen = 0;
                }

                ccmp_feed_cbc_mac ( ctx->aes_ctx, B, X );

                data += 16;
        }

        /* Get MIC from final value of X */
        memcpy ( mic, X, 8 );
}


/**
 * Encapsulate and encrypt a packet using CCMP
 *
 * @v crypto    CCMP cryptosystem
 * @v iob       I/O buffer containing cleartext packet
 * @ret eiob    I/O buffer containing encrypted packet
 */
struct io_buffer * ccmp_encrypt ( struct net80211_crypto *crypto,
                                  struct io_buffer *iob )
{
        struct ccmp_ctx *ctx = crypto->priv;
        struct ieee80211_frame *hdr = iob->data;
        struct io_buffer *eiob;
        const int hdrlen = IEEE80211_TYP_FRAME_HEADER_LEN;
        int datalen = iob_len ( iob ) - hdrlen;
        struct ccmp_head head;
        struct ccmp_nonce nonce;
        struct ccmp_aad aad;
        u8 mic[8], tx_pn[6];
        void *edata, *emic;

        ctx->tx_seq++;
        u64_to_pn ( ctx->tx_seq, tx_pn, PN_LSB );

        /* Allocate memory */
        eiob = alloc_iob ( iob_len ( iob ) + CCMP_HEAD_LEN + CCMP_MIC_LEN );
        if ( ! eiob )
                return NULL;

        /* Copy frame header */
        memcpy ( iob_put ( eiob, hdrlen ), iob->data, hdrlen );
        hdr = eiob->data;
        hdr->fc |= IEEE80211_FC_PROTECTED;

        /* Fill in packet number and extended IV */
        memcpy ( head.pn_lo, tx_pn, 2 );
        memcpy ( head.pn_hi, tx_pn + 2, 4 );
        head.kid = 0x20;        /* have Extended IV, key ID 0 */
        head._rsvd = 0;
        memcpy ( iob_put ( eiob, sizeof ( head ) ), &head, sizeof ( head ) );

        /* Form nonce */
        nonce.prio = 0;
        memcpy ( nonce.a2, hdr->addr2, ETH_ALEN );
        u64_to_pn ( ctx->tx_seq, nonce.pn, PN_MSB );

        /* Form additional authentication data */
        aad.fc = hdr->fc & CCMP_AAD_FC_MASK;
        memcpy ( aad.a1, hdr->addr1, 3 * ETH_ALEN ); /* all 3 at once */
        aad.seq = hdr->seq & CCMP_AAD_SEQ_MASK;

        /* Calculate MIC over the data */
        ccmp_cbc_mac ( ctx, &nonce, iob->data + hdrlen, datalen, &aad, mic );

        /* Copy and encrypt data and MIC */
        edata = iob_put ( eiob, datalen );
        emic = iob_put ( eiob, CCMP_MIC_LEN );
        ccmp_ctr_xor ( ctx, &nonce,
                       iob->data + hdrlen, edata, datalen,
                       mic, emic );

        /* Done! */
        DBGC2 ( ctx, "WPA-CCMP %p: encrypted packet %p -> %p\n", ctx,
                iob, eiob );

        return eiob;
}

/**
 * Decrypt a packet using CCMP
 *
 * @v crypto    CCMP cryptosystem
 * @v eiob      I/O buffer containing encrypted packet
 * @ret iob     I/O buffer containing cleartext packet
 */
static struct io_buffer * ccmp_decrypt ( struct net80211_crypto *crypto,
                                         struct io_buffer *eiob )
{
        struct ccmp_ctx *ctx = crypto->priv;
        struct ieee80211_frame *hdr;
        struct io_buffer *iob;
        const int hdrlen = IEEE80211_TYP_FRAME_HEADER_LEN;
        int datalen = iob_len ( eiob ) - hdrlen - CCMP_HEAD_LEN - CCMP_MIC_LEN;
        struct ccmp_head *head;
        struct ccmp_nonce nonce;
        struct ccmp_aad aad;
        u8 rx_pn[6], their_mic[8], our_mic[8];

        iob = alloc_iob ( hdrlen + datalen );
        if ( ! iob )
                return NULL;

        /* Copy frame header */
        memcpy ( iob_put ( iob, hdrlen ), eiob->data, hdrlen );
        hdr = iob->data;
        hdr->fc &= ~IEEE80211_FC_PROTECTED;

        /* Check and update RX packet number */
        head = eiob->data + hdrlen;
        memcpy ( rx_pn, head->pn_lo, 2 );
        memcpy ( rx_pn + 2, head->pn_hi, 4 );

        if ( pn_to_u64 ( rx_pn ) <= ctx->rx_seq ) {
                DBGC ( ctx, "WPA-CCMP %p: packet received out of order "
                       "(%012llx <= %012llx)\n", ctx, pn_to_u64 ( rx_pn ),
                       ctx->rx_seq );
                free_iob ( iob );
                return NULL;
        }

        ctx->rx_seq = pn_to_u64 ( rx_pn );
        DBGC2 ( ctx, "WPA-CCMP %p: RX packet number %012llx\n", ctx, ctx->rx_seq );

        /* Form nonce */
        nonce.prio = 0;
        memcpy ( nonce.a2, hdr->addr2, ETH_ALEN );
        u64_to_pn ( ctx->rx_seq, nonce.pn, PN_MSB );

        /* Form additional authentication data */
        aad.fc = ( hdr->fc & CCMP_AAD_FC_MASK ) | IEEE80211_FC_PROTECTED;
        memcpy ( aad.a1, hdr->addr1, 3 * ETH_ALEN ); /* all 3 at once */
        aad.seq = hdr->seq & CCMP_AAD_SEQ_MASK;

        /* Copy-decrypt data and MIC */
        ccmp_ctr_xor ( ctx, &nonce, eiob->data + hdrlen + sizeof ( *head ),
                       iob_put ( iob, datalen ), datalen,
                       eiob->tail - CCMP_MIC_LEN, their_mic );

        /* Check MIC */
        ccmp_cbc_mac ( ctx, &nonce, iob->data + hdrlen, datalen, &aad,
                       our_mic );

        if ( memcmp ( their_mic, our_mic, CCMP_MIC_LEN ) != 0 ) {
                DBGC2 ( ctx, "WPA-CCMP %p: MIC failure\n", ctx );
                free_iob ( iob );
                return NULL;
        }

        DBGC2 ( ctx, "WPA-CCMP %p: decrypted packet %p -> %p\n", ctx,
                eiob, iob );

        return iob;
}


/** CCMP cryptosystem */
struct net80211_crypto ccmp_crypto __net80211_crypto = {
        .algorithm = NET80211_CRYPT_CCMP,
        .init = ccmp_init,
        .encrypt = ccmp_encrypt,
        .decrypt = ccmp_decrypt,
        .priv_len = sizeof ( struct ccmp_ctx ),
};




/**
 * Calculate HMAC-SHA1 MIC for EAPOL-Key frame
 *
 * @v kck       Key Confirmation Key, 16 bytes
 * @v msg       Message to calculate MIC over
 * @v len       Number of bytes to calculate MIC over
 * @ret mic     Calculated MIC, 16 bytes long
 */
static void ccmp_kie_mic ( const void *kck, const void *msg, size_t len,
                           void *mic )
{
        u8 sha1_ctx[SHA1_CTX_SIZE];
        u8 kckb[16];
        u8 hash[SHA1_SIZE];
        size_t kck_len = 16;

        memcpy ( kckb, kck, kck_len );

        hmac_init ( &sha1_algorithm, sha1_ctx, kckb, &kck_len );
        hmac_update ( &sha1_algorithm, sha1_ctx, msg, len );
        hmac_final ( &sha1_algorithm, sha1_ctx, kckb, &kck_len, hash );

        memcpy ( mic, hash, 16 );
}

/**
 * Decrypt key data in EAPOL-Key frame
 *
 * @v kek       Key Encryption Key, 16 bytes
 * @v iv        Initialisation vector, 16 bytes (unused)
 * @v msg       Message to decrypt
 * @v len       Length of message
 * @ret msg     Decrypted message in place of original
 * @ret len     Adjusted downward for 8 bytes of overhead
 * @ret rc      Return status code
 *
 * The returned message may still contain padding of 0xDD followed by
 * zero or more 0x00 octets. It is impossible to remove the padding
 * without parsing the IEs in the packet (another design decision that
 * tends to make one question the 802.11i committee's intelligence...)
 */
static int ccmp_kie_decrypt ( const void *kek, const void *iv __unused,
                              void *msg, u16 *len )
{
        if ( *len % 8 != 0 )
                return -EINVAL;

        if ( aes_unwrap ( kek, msg, msg, *len / 8 - 1 ) != 0 )
                return -EINVAL;

        *len -= 8;

        return 0;
}

/** CCMP-style key integrity and encryption handler */
struct wpa_kie ccmp_kie __wpa_kie = {
        .version = EAPOL_KEY_VERSION_WPA2,
        .mic = ccmp_kie_mic,
        .decrypt = ccmp_kie_decrypt,
};