crypto.c

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/*
 * Ultra Wide Band
 * AES-128 CCM Encryption
 *
 * Copyright (C) 2007 Intel Corporation
 * Inaky Perez-Gonzalez <[email protected]>
 *
 * 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.
 *
 * 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., 51 Franklin Street, Fifth Floor, Boston, MA
 * 02110-1301, USA.
 *
 *
 * We don't do any encryption here; we use the Linux Kernel's AES-128
 * crypto modules to construct keys and payload blocks in a way
 * defined by WUSB1.0[6]. Check the erratas, as typos are are patched
 * there.
 *
 * Thanks a zillion to John Keys for his help and clarifications over
 * the designed-by-a-committee text.
 *
 * So the idea is that there is this basic Pseudo-Random-Function
 * defined in WUSB1.0[6.5] which is the core of everything. It works
 * by tweaking some blocks, AES crypting them and then xoring
 * something else with them (this seems to be called CBC(AES) -- can
 * you tell I know jack about crypto?). So we just funnel it into the
 * Linux Crypto API.
 *
 * We leave a crypto test module so we can verify that vectors match,
 * every now and then.
 *
 * Block size: 16 bytes -- AES seems to do things in 'block sizes'. I
 *             am learning a lot...
 *
 *             Conveniently, some data structures that need to be
 *             funneled through AES are...16 bytes in size!
 */

#include <linux/crypto.h>
#include <linux/module.h>
#include <linux/err.h>
#include <linux/uwb.h>
#include <linux/slab.h>
#include <linux/usb/wusb.h>
#include <linux/scatterlist.h>

static int debug_crypto_verify = 0;

module_param(debug_crypto_verify, int, 0);
MODULE_PARM_DESC(debug_crypto_verify, "verify the key generation algorithms");

static void wusb_key_dump(const void *buf, size_t len)
{
    print_hex_dump(KERN_ERR, "  ", DUMP_PREFIX_OFFSET, 16, 1,
               buf, len, 0);
}

/*
 * Block of data, as understood by AES-CCM
 *
 * The code assumes this structure is nothing but a 16 byte array
 * (packed in a struct to avoid common mess ups that I usually do with
 * arrays and enforcing type checking).
 */
struct aes_ccm_block {
    u8 data[16];
} __attribute__((packed));

/*
 * Counter-mode Blocks (WUSB1.0[6.4])
 *
 * According to CCM (or so it seems), for the purpose of calculating
 * the MIC, the message is broken in N counter-mode blocks, B0, B1,
 * ... BN.
 *
 * B0 contains flags, the CCM nonce and l(m).
 *
 * B1 contains l(a), the MAC header, the encryption offset and padding.
 *
 * If EO is nonzero, additional blocks are built from payload bytes
 * until EO is exahusted (FIXME: padding to 16 bytes, I guess). The
 * padding is not xmitted.
 */

/* WUSB1.0[T6.4] */
struct aes_ccm_b0 {
    u8 flags;   /* 0x59, per CCM spec */
    struct aes_ccm_nonce ccm_nonce;
    __be16 lm;
} __attribute__((packed));

/* WUSB1.0[T6.5] */
struct aes_ccm_b1 {
    __be16 la;
    u8 mac_header[10];
    __le16 eo;
    u8 security_reserved;   /* This is always zero */
    u8 padding;     /* 0 */
} __attribute__((packed));

/*
 * Encryption Blocks (WUSB1.0[6.4.4])
 *
 * CCM uses Ax blocks to generate a keystream with which the MIC and
 * the message's payload are encoded. A0 always encrypts/decrypts the
 * MIC. Ax (x>0) are used for the successive payload blocks.
 *
 * The x is the counter, and is increased for each block.
 */
struct aes_ccm_a {
    u8 flags;   /* 0x01, per CCM spec */
    struct aes_ccm_nonce ccm_nonce;
    __be16 counter; /* Value of x */
} __attribute__((packed));

static void bytewise_xor(void *_bo, const void *_bi1, const void *_bi2,
             size_t size)
{
    u8 *bo = _bo;
    const u8 *bi1 = _bi1, *bi2 = _bi2;
    size_t itr;
    for (itr = 0; itr < size; itr++)
        bo[itr] = bi1[itr] ^ bi2[itr];
}

/*
 * CC-MAC function WUSB1.0[6.5]
 *
 * Take a data string and produce the encrypted CBC Counter-mode MIC
 *
 * Note the names for most function arguments are made to (more or
 * less) match those used in the pseudo-function definition given in
 * WUSB1.0[6.5].
 *
 * @tfm_cbc: CBC(AES) blkcipher handle (initialized)
 *
 * @tfm_aes: AES cipher handle (initialized)
 *
 * @mic: buffer for placing the computed MIC (Message Integrity
 *       Code). This is exactly 8 bytes, and we expect the buffer to
 *       be at least eight bytes in length.
 *
 * @key: 128 bit symmetric key
 *
 * @n: CCM nonce
 *
 * @a: ASCII string, 14 bytes long (I guess zero padded if needed;
 *     we use exactly 14 bytes).
 *
 * @b: data stream to be processed; cannot be a global or const local
 *     (will confuse the scatterlists)
 *
 * @blen: size of b...
 *
 * Still not very clear how this is done, but looks like this: we
 * create block B0 (as WUSB1.0[6.5] says), then we AES-crypt it with
 * @key. We bytewise xor B0 with B1 (1) and AES-crypt that. Then we
 * take the payload and divide it in blocks (16 bytes), xor them with
 * the previous crypto result (16 bytes) and crypt it, repeat the next
 * block with the output of the previous one, rinse wash (I guess this
 * is what AES CBC mode means...but I truly have no idea). So we use
 * the CBC(AES) blkcipher, that does precisely that. The IV (Initial
 * Vector) is 16 bytes and is set to zero, so
 *
 * See rfc3610. Linux crypto has a CBC implementation, but the
 * documentation is scarce, to say the least, and the example code is
 * so intricated that is difficult to understand how things work. Most
 * of this is guess work -- bite me.
 *
 * (1) Created as 6.5 says, again, using as l(a) 'Blen + 14', and
 *     using the 14 bytes of @a to fill up
 *     b1.{mac_header,e0,security_reserved,padding}.
 *
 * NOTE: The definition of l(a) in WUSB1.0[6.5] vs the definition of
 *       l(m) is orthogonal, they bear no relationship, so it is not
 *       in conflict with the parameter's relation that
 *       WUSB1.0[6.4.2]) defines.
 *
 * NOTE: WUSB1.0[A.1]: Host Nonce is missing a nibble? (1e); fixed in
 *       first errata released on 2005/07.
 *
 * NOTE: we need to clean IV to zero at each invocation to make sure
 *       we start with a fresh empty Initial Vector, so that the CBC
 *       works ok.
 *
 * NOTE: blen is not aligned to a block size, we'll pad zeros, that's
 *       what sg[4] is for. Maybe there is a smarter way to do this.
 */
static int wusb_ccm_mac(struct crypto_blkcipher *tfm_cbc,
            struct crypto_cipher *tfm_aes, void *mic,
            const struct aes_ccm_nonce *n,
            const struct aes_ccm_label *a, const void *b,
            size_t blen)
{
    int result = 0;
    struct blkcipher_desc desc;
    struct aes_ccm_b0 b0;
    struct aes_ccm_b1 b1;
    struct aes_ccm_a ax;
    struct scatterlist sg[4], sg_dst;
    void *iv, *dst_buf;
    size_t ivsize, dst_size;
    const u8 bzero[16] = { 0 };
    size_t zero_padding;

    /*
     * These checks should be compile time optimized out
     * ensure @a fills b1's mac_header and following fields
     */
    WARN_ON(sizeof(*a) != sizeof(b1) - sizeof(b1.la));
    WARN_ON(sizeof(b0) != sizeof(struct aes_ccm_block));
    WARN_ON(sizeof(b1) != sizeof(struct aes_ccm_block));
    WARN_ON(sizeof(ax) != sizeof(struct aes_ccm_block));

    result = -ENOMEM;
    zero_padding = sizeof(struct aes_ccm_block)
        - blen % sizeof(struct aes_ccm_block);
    zero_padding = blen % sizeof(struct aes_ccm_block);
    if (zero_padding)
        zero_padding = sizeof(struct aes_ccm_block) - zero_padding;
    dst_size = blen + sizeof(b0) + sizeof(b1) + zero_padding;
    dst_buf = kzalloc(dst_size, GFP_KERNEL);
    if (dst_buf == NULL) {
        printk(KERN_ERR "E: can't alloc destination buffer\n");
        goto error_dst_buf;
    }

    iv = crypto_blkcipher_crt(tfm_cbc)->iv;
    ivsize = crypto_blkcipher_ivsize(tfm_cbc);
    memset(iv, 0, ivsize);

    /* Setup B0 */
    b0.flags = 0x59;    /* Format B0 */
    b0.ccm_nonce = *n;
    b0.lm = cpu_to_be16(0); /* WUSB1.0[6.5] sez l(m) is 0 */

    /* Setup B1
     *
     * The WUSB spec is anything but clear! WUSB1.0[6.5]
     * says that to initialize B1 from A with 'l(a) = blen +
     * 14'--after clarification, it means to use A's contents
     * for MAC Header, EO, sec reserved and padding.
     */
    b1.la = cpu_to_be16(blen + 14);
    memcpy(&b1.mac_header, a, sizeof(*a));

    sg_init_table(sg, ARRAY_SIZE(sg));
    sg_set_buf(&sg[0], &b0, sizeof(b0));
    sg_set_buf(&sg[1], &b1, sizeof(b1));
    sg_set_buf(&sg[2], b, blen);
    /* 0 if well behaved :) */
    sg_set_buf(&sg[3], bzero, zero_padding);
    sg_init_one(&sg_dst, dst_buf, dst_size);

    desc.tfm = tfm_cbc;
    desc.flags = 0;
    result = crypto_blkcipher_encrypt(&desc, &sg_dst, sg, dst_size);
    if (result < 0) {
        printk(KERN_ERR "E: can't compute CBC-MAC tag (MIC): %d\n",
               result);
        goto error_cbc_crypt;
    }

    /* Now we crypt the MIC Tag (*iv) with Ax -- values per WUSB1.0[6.5]
     * The procedure is to AES crypt the A0 block and XOR the MIC
     * Tag against it; we only do the first 8 bytes and place it
     * directly in the destination buffer.
     *
     * POS Crypto API: size is assumed to be AES's block size.
     * Thanks for documenting it -- tip taken from airo.c
     */
    ax.flags = 0x01;        /* as per WUSB 1.0 spec */
    ax.ccm_nonce = *n;
    ax.counter = 0;
    crypto_cipher_encrypt_one(tfm_aes, (void *)&ax, (void *)&ax);
    bytewise_xor(mic, &ax, iv, 8);
    result = 8;
error_cbc_crypt:
    kfree(dst_buf);
error_dst_buf:
    return result;
}

/*
 * WUSB Pseudo Random Function (WUSB1.0[6.5])
 *
 * @b: buffer to the source data; cannot be a global or const local
 *     (will confuse the scatterlists)
 */
ssize_t wusb_prf(void *out, size_t out_size,
         const u8 key[16], const struct aes_ccm_nonce *_n,
         const struct aes_ccm_label *a,
         const void *b, size_t blen, size_t len)
{
    ssize_t result, bytes = 0, bitr;
    struct aes_ccm_nonce n = *_n;
    struct crypto_blkcipher *tfm_cbc;
    struct crypto_cipher *tfm_aes;
    u64 sfn = 0;
    __le64 sfn_le;

    tfm_cbc = crypto_alloc_blkcipher("cbc(aes)", 0, CRYPTO_ALG_ASYNC);
    if (IS_ERR(tfm_cbc)) {
        result = PTR_ERR(tfm_cbc);
        printk(KERN_ERR "E: can't load CBC(AES): %d\n", (int)result);
        goto error_alloc_cbc;
    }
    result = crypto_blkcipher_setkey(tfm_cbc, key, 16);
    if (result < 0) {
        printk(KERN_ERR "E: can't set CBC key: %d\n", (int)result);
        goto error_setkey_cbc;
    }

    tfm_aes = crypto_alloc_cipher("aes", 0, CRYPTO_ALG_ASYNC);
    if (IS_ERR(tfm_aes)) {
        result = PTR_ERR(tfm_aes);
        printk(KERN_ERR "E: can't load AES: %d\n", (int)result);
        goto error_alloc_aes;
    }
    result = crypto_cipher_setkey(tfm_aes, key, 16);
    if (result < 0) {
        printk(KERN_ERR "E: can't set AES key: %d\n", (int)result);
        goto error_setkey_aes;
    }

    for (bitr = 0; bitr < (len + 63) / 64; bitr++) {
        sfn_le = cpu_to_le64(sfn++);
        memcpy(&n.sfn, &sfn_le, sizeof(n.sfn)); /* n.sfn++... */
        result = wusb_ccm_mac(tfm_cbc, tfm_aes, out + bytes,
                      &n, a, b, blen);
        if (result < 0)
            goto error_ccm_mac;
        bytes += result;
    }
    result = bytes;
error_ccm_mac:
error_setkey_aes:
    crypto_free_cipher(tfm_aes);
error_alloc_aes:
error_setkey_cbc:
    crypto_free_blkcipher(tfm_cbc);
error_alloc_cbc:
    return result;
}

/* WUSB1.0[A.2] test vectors */
static const u8 stv_hsmic_key[16] = {
    0x4b, 0x79, 0xa3, 0xcf, 0xe5, 0x53, 0x23, 0x9d,
    0xd7, 0xc1, 0x6d, 0x1c, 0x2d, 0xab, 0x6d, 0x3f
};

static const struct aes_ccm_nonce stv_hsmic_n = {
    .sfn = { 0 },
    .tkid = { 0x76, 0x98, 0x01,  },
    .dest_addr = { .data = { 0xbe, 0x00 } },
        .src_addr = { .data = { 0x76, 0x98 } },
};

/*
 * Out-of-band MIC Generation verification code
 *
 */
static int wusb_oob_mic_verify(void)
{
    int result;
    u8 mic[8];
    /* WUSB1.0[A.2] test vectors
     *
     * Need to keep it in the local stack as GCC 4.1.3something
     * messes up and generates noise.
     */
    struct usb_handshake stv_hsmic_hs = {
        .bMessageNumber = 2,
        .bStatus    = 00,
        .tTKID      = { 0x76, 0x98, 0x01 },
        .bReserved  = 00,
        .CDID       = { 0x30, 0x31, 0x32, 0x33, 0x34, 0x35,
                    0x36, 0x37, 0x38, 0x39, 0x3a, 0x3b,
                    0x3c, 0x3d, 0x3e, 0x3f },
        .nonce      = { 0x20, 0x21, 0x22, 0x23, 0x24, 0x25,
                    0x26, 0x27, 0x28, 0x29, 0x2a, 0x2b,
                    0x2c, 0x2d, 0x2e, 0x2f },
        .MIC        = { 0x75, 0x6a, 0x97, 0x51, 0x0c, 0x8c,
                    0x14, 0x7b } ,
    };
    size_t hs_size;

    result = wusb_oob_mic(mic, stv_hsmic_key, &stv_hsmic_n, &stv_hsmic_hs);
    if (result < 0)
        printk(KERN_ERR "E: WUSB OOB MIC test: failed: %d\n", result);
    else if (memcmp(stv_hsmic_hs.MIC, mic, sizeof(mic))) {
        printk(KERN_ERR "E: OOB MIC test: "
               "mismatch between MIC result and WUSB1.0[A2]\n");
        hs_size = sizeof(stv_hsmic_hs) - sizeof(stv_hsmic_hs.MIC);
        printk(KERN_ERR "E: Handshake2 in: (%zu bytes)\n", hs_size);
        wusb_key_dump(&stv_hsmic_hs, hs_size);
        printk(KERN_ERR "E: CCM Nonce in: (%zu bytes)\n",
               sizeof(stv_hsmic_n));
        wusb_key_dump(&stv_hsmic_n, sizeof(stv_hsmic_n));
        printk(KERN_ERR "E: MIC out:\n");
        wusb_key_dump(mic, sizeof(mic));
        printk(KERN_ERR "E: MIC out (from WUSB1.0[A.2]):\n");
        wusb_key_dump(stv_hsmic_hs.MIC, sizeof(stv_hsmic_hs.MIC));
        result = -EINVAL;
    } else
        result = 0;
    return result;
}

/*
 * Test vectors for Key derivation
 *
 * These come from WUSB1.0[6.5.1], the vectors in WUSB1.0[A.1]
 * (errata corrected in 2005/07).
 */
static const u8 stv_key_a1[16] __attribute__ ((__aligned__(4))) = {
    0xf0, 0xe1, 0xd2, 0xc3, 0xb4, 0xa5, 0x96, 0x87,
    0x78, 0x69, 0x5a, 0x4b, 0x3c, 0x2d, 0x1e, 0x0f
};

static const struct aes_ccm_nonce stv_keydvt_n_a1 = {
    .sfn = { 0 },
    .tkid = { 0x76, 0x98, 0x01,  },
    .dest_addr = { .data = { 0xbe, 0x00 } },
    .src_addr = { .data = { 0x76, 0x98 } },
};

static const struct wusb_keydvt_out stv_keydvt_out_a1 = {
    .kck = {
        0x4b, 0x79, 0xa3, 0xcf, 0xe5, 0x53, 0x23, 0x9d,
        0xd7, 0xc1, 0x6d, 0x1c, 0x2d, 0xab, 0x6d, 0x3f
    },
    .ptk = {
        0xc8, 0x70, 0x62, 0x82, 0xb6, 0x7c, 0xe9, 0x06,
        0x7b, 0xc5, 0x25, 0x69, 0xf2, 0x36, 0x61, 0x2d
    }
};

/*
 * Performa a test to make sure we match the vectors defined in
 * WUSB1.0[A.1](Errata2006/12)
 */
static int wusb_key_derive_verify(void)
{
    int result = 0;
    struct wusb_keydvt_out keydvt_out;
    /* These come from WUSB1.0[A.1] + 2006/12 errata
     * NOTE: can't make this const or global -- somehow it seems
     *       the scatterlists for crypto get confused and we get
     *       bad data. There is no doc on this... */
    struct wusb_keydvt_in stv_keydvt_in_a1 = {
        .hnonce = {
            0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17,
            0x18, 0x19, 0x1a, 0x1b, 0x1c, 0x1d, 0x1e, 0x1f
        },
        .dnonce = {
            0x20, 0x21, 0x22, 0x23, 0x24, 0x25, 0x26, 0x27,
            0x28, 0x29, 0x2a, 0x2b, 0x2c, 0x2d, 0x2e, 0x2f
        }
    };

    result = wusb_key_derive(&keydvt_out, stv_key_a1, &stv_keydvt_n_a1,
                 &stv_keydvt_in_a1);
    if (result < 0)
        printk(KERN_ERR "E: WUSB key derivation test: "
               "derivation failed: %d\n", result);
    if (memcmp(&stv_keydvt_out_a1, &keydvt_out, sizeof(keydvt_out))) {
        printk(KERN_ERR "E: WUSB key derivation test: "
               "mismatch between key derivation result "
               "and WUSB1.0[A1] Errata 2006/12\n");
        printk(KERN_ERR "E: keydvt in: key\n");
        wusb_key_dump(stv_key_a1, sizeof(stv_key_a1));
        printk(KERN_ERR "E: keydvt in: nonce\n");
        wusb_key_dump( &stv_keydvt_n_a1, sizeof(stv_keydvt_n_a1));
        printk(KERN_ERR "E: keydvt in: hnonce & dnonce\n");
        wusb_key_dump(&stv_keydvt_in_a1, sizeof(stv_keydvt_in_a1));
        printk(KERN_ERR "E: keydvt out: KCK\n");
        wusb_key_dump(&keydvt_out.kck, sizeof(keydvt_out.kck));
        printk(KERN_ERR "E: keydvt out: PTK\n");
        wusb_key_dump(&keydvt_out.ptk, sizeof(keydvt_out.ptk));
        result = -EINVAL;
    } else
        result = 0;
    return result;
}

/*
 * Initialize crypto system
 *
 * FIXME: we do nothing now, other than verifying. Later on we'll
 * cache the encryption stuff, so that's why we have a separate init.
 */
int wusb_crypto_init(void)
{
    int result;

    if (debug_crypto_verify) {
        result = wusb_key_derive_verify();
        if (result < 0)
            return result;
        return wusb_oob_mic_verify();
    }
    return 0;
}

void wusb_crypto_exit(void)
{
    /* FIXME: free cached crypto transforms */
}