drivers/usb/wusbcore/crypto.c

   1 /*
   2  * Ultra Wide Band
   3  * AES-128 CCM Encryption
   4  *
   5  * Copyright (C) 2007 Intel Corporation
   6  * Inaky Perez-Gonzalez <inaky.perez-gonzalez@intel.com>
   7  *
   8  * This program is free software; you can redistribute it and/or
   9  * modify it under the terms of the GNU General Public License version
  10  * 2 as published by the Free Software Foundation.
  11  *
  12  * This program is distributed in the hope that it will be useful,
  13  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  14  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15  * GNU General Public License for more details.
  16  *
  17  * You should have received a copy of the GNU General Public License
  18  * along with this program; if not, write to the Free Software
  19  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
  20  * 02110-1301, USA.
  21  *
  22  *
  23  * We don't do any encryption here; we use the Linux Kernel's AES-128
  24  * crypto modules to construct keys and payload blocks in a way
  25  * defined by WUSB1.0[6]. Check the erratas, as typos are are patched
  26  * there.
  27  *
  28  * Thanks a zillion to John Keys for his help and clarifications over
  29  * the designed-by-a-committee text.
  30  *
  31  * So the idea is that there is this basic Pseudo-Random-Function
  32  * defined in WUSB1.0[6.5] which is the core of everything. It works
  33  * by tweaking some blocks, AES crypting them and then xoring
  34  * something else with them (this seems to be called CBC(AES) -- can
  35  * you tell I know jack about crypto?). So we just funnel it into the
  36  * Linux Crypto API.
  37  *
  38  * We leave a crypto test module so we can verify that vectors match,
  39  * every now and then.
  40  *
  41  * Block size: 16 bytes -- AES seems to do things in 'block sizes'. I
  42  *             am learning a lot...
  43  *
  44  *             Conveniently, some data structures that need to be
  45  *             funneled through AES are...16 bytes in size!
  46  */
  47
  48 #include <linux/crypto.h>
  49 #include <linux/module.h>
  50 #include <linux/err.h>
  51 #include <linux/uwb.h>
  52 #include <linux/slab.h>
  53 #include <linux/usb/wusb.h>
  54 #include <linux/scatterlist.h>
  55
  56 static int debug_crypto_verify = 0;
  57
  58 module_param(debug_crypto_verify, int, 0);
  59 MODULE_PARM_DESC(debug_crypto_verify, "verify the key generation algorithms");
  60
  61 static void wusb_key_dump(const void *buf, size_t len)
  62 {
  63         print_hex_dump(KERN_ERR, "  ", DUMP_PREFIX_OFFSET, 16, 1,
  64                        buf, len, 0);
  65 }
  66
  67 /*
  68  * Block of data, as understood by AES-CCM
  69  *
  70  * The code assumes this structure is nothing but a 16 byte array
  71  * (packed in a struct to avoid common mess ups that I usually do with
  72  * arrays and enforcing type checking).
  73  */
  74 struct aes_ccm_block {
  75         u8 data[16];
  76 } __attribute__((packed));
  77
  78 /*
  79  * Counter-mode Blocks (WUSB1.0[6.4])
  80  *
  81  * According to CCM (or so it seems), for the purpose of calculating
  82  * the MIC, the message is broken in N counter-mode blocks, B0, B1,
  83  * ... BN.
  84  *
  85  * B0 contains flags, the CCM nonce and l(m).
  86  *
  87  * B1 contains l(a), the MAC header, the encryption offset and padding.
  88  *
  89  * If EO is nonzero, additional blocks are built from payload bytes
  90  * until EO is exhausted (FIXME: padding to 16 bytes, I guess). The
  91  * padding is not xmitted.
  92  */
  93
  94 /* WUSB1.0[T6.4] */
  95 struct aes_ccm_b0 {
  96         u8 flags;       /* 0x59, per CCM spec */
  97         struct aes_ccm_nonce ccm_nonce;
  98         __be16 lm;
  99 } __attribute__((packed));
 100
 101 /* WUSB1.0[T6.5] */
 102 struct aes_ccm_b1 {
 103         __be16 la;
 104         u8 mac_header[10];
 105         __le16 eo;
 106         u8 security_reserved;   /* This is always zero */
 107         u8 padding;             /* 0 */
 108 } __attribute__((packed));
 109
 110 /*
 111  * Encryption Blocks (WUSB1.0[6.4.4])
 112  *
 113  * CCM uses Ax blocks to generate a keystream with which the MIC and
 114  * the message's payload are encoded. A0 always encrypts/decrypts the
 115  * MIC. Ax (x>0) are used for the successive payload blocks.
 116  *
 117  * The x is the counter, and is increased for each block.
 118  */
 119 struct aes_ccm_a {
 120         u8 flags;       /* 0x01, per CCM spec */
 121         struct aes_ccm_nonce ccm_nonce;
 122         __be16 counter; /* Value of x */
 123 } __attribute__((packed));
 124
 125 static void bytewise_xor(void *_bo, const void *_bi1, const void *_bi2,
 126                          size_t size)
 127 {
 128         u8 *bo = _bo;
 129         const u8 *bi1 = _bi1, *bi2 = _bi2;
 130         size_t itr;
 131         for (itr = 0; itr < size; itr++)
 132                 bo[itr] = bi1[itr] ^ bi2[itr];
 133 }
 134
 135 /*
 136  * CC-MAC function WUSB1.0[6.5]
 137  *
 138  * Take a data string and produce the encrypted CBC Counter-mode MIC
 139  *
 140  * Note the names for most function arguments are made to (more or
 141  * less) match those used in the pseudo-function definition given in
 142  * WUSB1.0[6.5].
 143  *
 144  * @tfm_cbc: CBC(AES) blkcipher handle (initialized)
 145  *
 146  * @tfm_aes: AES cipher handle (initialized)
 147  *
 148  * @mic: buffer for placing the computed MIC (Message Integrity
 149  *       Code). This is exactly 8 bytes, and we expect the buffer to
 150  *       be at least eight bytes in length.
 151  *
 152  * @key: 128 bit symmetric key
 153  *
 154  * @n: CCM nonce
 155  *
 156  * @a: ASCII string, 14 bytes long (I guess zero padded if needed;
 157  *     we use exactly 14 bytes).
 158  *
 159  * @b: data stream to be processed; cannot be a global or const local
 160  *     (will confuse the scatterlists)
 161  *
 162  * @blen: size of b...
 163  *
 164  * Still not very clear how this is done, but looks like this: we
 165  * create block B0 (as WUSB1.0[6.5] says), then we AES-crypt it with
 166  * @key. We bytewise xor B0 with B1 (1) and AES-crypt that. Then we
 167  * take the payload and divide it in blocks (16 bytes), xor them with
 168  * the previous crypto result (16 bytes) and crypt it, repeat the next
 169  * block with the output of the previous one, rinse wash (I guess this
 170  * is what AES CBC mode means...but I truly have no idea). So we use
 171  * the CBC(AES) blkcipher, that does precisely that. The IV (Initial
 172  * Vector) is 16 bytes and is set to zero, so
 173  *
 174  * See rfc3610. Linux crypto has a CBC implementation, but the
 175  * documentation is scarce, to say the least, and the example code is
 176  * so intricated that is difficult to understand how things work. Most
 177  * of this is guess work -- bite me.
 178  *
 179  * (1) Created as 6.5 says, again, using as l(a) 'Blen + 14', and
 180  *     using the 14 bytes of @a to fill up
 181  *     b1.{mac_header,e0,security_reserved,padding}.
 182  *
 183  * NOTE: The definition of l(a) in WUSB1.0[6.5] vs the definition of
 184  *       l(m) is orthogonal, they bear no relationship, so it is not
 185  *       in conflict with the parameter's relation that
 186  *       WUSB1.0[6.4.2]) defines.
 187  *
 188  * NOTE: WUSB1.0[A.1]: Host Nonce is missing a nibble? (1e); fixed in
 189  *       first errata released on 2005/07.
 190  *
 191  * NOTE: we need to clean IV to zero at each invocation to make sure
 192  *       we start with a fresh empty Initial Vector, so that the CBC
 193  *       works ok.
 194  *
 195  * NOTE: blen is not aligned to a block size, we'll pad zeros, that's
 196  *       what sg[4] is for. Maybe there is a smarter way to do this.
 197  */
 198 static int wusb_ccm_mac(struct crypto_blkcipher *tfm_cbc,
 199                         struct crypto_cipher *tfm_aes, void *mic,
 200                         const struct aes_ccm_nonce *n,
 201                         const struct aes_ccm_label *a, const void *b,
 202                         size_t blen)
 203 {
 204         int result = 0;
 205         struct blkcipher_desc desc;
 206         struct aes_ccm_b0 b0;
 207         struct aes_ccm_b1 b1;
 208         struct aes_ccm_a ax;
 209         struct scatterlist sg[4], sg_dst;
 210         void *iv, *dst_buf;
 211         size_t ivsize, dst_size;
 212         const u8 bzero[16] = { 0 };
 213         size_t zero_padding;
 214
 215         /*
 216          * These checks should be compile time optimized out
 217          * ensure @a fills b1's mac_header and following fields
 218          */
 219         WARN_ON(sizeof(*a) != sizeof(b1) - sizeof(b1.la));
 220         WARN_ON(sizeof(b0) != sizeof(struct aes_ccm_block));
 221         WARN_ON(sizeof(b1) != sizeof(struct aes_ccm_block));
 222         WARN_ON(sizeof(ax) != sizeof(struct aes_ccm_block));
 223
 224         result = -ENOMEM;
 225         zero_padding = blen % sizeof(struct aes_ccm_block);
 226         if (zero_padding)
 227                 zero_padding = sizeof(struct aes_ccm_block) - zero_padding;
 228         dst_size = blen + sizeof(b0) + sizeof(b1) + zero_padding;
 229         dst_buf = kzalloc(dst_size, GFP_KERNEL);
 230         if (dst_buf == NULL) {
 231                 printk(KERN_ERR "E: can't alloc destination buffer\n");
 232                 goto error_dst_buf;
 233         }
 234
 235         iv = crypto_blkcipher_crt(tfm_cbc)->iv;
 236         ivsize = crypto_blkcipher_ivsize(tfm_cbc);
 237         memset(iv, 0, ivsize);
 238
 239         /* Setup B0 */
 240         b0.flags = 0x59;        /* Format B0 */
 241         b0.ccm_nonce = *n;
 242         b0.lm = cpu_to_be16(0); /* WUSB1.0[6.5] sez l(m) is 0 */
 243
 244         /* Setup B1
 245          *
 246          * The WUSB spec is anything but clear! WUSB1.0[6.5]
 247          * says that to initialize B1 from A with 'l(a) = blen +
 248          * 14'--after clarification, it means to use A's contents
 249          * for MAC Header, EO, sec reserved and padding.
 250          */
 251         b1.la = cpu_to_be16(blen + 14);
 252         memcpy(&b1.mac_header, a, sizeof(*a));
 253
 254         sg_init_table(sg, ARRAY_SIZE(sg));
 255         sg_set_buf(&sg[0], &b0, sizeof(b0));
 256         sg_set_buf(&sg[1], &b1, sizeof(b1));
 257         sg_set_buf(&sg[2], b, blen);
 258         /* 0 if well behaved :) */
 259         sg_set_buf(&sg[3], bzero, zero_padding);
 260         sg_init_one(&sg_dst, dst_buf, dst_size);
 261
 262         desc.tfm = tfm_cbc;
 263         desc.flags = 0;
 264         result = crypto_blkcipher_encrypt(&desc, &sg_dst, sg, dst_size);
 265         if (result < 0) {
 266                 printk(KERN_ERR "E: can't compute CBC-MAC tag (MIC): %d\n",
 267                        result);
 268                 goto error_cbc_crypt;
 269         }
 270
 271         /* Now we crypt the MIC Tag (*iv) with Ax -- values per WUSB1.0[6.5]
 272          * The procedure is to AES crypt the A0 block and XOR the MIC
 273          * Tag against it; we only do the first 8 bytes and place it
 274          * directly in the destination buffer.
 275          *
 276          * POS Crypto API: size is assumed to be AES's block size.
 277          * Thanks for documenting it -- tip taken from airo.c
 278          */
 279         ax.flags = 0x01;                /* as per WUSB 1.0 spec */
 280         ax.ccm_nonce = *n;
 281         ax.counter = 0;
 282         crypto_cipher_encrypt_one(tfm_aes, (void *)&ax, (void *)&ax);
 283         bytewise_xor(mic, &ax, iv, 8);
 284         result = 8;
 285 error_cbc_crypt:
 286         kfree(dst_buf);
 287 error_dst_buf:
 288         return result;
 289 }
 290
 291 /*
 292  * WUSB Pseudo Random Function (WUSB1.0[6.5])
 293  *
 294  * @b: buffer to the source data; cannot be a global or const local
 295  *     (will confuse the scatterlists)
 296  */
 297 ssize_t wusb_prf(void *out, size_t out_size,
 298                  const u8 key[16], const struct aes_ccm_nonce *_n,
 299                  const struct aes_ccm_label *a,
 300                  const void *b, size_t blen, size_t len)
 301 {
 302         ssize_t result, bytes = 0, bitr;
 303         struct aes_ccm_nonce n = *_n;
 304         struct crypto_blkcipher *tfm_cbc;
 305         struct crypto_cipher *tfm_aes;
 306         u64 sfn = 0;
 307         __le64 sfn_le;
 308
 309         tfm_cbc = crypto_alloc_blkcipher("cbc(aes)", 0, CRYPTO_ALG_ASYNC);
 310         if (IS_ERR(tfm_cbc)) {
 311                 result = PTR_ERR(tfm_cbc);
 312                 printk(KERN_ERR "E: can't load CBC(AES): %d\n", (int)result);
 313                 goto error_alloc_cbc;
 314         }
 315         result = crypto_blkcipher_setkey(tfm_cbc, key, 16);
 316         if (result < 0) {
 317                 printk(KERN_ERR "E: can't set CBC key: %d\n", (int)result);
 318                 goto error_setkey_cbc;
 319         }
 320
 321         tfm_aes = crypto_alloc_cipher("aes", 0, CRYPTO_ALG_ASYNC);
 322         if (IS_ERR(tfm_aes)) {
 323                 result = PTR_ERR(tfm_aes);
 324                 printk(KERN_ERR "E: can't load AES: %d\n", (int)result);
 325                 goto error_alloc_aes;
 326         }
 327         result = crypto_cipher_setkey(tfm_aes, key, 16);
 328         if (result < 0) {
 329                 printk(KERN_ERR "E: can't set AES key: %d\n", (int)result);
 330                 goto error_setkey_aes;
 331         }
 332
 333         for (bitr = 0; bitr < (len + 63) / 64; bitr++) {
 334                 sfn_le = cpu_to_le64(sfn++);
 335                 memcpy(&n.sfn, &sfn_le, sizeof(n.sfn)); /* n.sfn++... */
 336                 result = wusb_ccm_mac(tfm_cbc, tfm_aes, out + bytes,
 337                                       &n, a, b, blen);
 338                 if (result < 0)
 339                         goto error_ccm_mac;
 340                 bytes += result;
 341         }
 342         result = bytes;
 343 error_ccm_mac:
 344 error_setkey_aes:
 345         crypto_free_cipher(tfm_aes);
 346 error_alloc_aes:
 347 error_setkey_cbc:
 348         crypto_free_blkcipher(tfm_cbc);
 349 error_alloc_cbc:
 350         return result;
 351 }
 352
 353 /* WUSB1.0[A.2] test vectors */
 354 static const u8 stv_hsmic_key[16] = {
 355         0x4b, 0x79, 0xa3, 0xcf, 0xe5, 0x53, 0x23, 0x9d,
 356         0xd7, 0xc1, 0x6d, 0x1c, 0x2d, 0xab, 0x6d, 0x3f
 357 };
 358
 359 static const struct aes_ccm_nonce stv_hsmic_n = {
 360         .sfn = { 0 },
 361         .tkid = { 0x76, 0x98, 0x01,  },
 362         .dest_addr = { .data = { 0xbe, 0x00 } },
 363                 .src_addr = { .data = { 0x76, 0x98 } },
 364 };
 365
 366 /*
 367  * Out-of-band MIC Generation verification code
 368  *
 369  */
 370 static int wusb_oob_mic_verify(void)
 371 {
 372         int result;
 373         u8 mic[8];
 374         /* WUSB1.0[A.2] test vectors
 375          *
 376          * Need to keep it in the local stack as GCC 4.1.3something
 377          * messes up and generates noise.
 378          */
 379         struct usb_handshake stv_hsmic_hs = {
 380                 .bMessageNumber = 2,
 381                 .bStatus        = 00,
 382                 .tTKID          = { 0x76, 0x98, 0x01 },
 383                 .bReserved      = 00,
 384                 .CDID           = { 0x30, 0x31, 0x32, 0x33, 0x34, 0x35,
 385                                     0x36, 0x37, 0x38, 0x39, 0x3a, 0x3b,
 386                                     0x3c, 0x3d, 0x3e, 0x3f },
 387                 .nonce          = { 0x20, 0x21, 0x22, 0x23, 0x24, 0x25,
 388                                     0x26, 0x27, 0x28, 0x29, 0x2a, 0x2b,
 389                                     0x2c, 0x2d, 0x2e, 0x2f },
 390                 .MIC            = { 0x75, 0x6a, 0x97, 0x51, 0x0c, 0x8c,
 391                                     0x14, 0x7b } ,
 392         };
 393         size_t hs_size;
 394
 395         result = wusb_oob_mic(mic, stv_hsmic_key, &stv_hsmic_n, &stv_hsmic_hs);
 396         if (result < 0)
 397                 printk(KERN_ERR "E: WUSB OOB MIC test: failed: %d\n", result);
 398         else if (memcmp(stv_hsmic_hs.MIC, mic, sizeof(mic))) {
 399                 printk(KERN_ERR "E: OOB MIC test: "
 400                        "mismatch between MIC result and WUSB1.0[A2]\n");
 401                 hs_size = sizeof(stv_hsmic_hs) - sizeof(stv_hsmic_hs.MIC);
 402                 printk(KERN_ERR "E: Handshake2 in: (%zu bytes)\n", hs_size);
 403                 wusb_key_dump(&stv_hsmic_hs, hs_size);
 404                 printk(KERN_ERR "E: CCM Nonce in: (%zu bytes)\n",
 405                        sizeof(stv_hsmic_n));
 406                 wusb_key_dump(&stv_hsmic_n, sizeof(stv_hsmic_n));
 407                 printk(KERN_ERR "E: MIC out:\n");
 408                 wusb_key_dump(mic, sizeof(mic));
 409                 printk(KERN_ERR "E: MIC out (from WUSB1.0[A.2]):\n");
 410                 wusb_key_dump(stv_hsmic_hs.MIC, sizeof(stv_hsmic_hs.MIC));
 411                 result = -EINVAL;
 412         } else
 413                 result = 0;
 414         return result;
 415 }
 416
 417 /*
 418  * Test vectors for Key derivation
 419  *
 420  * These come from WUSB1.0[6.5.1], the vectors in WUSB1.0[A.1]
 421  * (errata corrected in 2005/07).
 422  */
 423 static const u8 stv_key_a1[16] __attribute__ ((__aligned__(4))) = {
 424         0xf0, 0xe1, 0xd2, 0xc3, 0xb4, 0xa5, 0x96, 0x87,
 425         0x78, 0x69, 0x5a, 0x4b, 0x3c, 0x2d, 0x1e, 0x0f
 426 };
 427
 428 static const struct aes_ccm_nonce stv_keydvt_n_a1 = {
 429         .sfn = { 0 },
 430         .tkid = { 0x76, 0x98, 0x01,  },
 431         .dest_addr = { .data = { 0xbe, 0x00 } },
 432         .src_addr = { .data = { 0x76, 0x98 } },
 433 };
 434
 435 static const struct wusb_keydvt_out stv_keydvt_out_a1 = {
 436         .kck = {
 437                 0x4b, 0x79, 0xa3, 0xcf, 0xe5, 0x53, 0x23, 0x9d,
 438                 0xd7, 0xc1, 0x6d, 0x1c, 0x2d, 0xab, 0x6d, 0x3f
 439         },
 440         .ptk = {
 441                 0xc8, 0x70, 0x62, 0x82, 0xb6, 0x7c, 0xe9, 0x06,
 442                 0x7b, 0xc5, 0x25, 0x69, 0xf2, 0x36, 0x61, 0x2d
 443         }
 444 };
 445
 446 /*
 447  * Performa a test to make sure we match the vectors defined in
 448  * WUSB1.0[A.1](Errata2006/12)
 449  */
 450 static int wusb_key_derive_verify(void)
 451 {
 452         int result = 0;
 453         struct wusb_keydvt_out keydvt_out;
 454         /* These come from WUSB1.0[A.1] + 2006/12 errata
 455          * NOTE: can't make this const or global -- somehow it seems
 456          *       the scatterlists for crypto get confused and we get
 457          *       bad data. There is no doc on this... */
 458         struct wusb_keydvt_in stv_keydvt_in_a1 = {
 459                 .hnonce = {
 460                         0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17,
 461                         0x18, 0x19, 0x1a, 0x1b, 0x1c, 0x1d, 0x1e, 0x1f
 462                 },
 463                 .dnonce = {
 464                         0x20, 0x21, 0x22, 0x23, 0x24, 0x25, 0x26, 0x27,
 465                         0x28, 0x29, 0x2a, 0x2b, 0x2c, 0x2d, 0x2e, 0x2f
 466                 }
 467         };
 468
 469         result = wusb_key_derive(&keydvt_out, stv_key_a1, &stv_keydvt_n_a1,
 470                                  &stv_keydvt_in_a1);
 471         if (result < 0)
 472                 printk(KERN_ERR "E: WUSB key derivation test: "
 473                        "derivation failed: %d\n", result);
 474         if (memcmp(&stv_keydvt_out_a1, &keydvt_out, sizeof(keydvt_out))) {
 475                 printk(KERN_ERR "E: WUSB key derivation test: "
 476                        "mismatch between key derivation result "
 477                        "and WUSB1.0[A1] Errata 2006/12\n");
 478                 printk(KERN_ERR "E: keydvt in: key\n");
 479                 wusb_key_dump(stv_key_a1, sizeof(stv_key_a1));
 480                 printk(KERN_ERR "E: keydvt in: nonce\n");
 481                 wusb_key_dump( &stv_keydvt_n_a1, sizeof(stv_keydvt_n_a1));
 482                 printk(KERN_ERR "E: keydvt in: hnonce & dnonce\n");
 483                 wusb_key_dump(&stv_keydvt_in_a1, sizeof(stv_keydvt_in_a1));
 484                 printk(KERN_ERR "E: keydvt out: KCK\n");
 485                 wusb_key_dump(&keydvt_out.kck, sizeof(keydvt_out.kck));
 486                 printk(KERN_ERR "E: keydvt out: PTK\n");
 487                 wusb_key_dump(&keydvt_out.ptk, sizeof(keydvt_out.ptk));
 488                 result = -EINVAL;
 489         } else
 490                 result = 0;
 491         return result;
 492 }
 493
 494 /*
 495  * Initialize crypto system
 496  *
 497  * FIXME: we do nothing now, other than verifying. Later on we'll
 498  * cache the encryption stuff, so that's why we have a separate init.
 499  */
 500 int wusb_crypto_init(void)
 501 {
 502         int result;
 503
 504         if (debug_crypto_verify) {
 505                 result = wusb_key_derive_verify();
 506                 if (result < 0)
 507                         return result;
 508                 return wusb_oob_mic_verify();
 509         }
 510         return 0;
 511 }
 512
 513 void wusb_crypto_exit(void)
 514 {
 515         /* FIXME: free cached crypto transforms */
 516 }