drivers/usb/wusbcore/crypto.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * Ultra Wide Band
   4  * AES-128 CCM Encryption
   5  *
   6  * Copyright (C) 2007 Intel Corporation
   7  * Inaky Perez-Gonzalez <inaky.perez-gonzalez@intel.com>
   8  *
   9  * We don't do any encryption here; we use the Linux Kernel's AES-128
  10  * crypto modules to construct keys and payload blocks in a way
  11  * defined by WUSB1.0[6]. Check the erratas, as typos are are patched
  12  * there.
  13  *
  14  * Thanks a zillion to John Keys for his help and clarifications over
  15  * the designed-by-a-committee text.
  16  *
  17  * So the idea is that there is this basic Pseudo-Random-Function
  18  * defined in WUSB1.0[6.5] which is the core of everything. It works
  19  * by tweaking some blocks, AES crypting them and then xoring
  20  * something else with them (this seems to be called CBC(AES) -- can
  21  * you tell I know jack about crypto?). So we just funnel it into the
  22  * Linux Crypto API.
  23  *
  24  * We leave a crypto test module so we can verify that vectors match,
  25  * every now and then.
  26  *
  27  * Block size: 16 bytes -- AES seems to do things in 'block sizes'. I
  28  *             am learning a lot...
  29  *
  30  *             Conveniently, some data structures that need to be
  31  *             funneled through AES are...16 bytes in size!
  32  */
  33
  34 #include <crypto/skcipher.h>
  35 #include <linux/crypto.h>
  36 #include <linux/module.h>
  37 #include <linux/err.h>
  38 #include <linux/uwb.h>
  39 #include <linux/slab.h>
  40 #include <linux/usb/wusb.h>
  41 #include <linux/scatterlist.h>
  42
  43 static int debug_crypto_verify;
  44
  45 module_param(debug_crypto_verify, int, 0);
  46 MODULE_PARM_DESC(debug_crypto_verify, "verify the key generation algorithms");
  47
  48 static void wusb_key_dump(const void *buf, size_t len)
  49 {
  50         print_hex_dump(KERN_ERR, "  ", DUMP_PREFIX_OFFSET, 16, 1,
  51                        buf, len, 0);
  52 }
  53
  54 /*
  55  * Block of data, as understood by AES-CCM
  56  *
  57  * The code assumes this structure is nothing but a 16 byte array
  58  * (packed in a struct to avoid common mess ups that I usually do with
  59  * arrays and enforcing type checking).
  60  */
  61 struct aes_ccm_block {
  62         u8 data[16];
  63 } __attribute__((packed));
  64
  65 /*
  66  * Counter-mode Blocks (WUSB1.0[6.4])
  67  *
  68  * According to CCM (or so it seems), for the purpose of calculating
  69  * the MIC, the message is broken in N counter-mode blocks, B0, B1,
  70  * ... BN.
  71  *
  72  * B0 contains flags, the CCM nonce and l(m).
  73  *
  74  * B1 contains l(a), the MAC header, the encryption offset and padding.
  75  *
  76  * If EO is nonzero, additional blocks are built from payload bytes
  77  * until EO is exhausted (FIXME: padding to 16 bytes, I guess). The
  78  * padding is not xmitted.
  79  */
  80
  81 /* WUSB1.0[T6.4] */
  82 struct aes_ccm_b0 {
  83         u8 flags;       /* 0x59, per CCM spec */
  84         struct aes_ccm_nonce ccm_nonce;
  85         __be16 lm;
  86 } __attribute__((packed));
  87
  88 /* WUSB1.0[T6.5] */
  89 struct aes_ccm_b1 {
  90         __be16 la;
  91         u8 mac_header[10];
  92         __le16 eo;
  93         u8 security_reserved;   /* This is always zero */
  94         u8 padding;             /* 0 */
  95 } __attribute__((packed));
  96
  97 /*
  98  * Encryption Blocks (WUSB1.0[6.4.4])
  99  *
 100  * CCM uses Ax blocks to generate a keystream with which the MIC and
 101  * the message's payload are encoded. A0 always encrypts/decrypts the
 102  * MIC. Ax (x>0) are used for the successive payload blocks.
 103  *
 104  * The x is the counter, and is increased for each block.
 105  */
 106 struct aes_ccm_a {
 107         u8 flags;       /* 0x01, per CCM spec */
 108         struct aes_ccm_nonce ccm_nonce;
 109         __be16 counter; /* Value of x */
 110 } __attribute__((packed));
 111
 112 static void bytewise_xor(void *_bo, const void *_bi1, const void *_bi2,
 113                          size_t size)
 114 {
 115         u8 *bo = _bo;
 116         const u8 *bi1 = _bi1, *bi2 = _bi2;
 117         size_t itr;
 118         for (itr = 0; itr < size; itr++)
 119                 bo[itr] = bi1[itr] ^ bi2[itr];
 120 }
 121
 122 /* Scratch space for MAC calculations. */
 123 struct wusb_mac_scratch {
 124         struct aes_ccm_b0 b0;
 125         struct aes_ccm_b1 b1;
 126         struct aes_ccm_a ax;
 127 };
 128
 129 /*
 130  * CC-MAC function WUSB1.0[6.5]
 131  *
 132  * Take a data string and produce the encrypted CBC Counter-mode MIC
 133  *
 134  * Note the names for most function arguments are made to (more or
 135  * less) match those used in the pseudo-function definition given in
 136  * WUSB1.0[6.5].
 137  *
 138  * @tfm_cbc: CBC(AES) blkcipher handle (initialized)
 139  *
 140  * @tfm_aes: AES cipher handle (initialized)
 141  *
 142  * @mic: buffer for placing the computed MIC (Message Integrity
 143  *       Code). This is exactly 8 bytes, and we expect the buffer to
 144  *       be at least eight bytes in length.
 145  *
 146  * @key: 128 bit symmetric key
 147  *
 148  * @n: CCM nonce
 149  *
 150  * @a: ASCII string, 14 bytes long (I guess zero padded if needed;
 151  *     we use exactly 14 bytes).
 152  *
 153  * @b: data stream to be processed; cannot be a global or const local
 154  *     (will confuse the scatterlists)
 155  *
 156  * @blen: size of b...
 157  *
 158  * Still not very clear how this is done, but looks like this: we
 159  * create block B0 (as WUSB1.0[6.5] says), then we AES-crypt it with
 160  * @key. We bytewise xor B0 with B1 (1) and AES-crypt that. Then we
 161  * take the payload and divide it in blocks (16 bytes), xor them with
 162  * the previous crypto result (16 bytes) and crypt it, repeat the next
 163  * block with the output of the previous one, rinse wash (I guess this
 164  * is what AES CBC mode means...but I truly have no idea). So we use
 165  * the CBC(AES) blkcipher, that does precisely that. The IV (Initial
 166  * Vector) is 16 bytes and is set to zero, so
 167  *
 168  * See rfc3610. Linux crypto has a CBC implementation, but the
 169  * documentation is scarce, to say the least, and the example code is
 170  * so intricated that is difficult to understand how things work. Most
 171  * of this is guess work -- bite me.
 172  *
 173  * (1) Created as 6.5 says, again, using as l(a) 'Blen + 14', and
 174  *     using the 14 bytes of @a to fill up
 175  *     b1.{mac_header,e0,security_reserved,padding}.
 176  *
 177  * NOTE: The definition of l(a) in WUSB1.0[6.5] vs the definition of
 178  *       l(m) is orthogonal, they bear no relationship, so it is not
 179  *       in conflict with the parameter's relation that
 180  *       WUSB1.0[6.4.2]) defines.
 181  *
 182  * NOTE: WUSB1.0[A.1]: Host Nonce is missing a nibble? (1e); fixed in
 183  *       first errata released on 2005/07.
 184  *
 185  * NOTE: we need to clean IV to zero at each invocation to make sure
 186  *       we start with a fresh empty Initial Vector, so that the CBC
 187  *       works ok.
 188  *
 189  * NOTE: blen is not aligned to a block size, we'll pad zeros, that's
 190  *       what sg[4] is for. Maybe there is a smarter way to do this.
 191  */
 192 static int wusb_ccm_mac(struct crypto_skcipher *tfm_cbc,
 193                         struct crypto_cipher *tfm_aes,
 194                         struct wusb_mac_scratch *scratch,
 195                         void *mic,
 196                         const struct aes_ccm_nonce *n,
 197                         const struct aes_ccm_label *a, const void *b,
 198                         size_t blen)
 199 {
 200         int result = 0;
 201         SKCIPHER_REQUEST_ON_STACK(req, tfm_cbc);
 202         struct scatterlist sg[4], sg_dst;
 203         void *dst_buf;
 204         size_t dst_size;
 205         u8 iv[crypto_skcipher_ivsize(tfm_cbc)];
 206         size_t zero_padding;
 207
 208         /*
 209          * These checks should be compile time optimized out
 210          * ensure @a fills b1's mac_header and following fields
 211          */
 212         WARN_ON(sizeof(*a) != sizeof(scratch->b1) - sizeof(scratch->b1.la));
 213         WARN_ON(sizeof(scratch->b0) != sizeof(struct aes_ccm_block));
 214         WARN_ON(sizeof(scratch->b1) != sizeof(struct aes_ccm_block));
 215         WARN_ON(sizeof(scratch->ax) != sizeof(struct aes_ccm_block));
 216
 217         result = -ENOMEM;
 218         zero_padding = blen % sizeof(struct aes_ccm_block);
 219         if (zero_padding)
 220                 zero_padding = sizeof(struct aes_ccm_block) - zero_padding;
 221         dst_size = blen + sizeof(scratch->b0) + sizeof(scratch->b1) +
 222                 zero_padding;
 223         dst_buf = kzalloc(dst_size, GFP_KERNEL);
 224         if (!dst_buf)
 225                 goto error_dst_buf;
 226
 227         memset(iv, 0, sizeof(iv));
 228
 229         /* Setup B0 */
 230         scratch->b0.flags = 0x59;       /* Format B0 */
 231         scratch->b0.ccm_nonce = *n;
 232         scratch->b0.lm = cpu_to_be16(0);        /* WUSB1.0[6.5] sez l(m) is 0 */
 233
 234         /* Setup B1
 235          *
 236          * The WUSB spec is anything but clear! WUSB1.0[6.5]
 237          * says that to initialize B1 from A with 'l(a) = blen +
 238          * 14'--after clarification, it means to use A's contents
 239          * for MAC Header, EO, sec reserved and padding.
 240          */
 241         scratch->b1.la = cpu_to_be16(blen + 14);
 242         memcpy(&scratch->b1.mac_header, a, sizeof(*a));
 243
 244         sg_init_table(sg, ARRAY_SIZE(sg));
 245         sg_set_buf(&sg[0], &scratch->b0, sizeof(scratch->b0));
 246         sg_set_buf(&sg[1], &scratch->b1, sizeof(scratch->b1));
 247         sg_set_buf(&sg[2], b, blen);
 248         /* 0 if well behaved :) */
 249         sg_set_page(&sg[3], ZERO_PAGE(0), zero_padding, 0);
 250         sg_init_one(&sg_dst, dst_buf, dst_size);
 251
 252         skcipher_request_set_tfm(req, tfm_cbc);
 253         skcipher_request_set_callback(req, 0, NULL, NULL);
 254         skcipher_request_set_crypt(req, sg, &sg_dst, dst_size, iv);
 255         result = crypto_skcipher_encrypt(req);
 256         skcipher_request_zero(req);
 257         if (result < 0) {
 258                 printk(KERN_ERR "E: can't compute CBC-MAC tag (MIC): %d\n",
 259                        result);
 260                 goto error_cbc_crypt;
 261         }
 262
 263         /* Now we crypt the MIC Tag (*iv) with Ax -- values per WUSB1.0[6.5]
 264          * The procedure is to AES crypt the A0 block and XOR the MIC
 265          * Tag against it; we only do the first 8 bytes and place it
 266          * directly in the destination buffer.
 267          *
 268          * POS Crypto API: size is assumed to be AES's block size.
 269          * Thanks for documenting it -- tip taken from airo.c
 270          */
 271         scratch->ax.flags = 0x01;               /* as per WUSB 1.0 spec */
 272         scratch->ax.ccm_nonce = *n;
 273         scratch->ax.counter = 0;
 274         crypto_cipher_encrypt_one(tfm_aes, (void *)&scratch->ax,
 275                                   (void *)&scratch->ax);
 276         bytewise_xor(mic, &scratch->ax, iv, 8);
 277         result = 8;
 278 error_cbc_crypt:
 279         kfree(dst_buf);
 280 error_dst_buf:
 281         return result;
 282 }
 283
 284 /*
 285  * WUSB Pseudo Random Function (WUSB1.0[6.5])
 286  *
 287  * @b: buffer to the source data; cannot be a global or const local
 288  *     (will confuse the scatterlists)
 289  */
 290 ssize_t wusb_prf(void *out, size_t out_size,
 291                  const u8 key[16], const struct aes_ccm_nonce *_n,
 292                  const struct aes_ccm_label *a,
 293                  const void *b, size_t blen, size_t len)
 294 {
 295         ssize_t result, bytes = 0, bitr;
 296         struct aes_ccm_nonce n = *_n;
 297         struct crypto_skcipher *tfm_cbc;
 298         struct crypto_cipher *tfm_aes;
 299         struct wusb_mac_scratch *scratch;
 300         u64 sfn = 0;
 301         __le64 sfn_le;
 302
 303         tfm_cbc = crypto_alloc_skcipher("cbc(aes)", 0, CRYPTO_ALG_ASYNC);
 304         if (IS_ERR(tfm_cbc)) {
 305                 result = PTR_ERR(tfm_cbc);
 306                 printk(KERN_ERR "E: can't load CBC(AES): %d\n", (int)result);
 307                 goto error_alloc_cbc;
 308         }
 309         result = crypto_skcipher_setkey(tfm_cbc, key, 16);
 310         if (result < 0) {
 311                 printk(KERN_ERR "E: can't set CBC key: %d\n", (int)result);
 312                 goto error_setkey_cbc;
 313         }
 314
 315         tfm_aes = crypto_alloc_cipher("aes", 0, CRYPTO_ALG_ASYNC);
 316         if (IS_ERR(tfm_aes)) {
 317                 result = PTR_ERR(tfm_aes);
 318                 printk(KERN_ERR "E: can't load AES: %d\n", (int)result);
 319                 goto error_alloc_aes;
 320         }
 321         result = crypto_cipher_setkey(tfm_aes, key, 16);
 322         if (result < 0) {
 323                 printk(KERN_ERR "E: can't set AES key: %d\n", (int)result);
 324                 goto error_setkey_aes;
 325         }
 326         scratch = kmalloc(sizeof(*scratch), GFP_KERNEL);
 327         if (!scratch) {
 328                 result = -ENOMEM;
 329                 goto error_alloc_scratch;
 330         }
 331
 332         for (bitr = 0; bitr < (len + 63) / 64; bitr++) {
 333                 sfn_le = cpu_to_le64(sfn++);
 334                 memcpy(&n.sfn, &sfn_le, sizeof(n.sfn)); /* n.sfn++... */
 335                 result = wusb_ccm_mac(tfm_cbc, tfm_aes, scratch, out + bytes,
 336                                       &n, a, b, blen);
 337                 if (result < 0)
 338                         goto error_ccm_mac;
 339                 bytes += result;
 340         }
 341         result = bytes;
 342
 343         kfree(scratch);
 344 error_alloc_scratch:
 345 error_ccm_mac:
 346 error_setkey_aes:
 347         crypto_free_cipher(tfm_aes);
 348 error_alloc_aes:
 349 error_setkey_cbc:
 350         crypto_free_skcipher(tfm_cbc);
 351 error_alloc_cbc:
 352         return result;
 353 }
 354
 355 /* WUSB1.0[A.2] test vectors */
 356 static const u8 stv_hsmic_key[16] = {
 357         0x4b, 0x79, 0xa3, 0xcf, 0xe5, 0x53, 0x23, 0x9d,
 358         0xd7, 0xc1, 0x6d, 0x1c, 0x2d, 0xab, 0x6d, 0x3f
 359 };
 360
 361 static const struct aes_ccm_nonce stv_hsmic_n = {
 362         .sfn = { 0 },
 363         .tkid = { 0x76, 0x98, 0x01,  },
 364         .dest_addr = { .data = { 0xbe, 0x00 } },
 365                 .src_addr = { .data = { 0x76, 0x98 } },
 366 };
 367
 368 /*
 369  * Out-of-band MIC Generation verification code
 370  *
 371  */
 372 static int wusb_oob_mic_verify(void)
 373 {
 374         int result;
 375         u8 mic[8];
 376         /* WUSB1.0[A.2] test vectors
 377          *
 378          * Need to keep it in the local stack as GCC 4.1.3something
 379          * messes up and generates noise.
 380          */
 381         struct usb_handshake stv_hsmic_hs = {
 382                 .bMessageNumber = 2,
 383                 .bStatus        = 00,
 384                 .tTKID          = { 0x76, 0x98, 0x01 },
 385                 .bReserved      = 00,
 386                 .CDID           = { 0x30, 0x31, 0x32, 0x33, 0x34, 0x35,
 387                                     0x36, 0x37, 0x38, 0x39, 0x3a, 0x3b,
 388                                     0x3c, 0x3d, 0x3e, 0x3f },
 389                 .nonce          = { 0x20, 0x21, 0x22, 0x23, 0x24, 0x25,
 390                                     0x26, 0x27, 0x28, 0x29, 0x2a, 0x2b,
 391                                     0x2c, 0x2d, 0x2e, 0x2f },
 392                 .MIC            = { 0x75, 0x6a, 0x97, 0x51, 0x0c, 0x8c,
 393                                     0x14, 0x7b },
 394         };
 395         size_t hs_size;
 396
 397         result = wusb_oob_mic(mic, stv_hsmic_key, &stv_hsmic_n, &stv_hsmic_hs);
 398         if (result < 0)
 399                 printk(KERN_ERR "E: WUSB OOB MIC test: failed: %d\n", result);
 400         else if (memcmp(stv_hsmic_hs.MIC, mic, sizeof(mic))) {
 401                 printk(KERN_ERR "E: OOB MIC test: "
 402                        "mismatch between MIC result and WUSB1.0[A2]\n");
 403                 hs_size = sizeof(stv_hsmic_hs) - sizeof(stv_hsmic_hs.MIC);
 404                 printk(KERN_ERR "E: Handshake2 in: (%zu bytes)\n", hs_size);
 405                 wusb_key_dump(&stv_hsmic_hs, hs_size);
 406                 printk(KERN_ERR "E: CCM Nonce in: (%zu bytes)\n",
 407                        sizeof(stv_hsmic_n));
 408                 wusb_key_dump(&stv_hsmic_n, sizeof(stv_hsmic_n));
 409                 printk(KERN_ERR "E: MIC out:\n");
 410                 wusb_key_dump(mic, sizeof(mic));
 411                 printk(KERN_ERR "E: MIC out (from WUSB1.0[A.2]):\n");
 412                 wusb_key_dump(stv_hsmic_hs.MIC, sizeof(stv_hsmic_hs.MIC));
 413                 result = -EINVAL;
 414         } else
 415                 result = 0;
 416         return result;
 417 }
 418
 419 /*
 420  * Test vectors for Key derivation
 421  *
 422  * These come from WUSB1.0[6.5.1], the vectors in WUSB1.0[A.1]
 423  * (errata corrected in 2005/07).
 424  */
 425 static const u8 stv_key_a1[16] __attribute__ ((__aligned__(4))) = {
 426         0xf0, 0xe1, 0xd2, 0xc3, 0xb4, 0xa5, 0x96, 0x87,
 427         0x78, 0x69, 0x5a, 0x4b, 0x3c, 0x2d, 0x1e, 0x0f
 428 };
 429
 430 static const struct aes_ccm_nonce stv_keydvt_n_a1 = {
 431         .sfn = { 0 },
 432         .tkid = { 0x76, 0x98, 0x01,  },
 433         .dest_addr = { .data = { 0xbe, 0x00 } },
 434         .src_addr = { .data = { 0x76, 0x98 } },
 435 };
 436
 437 static const struct wusb_keydvt_out stv_keydvt_out_a1 = {
 438         .kck = {
 439                 0x4b, 0x79, 0xa3, 0xcf, 0xe5, 0x53, 0x23, 0x9d,
 440                 0xd7, 0xc1, 0x6d, 0x1c, 0x2d, 0xab, 0x6d, 0x3f
 441         },
 442         .ptk = {
 443                 0xc8, 0x70, 0x62, 0x82, 0xb6, 0x7c, 0xe9, 0x06,
 444                 0x7b, 0xc5, 0x25, 0x69, 0xf2, 0x36, 0x61, 0x2d
 445         }
 446 };
 447
 448 /*
 449  * Performa a test to make sure we match the vectors defined in
 450  * WUSB1.0[A.1](Errata2006/12)
 451  */
 452 static int wusb_key_derive_verify(void)
 453 {
 454         int result = 0;
 455         struct wusb_keydvt_out keydvt_out;
 456         /* These come from WUSB1.0[A.1] + 2006/12 errata
 457          * NOTE: can't make this const or global -- somehow it seems
 458          *       the scatterlists for crypto get confused and we get
 459          *       bad data. There is no doc on this... */
 460         struct wusb_keydvt_in stv_keydvt_in_a1 = {
 461                 .hnonce = {
 462                         0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17,
 463                         0x18, 0x19, 0x1a, 0x1b, 0x1c, 0x1d, 0x1e, 0x1f
 464                 },
 465                 .dnonce = {
 466                         0x20, 0x21, 0x22, 0x23, 0x24, 0x25, 0x26, 0x27,
 467                         0x28, 0x29, 0x2a, 0x2b, 0x2c, 0x2d, 0x2e, 0x2f
 468                 }
 469         };
 470
 471         result = wusb_key_derive(&keydvt_out, stv_key_a1, &stv_keydvt_n_a1,
 472                                  &stv_keydvt_in_a1);
 473         if (result < 0)
 474                 printk(KERN_ERR "E: WUSB key derivation test: "
 475                        "derivation failed: %d\n", result);
 476         if (memcmp(&stv_keydvt_out_a1, &keydvt_out, sizeof(keydvt_out))) {
 477                 printk(KERN_ERR "E: WUSB key derivation test: "
 478                        "mismatch between key derivation result "
 479                        "and WUSB1.0[A1] Errata 2006/12\n");
 480                 printk(KERN_ERR "E: keydvt in: key\n");
 481                 wusb_key_dump(stv_key_a1, sizeof(stv_key_a1));
 482                 printk(KERN_ERR "E: keydvt in: nonce\n");
 483                 wusb_key_dump(&stv_keydvt_n_a1, sizeof(stv_keydvt_n_a1));
 484                 printk(KERN_ERR "E: keydvt in: hnonce & dnonce\n");
 485                 wusb_key_dump(&stv_keydvt_in_a1, sizeof(stv_keydvt_in_a1));
 486                 printk(KERN_ERR "E: keydvt out: KCK\n");
 487                 wusb_key_dump(&keydvt_out.kck, sizeof(keydvt_out.kck));
 488                 printk(KERN_ERR "E: keydvt out: PTK\n");
 489                 wusb_key_dump(&keydvt_out.ptk, sizeof(keydvt_out.ptk));
 490                 result = -EINVAL;
 491         } else
 492                 result = 0;
 493         return result;
 494 }
 495
 496 /*
 497  * Initialize crypto system
 498  *
 499  * FIXME: we do nothing now, other than verifying. Later on we'll
 500  * cache the encryption stuff, so that's why we have a separate init.
 501  */
 502 int wusb_crypto_init(void)
 503 {
 504         int result;
 505
 506         if (debug_crypto_verify) {
 507                 result = wusb_key_derive_verify();
 508                 if (result < 0)
 509                         return result;
 510                 return wusb_oob_mic_verify();
 511         }
 512         return 0;
 513 }
 514
 515 void wusb_crypto_exit(void)
 516 {
 517         /* FIXME: free cached crypto transforms */
 518 }