res/res_crypto.c

   1 /*
   2  * Asterisk -- An open source telephony toolkit.
   3  *
   4  * Copyright (C) 1999 - 2006, Digium, Inc.
   5  *
   6  * Mark Spencer <markster@digium.com>
   7  *
   8  * See http://www.asterisk.org for more information about
   9  * the Asterisk project. Please do not directly contact
  10  * any of the maintainers of this project for assistance;
  11  * the project provides a web site, mailing lists and IRC
  12  * channels for your use.
  13  *
  14  * This program is free software, distributed under the terms of
  15  * the GNU General Public License Version 2. See the LICENSE file
  16  * at the top of the source tree.
  17  */
  18
  19 /*! \file
  20  *
  21  * \brief Provide Cryptographic Signature capability
  22  *
  23  * \author Mark Spencer <markster@digium.com>
  24  *
  25  * \extref Uses the OpenSSL library, available at
  26  *      http://www.openssl.org/
  27  */
  28
  29 /*** MODULEINFO
  30         <depend>ssl</depend>
  31  ***/
  32
  33 #include "asterisk.h"
  34
  35 ASTERISK_FILE_VERSION(__FILE__, "$Revision$")
  36
  37 #include "asterisk/paths.h"     /* use ast_config_AST_KEY_DIR */
  38 #include <openssl/ssl.h>
  39 #include <openssl/err.h>
  40 #include <dirent.h>
  41
  42 #include "asterisk/module.h"
  43 #include "asterisk/crypto.h"
  44 #include "asterisk/md5.h"
  45 #include "asterisk/cli.h"
  46 #include "asterisk/io.h"
  47 #include "asterisk/lock.h"
  48 #include "asterisk/utils.h"
  49
  50 /*
  51  * Asterisk uses RSA keys with SHA-1 message digests for its
  52  * digital signatures.  The choice of RSA is due to its higher
  53  * throughput on verification, and the choice of SHA-1 based
  54  * on the recently discovered collisions in MD5's compression
  55  * algorithm and recommendations of avoiding MD5 in new schemes
  56  * from various industry experts.
  57  *
  58  * We use OpenSSL to provide our crypto routines, although we never
  59  * actually use full-up SSL
  60  *
  61  */
  62
  63 #define KEY_NEEDS_PASSCODE (1 << 16)
  64
  65 struct ast_key {
  66         /*! Name of entity */
  67         char name[80];
  68         /*! File name */
  69         char fn[256];
  70         /*! Key type (AST_KEY_PUB or AST_KEY_PRIV, along with flags from above) */
  71         int ktype;
  72         /*! RSA structure (if successfully loaded) */
  73         RSA *rsa;
  74         /*! Whether we should be deleted */
  75         int delme;
  76         /*! FD for input (or -1 if no input allowed, or -2 if we needed input) */
  77         int infd;
  78         /*! FD for output */
  79         int outfd;
  80         /*! Last MD5 Digest */
  81         unsigned char digest[16];
  82         AST_RWLIST_ENTRY(ast_key) list;
  83 };
  84
  85 static AST_RWLIST_HEAD_STATIC(keys, ast_key);
  86
  87 /*!
  88  * \brief setting of priv key
  89  * \param buf
  90  * \param size
  91  * \param rwflag
  92  * \param userdata
  93  * \return length of string,-1 on failure
  94 */
  95 static int pw_cb(char *buf, int size, int rwflag, void *userdata)
  96 {
  97         struct ast_key *key = (struct ast_key *)userdata;
  98         char prompt[256];
  99         int res, tmp;
 100
 101         if (key->infd < 0) {
 102                 /* Note that we were at least called */
 103                 key->infd = -2;
 104                 return -1;
 105         }
 106
 107         snprintf(prompt, sizeof(prompt), ">>>> passcode for %s key '%s': ",
 108                  key->ktype == AST_KEY_PRIVATE ? "PRIVATE" : "PUBLIC", key->name);
 109         write(key->outfd, prompt, strlen(prompt));
 110         memset(buf, 0, sizeof(buf));
 111         tmp = ast_hide_password(key->infd);
 112         memset(buf, 0, size);
 113         res = read(key->infd, buf, size);
 114         ast_restore_tty(key->infd, tmp);
 115         if (buf[strlen(buf) -1] == '\n')
 116                 buf[strlen(buf) - 1] = '\0';
 117         return strlen(buf);
 118 }
 119
 120 /*!
 121  * \brief return the ast_key structure for name
 122  * \see ast_key_get
 123 */
 124 static struct ast_key *__ast_key_get(const char *kname, int ktype)
 125 {
 126         struct ast_key *key;
 127
 128         AST_RWLIST_RDLOCK(&keys);
 129         AST_RWLIST_TRAVERSE(&keys, key, list) {
 130                 if (!strcmp(kname, key->name) &&
 131                     (ktype == key->ktype))
 132                         break;
 133         }
 134         AST_RWLIST_UNLOCK(&keys);
 135
 136         return key;
 137 }
 138
 139 /*!
 140  * \brief load RSA key from file
 141  * \param dir directory string
 142  * \param fname name of file
 143  * \param ifd incoming file descriptor
 144  * \param ofd outgoing file descriptor
 145  * \param not2
 146  * \retval key on success.
 147  * \retval NULL on failure.
 148 */
 149 static struct ast_key *try_load_key(const char *dir, const char *fname, int ifd, int ofd, int *not2)
 150 {
 151         int ktype = 0, found = 0;
 152         char *c = NULL, ffname[256];
 153         unsigned char digest[16];
 154         FILE *f;
 155         struct MD5Context md5;
 156         struct ast_key *key;
 157         static int notice = 0;
 158
 159         /* Make sure its name is a public or private key */
 160         if ((c = strstr(fname, ".pub")) && !strcmp(c, ".pub"))
 161                 ktype = AST_KEY_PUBLIC;
 162         else if ((c = strstr(fname, ".key")) && !strcmp(c, ".key"))
 163                 ktype = AST_KEY_PRIVATE;
 164         else
 165                 return NULL;
 166
 167         /* Get actual filename */
 168         snprintf(ffname, sizeof(ffname), "%s/%s", dir, fname);
 169
 170         /* Open file */
 171         if (!(f = fopen(ffname, "r"))) {
 172                 ast_log(LOG_WARNING, "Unable to open key file %s: %s\n", ffname, strerror(errno));
 173                 return NULL;
 174         }
 175
 176         MD5Init(&md5);
 177         while(!feof(f)) {
 178                 /* Calculate a "whatever" quality md5sum of the key */
 179                 char buf[256] = "";
 180                 fgets(buf, sizeof(buf), f);
 181                 if (!feof(f))
 182                         MD5Update(&md5, (unsigned char *) buf, strlen(buf));
 183         }
 184         MD5Final(digest, &md5);
 185
 186         /* Look for an existing key */
 187         AST_RWLIST_TRAVERSE(&keys, key, list) {
 188                 if (!strcasecmp(key->fn, ffname))
 189                         break;
 190         }
 191
 192         if (key) {
 193                 /* If the MD5 sum is the same, and it isn't awaiting a passcode
 194                    then this is far enough */
 195                 if (!memcmp(digest, key->digest, 16) &&
 196                     !(key->ktype & KEY_NEEDS_PASSCODE)) {
 197                         fclose(f);
 198                         key->delme = 0;
 199                         return NULL;
 200                 } else {
 201                         /* Preserve keytype */
 202                         ktype = key->ktype;
 203                         /* Recycle the same structure */
 204                         found++;
 205                 }
 206         }
 207
 208         /* Make fname just be the normal name now */
 209         *c = '\0';
 210         if (!key) {
 211                 if (!(key = ast_calloc(1, sizeof(*key)))) {
 212                         fclose(f);
 213                         return NULL;
 214                 }
 215         }
 216         /* First the filename */
 217         ast_copy_string(key->fn, ffname, sizeof(key->fn));
 218         /* Then the name */
 219         ast_copy_string(key->name, fname, sizeof(key->name));
 220         key->ktype = ktype;
 221         /* Yes, assume we're going to be deleted */
 222         key->delme = 1;
 223         /* Keep the key type */
 224         memcpy(key->digest, digest, 16);
 225         /* Can I/O takes the FD we're given */
 226         key->infd = ifd;
 227         key->outfd = ofd;
 228         /* Reset the file back to the beginning */
 229         rewind(f);
 230         /* Now load the key with the right method */
 231         if (ktype == AST_KEY_PUBLIC)
 232                 key->rsa = PEM_read_RSA_PUBKEY(f, NULL, pw_cb, key);
 233         else
 234                 key->rsa = PEM_read_RSAPrivateKey(f, NULL, pw_cb, key);
 235         fclose(f);
 236         if (key->rsa) {
 237                 if (RSA_size(key->rsa) == 128) {
 238                         /* Key loaded okay */
 239                         key->ktype &= ~KEY_NEEDS_PASSCODE;
 240                         ast_verb(3, "Loaded %s key '%s'\n", key->ktype == AST_KEY_PUBLIC ? "PUBLIC" : "PRIVATE", key->name);
 241                         ast_debug(1, "Key '%s' loaded OK\n", key->name);
 242                         key->delme = 0;
 243                 } else
 244                         ast_log(LOG_NOTICE, "Key '%s' is not expected size.\n", key->name);
 245         } else if (key->infd != -2) {
 246                 ast_log(LOG_WARNING, "Key load %s '%s' failed\n",key->ktype == AST_KEY_PUBLIC ? "PUBLIC" : "PRIVATE", key->name);
 247                 if (ofd > -1)
 248                         ERR_print_errors_fp(stderr);
 249                 else
 250                         ERR_print_errors_fp(stderr);
 251         } else {
 252                 ast_log(LOG_NOTICE, "Key '%s' needs passcode.\n", key->name);
 253                 key->ktype |= KEY_NEEDS_PASSCODE;
 254                 if (!notice) {
 255                         if (!ast_opt_init_keys)
 256                                 ast_log(LOG_NOTICE, "Add the '-i' flag to the asterisk command line if you want to automatically initialize passcodes at launch.\n");
 257                         notice++;
 258                 }
 259                 /* Keep it anyway */
 260                 key->delme = 0;
 261                 /* Print final notice about "init keys" when done */
 262                 *not2 = 1;
 263         }
 264
 265         /* If this is a new key add it to the list */
 266         if (!found)
 267                 AST_RWLIST_INSERT_TAIL(&keys, key, list);
 268
 269         return key;
 270 }
 271
 272 /*!
 273  * \brief signs outgoing message with public key
 274  * \see ast_sign_bin
 275 */
 276 static int __ast_sign_bin(struct ast_key *key, const char *msg, int msglen, unsigned char *dsig)
 277 {
 278         unsigned char digest[20];
 279         unsigned int siglen = 128;
 280         int res;
 281
 282         if (key->ktype != AST_KEY_PRIVATE) {
 283                 ast_log(LOG_WARNING, "Cannot sign with a public key\n");
 284                 return -1;
 285         }
 286
 287         /* Calculate digest of message */
 288         SHA1((unsigned char *)msg, msglen, digest);
 289
 290         /* Verify signature */
 291         if (!(res = RSA_sign(NID_sha1, digest, sizeof(digest), dsig, &siglen, key->rsa))) {
 292                 ast_log(LOG_WARNING, "RSA Signature (key %s) failed\n", key->name);
 293                 return -1;
 294         }
 295
 296         if (siglen != 128) {
 297                 ast_log(LOG_WARNING, "Unexpected signature length %d, expecting %d\n", (int)siglen, (int)128);
 298                 return -1;
 299         }
 300
 301         return 0;
 302
 303 }
 304
 305 /*!
 306  * \brief decrypt a message
 307  * \see ast_decrypt_bin
 308 */
 309 static int __ast_decrypt_bin(unsigned char *dst, const unsigned char *src, int srclen, struct ast_key *key)
 310 {
 311         int res, pos = 0;
 312
 313         if (key->ktype != AST_KEY_PRIVATE) {
 314                 ast_log(LOG_WARNING, "Cannot decrypt with a public key\n");
 315                 return -1;
 316         }
 317
 318         if (srclen % 128) {
 319                 ast_log(LOG_NOTICE, "Tried to decrypt something not a multiple of 128 bytes\n");
 320                 return -1;
 321         }
 322
 323         while(srclen) {
 324                 /* Process chunks 128 bytes at a time */
 325                 if ((res = RSA_private_decrypt(128, src, dst, key->rsa, RSA_PKCS1_OAEP_PADDING)) < 0)
 326                         return -1;
 327                 pos += res;
 328                 src += 128;
 329                 srclen -= 128;
 330                 dst += res;
 331         }
 332
 333         return pos;
 334 }
 335
 336 /*!
 337  * \brief encrypt a message
 338  * \see ast_encrypt_bin
 339 */
 340 static int __ast_encrypt_bin(unsigned char *dst, const unsigned char *src, int srclen, struct ast_key *key)
 341 {
 342         int res, bytes, pos = 0;
 343
 344         if (key->ktype != AST_KEY_PUBLIC) {
 345                 ast_log(LOG_WARNING, "Cannot encrypt with a private key\n");
 346                 return -1;
 347         }
 348
 349         while(srclen) {
 350                 bytes = srclen;
 351                 if (bytes > 128 - 41)
 352                         bytes = 128 - 41;
 353                 /* Process chunks 128-41 bytes at a time */
 354                 if ((res = RSA_public_encrypt(bytes, src, dst, key->rsa, RSA_PKCS1_OAEP_PADDING)) != 128) {
 355                         ast_log(LOG_NOTICE, "How odd, encrypted size is %d\n", res);
 356                         return -1;
 357                 }
 358                 src += bytes;
 359                 srclen -= bytes;
 360                 pos += res;
 361                 dst += res;
 362         }
 363         return pos;
 364 }
 365
 366 /*!
 367  * \brief wrapper for __ast_sign_bin then base64 encode it
 368  * \see ast_sign
 369 */
 370 static int __ast_sign(struct ast_key *key, char *msg, char *sig)
 371 {
 372         unsigned char dsig[128];
 373         int siglen = sizeof(dsig), res;
 374
 375         if (!(res = ast_sign_bin(key, msg, strlen(msg), dsig)))
 376                 /* Success -- encode (256 bytes max as documented) */
 377                 ast_base64encode(sig, dsig, siglen, 256);
 378
 379         return res;
 380 }
 381
 382 /*!
 383  * \brief check signature of a message
 384  * \see ast_check_signature_bin
 385 */
 386 static int __ast_check_signature_bin(struct ast_key *key, const char *msg, int msglen, const unsigned char *dsig)
 387 {
 388         unsigned char digest[20];
 389         int res;
 390
 391         if (key->ktype != AST_KEY_PUBLIC) {
 392                 /* Okay, so of course you really *can* but for our purposes
 393                    we're going to say you can't */
 394                 ast_log(LOG_WARNING, "Cannot check message signature with a private key\n");
 395                 return -1;
 396         }
 397
 398         /* Calculate digest of message */
 399         SHA1((unsigned char *)msg, msglen, digest);
 400
 401         /* Verify signature */
 402         if (!(res = RSA_verify(NID_sha1, digest, sizeof(digest), (unsigned char *)dsig, 128, key->rsa))) {
 403                 ast_debug(1, "Key failed verification: %s\n", key->name);
 404                 return -1;
 405         }
 406
 407         /* Pass */
 408         return 0;
 409 }
 410
 411 /*!
 412  * \brief base64 decode then sent to __ast_check_signature_bin
 413  * \see ast_check_signature
 414 */
 415 static int __ast_check_signature(struct ast_key *key, const char *msg, const char *sig)
 416 {
 417         unsigned char dsig[128];
 418         int res;
 419
 420         /* Decode signature */
 421         if ((res = ast_base64decode(dsig, sig, sizeof(dsig))) != sizeof(dsig)) {
 422                 ast_log(LOG_WARNING, "Signature improper length (expect %d, got %d)\n", (int)sizeof(dsig), (int)res);
 423                 return -1;
 424         }
 425
 426         res = ast_check_signature_bin(key, msg, strlen(msg), dsig);
 427
 428         return res;
 429 }
 430
 431 /*!
 432  * \brief refresh RSA keys from file
 433  * \param ifd file descriptor
 434  * \param ofd file descriptor
 435  * \return void
 436 */
 437 static void crypto_load(int ifd, int ofd)
 438 {
 439         struct ast_key *key;
 440         DIR *dir = NULL;
 441         struct dirent *ent;
 442         int note = 0;
 443
 444         AST_RWLIST_WRLOCK(&keys);
 445
 446         /* Mark all keys for deletion */
 447         AST_RWLIST_TRAVERSE(&keys, key, list) {
 448                 key->delme = 1;
 449         }
 450
 451         /* Load new keys */
 452         if ((dir = opendir(ast_config_AST_KEY_DIR))) {
 453                 while((ent = readdir(dir))) {
 454                         try_load_key(ast_config_AST_KEY_DIR, ent->d_name, ifd, ofd, &note);
 455                 }
 456                 closedir(dir);
 457         } else
 458                 ast_log(LOG_WARNING, "Unable to open key directory '%s'\n", ast_config_AST_KEY_DIR);
 459
 460         if (note)
 461                 ast_log(LOG_NOTICE, "Please run the command 'init keys' to enter the passcodes for the keys\n");
 462
 463         /* Delete any keys that are no longer present */
 464         AST_RWLIST_TRAVERSE_SAFE_BEGIN(&keys, key, list) {
 465                 if (key->delme) {
 466                         ast_debug(1, "Deleting key %s type %d\n", key->name, key->ktype);
 467                         AST_RWLIST_REMOVE_CURRENT(list);
 468                         if (key->rsa)
 469                                 RSA_free(key->rsa);
 470                         ast_free(key);
 471                 }
 472         }
 473         AST_RWLIST_TRAVERSE_SAFE_END;
 474
 475         AST_RWLIST_UNLOCK(&keys);
 476 }
 477
 478 static void md52sum(char *sum, unsigned char *md5)
 479 {
 480         int x;
 481         for (x = 0; x < 16; x++)
 482                 sum += sprintf(sum, "%02x", *(md5++));
 483 }
 484
 485 /*!
 486  * \brief show the list of RSA keys
 487  * \param e CLI command
 488  * \param cmd
 489  * \param a list of CLI arguments
 490  * \return CLI_SUCCESS
 491 */
 492 static char *handle_cli_keys_show(struct ast_cli_entry *e, int cmd, struct ast_cli_args *a)
 493 {
 494 #define FORMAT "%-18s %-8s %-16s %-33s\n"
 495
 496         struct ast_key *key;
 497         char sum[16 * 2 + 1];
 498         int count_keys = 0;
 499
 500         switch (cmd) {
 501         case CLI_INIT:
 502                 e->command = "keys show";
 503                 e->usage =
 504                         "Usage: keys show\n"
 505                         "       Displays information about RSA keys known by Asterisk\n";
 506                 return NULL;
 507         case CLI_GENERATE:
 508                 return NULL;
 509         }
 510
 511         ast_cli(a->fd, FORMAT, "Key Name", "Type", "Status", "Sum");
 512         ast_cli(a->fd, FORMAT, "------------------", "--------", "----------------", "--------------------------------");
 513
 514         AST_RWLIST_RDLOCK(&keys);
 515         AST_RWLIST_TRAVERSE(&keys, key, list) {
 516                 md52sum(sum, key->digest);
 517                 ast_cli(a->fd, FORMAT, key->name,
 518                         (key->ktype & 0xf) == AST_KEY_PUBLIC ? "PUBLIC" : "PRIVATE",
 519                         key->ktype & KEY_NEEDS_PASSCODE ? "[Needs Passcode]" : "[Loaded]", sum);
 520                 count_keys++;
 521         }
 522         AST_RWLIST_UNLOCK(&keys);
 523
 524         ast_cli(a->fd, "\n%d known RSA keys.\n", count_keys);
 525
 526         return CLI_SUCCESS;
 527
 528 #undef FORMAT
 529 }
 530
 531 /*!
 532  * \brief initialize all RSA keys
 533  * \param e CLI command
 534  * \param cmd
 535  * \param a list of CLI arguments
 536  * \return CLI_SUCCESS
 537 */
 538 static char *handle_cli_keys_init(struct ast_cli_entry *e, int cmd, struct ast_cli_args *a)
 539 {
 540         struct ast_key *key;
 541         int ign;
 542         char *kn, tmp[256] = "";
 543
 544         switch (cmd) {
 545         case CLI_INIT:
 546                 e->command = "keys init";
 547                 e->usage =
 548                         "Usage: keys init\n"
 549                         "       Initializes private keys (by reading in pass code from\n"
 550                         "       the user)\n";
 551                 return NULL;
 552         case CLI_GENERATE:
 553                 return NULL;
 554         }
 555
 556         if (a->argc != 2)
 557                 return CLI_SHOWUSAGE;
 558
 559         AST_RWLIST_WRLOCK(&keys);
 560         AST_RWLIST_TRAVERSE_SAFE_BEGIN(&keys, key, list) {
 561                 /* Reload keys that need pass codes now */
 562                 if (key->ktype & KEY_NEEDS_PASSCODE) {
 563                         kn = key->fn + strlen(ast_config_AST_KEY_DIR) + 1;
 564                         ast_copy_string(tmp, kn, sizeof(tmp));
 565                         try_load_key(ast_config_AST_KEY_DIR, tmp, a->fd, a->fd, &ign);
 566                 }
 567         }
 568         AST_RWLIST_TRAVERSE_SAFE_END
 569         AST_RWLIST_UNLOCK(&keys);
 570
 571         return CLI_SUCCESS;
 572 }
 573
 574 static struct ast_cli_entry cli_crypto[] = {
 575         AST_CLI_DEFINE(handle_cli_keys_show, "Displays RSA key information"),
 576         AST_CLI_DEFINE(handle_cli_keys_init, "Initialize RSA key passcodes")
 577 };
 578
 579 /*! \brief initialise the res_crypto module */
 580 static int crypto_init(void)
 581 {
 582         SSL_library_init();
 583         ERR_load_crypto_strings();
 584         ast_cli_register_multiple(cli_crypto, sizeof(cli_crypto) / sizeof(struct ast_cli_entry));
 585
 586         /* Install ourselves into stubs */
 587         ast_key_get = __ast_key_get;
 588         ast_check_signature = __ast_check_signature;
 589         ast_check_signature_bin = __ast_check_signature_bin;
 590         ast_sign = __ast_sign;
 591         ast_sign_bin = __ast_sign_bin;
 592         ast_encrypt_bin = __ast_encrypt_bin;
 593         ast_decrypt_bin = __ast_decrypt_bin;
 594         return 0;
 595 }
 596
 597 static int reload(void)
 598 {
 599         crypto_load(-1, -1);
 600         return 0;
 601 }
 602
 603 static int load_module(void)
 604 {
 605         crypto_init();
 606         if (ast_opt_init_keys)
 607                 crypto_load(STDIN_FILENO, STDOUT_FILENO);
 608         else
 609                 crypto_load(-1, -1);
 610         return AST_MODULE_LOAD_SUCCESS;
 611 }
 612
 613 static int unload_module(void)
 614 {
 615         /* Can't unload this once we're loaded */
 616         return -1;
 617 }
 618
 619 /* needs usecount semantics defined */
 620 AST_MODULE_INFO(ASTERISK_GPL_KEY, AST_MODFLAG_DEFAULT, "Cryptographic Digital Signatures",
 621                 .load = load_module,
 622                 .unload = unload_module,
 623                 .reload = reload
 624         );