Asterisk.org: Developer Documentation (28 Oct 2009)

Wed Oct 28 15:47:55 2009

## Asterisk developer's documentation

# res_crypto.c

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    00001 /*
    00002  * Asterisk -- An open source telephony toolkit.
    00003  *
    00004  * Copyright (C) 1999 - 2005, Digium, Inc.
    00005  *
    00006  * Mark Spencer <markster@digium.com>
    00007  *
    00008  * See http://www.asterisk.org for more information about
    00009  * the Asterisk project. Please do not directly contact
    00010  * any of the maintainers of this project for assistance;
    00011  * the project provides a web site, mailing lists and IRC
    00012  * channels for your use.
    00013  *
    00014  * This program is free software, distributed under the terms of
    00015  * the GNU General Public License Version 2. See the LICENSE file
    00016  * at the top of the source tree.
    00017  */
    00018
    00019 /*! \file
    00020  *
    00021  * \brief Provide Cryptographic Signature capability
    00022  *
    00023  */
    00024
    00025 #include <sys/types.h>
    00026 #include <openssl/ssl.h>
    00027 #include <openssl/err.h>
    00028 #include <stdio.h>
    00029 #include <dirent.h>
    00030 #include <string.h>
    00031 #include <errno.h>
    00032 #include <unistd.h>
    00033 #include <fcntl.h>
    00034
    00035 #include "asterisk.h"
    00036
    00037 ASTERISK_FILE_VERSION(__FILE__, "$Revision: 7221 $")
    00038
    00039 #include "asterisk/file.h"
    00040 #include "asterisk/channel.h"
    00041 #include "asterisk/logger.h"
    00042 #include "asterisk/say.h"
    00043 #include "asterisk/module.h"
    00044 #include "asterisk/options.h"
    00045 #include "asterisk/crypto.h"
    00046 #include "asterisk/md5.h"
    00047 #include "asterisk/cli.h"
    00048 #include "asterisk/io.h"
    00049 #include "asterisk/lock.h"
    00050 #include "asterisk/utils.h"
    00051
    00052 /*
    00053  * Asterisk uses RSA keys with SHA-1 message digests for its
    00054  * digital signatures.  The choice of RSA is due to its higher
    00055  * throughput on verification, and the choice of SHA-1 based
    00056  * on the recently discovered collisions in MD5's compression
    00057  * algorithm and recommendations of avoiding MD5 in new schemes
    00058  * from various industry experts.
    00059  *
    00060  * We use OpenSSL to provide our crypto routines, although we never
    00061  * actually use full-up SSL
    00062  *
    00063  */
    00064
    00065 /*
    00066  * XXX This module is not very thread-safe.  It is for everyday stuff
    00067  *     like reading keys and stuff, but there are all kinds of weird
    00068  *     races with people running reload and key init at the same time
    00069  *     for example
    00070  *
    00071  * XXXX
    00072  */
    00073
    00074 AST_MUTEX_DEFINE_STATIC(keylock);
    00075
    00076 #define KEY_NEEDS_PASSCODE (1 << 16)
    00077
    00078 struct ast_key {
    00079    /* Name of entity */
    00080    char name[80];
    00081    /* File name */
    00082    char fn[256];
    00083    /* Key type (AST_KEY_PUB or AST_KEY_PRIV, along with flags from above) */
    00084    int ktype;
    00085    /* RSA structure (if successfully loaded) */
    00086    RSA *rsa;
    00087    /* Whether we should be deleted */
    00088    int delme;
    00089    /* FD for input (or -1 if no input allowed, or -2 if we needed input) */
    00090    int infd;
    00091    /* FD for output */
    00092    int outfd;
    00093    /* Last MD5 Digest */
    00094    unsigned char digest[16];
    00095    struct ast_key *next;
    00096 };
    00097
    00098 static struct ast_key *keys = NULL;
    00099
    00100
    00101 #if 0
    00102 static int fdprint(int fd, char *s)
    00103 {
    00104         return write(fd, s, strlen(s) + 1);
    00105 }
    00106 #endif
    00107 static int pw_cb(char *buf, int size, int rwflag, void *userdata)
    00108 {
    00109    struct ast_key *key = (struct ast_key *)userdata;
    00110    char prompt[256];
    00111    int res;
    00112    int tmp;
    00113    if (key->infd > -1) {
    00114       snprintf(prompt, sizeof(prompt), ">>>> passcode for %s key '%s': ",
    00115           key->ktype == AST_KEY_PRIVATE ? "PRIVATE" : "PUBLIC", key->name);
    00116       write(key->outfd, prompt, strlen(prompt));
    00117       memset(buf, 0, sizeof(buf));
    00118       tmp = ast_hide_password(key->infd);
    00119       memset(buf, 0, size);
    00120       res = read(key->infd, buf, size);
    00121       ast_restore_tty(key->infd, tmp);
    00122       if (buf[strlen(buf) -1] == '\n')
    00123          buf[strlen(buf) - 1] = '\0';
    00124       return strlen(buf);
    00125    } else {
    00126       /* Note that we were at least called */
    00127       key->infd = -2;
    00128    }
    00129    return -1;
    00130 }
    00131
    00132 static struct ast_key *__ast_key_get(const char *kname, int ktype)
    00133 {
    00134    struct ast_key *key;
    00135    ast_mutex_lock(&keylock);
    00136    key = keys;
    00137    while(key) {
    00138       if (!strcmp(kname, key->name) &&
    00139           (ktype == key->ktype))
    00140          break;
    00141       key = key->next;
    00142    }
    00143    ast_mutex_unlock(&keylock);
    00144    return key;
    00145 }
    00146
    00147 static struct ast_key *try_load_key (char *dir, char *fname, int ifd, int ofd, int *not2)
    00148 {
    00149    int ktype = 0;
    00150    char *c = NULL;
    00151    char ffname[256];
    00152    unsigned char digest[16];
    00153    FILE *f;
    00154    struct MD5Context md5;
    00155    struct ast_key *key;
    00156    static int notice = 0;
    00157    int found = 0;
    00158
    00159    /* Make sure its name is a public or private key */
    00160
    00161    if ((c = strstr(fname, ".pub")) && !strcmp(c, ".pub")) {
    00162       ktype = AST_KEY_PUBLIC;
    00163    } else if ((c = strstr(fname, ".key")) && !strcmp(c, ".key")) {
    00164       ktype = AST_KEY_PRIVATE;
    00165    } else
    00166       return NULL;
    00167
    00168    /* Get actual filename */
    00169    snprintf(ffname, sizeof(ffname), "%s/%s", dir, fname);
    00170
    00171    ast_mutex_lock(&keylock);
    00172    key = keys;
    00173    while(key) {
    00174       /* Look for an existing version already */
    00175       if (!strcasecmp(key->fn, ffname))
    00176          break;
    00177       key = key->next;
    00178    }
    00179    ast_mutex_unlock(&keylock);
    00180
    00181    /* Open file */
    00182    f = fopen(ffname, "r");
    00183    if (!f) {
    00184       ast_log(LOG_WARNING, "Unable to open key file %s: %s\n", ffname, strerror(errno));
    00185       return NULL;
    00186    }
    00187    MD5Init(&md5);
    00188    while(!feof(f)) {
    00189       /* Calculate a "whatever" quality md5sum of the key */
    00190       char buf[256];
    00191       memset(buf, 0, 256);
    00192       fgets(buf, sizeof(buf), f);
    00193       if (!feof(f)) {
    00194          MD5Update(&md5, (unsigned char *) buf, strlen(buf));
    00195       }
    00196    }
    00197    MD5Final(digest, &md5);
    00198    if (key) {
    00199       /* If the MD5 sum is the same, and it isn't awaiting a passcode
    00200          then this is far enough */
    00201       if (!memcmp(digest, key->digest, 16) &&
    00202           !(key->ktype & KEY_NEEDS_PASSCODE)) {
    00203          fclose(f);
    00204          key->delme = 0;
    00205          return NULL;
    00206       } else {
    00207          /* Preserve keytype */
    00208          ktype = key->ktype;
    00209          /* Recycle the same structure */
    00210          found++;
    00211       }
    00212    }
    00213
    00214    /* Make fname just be the normal name now */
    00215    *c = '\0';
    00216    if (!key) {
    00217       key = (struct ast_key *)malloc(sizeof(struct ast_key));
    00218       if (!key) {
    00219          ast_log(LOG_WARNING, "Out of memory\n");
    00220          fclose(f);
    00221          return NULL;
    00222       }
    00223       memset(key, 0, sizeof(struct ast_key));
    00224    }
    00225    /* At this point we have a key structure (old or new).  Time to
    00226       fill it with what we know */
    00227    /* Gotta lock if this one already exists */
    00228    if (found)
    00229       ast_mutex_lock(&keylock);
    00230    /* First the filename */
    00231    ast_copy_string(key->fn, ffname, sizeof(key->fn));
    00232    /* Then the name */
    00233    ast_copy_string(key->name, fname, sizeof(key->name));
    00234    key->ktype = ktype;
    00235    /* Yes, assume we're going to be deleted */
    00236    key->delme = 1;
    00237    /* Keep the key type */
    00238    memcpy(key->digest, digest, 16);
    00239    /* Can I/O takes the FD we're given */
    00240    key->infd = ifd;
    00241    key->outfd = ofd;
    00242    /* Reset the file back to the beginning */
    00243    rewind(f);
    00244    /* Now load the key with the right method */
    00245    if (ktype == AST_KEY_PUBLIC)
    00246       key->rsa = PEM_read_RSA_PUBKEY(f, NULL, pw_cb, key);
    00247    else
    00248       key->rsa = PEM_read_RSAPrivateKey(f, NULL, pw_cb, key);
    00249    fclose(f);
    00250    if (key->rsa) {
    00251       if (RSA_size(key->rsa) == 128) {
    00252          /* Key loaded okay */
    00253          key->ktype &= ~KEY_NEEDS_PASSCODE;
    00254          if (option_verbose > 2)
    00255             ast_verbose(VERBOSE_PREFIX_3 "Loaded %s key '%s'\n", key->ktype == AST_KEY_PUBLIC ? "PUBLIC" : "PRIVATE", key->name);
    00256          if (option_debug)
    00257             ast_log(LOG_DEBUG, "Key '%s' loaded OK\n", key->name);
    00258          key->delme = 0;
    00259       } else
    00260          ast_log(LOG_NOTICE, "Key '%s' is not expected size.\n", key->name);
    00261    } else if (key->infd != -2) {
    00262       ast_log(LOG_WARNING, "Key load %s '%s' failed\n",key->ktype == AST_KEY_PUBLIC ? "PUBLIC" : "PRIVATE", key->name);
    00263       if (ofd > -1) {
    00264          ERR_print_errors_fp(stderr);
    00265       } else
    00266          ERR_print_errors_fp(stderr);
    00267    } else {
    00268       ast_log(LOG_NOTICE, "Key '%s' needs passcode.\n", key->name);
    00269       key->ktype |= KEY_NEEDS_PASSCODE;
    00270       if (!notice) {
    00271          if (!option_initcrypto)
    00272             ast_log(LOG_NOTICE, "Add the '-i' flag to the asterisk command line if you want to automatically initialize passcodes at launch.\n");
    00273          notice++;
    00274       }
    00275       /* Keep it anyway */
    00276       key->delme = 0;
    00277       /* Print final notice about "init keys" when done */
    00278       *not2 = 1;
    00279    }
    00280    if (found)
    00281       ast_mutex_unlock(&keylock);
    00282    if (!found) {
    00283       ast_mutex_lock(&keylock);
    00284       key->next = keys;
    00285       keys = key;
    00286       ast_mutex_unlock(&keylock);
    00287    }
    00288    return key;
    00289 }
    00290
    00291 #if 0
    00292
    00293 static void dump(unsigned char *src, int len)
    00294 {
    00295    int x;
    00296    for (x=0;x<len;x++)
    00297       printf("%02x", *(src++));
    00298    printf("\n");
    00299 }
    00300
    00301 static char *binary(int y, int len)
    00302 {
    00303    static char res[80];
    00304    int x;
    00305    memset(res, 0, sizeof(res));
    00306    for (x=0;x<len;x++) {
    00307       if (y & (1 << x))
    00308          res[(len - x - 1)] = '1';
    00309       else
    00310          res[(len - x - 1)] = '0';
    00311    }
    00312    return res;
    00313 }
    00314
    00315 #endif
    00316
    00317 static int __ast_sign_bin(struct ast_key *key, const char *msg, int msglen, unsigned char *dsig)
    00318 {
    00319    unsigned char digest[20];
    00320    unsigned int siglen = 128;
    00321    int res;
    00322
    00323    if (key->ktype != AST_KEY_PRIVATE) {
    00324       ast_log(LOG_WARNING, "Cannot sign with a public key\n");
    00325       return -1;
    00326    }
    00327
    00328    /* Calculate digest of message */
    00329    SHA1((unsigned char *)msg, msglen, digest);
    00330
    00331    /* Verify signature */
    00332    res = RSA_sign(NID_sha1, digest, sizeof(digest), dsig, &siglen, key->rsa);
    00333
    00334    if (!res) {
    00335       ast_log(LOG_WARNING, "RSA Signature (key %s) failed\n", key->name);
    00336       return -1;
    00337    }
    00338
    00339    if (siglen != 128) {
    00340       ast_log(LOG_WARNING, "Unexpected signature length %d, expecting %d\n", (int)siglen, (int)128);
    00341       return -1;
    00342    }
    00343
    00344    return 0;
    00345
    00346 }
    00347
    00348 static int __ast_decrypt_bin(unsigned char *dst, const unsigned char *src, int srclen, struct ast_key *key)
    00349 {
    00350    int res;
    00351    int pos = 0;
    00352    if (key->ktype != AST_KEY_PRIVATE) {
    00353       ast_log(LOG_WARNING, "Cannot decrypt with a public key\n");
    00354       return -1;
    00355    }
    00356
    00357    if (srclen % 128) {
    00358       ast_log(LOG_NOTICE, "Tried to decrypt something not a multiple of 128 bytes\n");
    00359       return -1;
    00360    }
    00361    while(srclen) {
    00362       /* Process chunks 128 bytes at a time */
    00363       res = RSA_private_decrypt(128, src, dst, key->rsa, RSA_PKCS1_OAEP_PADDING);
    00364       if (res < 0)
    00365          return -1;
    00366       pos += res;
    00367       src += 128;
    00368       srclen -= 128;
    00369       dst += res;
    00370    }
    00371    return pos;
    00372 }
    00373
    00374 static int __ast_encrypt_bin(unsigned char *dst, const unsigned char *src, int srclen, struct ast_key *key)
    00375 {
    00376    int res;
    00377    int bytes;
    00378    int pos = 0;
    00379    if (key->ktype != AST_KEY_PUBLIC) {
    00380       ast_log(LOG_WARNING, "Cannot encrypt with a private key\n");
    00381       return -1;
    00382    }
    00383
    00384    while(srclen) {
    00385       bytes = srclen;
    00386       if (bytes > 128 - 41)
    00387          bytes = 128 - 41;
    00388       /* Process chunks 128-41 bytes at a time */
    00389       res = RSA_public_encrypt(bytes, src, dst, key->rsa, RSA_PKCS1_OAEP_PADDING);
    00390       if (res != 128) {
    00391          ast_log(LOG_NOTICE, "How odd, encrypted size is %d\n", res);
    00392          return -1;
    00393       }
    00394       src += bytes;
    00395       srclen -= bytes;
    00396       pos += res;
    00397       dst += res;
    00398    }
    00399    return pos;
    00400 }
    00401
    00402 static int __ast_sign(struct ast_key *key, char *msg, char *sig)
    00403 {
    00404    unsigned char dsig[128];
    00405    int siglen = sizeof(dsig);
    00406    int res;
    00407    res = ast_sign_bin(key, msg, strlen(msg), dsig);
    00408    if (!res)
    00409       /* Success -- encode (256 bytes max as documented) */
    00410       ast_base64encode(sig, dsig, siglen, 256);
    00411    return res;
    00412
    00413 }
    00414
    00415 static int __ast_check_signature_bin(struct ast_key *key, const char *msg, int msglen, const unsigned char *dsig)
    00416 {
    00417    unsigned char digest[20];
    00418    int res;
    00419
    00420    if (key->ktype != AST_KEY_PUBLIC) {
    00421       /* Okay, so of course you really *can* but for our purposes
    00422          we're going to say you can't */
    00423       ast_log(LOG_WARNING, "Cannot check message signature with a private key\n");
    00424       return -1;
    00425    }
    00426
    00427    /* Calculate digest of message */
    00428    SHA1((unsigned char *)msg, msglen, digest);
    00429
    00430    /* Verify signature */
    00431    res = RSA_verify(NID_sha1, digest, sizeof(digest), (unsigned char *)dsig, 128, key->rsa);
    00432
    00433    if (!res) {
    00434       ast_log(LOG_DEBUG, "Key failed verification: %s\n", key->name);
    00435       return -1;
    00436    }
    00437    /* Pass */
    00438    return 0;
    00439 }
    00440
    00441 static int __ast_check_signature(struct ast_key *key, const char *msg, const char *sig)
    00442 {
    00443    unsigned char dsig[128];
    00444    int res;
    00445
    00446    /* Decode signature */
    00447    res = ast_base64decode(dsig, sig, sizeof(dsig));
    00448    if (res != sizeof(dsig)) {
    00449       ast_log(LOG_WARNING, "Signature improper length (expect %d, got %d)\n", (int)sizeof(dsig), (int)res);
    00450       return -1;
    00451    }
    00452    res = ast_check_signature_bin(key, msg, strlen(msg), dsig);
    00453    return res;
    00454 }
    00455
    00456 static void crypto_load(int ifd, int ofd)
    00457 {
    00458    struct ast_key *key, *nkey, *last;
    00459    DIR *dir = NULL;
    00460    struct dirent *ent;
    00461    int note = 0;
    00462    /* Mark all keys for deletion */
    00463    ast_mutex_lock(&keylock);
    00464    key = keys;
    00465    while(key) {
    00466       key->delme = 1;
    00467       key = key->next;
    00468    }
    00469    ast_mutex_unlock(&keylock);
    00470    /* Load new keys */
    00471    dir = opendir((char *)ast_config_AST_KEY_DIR);
    00472    if (dir) {
    00473       while((ent = readdir(dir))) {
    00474          try_load_key((char *)ast_config_AST_KEY_DIR, ent->d_name, ifd, ofd, &note);
    00475       }
    00476       closedir(dir);
    00477    } else
    00478       ast_log(LOG_WARNING, "Unable to open key directory '%s'\n", (char *)ast_config_AST_KEY_DIR);
    00479    if (note) {
    00480       ast_log(LOG_NOTICE, "Please run the command 'init keys' to enter the passcodes for the keys\n");
    00481    }
    00482    ast_mutex_lock(&keylock);
    00483    key = keys;
    00484    last = NULL;
    00485    while(key) {
    00486       nkey = key->next;
    00487       if (key->delme) {
    00488          ast_log(LOG_DEBUG, "Deleting key %s type %d\n", key->name, key->ktype);
    00489          /* Do the delete */
    00490          if (last)
    00491             last->next = nkey;
    00492          else
    00493             keys = nkey;
    00494          if (key->rsa)
    00495             RSA_free(key->rsa);
    00496          free(key);
    00497       } else
    00498          last = key;
    00499       key = nkey;
    00500    }
    00501    ast_mutex_unlock(&keylock);
    00502 }
    00503
    00504 static void md52sum(char *sum, unsigned char *md5)
    00505 {
    00506    int x;
    00507    for (x=0;x<16;x++)
    00508       sum += sprintf(sum, "%02x", *(md5++));
    00509 }
    00510
    00511 static int show_keys(int fd, int argc, char *argv[])
    00512 {
    00513    struct ast_key *key;
    00514    char sum[16 * 2 + 1];
    00515    int count_keys = 0;
    00516
    00517    ast_mutex_lock(&keylock);
    00518    key = keys;
    00519    ast_cli(fd, "%-18s %-8s %-16s %-33s\n", "Key Name", "Type", "Status", "Sum");
    00520    while(key) {
    00521       md52sum(sum, key->digest);
    00522       ast_cli(fd, "%-18s %-8s %-16s %-33s\n", key->name,
    00523          (key->ktype & 0xf) == AST_KEY_PUBLIC ? "PUBLIC" : "PRIVATE",
    00524          key->ktype & KEY_NEEDS_PASSCODE ? "[Needs Passcode]" : "[Loaded]", sum);
    00525
    00526       key = key->next;
    00527       count_keys++;
    00528    }
    00529    ast_mutex_unlock(&keylock);
    00530    ast_cli(fd, "%d known RSA keys.\n", count_keys);
    00531    return RESULT_SUCCESS;
    00532 }
    00533
    00534 static int init_keys(int fd, int argc, char *argv[])
    00535 {
    00536    struct ast_key *key;
    00537    int ign;
    00538    char *kn;
    00539    char tmp[256] = "";
    00540
    00541    key = keys;
    00542    while(key) {
    00543       /* Reload keys that need pass codes now */
    00544       if (key->ktype & KEY_NEEDS_PASSCODE) {
    00545          kn = key->fn + strlen(ast_config_AST_KEY_DIR) + 1;
    00546          ast_copy_string(tmp, kn, sizeof(tmp));
    00547          try_load_key((char *)ast_config_AST_KEY_DIR, tmp, fd, fd, &ign);
    00548       }
    00549       key = key->next;
    00550    }
    00551    return RESULT_SUCCESS;
    00552 }
    00553
    00554 static char show_key_usage[] =
    00555 "Usage: show keys\n"
    00556 "       Displays information about RSA keys known by Asterisk\n";
    00557
    00558 static char init_keys_usage[] =
    00559 "Usage: init keys\n"
    00560 "       Initializes private keys (by reading in pass code from the user)\n";
    00561
    00562 static struct ast_cli_entry cli_show_keys =
    00563 { { "show", "keys", NULL }, show_keys, "Displays RSA key information", show_key_usage };
    00564
    00565 static struct ast_cli_entry cli_init_keys =
    00566 { { "init", "keys", NULL }, init_keys, "Initialize RSA key passcodes", init_keys_usage };
    00567
    00568 static int crypto_init(void)
    00569 {
    00570    SSL_library_init();
    00571    ERR_load_crypto_strings();
    00572    ast_cli_register(&cli_show_keys);
    00573    ast_cli_register(&cli_init_keys);
    00574
    00575    /* Install ourselves into stubs */
    00576    ast_key_get = __ast_key_get;
    00577    ast_check_signature = __ast_check_signature;
    00578    ast_check_signature_bin = __ast_check_signature_bin;
    00579    ast_sign = __ast_sign;
    00580    ast_sign_bin = __ast_sign_bin;
    00581    ast_encrypt_bin = __ast_encrypt_bin;
    00582    ast_decrypt_bin = __ast_decrypt_bin;
    00583    return 0;
    00584 }
    00585
    00586 int reload(void)
    00587 {
    00588    crypto_load(-1, -1);
    00589    return 0;
    00590 }
    00591
    00592 int load_module(void)
    00593 {
    00594    crypto_init();
    00595    if (option_initcrypto)
    00596       crypto_load(STDIN_FILENO, STDOUT_FILENO);
    00597    else
    00598       crypto_load(-1, -1);
    00599    return 0;
    00600 }
    00601
    00602 int unload_module(void)
    00603 {
    00604    /* Can't unload this once we're loaded */
    00605    return -1;
    00606 }
    00607
    00608 char *description(void)
    00609 {
    00610    return "Cryptographic Digital Signatures";
    00611 }
    00612
    00613 int usecount(void)
    00614 {
    00615    /* We should never be unloaded */
    00616    return 1;
    00617 }
    00618
    00619 char *key()
    00620 {
    00621    return ASTERISK_GPL_KEY;
    00622 }