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Last updated: Sat Feb 3 05:00:53 2007

Asterisk developer's documentation :: Codename Pineapple

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res_crypto.c

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/*
 * Asterisk -- An open source telephony toolkit.
 *
 * Copyright (C) 1999 - 2006, Digium, Inc.
 *
 * Mark Spencer <markster@digium.com>
 *
 * See http://www.asterisk.org for more information about
 * the Asterisk project. Please do not directly contact
 * any of the maintainers of this project for assistance;
 * the project provides a web site, mailing lists and IRC
 * channels for your use.
 *
 * This program is free software, distributed under the terms of
 * the GNU General Public License Version 2. See the LICENSE file
 * at the top of the source tree.
 */

/*! \file
 *
 * \brief Provide Cryptographic Signature capability
 *
 * \author Mark Spencer <markster@digium.com> 
 */

/*** MODULEINFO
   <depend>ssl</depend>
 ***/

#include "asterisk.h"

ASTERISK_FILE_VERSION(__FILE__, "$Revision: 48395 $")

#include <sys/types.h>
#include <openssl/ssl.h>
#include <openssl/err.h>
#include <stdio.h>
#include <dirent.h>
#include <string.h>
#include <errno.h>
#include <unistd.h>
#include <fcntl.h>

#include "asterisk/file.h"
#include "asterisk/channel.h"
#include "asterisk/logger.h"
#include "asterisk/say.h"
#include "asterisk/module.h"
#include "asterisk/options.h"
#include "asterisk/crypto.h"
#include "asterisk/md5.h"
#include "asterisk/cli.h"
#include "asterisk/io.h"
#include "asterisk/lock.h"
#include "asterisk/utils.h"

/*
 * Asterisk uses RSA keys with SHA-1 message digests for its
 * digital signatures.  The choice of RSA is due to its higher
 * throughput on verification, and the choice of SHA-1 based
 * on the recently discovered collisions in MD5's compression 
 * algorithm and recommendations of avoiding MD5 in new schemes
 * from various industry experts.
 *
 * We use OpenSSL to provide our crypto routines, although we never
 * actually use full-up SSL
 *
 */

/*
 * XXX This module is not very thread-safe.  It is for everyday stuff
 *     like reading keys and stuff, but there are all kinds of weird
 *     races with people running reload and key init at the same time
 *     for example
 *
 * XXXX
 */

AST_MUTEX_DEFINE_STATIC(keylock);

#define KEY_NEEDS_PASSCODE (1 << 16)

struct ast_key {
   /* Name of entity */
   char name[80];
   /* File name */
   char fn[256];
   /* Key type (AST_KEY_PUB or AST_KEY_PRIV, along with flags from above) */
   int ktype;
   /* RSA structure (if successfully loaded) */
   RSA *rsa;
   /* Whether we should be deleted */
   int delme;
   /* FD for input (or -1 if no input allowed, or -2 if we needed input) */
   int infd;
   /* FD for output */
   int outfd;
   /* Last MD5 Digest */
   unsigned char digest[16];
   struct ast_key *next;
};

static struct ast_key *keys = NULL;


#if 0
static int fdprint(int fd, char *s)
{
        return write(fd, s, strlen(s) + 1);
}
#endif
static int pw_cb(char *buf, int size, int rwflag, void *userdata)
{
   struct ast_key *key = (struct ast_key *)userdata;
   char prompt[256];
   int res;
   int tmp;
   if (key->infd > -1) {
      snprintf(prompt, sizeof(prompt), ">>>> passcode for %s key '%s': ",
          key->ktype == AST_KEY_PRIVATE ? "PRIVATE" : "PUBLIC", key->name);
      write(key->outfd, prompt, strlen(prompt));
      memset(buf, 0, sizeof(buf));
      tmp = ast_hide_password(key->infd);
      memset(buf, 0, size);
      res = read(key->infd, buf, size);
      ast_restore_tty(key->infd, tmp);
      if (buf[strlen(buf) -1] == '\n')
         buf[strlen(buf) - 1] = '\0';
      return strlen(buf);
   } else {
      /* Note that we were at least called */
      key->infd = -2;
   }
   return -1;
}

static struct ast_key *__ast_key_get(const char *kname, int ktype)
{
   struct ast_key *key;
   ast_mutex_lock(&keylock);
   key = keys;
   while(key) {
      if (!strcmp(kname, key->name) &&
          (ktype == key->ktype))
         break;
      key = key->next;
   }
   ast_mutex_unlock(&keylock);
   return key;
}

static struct ast_key *try_load_key (char *dir, char *fname, int ifd, int ofd, int *not2)
{
   int ktype = 0;
   char *c = NULL;
   char ffname[256];
   unsigned char digest[16];
   FILE *f;
   struct MD5Context md5;
   struct ast_key *key;
   static int notice = 0;
   int found = 0;

   /* Make sure its name is a public or private key */

   if ((c = strstr(fname, ".pub")) && !strcmp(c, ".pub")) {
      ktype = AST_KEY_PUBLIC;
   } else if ((c = strstr(fname, ".key")) && !strcmp(c, ".key")) {
      ktype = AST_KEY_PRIVATE;
   } else
      return NULL;

   /* Get actual filename */
   snprintf(ffname, sizeof(ffname), "%s/%s", dir, fname);

   ast_mutex_lock(&keylock);
   key = keys;
   while(key) {
      /* Look for an existing version already */
      if (!strcasecmp(key->fn, ffname)) 
         break;
      key = key->next;
   }
   ast_mutex_unlock(&keylock);

   /* Open file */
   f = fopen(ffname, "r");
   if (!f) {
      ast_log(LOG_WARNING, "Unable to open key file %s: %s\n", ffname, strerror(errno));
      return NULL;
   }
   MD5Init(&md5);
   while(!feof(f)) {
      /* Calculate a "whatever" quality md5sum of the key */
      char buf[256];
      memset(buf, 0, 256);
      fgets(buf, sizeof(buf), f);
      if (!feof(f)) {
         MD5Update(&md5, (unsigned char *) buf, strlen(buf));
      }
   }
   MD5Final(digest, &md5);
   if (key) {
      /* If the MD5 sum is the same, and it isn't awaiting a passcode 
         then this is far enough */
      if (!memcmp(digest, key->digest, 16) &&
          !(key->ktype & KEY_NEEDS_PASSCODE)) {
         fclose(f);
         key->delme = 0;
         return NULL;
      } else {
         /* Preserve keytype */
         ktype = key->ktype;
         /* Recycle the same structure */
         found++;
      }
   }

   /* Make fname just be the normal name now */
   *c = '\0';
   if (!key) {
      if (!(key = ast_calloc(1, sizeof(*key)))) {
         fclose(f);
         return NULL;
      }
   }
   /* At this point we have a key structure (old or new).  Time to
      fill it with what we know */
   /* Gotta lock if this one already exists */
   if (found)
      ast_mutex_lock(&keylock);
   /* First the filename */
   ast_copy_string(key->fn, ffname, sizeof(key->fn));
   /* Then the name */
   ast_copy_string(key->name, fname, sizeof(key->name));
   key->ktype = ktype;
   /* Yes, assume we're going to be deleted */
   key->delme = 1;
   /* Keep the key type */
   memcpy(key->digest, digest, 16);
   /* Can I/O takes the FD we're given */
   key->infd = ifd;
   key->outfd = ofd;
   /* Reset the file back to the beginning */
   rewind(f);
   /* Now load the key with the right method */
   if (ktype == AST_KEY_PUBLIC)
      key->rsa = PEM_read_RSA_PUBKEY(f, NULL, pw_cb, key);
   else
      key->rsa = PEM_read_RSAPrivateKey(f, NULL, pw_cb, key);
   fclose(f);
   if (key->rsa) {
      if (RSA_size(key->rsa) == 128) {
         /* Key loaded okay */
         key->ktype &= ~KEY_NEEDS_PASSCODE;
         if (option_verbose > 2)
            ast_verbose(VERBOSE_PREFIX_3 "Loaded %s key '%s'\n", key->ktype == AST_KEY_PUBLIC ? "PUBLIC" : "PRIVATE", key->name);
         if (option_debug)
            ast_log(LOG_DEBUG, "Key '%s' loaded OK\n", key->name);
         key->delme = 0;
      } else
         ast_log(LOG_NOTICE, "Key '%s' is not expected size.\n", key->name);
   } else if (key->infd != -2) {
      ast_log(LOG_WARNING, "Key load %s '%s' failed\n",key->ktype == AST_KEY_PUBLIC ? "PUBLIC" : "PRIVATE", key->name);
      if (ofd > -1) {
         ERR_print_errors_fp(stderr);
      } else
         ERR_print_errors_fp(stderr);
   } else {
      ast_log(LOG_NOTICE, "Key '%s' needs passcode.\n", key->name);
      key->ktype |= KEY_NEEDS_PASSCODE;
      if (!notice) {
         if (!ast_opt_init_keys) 
            ast_log(LOG_NOTICE, "Add the '-i' flag to the asterisk command line if you want to automatically initialize passcodes at launch.\n");
         notice++;
      }
      /* Keep it anyway */
      key->delme = 0;
      /* Print final notice about "init keys" when done */
      *not2 = 1;
   }
   if (found)
      ast_mutex_unlock(&keylock);
   if (!found) {
      ast_mutex_lock(&keylock);
      key->next = keys;
      keys = key;
      ast_mutex_unlock(&keylock);
   }
   return key;
}

#if 0

static void dump(unsigned char *src, int len)
{
   int x; 
   for (x=0;x<len;x++)
      printf("%02x", *(src++));
   printf("\n");
}

static char *binary(int y, int len)
{
   static char res[80];
   int x;
   memset(res, 0, sizeof(res));
   for (x=0;x<len;x++) {
      if (y & (1 << x))
         res[(len - x - 1)] = '1';
      else
         res[(len - x - 1)] = '0';
   }
   return res;
}

#endif

static int __ast_sign_bin(struct ast_key *key, const char *msg, int msglen, unsigned char *dsig)
{
   unsigned char digest[20];
   unsigned int siglen = 128;
   int res;

   if (key->ktype != AST_KEY_PRIVATE) {
      ast_log(LOG_WARNING, "Cannot sign with a public key\n");
      return -1;
   }

   /* Calculate digest of message */
   SHA1((unsigned char *)msg, msglen, digest);

   /* Verify signature */
   res = RSA_sign(NID_sha1, digest, sizeof(digest), dsig, &siglen, key->rsa);
   
   if (!res) {
      ast_log(LOG_WARNING, "RSA Signature (key %s) failed\n", key->name);
      return -1;
   }

   if (siglen != 128) {
      ast_log(LOG_WARNING, "Unexpected signature length %d, expecting %d\n", (int)siglen, (int)128);
      return -1;
   }

   return 0;
   
}

static int __ast_decrypt_bin(unsigned char *dst, const unsigned char *src, int srclen, struct ast_key *key)
{
   int res;
   int pos = 0;
   if (key->ktype != AST_KEY_PRIVATE) {
      ast_log(LOG_WARNING, "Cannot decrypt with a public key\n");
      return -1;
   }

   if (srclen % 128) {
      ast_log(LOG_NOTICE, "Tried to decrypt something not a multiple of 128 bytes\n");
      return -1;
   }
   while(srclen) {
      /* Process chunks 128 bytes at a time */
      res = RSA_private_decrypt(128, src, dst, key->rsa, RSA_PKCS1_OAEP_PADDING);
      if (res < 0)
         return -1;
      pos += res;
      src += 128;
      srclen -= 128;
      dst += res;
   }
   return pos;
}

static int __ast_encrypt_bin(unsigned char *dst, const unsigned char *src, int srclen, struct ast_key *key)
{
   int res;
   int bytes;
   int pos = 0;
   if (key->ktype != AST_KEY_PUBLIC) {
      ast_log(LOG_WARNING, "Cannot encrypt with a private key\n");
      return -1;
   }
   
   while(srclen) {
      bytes = srclen;
      if (bytes > 128 - 41)
         bytes = 128 - 41;
      /* Process chunks 128-41 bytes at a time */
      res = RSA_public_encrypt(bytes, src, dst, key->rsa, RSA_PKCS1_OAEP_PADDING);
      if (res != 128) {
         ast_log(LOG_NOTICE, "How odd, encrypted size is %d\n", res);
         return -1;
      }
      src += bytes;
      srclen -= bytes;
      pos += res;
      dst += res;
   }
   return pos;
}

static int __ast_sign(struct ast_key *key, char *msg, char *sig)
{
   unsigned char dsig[128];
   int siglen = sizeof(dsig);
   int res;
   res = ast_sign_bin(key, msg, strlen(msg), dsig);
   if (!res)
      /* Success -- encode (256 bytes max as documented) */
      ast_base64encode(sig, dsig, siglen, 256);
   return res;
   
}

static int __ast_check_signature_bin(struct ast_key *key, const char *msg, int msglen, const unsigned char *dsig)
{
   unsigned char digest[20];
   int res;

   if (key->ktype != AST_KEY_PUBLIC) {
      /* Okay, so of course you really *can* but for our purposes
         we're going to say you can't */
      ast_log(LOG_WARNING, "Cannot check message signature with a private key\n");
      return -1;
   }

   /* Calculate digest of message */
   SHA1((unsigned char *)msg, msglen, digest);

   /* Verify signature */
   res = RSA_verify(NID_sha1, digest, sizeof(digest), (unsigned char *)dsig, 128, key->rsa);
   
   if (!res) {
      if (option_debug)
         ast_log(LOG_DEBUG, "Key failed verification: %s\n", key->name);
      return -1;
   }
   /* Pass */
   return 0;
}

static int __ast_check_signature(struct ast_key *key, const char *msg, const char *sig)
{
   unsigned char dsig[128];
   int res;

   /* Decode signature */
   res = ast_base64decode(dsig, sig, sizeof(dsig));
   if (res != sizeof(dsig)) {
      ast_log(LOG_WARNING, "Signature improper length (expect %d, got %d)\n", (int)sizeof(dsig), (int)res);
      return -1;
   }
   res = ast_check_signature_bin(key, msg, strlen(msg), dsig);
   return res;
}

static void crypto_load(int ifd, int ofd)
{
   struct ast_key *key, *nkey, *last;
   DIR *dir = NULL;
   struct dirent *ent;
   int note = 0;
   /* Mark all keys for deletion */
   ast_mutex_lock(&keylock);
   key = keys;
   while(key) {
      key->delme = 1;
      key = key->next;
   }
   ast_mutex_unlock(&keylock);
   /* Load new keys */
   dir = opendir((char *)ast_config_AST_KEY_DIR);
   if (dir) {
      while((ent = readdir(dir))) {
         try_load_key((char *)ast_config_AST_KEY_DIR, ent->d_name, ifd, ofd, &note);
      }
      closedir(dir);
   } else
      ast_log(LOG_WARNING, "Unable to open key directory '%s'\n", (char *)ast_config_AST_KEY_DIR);
   if (note) {
      ast_log(LOG_NOTICE, "Please run the command 'init keys' to enter the passcodes for the keys\n");
   }
   ast_mutex_lock(&keylock);
   key = keys;
   last = NULL;
   while(key) {
      nkey = key->next;
      if (key->delme) {
         if (option_debug)
            ast_log(LOG_DEBUG, "Deleting key %s type %d\n", key->name, key->ktype);
         /* Do the delete */
         if (last)
            last->next = nkey;
         else
            keys = nkey;
         if (key->rsa)
            RSA_free(key->rsa);
         free(key);
      } else 
         last = key;
      key = nkey;
   }
   ast_mutex_unlock(&keylock);
}

static void md52sum(char *sum, unsigned char *md5)
{
   int x;
   for (x=0;x<16;x++) 
      sum += sprintf(sum, "%02x", *(md5++));
}

static int show_keys(int fd, int argc, char *argv[])
{
   struct ast_key *key;
   char sum[16 * 2 + 1];
   int count_keys = 0;

   ast_mutex_lock(&keylock);
   key = keys;
   ast_cli(fd, "%-18s %-8s %-16s %-33s\n", "Key Name", "Type", "Status", "Sum");
   while(key) {
      md52sum(sum, key->digest);
      ast_cli(fd, "%-18s %-8s %-16s %-33s\n", key->name, 
         (key->ktype & 0xf) == AST_KEY_PUBLIC ? "PUBLIC" : "PRIVATE",
         key->ktype & KEY_NEEDS_PASSCODE ? "[Needs Passcode]" : "[Loaded]", sum);
            
      key = key->next;
      count_keys++;
   }
   ast_mutex_unlock(&keylock);
   ast_cli(fd, "%d known RSA keys.\n", count_keys);
   return RESULT_SUCCESS;
}

static int init_keys(int fd, int argc, char *argv[])
{
   struct ast_key *key;
   int ign;
   char *kn;
   char tmp[256] = "";

   key = keys;
   while(key) {
      /* Reload keys that need pass codes now */
      if (key->ktype & KEY_NEEDS_PASSCODE) {
         kn = key->fn + strlen(ast_config_AST_KEY_DIR) + 1;
         ast_copy_string(tmp, kn, sizeof(tmp));
         try_load_key((char *)ast_config_AST_KEY_DIR, tmp, fd, fd, &ign);
      }
      key = key->next;
   }
   return RESULT_SUCCESS;
}

static const char show_key_usage[] =
"Usage: keys show\n"
"       Displays information about RSA keys known by Asterisk\n";

static const char init_keys_usage[] =
"Usage: keys init\n"
"       Initializes private keys (by reading in pass code from the user)\n";

static struct ast_cli_entry cli_crypto[] = {
   { { "keys", "show", NULL },
   show_keys, "Displays RSA key information",
   show_key_usage },

   { { "keys", "init", NULL },
   init_keys, "Initialize RSA key passcodes",
   init_keys_usage },
};

static int crypto_init(void)
{
   SSL_library_init();
   ERR_load_crypto_strings();
   ast_cli_register_multiple(cli_crypto, sizeof(cli_crypto) / sizeof(struct ast_cli_entry));

   /* Install ourselves into stubs */
   ast_key_get = __ast_key_get;
   ast_check_signature = __ast_check_signature;
   ast_check_signature_bin = __ast_check_signature_bin;
   ast_sign = __ast_sign;
   ast_sign_bin = __ast_sign_bin;
   ast_encrypt_bin = __ast_encrypt_bin;
   ast_decrypt_bin = __ast_decrypt_bin;
   return 0;
}

static int reload(void)
{
   crypto_load(-1, -1);
   return 0;
}

static int load_module(void)
{
   crypto_init();
   if (ast_opt_init_keys)
      crypto_load(STDIN_FILENO, STDOUT_FILENO);
   else
      crypto_load(-1, -1);
   return 0;
}

static int unload_module(void)
{
   /* Can't unload this once we're loaded */
   return -1;
}

/* needs usecount semantics defined */
AST_MODULE_INFO(ASTERISK_GPL_KEY, AST_MODFLAG_GLOBAL_SYMBOLS, "Cryptographic Digital Signatures",
      .load = load_module,
      .unload = unload_module,
      .reload = reload
   );

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