res_crypto.c

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/*
 * Asterisk -- An open source telephony toolkit.
 *
 * Copyright (C) 1999 - 2006, Digium, Inc.
 *
 * Mark Spencer <[email protected]>
 *
 * 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 <[email protected]>
 *
 * Uses the OpenSSL library, available at
 * http://www.openssl.org/
 */

/*** MODULEINFO
   <depend>openssl</depend>
   <support_level>core</support_level>
 ***/

#include "asterisk.h"

#include <dirent.h>                 /* for closedir, opendir, readdir, DIR */

#include <openssl/aes.h>            /* for AES_decrypt, AES_encrypt, AES_set... */
#include <openssl/err.h>            /* for ERR_print_errors_fp */
#include <openssl/ssl.h>            /* for NID_sha1, RSA */
#include <openssl/pem.h>            /* for PEM_read_RSAPrivateKey, PEM_read_... */
#include <openssl/rsa.h>            /* for RSA_free, RSA_private_decrypt, RSA */
#include <openssl/sha.h>            /* for SHA1 */

#include "asterisk/cli.h"           /* for ast_cli, ast_cli_args, ast_cli_entry */
#include "asterisk/compat.h"        /* for strcasecmp */
#include "asterisk/io.h"            /* for ast_hide_password, ast_restore_tty */
#include "asterisk/linkedlists.h"   /* for AST_RWLIST_TRAVERSE, AST_RWLIST_U... */
#include "asterisk/logger.h"        /* for ast_log, LOG_WARNING, LOG_NOTICE */
#include "asterisk/md5.h"           /* for MD5Final, MD5Init, MD5Update, MD5... */
#include "asterisk/module.h"        /* for ast_module_flags::AST_MODFLAG_GLO... */
#include "asterisk/options.h"       /* for ast_opt_init_keys */
#include "asterisk/paths.h"         /* for ast_config_AST_KEY_DIR */
#include "asterisk/utils.h"         /* for ast_copy_string, ast_base64decode */

#define AST_API_MODULE
#include "asterisk/crypto.h"        /* for AST_KEY_PUBLIC, AST_KEY_PRIVATE */

/*
 * 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
 *
 */

#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];
   AST_RWLIST_ENTRY(ast_key) list;
};

static AST_RWLIST_HEAD_STATIC(keys, ast_key);

/*!
 * \brief setting of priv key
 * \param buf
 * \param size
 * \param rwflag
 * \param userdata
 * \return length of string,-1 on failure
*/
static int pw_cb(char *buf, int size, int rwflag, void *userdata)
{
   struct ast_key *key = (struct ast_key *)userdata;
   char prompt[256];
   int tmp;
   int res;

   if (key->infd < 0) {
      /* Note that we were at least called */
      key->infd = -2;
      return -1;
   }

   snprintf(prompt, sizeof(prompt), ">>>> passcode for %s key '%s': ",
       key->ktype == AST_KEY_PRIVATE ? "PRIVATE" : "PUBLIC", key->name);
   if (write(key->outfd, prompt, strlen(prompt)) < 0) {
      ast_log(LOG_WARNING, "write() failed: %s\n", strerror(errno));
      key->infd = -2;
      return -1;
   }
   tmp = ast_hide_password(key->infd);
   memset(buf, 0, size);
   res = read(key->infd, buf, size);
   if (res == -1) {
      ast_log(LOG_WARNING, "read() failed: %s\n", strerror(errno));
   }
   ast_restore_tty(key->infd, tmp);
   if (buf[strlen(buf) -1] == '\n') {
      buf[strlen(buf) - 1] = '\0';
   }
   return strlen(buf);
}

/*!
 * \brief return the ast_key structure for name
 * \see ast_key_get
*/
struct ast_key * AST_OPTIONAL_API_NAME(ast_key_get)(const char *kname, int ktype)
{
   struct ast_key *key;

   AST_RWLIST_RDLOCK(&keys);
   AST_RWLIST_TRAVERSE(&keys, key, list) {
      if (!strcmp(kname, key->name) &&
          (ktype == key->ktype)) {
         break;
      }
   }
   AST_RWLIST_UNLOCK(&keys);

   return key;
}

/*!
 * \brief load RSA key from file
 * \param dir directory string
 * \param fname name of file
 * \param ifd incoming file descriptor
 * \param ofd outgoing file descriptor
 * \param not2
 * \retval key on success.
 * \retval NULL on failure.
*/
static struct ast_key *try_load_key(const char *dir, const char *fname, int ifd, int ofd, int *not2)
{
   int ktype = 0, found = 0;
   char *c = NULL, ffname[256];
   unsigned char digest[16];
   FILE *f;
   struct MD5Context md5;
   struct ast_key *key;
   static int notice = 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);

   /* Open file */
   if (!(f = fopen(ffname, "r"))) {
      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] = "";
      if (!fgets(buf, sizeof(buf), f)) {
         continue;
      }
      if (!feof(f)) {
         MD5Update(&md5, (unsigned char *) buf, strlen(buf));
      }
   }
   MD5Final(digest, &md5);

   /* Look for an existing key */
   AST_RWLIST_TRAVERSE(&keys, key, list) {
      if (!strcasecmp(key->fn, ffname)) {
         break;
      }
   }

   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;
      }
   }
   /* 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;
         ast_verb(3, "Loaded %s key '%s'\n", key->ktype == AST_KEY_PUBLIC ? "PUBLIC" : "PRIVATE", key->name);
         ast_debug(1, "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 "keys init" when done */
      *not2 = 1;
   }

   /* If this is a new key add it to the list */
   if (!found) {
      AST_RWLIST_INSERT_TAIL(&keys, key, list);
   }

   return key;
}

/*!
 * \brief signs outgoing message with public key
 * \see ast_sign_bin
*/
int AST_OPTIONAL_API_NAME(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 */
   if (!(res = RSA_sign(NID_sha1, digest, sizeof(digest), dsig, &siglen, key->rsa))) {
      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;
}

/*!
 * \brief decrypt a message
 * \see ast_decrypt_bin
*/
int AST_OPTIONAL_API_NAME(ast_decrypt_bin)(unsigned char *dst, const unsigned char *src, int srclen, struct ast_key *key)
{
   int res, 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 */
      if ((res = RSA_private_decrypt(128, src, dst, key->rsa, RSA_PKCS1_OAEP_PADDING)) < 0) {
         return -1;
      }
      pos += res;
      src += 128;
      srclen -= 128;
      dst += res;
   }

   return pos;
}

/*!
 * \brief encrypt a message
 * \see ast_encrypt_bin
*/
int AST_OPTIONAL_API_NAME(ast_encrypt_bin)(unsigned char *dst, const unsigned char *src, int srclen, struct ast_key *key)
{
   int res, bytes, 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 */
      if ((res = RSA_public_encrypt(bytes, src, dst, key->rsa, RSA_PKCS1_OAEP_PADDING)) != 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;
}

/*!
 * \brief wrapper for __ast_sign_bin then base64 encode it
 * \see ast_sign
*/
int AST_OPTIONAL_API_NAME(ast_sign)(struct ast_key *key, char *msg, char *sig)
{
   unsigned char dsig[128];
   int siglen = sizeof(dsig), res;

   if (!(res = ast_sign_bin(key, msg, strlen(msg), dsig))) {
      /* Success -- encode (256 bytes max as documented) */
      ast_base64encode(sig, dsig, siglen, 256);
   }

   return res;
}

/*!
 * \brief check signature of a message
 * \see ast_check_signature_bin
*/
int AST_OPTIONAL_API_NAME(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 */
   if (!(res = RSA_verify(NID_sha1, digest, sizeof(digest), (unsigned char *)dsig, 128, key->rsa))) {
      ast_debug(1, "Key failed verification: %s\n", key->name);
      return -1;
   }

   /* Pass */
   return 0;
}

/*!
 * \brief base64 decode then sent to __ast_check_signature_bin
 * \see ast_check_signature
*/
int AST_OPTIONAL_API_NAME(ast_check_signature)(struct ast_key *key, const char *msg, const char *sig)
{
   unsigned char dsig[128];
   int res;

   /* Decode signature */
   if ((res = ast_base64decode(dsig, sig, sizeof(dsig))) != 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;
}

int AST_OPTIONAL_API_NAME(ast_crypto_loaded)(void)
{
   return 1;
}

int AST_OPTIONAL_API_NAME(ast_aes_set_encrypt_key)(const unsigned char *key, ast_aes_encrypt_key *ctx)
{
   return AES_set_encrypt_key(key, 128, ctx);
}

int AST_OPTIONAL_API_NAME(ast_aes_set_decrypt_key)(const unsigned char *key, ast_aes_decrypt_key *ctx)
{
   return AES_set_decrypt_key(key, 128, ctx);
}

void AST_OPTIONAL_API_NAME(ast_aes_encrypt)(const unsigned char *in, unsigned char *out, const ast_aes_encrypt_key *ctx)
{
   return AES_encrypt(in, out, ctx);
}

void AST_OPTIONAL_API_NAME(ast_aes_decrypt)(const unsigned char *in, unsigned char *out, const ast_aes_decrypt_key *ctx)
{
   return AES_decrypt(in, out, ctx);
}

/*!
 * \brief refresh RSA keys from file
 * \param ifd file descriptor
 * \param ofd file descriptor
 * \return void
*/
static void crypto_load(int ifd, int ofd)
{
   struct ast_key *key;
   DIR *dir = NULL;
   struct dirent *ent;
   int note = 0;

   AST_RWLIST_WRLOCK(&keys);

   /* Mark all keys for deletion */
   AST_RWLIST_TRAVERSE(&keys, key, list) {
      key->delme = 1;
   }

   /* Load new keys */
   if ((dir = opendir(ast_config_AST_KEY_DIR))) {
      while ((ent = readdir(dir))) {
         try_load_key(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", ast_config_AST_KEY_DIR);
   }

   if (note) {
      ast_log(LOG_NOTICE, "Please run the command 'keys init' to enter the passcodes for the keys\n");
   }

   /* Delete any keys that are no longer present */
   AST_RWLIST_TRAVERSE_SAFE_BEGIN(&keys, key, list) {
      if (key->delme) {
         ast_debug(1, "Deleting key %s type %d\n", key->name, key->ktype);
         AST_RWLIST_REMOVE_CURRENT(list);
         if (key->rsa) {
            RSA_free(key->rsa);
         }
         ast_free(key);
      }
   }
   AST_RWLIST_TRAVERSE_SAFE_END;

   AST_RWLIST_UNLOCK(&keys);
}

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

/*!
 * \brief show the list of RSA keys
 * \param e CLI command
 * \param cmd
 * \param a list of CLI arguments
 * \return CLI_SUCCESS
*/
static char *handle_cli_keys_show(struct ast_cli_entry *e, int cmd, struct ast_cli_args *a)
{
#define FORMAT "%-18s %-8s %-16s %-33s\n"

   struct ast_key *key;
   char sum[16 * 2 + 1];
   int count_keys = 0;

   switch (cmd) {
   case CLI_INIT:
      e->command = "keys show";
      e->usage =
         "Usage: keys show\n"
         "       Displays information about RSA keys known by Asterisk\n";
      return NULL;
   case CLI_GENERATE:
      return NULL;
   }

   ast_cli(a->fd, FORMAT, "Key Name", "Type", "Status", "Sum");
   ast_cli(a->fd, FORMAT, "------------------", "--------", "----------------", "--------------------------------");

   AST_RWLIST_RDLOCK(&keys);
   AST_RWLIST_TRAVERSE(&keys, key, list) {
      md52sum(sum, key->digest);
      ast_cli(a->fd, FORMAT, key->name,
         (key->ktype & 0xf) == AST_KEY_PUBLIC ? "PUBLIC" : "PRIVATE",
         key->ktype & KEY_NEEDS_PASSCODE ? "[Needs Passcode]" : "[Loaded]", sum);
      count_keys++;
   }
   AST_RWLIST_UNLOCK(&keys);

   ast_cli(a->fd, "\n%d known RSA keys.\n", count_keys);

   return CLI_SUCCESS;

#undef FORMAT
}

/*!
 * \brief initialize all RSA keys
 * \param e CLI command
 * \param cmd
 * \param a list of CLI arguments
 * \return CLI_SUCCESS
*/
static char *handle_cli_keys_init(struct ast_cli_entry *e, int cmd, struct ast_cli_args *a)
{
   struct ast_key *key;
   int ign;
   char *kn, tmp[256] = "";

   switch (cmd) {
   case CLI_INIT:
      e->command = "keys init";
      e->usage =
         "Usage: keys init\n"
         "       Initializes private keys (by reading in pass code from\n"
         "       the user)\n";
      return NULL;
   case CLI_GENERATE:
      return NULL;
   }

   if (a->argc != 2) {
      return CLI_SHOWUSAGE;
   }

   AST_RWLIST_WRLOCK(&keys);
   AST_RWLIST_TRAVERSE_SAFE_BEGIN(&keys, key, list) {
      /* 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(ast_config_AST_KEY_DIR, tmp, a->fd, a->fd, &ign);
      }
   }
   AST_RWLIST_TRAVERSE_SAFE_END
   AST_RWLIST_UNLOCK(&keys);

   return CLI_SUCCESS;
}

static struct ast_cli_entry cli_crypto[] = {
   AST_CLI_DEFINE(handle_cli_keys_show, "Displays RSA key information"),
   AST_CLI_DEFINE(handle_cli_keys_init, "Initialize RSA key passcodes")
};

/*! \brief initialise the res_crypto module */
static int crypto_init(void)
{
   ast_cli_register_multiple(cli_crypto, ARRAY_LEN(cli_crypto));
   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 AST_MODULE_LOAD_SUCCESS;
}

static int unload_module(void)
{
   ast_cli_unregister_multiple(cli_crypto, ARRAY_LEN(cli_crypto));

   return 0;
}

AST_MODULE_INFO(ASTERISK_GPL_KEY, AST_MODFLAG_GLOBAL_SYMBOLS | AST_MODFLAG_LOAD_ORDER, "Cryptographic Digital Signatures",
   .support_level = AST_MODULE_SUPPORT_CORE,
   .load = load_module,
   .unload = unload_module,
   .reload = reload,
   .load_pri = AST_MODPRI_CHANNEL_DEPEND, /*!< Since we don't have a config file, we could move up to REALTIME_DEPEND, if necessary */
);