func_aes.c

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/*
 * Asterisk -- An open source telephony toolkit.
 *
 * Copyright (C) 2009, Digium, Inc.
 *
 * 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 AES encryption/decryption dialplan functions
 *
 * \author David Vossel <[email protected]>
 * \ingroup functions
 */

/*** MODULEINFO
   <depend>res_crypto</depend>
   <depend>crypto</depend>
   <support_level>core</support_level>
 ***/

#include "asterisk.h"

#include "asterisk/module.h"
#include "asterisk/pbx.h"
#include "asterisk/app.h"
#include "asterisk/crypto.h"

#define AES_BLOCK_SIZE 16

/*** DOCUMENTATION
   <function name="AES_ENCRYPT" language="en_US">
      <synopsis>
         Encrypt a string with AES given a 16 character key.
      </synopsis>
      <syntax>
         <parameter name="key" required="true">
            <para>AES Key</para>
         </parameter>
         <parameter name="string" required="true">
            <para>Input string</para>
         </parameter>
      </syntax>
      <description>
         <para>Returns an AES encrypted string encoded in base64.</para>
      </description>
      <see-also>
         <ref type="function">AES_DECRYPT</ref>
         <ref type="function">BASE64_ENCODE</ref>
         <ref type="function">BASE64_DECODE</ref>
      </see-also>
   </function>
   <function name="AES_DECRYPT" language="en_US">
      <synopsis>
         Decrypt a string encoded in base64 with AES given a 16 character key.
      </synopsis>
      <syntax>
         <parameter name="key" required="true">
            <para>AES Key</para>
         </parameter>
         <parameter name="string" required="true">
            <para>Input string.</para>
         </parameter>
      </syntax>
      <description>
         <para>Returns the plain text string.</para>
      </description>
      <see-also>
         <ref type="function">AES_ENCRYPT</ref>
         <ref type="function">BASE64_ENCODE</ref>
         <ref type="function">BASE64_DECODE</ref>
      </see-also>
   </function>
 ***/


static int aes_helper(struct ast_channel *chan, const char *cmd, char *data,
          char *buf, size_t len)
{
   unsigned char curblock[AES_BLOCK_SIZE] = { 0, };
   char *tmp;
   char *tmpP;
   int data_len, encrypt;
   ast_aes_encrypt_key ecx;                        /*  AES 128 Encryption context */
   ast_aes_decrypt_key dcx;

   AST_DECLARE_APP_ARGS(args,
      AST_APP_ARG(key);
      AST_APP_ARG(data);
   );

   AST_STANDARD_APP_ARGS(args, data);

   if (ast_strlen_zero(args.data) || ast_strlen_zero(args.key)) {
      ast_log(LOG_WARNING, "Syntax: %s(<key>,<data>) - missing argument!\n", cmd);
      return -1;
   }

   if (strlen(args.key) != AES_BLOCK_SIZE) {        /* key must be of 16 characters in length, 128 bits */
      ast_log(LOG_WARNING, "Syntax: %s(<key>,<data>) - <key> parameter must be exactly 16 characters!\n", cmd);
      return -1;
   }

   ast_aes_set_encrypt_key((unsigned char *) args.key, &ecx);   /* encryption:  plaintext -> encryptedtext -> base64 */
   ast_aes_set_decrypt_key((unsigned char *) args.key, &dcx);   /* decryption:  base64 -> encryptedtext -> plaintext */
   tmp = ast_calloc(1, len);                     /* requires a tmp buffer for the base64 decode */
   if (!tmp) {
      ast_log(LOG_ERROR, "Unable to allocate memory for data\n");
      return -1;
   }
   tmpP = tmp;
   encrypt = strcmp("AES_DECRYPT", cmd);           /* -1 if encrypting, 0 if decrypting */

   if (encrypt) {                                  /* if decrypting first decode src to base64 */
      ast_copy_string(tmp, args.data, len);
      data_len = strlen(tmp);
   } else {
      data_len = ast_base64decode((unsigned char *) tmp, args.data, len);
   }

   if (data_len >= len) {                        /* make sure to not go over buffer len */
      ast_log(LOG_WARNING, "Syntax: %s(<keys>,<data>) - <data> exceeds buffer length.  Result may be truncated!\n", cmd);
      data_len = len - 1;
   }

   while (data_len > 0) {
      memset(curblock, 0, AES_BLOCK_SIZE);
      memcpy(curblock, tmpP, (data_len < AES_BLOCK_SIZE) ? data_len : AES_BLOCK_SIZE);
      if (encrypt) {
         ast_aes_encrypt(curblock, (unsigned char *) tmpP, &ecx);
      } else {
         ast_aes_decrypt(curblock, (unsigned char *) tmpP, &dcx);
      }
      tmpP += AES_BLOCK_SIZE;
      data_len -= AES_BLOCK_SIZE;
   }

   if (encrypt) {                            /* if encrypting encode result to base64 */
      ast_base64encode(buf, (unsigned char *) tmp, tmpP - tmp, len);
   } else {
      memcpy(buf, tmp, len);
   }
   ast_free(tmp);

   return 0;
}

static struct ast_custom_function aes_encrypt_function = {
   .name = "AES_ENCRYPT",
   .read = aes_helper,
};

static struct ast_custom_function aes_decrypt_function = {
   .name = "AES_DECRYPT",
   .read = aes_helper,
};

static int unload_module(void)
{
   int res = ast_custom_function_unregister(&aes_decrypt_function);
   return res | ast_custom_function_unregister(&aes_encrypt_function);
}

static int load_module(void)
{
   int res = ast_custom_function_register(&aes_decrypt_function);
   res |= ast_custom_function_register(&aes_encrypt_function);
   return res ? AST_MODULE_LOAD_DECLINE : AST_MODULE_LOAD_SUCCESS;
}

AST_MODULE_INFO(ASTERISK_GPL_KEY, AST_MODFLAG_DEFAULT, "AES dialplan functions",
   .support_level = AST_MODULE_SUPPORT_CORE,
   .load = load_module,
   .unload = unload_module,
   .requires = "res_crypto",
);