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 <dvossel@digium.com>
 * \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",
);