func_scramble.c

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/*
 * Asterisk -- An open source telephony toolkit.
 *
 * Copyright (C) 2021, Naveen Albert
 *
 * Naveen Albert <asterisk@phreaknet.org>
 *
 * 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 Frequency inverter
 *
 * \author Naveen Albert <asterisk@phreaknet.org>
 *
 * \ingroup functions
 *
 */
 
/*** MODULEINFO
    <support_level>extended</support_level>
 ***/
 
/*** DOCUMENTATION
    <function name="SCRAMBLE" language="en_US">
        <since>
            <version>16.21.0</version>
            <version>18.7.0</version>
        </since>
        <synopsis>
            Scrambles audio on a channel.
        </synopsis>
        <syntax>
            <parameter name="direction" required="false">
                <para>Must be <literal>TX</literal> or <literal>RX</literal>
                to limit to a specific direction, or <literal>both</literal>
                for both directions. <literal>remove</literal>
                will remove an existing scrambler.</para>
            </parameter>
        </syntax>
        <description>
            <para>Scrambles audio on a channel using whole spectrum inversion.
            This is not intended to be used for securely scrambling
            audio. It merely renders obfuscates audio on a channel
            to render it unintelligible, as a privacy enhancement.</para>
            <example title="Scramble speech in both directions">
            same => n,Set(SCRAMBLE()=both)
            </example>
        </description>
        <see-also>
            <ref type="application">ChanSpy</ref>
        </see-also>
    </function>
 ***/
 
#include "asterisk.h"
 
#include "asterisk/module.h"
#include "asterisk/channel.h"
#include "asterisk/pbx.h"
#include "asterisk/utils.h"
#include "asterisk/audiohook.h"
#include "asterisk/app.h"
 
#include <stdio.h>
#include <string.h>
 
struct scramble_information {
    struct ast_audiohook audiohook;
    unsigned short int tx;
    unsigned short int rx;
    unsigned short int state;
};
 
static void destroy_callback(void *data)
{
    struct scramble_information *ni = data;
 
    /* Destroy the audiohook, and destroy ourselves */
    ast_audiohook_lock(&ni->audiohook);
    ast_audiohook_detach(&ni->audiohook);
    ast_audiohook_unlock(&ni->audiohook);
    ast_audiohook_destroy(&ni->audiohook);
    ast_free(ni);
 
    return;
}
 
/*! \brief Static structure for datastore information */
static const struct ast_datastore_info scramble_datastore = {
    .type = "scramble",
    .destroy = destroy_callback
};
 
/* modifies buffer pointed to by 'amp' with inverted values */
static inline void freq_invert(short *amp, int samples)
{
    int i;
    /* invert every other sample by 1 */
    for (i = 0; i < samples; i += 2) {
        amp[i] = -amp[i];
    }
}
 
static int scramble_callback(struct ast_audiohook *audiohook, struct ast_channel *chan, struct ast_frame *frame, enum ast_audiohook_direction direction)
{
    struct ast_datastore *datastore = NULL;
    struct scramble_information *ni = NULL;
 
    /* If the audiohook is stopping it means the channel is shutting down.... but we let the datastore destroy take care of it */
    if (audiohook->status == AST_AUDIOHOOK_STATUS_DONE) {
        return 0;
    }
 
    /* Grab datastore which contains our gain information */
    if (!(datastore = ast_channel_datastore_find(chan, &scramble_datastore, NULL))) {
        return 0;
    }
 
    if (frame->frametype == AST_FRAME_VOICE) { /* only invert voice frequencies */
        ni = datastore->data;
        /* Based on direction of frame, and confirm it is applicable */
        if (!(direction == AST_AUDIOHOOK_DIRECTION_READ ? ni->rx : ni->tx)) {
            return 0;
        }
        /* Scramble the sample now */
        freq_invert(frame->data.ptr, frame->samples);
    }
    return 0;
}
 
/*! \internal \brief Disable scrambling on the channel */
static int remove_scrambler(struct ast_channel *chan)
{
    struct ast_datastore *datastore = NULL;
    struct scramble_information *data;
    SCOPED_CHANNELLOCK(chan_lock, chan);
 
    datastore = ast_channel_datastore_find(chan, &scramble_datastore, NULL);
    if (!datastore) {
        ast_log(AST_LOG_WARNING, "Cannot remove SCRAMBLE from %s: SCRAMBLE not currently enabled\n",
                ast_channel_name(chan));
        return -1;
    }
    data = datastore->data;
 
    if (ast_audiohook_remove(chan, &data->audiohook)) {
        ast_log(AST_LOG_WARNING, "Failed to remove SCRAMBLE audiohook from channel %s\n", ast_channel_name(chan));
        return -1;
    }
 
    if (ast_channel_datastore_remove(chan, datastore)) {
        ast_log(AST_LOG_WARNING, "Failed to remove SCRAMBLE datastore from channel %s\n",
                ast_channel_name(chan));
        return -1;
    }
    ast_datastore_free(datastore);
 
    return 0;
}
 
static int scramble_write(struct ast_channel *chan, const char *cmd, char *data, const char *value)
{
    char *parse;
    struct ast_datastore *datastore = NULL;
    struct scramble_information *ni = NULL;
    int tx = 1, rx = 1;
 
    AST_DECLARE_APP_ARGS(args,
        AST_APP_ARG(direction);
    );
 
    if (!chan) {
        ast_log(LOG_WARNING, "No channel was provided to %s function.\n", cmd);
        return -1;
    }
 
    parse = ast_strdupa(value);
    AST_STANDARD_APP_ARGS(args, parse);
 
    if (!strcasecmp(args.direction, "remove")) {
        return remove_scrambler(chan);
    }
    if (!strcasecmp(args.direction, "tx")) {
        tx = 1;
        rx = 0;
    } else if (!strcasecmp(args.direction, "rx")) {
        rx = 0;
        tx = 1;
    } else if (strcasecmp(args.direction, "both")) {
        ast_log(LOG_ERROR, "Direction must be either RX, TX, both, or remove\n");
        return -1;
    }
    ast_channel_lock(chan);
    if (!(datastore = ast_channel_datastore_find(chan, &scramble_datastore, NULL))) {
        /* Allocate a new datastore to hold the reference to this audiohook information */
        if (!(datastore = ast_datastore_alloc(&scramble_datastore, NULL))) {
            return 0;
        }
        if (!(ni = ast_calloc(1, sizeof(*ni)))) {
            ast_datastore_free(datastore);
            return 0;
        }
        ast_audiohook_init(&ni->audiohook, AST_AUDIOHOOK_TYPE_MANIPULATE, "Voice scrambler", AST_AUDIOHOOK_MANIPULATE_ALL_RATES);
        ni->audiohook.manipulate_callback = scramble_callback;
        datastore->data = ni;
        ast_channel_datastore_add(chan, datastore);
        ast_audiohook_attach(chan, &ni->audiohook);
    } else {
        ni = datastore->data;
    }
    ni->tx = tx;
    ni->rx = rx;
    ast_channel_unlock(chan);
 
    return 0;
}
 
static struct ast_custom_function scramble_function = {
    .name = "SCRAMBLE",
    .write = scramble_write,
};
 
static int unload_module(void)
{
    return ast_custom_function_unregister(&scramble_function);
}
 
static int load_module(void)
{
    return ast_custom_function_register(&scramble_function);
}
 
AST_MODULE_INFO_STANDARD(ASTERISK_GPL_KEY, "Frequency inverting voice scrambler");