[Asterisk-code-review] func_scramble: Audio scrambler function (asterisk[19])
Kevin Harwell
asteriskteam at digium.com
Thu Aug 19 11:19:30 CDT 2021
Kevin Harwell has submitted this change. ( https://gerrit.asterisk.org/c/asterisk/+/16339 )
Change subject: func_scramble: Audio scrambler function
......................................................................
func_scramble: Audio scrambler function
Adds a function to scramble audio on a channel using
whole spectrum frequency inversion. This can be used
as a privacy enhancement with applications like
ChanSpy or other potentially sensitive audio.
ASTERISK-29542
Change-Id: I01020769d91060a1f56a708eb405f87648d1a67e
---
A doc/CHANGES-staging/func_scramble.txt
A funcs/func_scramble.c
2 files changed, 240 insertions(+), 0 deletions(-)
Approvals:
George Joseph: Looks good to me, approved
Kevin Harwell: Approved for Submit
diff --git a/doc/CHANGES-staging/func_scramble.txt b/doc/CHANGES-staging/func_scramble.txt
new file mode 100644
index 0000000..4c1ffab
--- /dev/null
+++ b/doc/CHANGES-staging/func_scramble.txt
@@ -0,0 +1,5 @@
+Subject: func_scramble
+
+Adds an audio scrambler function that may be used to
+distort voice audio on a channel as a privacy
+enhancement.
diff --git a/funcs/func_scramble.c b/funcs/func_scramble.c
new file mode 100644
index 0000000..01756d9
--- /dev/null
+++ b/funcs/func_scramble.c
@@ -0,0 +1,235 @@
+/*
+ * Asterisk -- An open source telephony toolkit.
+ *
+ * Copyright (C) 2021, Naveen Albert
+ *
+ * Naveen Albert <asterisk at 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 at phreaknet.org>
+ *
+ * \ingroup functions
+ *
+ */
+
+/*** MODULEINFO
+ <support_level>extended</support_level>
+ ***/
+
+/*** DOCUMENTATION
+ <function name="SCRAMBLE" language="en_US">
+ <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>
+ </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 */
+ /* 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");
--
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Gerrit-Project: asterisk
Gerrit-Branch: 19
Gerrit-Change-Id: I01020769d91060a1f56a708eb405f87648d1a67e
Gerrit-Change-Number: 16339
Gerrit-PatchSet: 2
Gerrit-Owner: N A <mail at interlinked.x10host.com>
Gerrit-Reviewer: Friendly Automation
Gerrit-Reviewer: George Joseph <gjoseph at digium.com>
Gerrit-Reviewer: Kevin Harwell <kharwell at digium.com>
Gerrit-MessageType: merged
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