diff --git a/host/simtrace2-sniff.c b/host/simtrace2-sniff.c
new file mode 100644
index 0000000..dc4708f
--- /dev/null
+++ b/host/simtrace2-sniff.c
@@ -0,0 +1,534 @@
+/* simtrace2-sniff - main program for the host PC to communicate with the SIMtrace 2 firmware in sniffer mode */
+/* This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+ *
+ * (C) 2010-2017 by Harald Welte <hwelte@hmw-consulting.de>
+ * (C) 2018 by Kevin Redon <kredon@sysmocom.de>
+ */
+#include <errno.h>
+#include <unistd.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <stdint.h>
+#include <signal.h>
+#include <time.h>
+#define _GNU_SOURCE
+#include <getopt.h>
+
+#include <sys/time.h>
+#include <sys/types.h>
+#include <sys/socket.h>
+#include <netinet/in.h>
+#include <arpa/inet.h>
+
+#include <libusb.h>
+
+#include "libusb_util.h"
+#include "simtrace.h"
+#include "simtrace_usb.h"
+#include "simtrace_prot.h"
+#include "simtrace2-discovery.h"
+
+#include <osmocom/core/gsmtap.h>
+#include <osmocom/core/gsmtap_util.h>
+#include <osmocom/core/utils.h>
+#include <osmocom/core/socket.h>
+#include <osmocom/core/msgb.h>
+#include <osmocom/sim/class_tables.h>
+#include <osmocom/sim/sim.h>
+
+/* transport to a SIMtrace device */
+struct st_transport {
+	/* USB */
+	struct libusb_device_handle *usb_devh;
+	struct {
+		uint8_t in;
+		uint8_t out;
+		uint8_t irq_in;
+	} usb_ep;
+};
+
+/* global GSMTAP instance */
+static struct gsmtap_inst *g_gti;
+
+static int gsmtap_send_sim(const uint8_t *apdu, unsigned int len)
+{
+	struct gsmtap_hdr *gh;
+	unsigned int gross_len = len + sizeof(*gh);
+	uint8_t *buf = malloc(gross_len);
+	int rc;
+
+	if (!buf)
+		return -ENOMEM;
+
+	memset(buf, 0, sizeof(*gh));
+	gh = (struct gsmtap_hdr *) buf;
+	gh->version = GSMTAP_VERSION;
+	gh->hdr_len = sizeof(*gh)/4;
+	gh->type = GSMTAP_TYPE_SIM;
+
+	memcpy(buf + sizeof(*gh), apdu, len);
+
+	rc = write(gsmtap_inst_fd(g_gti), buf, gross_len);
+	if (rc < 0) {
+		perror("write gsmtap");
+		free(buf);
+		return rc;
+	}
+
+	free(buf);
+	return 0;
+}
+
+static int process_change(uint8_t *buf, int len)
+{
+	/* check if there is enough data for the structure */
+	if (len<sizeof(struct sniff_change)) {
+		return -1;
+	}
+	struct sniff_change *change = (struct sniff_change *)buf;
+
+	if (SNIFF_CHANGE_FLAG_TIMEOUT_WT!=change->flags) {
+		printf("Card state change: ");
+	}
+	if (change->flags&SNIFF_CHANGE_FLAG_CARD_INSERT) {
+		printf("card inserted ");
+	}
+	if (change->flags&SNIFF_CHANGE_FLAG_CARD_EJECT) {
+		printf("card ejected ");
+	}
+	if (change->flags&SNIFF_CHANGE_FLAG_RESET_HOLD) {
+		printf("reset hold ");
+	}
+	if (change->flags&SNIFF_CHANGE_FLAG_RESET_RELEASE) {
+		printf("reset release ");
+	}
+	if (change->flags&SNIFF_CHANGE_FLAG_TIMEOUT_WT) {
+		// do nothing since this also triggers on inactivity
+	}
+	if (SNIFF_CHANGE_FLAG_TIMEOUT_WT!=change->flags) {
+		printf("\n");
+	}
+
+	return 0;
+}
+
+/* Table 7 of ISO 7816-3:2006 */
+static const uint16_t fi_table[] = { 372, 372, 558, 744, 1116, 1488, 1860, 0, 0, 512, 768, 1024, 1536, 2048, 0, 0, };
+
+/* Table 8 from ISO 7816-3:2006 */
+static const uint8_t di_table[] = { 0, 1, 2, 4, 8, 16, 32, 64, 12, 20, 2, 4, 8, 16, 32, 64, };
+
+static int process_fidi(uint8_t *buf, int len)
+{
+	/* check if there is enough data for the structure */
+	if (len<sizeof(struct sniff_fidi)) {
+		return -1;
+	}
+	struct sniff_fidi *fidi = (struct sniff_fidi *)buf;
+
+	printf("Fi/Di switched to %u/%u\n", fi_table[fidi->fidi>>4], di_table[fidi->fidi&0x0f]);
+	return 0;
+}
+
+static int process_atr(uint8_t *buf, int len)
+{
+	/* check if there is enough data for the structure */
+	if (len<sizeof(struct sniff_data)) {
+		return -1;
+	}
+	struct sniff_data *atr = (struct sniff_data *)buf;
+
+	/* check if the data is available */
+	if (len<sizeof(struct sniff_data)+atr->length) {
+		return -2;
+	}
+
+	printf("ATR%s: ", atr->complete ? "" : " (incomplete)");
+	uint16_t i;
+	for (i = 0; i < atr->length; i++) {
+		printf("%02x ", atr->data[i]);
+	}
+	printf("\n");
+	return 0;
+}
+
+static int process_pps(uint8_t *buf, int len)
+{
+	/* check if there is enough data for the structure */
+	if (len<sizeof(struct sniff_data)) {
+		return -1;
+	}
+	struct sniff_data *pps = (struct sniff_data *)buf;
+
+	/* check if the data is available */
+	if (len<sizeof(struct sniff_data)+pps->length) {
+		return -2;
+	}
+
+	printf("PPS%s: ", pps->complete ? "" : " (incomplete) ");
+	uint16_t i;
+	for (i = 0; i < pps->length; i++) {
+		printf("%02x ", pps->data[i]);
+	}
+	printf("\n");
+	return 0;
+}
+
+static int process_tpdu(uint8_t *buf, int len)
+{
+	/* check if there is enough data for the structure */
+	if (len<sizeof(struct sniff_data)) {
+		return -1;
+	}
+	struct sniff_data *tpdu = (struct sniff_data *)buf;
+
+	/* check if the data is available */
+	if (len<sizeof(struct sniff_data)+tpdu->length) {
+		return -2;
+	}
+
+	printf("TPDU%s: ", tpdu->complete ? "" : " (incomplete)");
+	uint16_t i;
+	for (i = 0; i < tpdu->length; i++) {
+		printf("%02x ", tpdu->data[i]);
+	}
+	printf("\n");
+	return 0;
+}
+
+/*! \brief Process an incoming message from the SIMtrace2 */
+static int process_usb_msg(uint8_t *buf, int len)
+{
+	/* check if enough data for the header is present */
+	if (len<sizeof(struct simtrace_msg_hdr)) {
+		return 0;
+	}
+
+	/* check if message is complete */
+	struct simtrace_msg_hdr *msg_hdr = (struct simtrace_msg_hdr *)buf;
+	if (len<msg_hdr->msg_len) {
+		return 0;
+	}
+	//printf("msg: %s\n", osmo_hexdump(buf, msg_hdr->msg_len));
+
+	/* check for message class */
+	if (SIMTRACE_MSGC_SNIFF!=msg_hdr->msg_class) { /* we only care about sniffing messages */
+		return msg_hdr->msg_len; /* discard non-sniffing messaged */
+	}
+
+	/* process sniff message payload */
+	buf += sizeof(struct simtrace_msg_hdr);
+	len -= sizeof(struct simtrace_msg_hdr);
+	switch (msg_hdr->msg_type) {
+	case SIMTRACE_MSGT_SNIFF_CHANGE:
+		process_change(buf, len);
+		break;
+	case SIMTRACE_MSGT_SNIFF_FIDI:
+		process_fidi(buf, len);
+		break;
+	case SIMTRACE_MSGT_SNIFF_ATR:
+		process_atr(buf, len);
+		break;
+	case SIMTRACE_MSGT_SNIFF_PPS:
+		process_pps(buf, len);
+		break;
+	case SIMTRACE_MSGT_SNIFF_TPDU:
+		process_tpdu(buf, len);
+		break;
+	default:
+		printf("unknown SIMtrace msg type 0x%02x\n", msg_hdr->msg_type);
+		break;
+	}
+
+	return msg_hdr->msg_len;
+}
+
+/*! Transport to SIMtrace device (e.g. USB handle) */
+static struct st_transport _transp;
+
+static void run_mainloop()
+{
+	int rc;
+	uint8_t buf[16*256];
+	unsigned int i, buf_i = 0;
+	int xfer_len;
+
+	printf("Entering main loop\n");
+
+	while (true) {
+		/* read data from SIMtrace2 device (via USB) */
+		rc = libusb_bulk_transfer(_transp.usb_devh, _transp.usb_ep.in,
+					  &buf[buf_i], sizeof(buf)-buf_i, &xfer_len, 100000);
+		if (rc < 0 && rc != LIBUSB_ERROR_TIMEOUT &&
+		              rc != LIBUSB_ERROR_INTERRUPTED &&
+		              rc != LIBUSB_ERROR_IO) {
+			fprintf(stderr, "BULK IN transfer error; rc=%d\n", rc);
+			return;
+		}
+		/* dispatch any incoming data */
+		if (xfer_len > 0) {
+			//printf("URB: %s\n", osmo_hexdump(&buf[buf_i], xfer_len));
+			buf_i += xfer_len;
+			if (buf_i>=sizeof(buf)) {
+				perror("preventing USB buffer overflow");
+				return;
+			}
+			int processed = process_usb_msg(buf, buf_i);
+			if (processed > 0 && processed <= buf_i) {
+				for (i = processed; i < buf_i; i++) {
+					buf[i-processed] = buf[i];
+				}
+				buf_i -= processed;
+			}
+		}
+	}
+}
+
+static void print_welcome(void)
+{
+	printf("simtrace2-sniff - Phone-SIM card communication sniffer \n"
+	       "(C) 2010-2017 by Harald Welte <laforge@gnumonks.org>\n"
+	       "(C) 2018 by Kevin Redon <kredon@sysmocom.de>\n"
+	       "\n"
+	);
+}
+
+static void print_help(void)
+{
+	printf(
+		"\t-h\t--help\n"
+		"\t-i\t--gsmtap-ip\tA.B.C.D\n"
+		"\t-k\t--keep-running\n"
+		"\t-V\t--usb-vendor\tVENDOR_ID\n"
+		"\t-P\t--usb-product\tPRODUCT_ID\n"
+		"\t-C\t--usb-config\tCONFIG_ID\n"
+		"\t-I\t--usb-interface\tINTERFACE_ID\n"
+		"\t-S\t--usb-altsetting ALTSETTING_ID\n"
+		"\t-A\t--usb-address\tADDRESS\n"
+		"\n"
+		);
+}
+
+static const struct option opts[] = {
+	{ "help", 0, 0, 'h' },
+	{ "gsmtap-ip", 1, 0, 'i' },
+	{ "keep-running", 0, 0, 'k' },
+	{ "usb-vendor", 1, 0, 'V' },
+	{ "usb-product", 1, 0, 'P' },
+	{ "usb-config", 1, 0, 'C' },
+	{ "usb-interface", 1, 0, 'I' },
+	{ "usb-altsetting", 1, 0, 'S' },
+	{ "usb-address", 1, 0, 'A' },
+	{ NULL, 0, 0, 0 }
+};
+
+/* Known USB device with SIMtrace firmware supporting sniffer */
+static const struct dev_id compatible_dev_ids[] = {
+	{ USB_VENDOR_OPENMOKO, USB_PRODUCT_SIMTRACE2 },
+	{ 0, 0 }
+};
+
+static void signal_handler(int signal)
+{
+	switch (signal) {
+	case SIGINT:
+		exit(0);
+		break;
+	default:
+		break;
+	}
+}
+
+int main(int argc, char **argv)
+{
+	int i, rc, ret;
+	print_welcome();
+
+	/* Parse arguments */
+	char *gsmtap_host = "127.0.0.1";
+	int keep_running = 0;
+	int vendor_id = -1, product_id = -1, addr = -1, config_id = -1, if_num = -1, altsetting = -1;
+
+	while (1) {
+		int option_index = 0;
+
+		char c = getopt_long(argc, argv, "hi:kV:P:C:I:S:A:", opts, &option_index);
+		if (c == -1)
+			break;
+		switch (c) {
+		case 'h':
+			print_help();
+			exit(0);
+			break;
+		case 'i':
+			gsmtap_host = optarg;
+			break;
+		case 'k':
+			keep_running = 1;
+			break;
+		case 'V':
+			vendor_id = strtol(optarg, NULL, 16);
+			break;
+		case 'P':
+			product_id = strtol(optarg, NULL, 16);
+			break;
+		case 'C':
+			config_id = atoi(optarg);
+			break;
+		case 'I':
+			if_num = atoi(optarg);
+			break;
+		case 'S':
+			altsetting = atoi(optarg);
+			break;
+		case 'A':
+			addr = atoi(optarg);
+			break;
+		}
+	}
+
+	/* Scan for available SIMtrace USB devices supporting sniffing */
+	rc = libusb_init(NULL);
+	if (rc < 0) {
+		fprintf(stderr, "libusb initialization failed\n");
+		goto do_exit;
+	}
+	struct usb_interface_match ifm_scan[16];
+	int num_interfaces = usb_match_interfaces(NULL, compatible_dev_ids,
+				 USB_CLASS_PROPRIETARY, SIMTRACE_SNIFFER_USB_SUBCLASS, -1, ifm_scan, ARRAY_SIZE(ifm_scan));
+	if (num_interfaces <= 0) {
+		perror("No compatible USB devices found");
+		goto do_exit;
+	}
+
+	/* Only keep USB matching arguments */
+	struct usb_interface_match ifm_filtered[ARRAY_SIZE(ifm_scan)];
+	int num_filtered = 0;
+	for (i = 0; i < num_interfaces; i++) {
+		if (vendor_id>=0 && vendor_id!=ifm_scan[i].vendor) {
+			continue;
+		}
+		if (product_id>=0 && product_id!=ifm_scan[i].product) {
+			continue;
+		}
+		if (config_id>=0 && config_id!=ifm_scan[i].configuration) {
+			continue;
+		}
+		if (if_num>=0 && if_num!=ifm_scan[i].interface) {
+			continue;
+		}
+		if (altsetting>=0 && altsetting!=ifm_scan[i].altsetting) {
+			continue;
+		}
+		if (addr>=0 && addr!=ifm_scan[i].addr) {
+			continue;
+		}
+		ifm_filtered[num_filtered++] = ifm_scan[i];
+	}
+	if (1!=num_filtered) {
+		perror("No individual matching USB devices found");
+		printf("Available USB devices:\n");
+		for (i = 0; i < num_interfaces; i++) {
+			printf("\t%04x:%04x Addr=%u, Path=%s, Cfg=%u, Intf=%u, Alt=%u: %d/%d/%d ",
+			ifm_scan[i].vendor, ifm_scan[i].product, ifm_scan[i].addr, ifm_scan[i].path,
+			ifm_scan[i].configuration, ifm_scan[i].interface, ifm_scan[i].altsetting,
+			ifm_scan[i].class, ifm_scan[i].sub_class, ifm_scan[i].protocol);
+			libusb_device_handle *dev_handle;
+			rc = libusb_open(ifm_scan[i].usb_dev, &dev_handle);
+			if (rc < 0) {
+				printf("\n");
+				perror("Cannot open device");
+				continue;
+			}
+			char strbuf[256];
+			rc = libusb_get_string_descriptor_ascii(dev_handle, ifm_scan[i].string_idx,
+					(unsigned char *)strbuf, sizeof(strbuf));
+			libusb_close(dev_handle);
+			if (rc < 0) {
+				printf("\n");
+				perror("Cannot read string");
+				continue;
+			}
+			printf("(%s)\n", strbuf);
+		}
+		goto do_exit;
+	}
+	struct usb_interface_match ifm_selected = ifm_filtered[0];
+	printf("Using USB device %04x:%04x Addr=%u, Path=%s, Cfg=%u, Intf=%u, Alt=%u: %d/%d/%d ",
+	ifm_selected.vendor, ifm_selected.product, ifm_selected.addr, ifm_selected.path,
+	ifm_selected.configuration, ifm_selected.interface, ifm_selected.altsetting,
+	ifm_selected.class, ifm_selected.sub_class, ifm_selected.protocol);
+	libusb_device_handle *dev_handle;
+	rc = libusb_open(ifm_selected.usb_dev, &dev_handle);
+	if (rc < 0) {
+		printf("\n");
+		perror("Cannot open device");
+	}
+	char strbuf[256];
+	rc = libusb_get_string_descriptor_ascii(dev_handle, ifm_selected.string_idx,
+			(unsigned char *)strbuf, sizeof(strbuf));
+	libusb_close(dev_handle);
+	if (rc < 0) {
+		printf("\n");
+		perror("Cannot read string");
+	}
+	printf("(%s)\n", strbuf);
+
+	g_gti = gsmtap_source_init(gsmtap_host, GSMTAP_UDP_PORT, 0);
+	if (!g_gti) {
+		perror("unable to open GSMTAP");
+		goto close_exit;
+	}
+	gsmtap_source_add_sink(g_gti);
+
+	signal(SIGINT, &signal_handler);
+
+	do {
+		_transp.usb_devh = usb_open_claim_interface(NULL, &ifm_selected);
+		if (!_transp.usb_devh) {
+			fprintf(stderr, "can't open USB device\n");
+			goto close_exit;
+		}
+
+		rc = libusb_claim_interface(_transp.usb_devh, ifm_selected.interface);
+		if (rc < 0) {
+			fprintf(stderr, "can't claim interface %d; rc=%d\n", ifm_selected.interface, rc);
+			goto close_exit;
+		}
+
+		rc = get_usb_ep_addrs(_transp.usb_devh, ifm_selected.interface, &_transp.usb_ep.out,
+				      &_transp.usb_ep.in, &_transp.usb_ep.irq_in);
+		if (rc < 0) {
+			fprintf(stderr, "can't obtain EP addrs; rc=%d\n", rc);
+			goto close_exit;
+		}
+
+		run_mainloop();
+		ret = 0;
+
+		if (_transp.usb_devh)
+			libusb_release_interface(_transp.usb_devh, 0);
+close_exit:
+		if (_transp.usb_devh)
+			libusb_close(_transp.usb_devh);
+		if (keep_running)
+			sleep(1);
+	} while (keep_running);
+
+	libusb_exit(NULL);
+do_exit:
+	return ret;
+}