Are you using CenTrace? If so, let us know! Shoot us an email at [email protected].

CenTrace is a general-purpose application-layer censorship traceroute tool, that sends TTL-limited HTTP and TLS packets to detect the network locations of censorship devices. CenTrace can perform requests to different endpoints parallely using specified domains. It first tests to see whether there is any sign of interference for a particular measurement, by comparing responses with a control measurement. If there is an indication of blocking, it then performs multiple repetitions of two traceroutes to the endpoint - one with the test domain and the other with a control domain- to determine the network path to the endpoint, and the exact location of the blocking. CenTrace has the following features:

1. It can detect censorship devices that inject packets (such as a TCP RST packet or a blockpage) as well as devices that drop packets (and induce a timeout).
2. CenTrace can differentiate between in-path (processing packets at line rate) and on-path (receiving only a copy of the packets) devices.
3. CenTrace accounts for stateful blocking by including a customizable delay between successive traceroutes and measurements.
4. CenTrace follows the method used by Tracebox to compare the quoted packets in ICMP error response to detect middleboxes.
5. CenTrace uses the IP record-route option to add additional information about the location of middleboxes when the network path supports the option.
6. CenTrace repeats probes multiple times to account for network path variance and calculates the most likely location of the middlebox.
7. CenTrace can identify censorship devices that copy TTL values from the IP header of sent packets.

CenTrace can record packet captures, and analyze them to produce a final outcome containing a response code (overall type of outcome), the type of censorship response, the terminating hops in the control and test CenTrace measurement, the payloads in the control and test CenTrace measurement and whether they differ, whether the device is on-path or in-path, and the IP, ASN, and Country of the censoring and surrounding hops. Each measurement is recorded in a different packet capture file (refer to examples/pcaps/). These pcaps can then be analyzed using the analysis component of CenTrace.

For more information, refer to our paper.

• Install Python v3.9 or newer, see https://www.python.org/downloads/release/python-390/
• Set your IPTABLES to drop outbound RST packets for the measurement, since CenTrace uses the scapy library, which runs at user-level.
• Install required dependencies using pip - pip install -r requirements.txt

The following flags can be provided for running measurements:

The following flags can be provided for analyzing pcaps:

The CenTrace tool provides two functions:

1. Run traceroute measurements across a list of endpoints:

sudo python3 traceroute.py --filename examples/input.csv -o examples/output.csv -v -l examples/log.txt --iprr --comparequoted -r 5 -R 120 -p -pd examples/pcaps -m 2 -i enp1s0f1 -rv routeviews_file -an asnames_file --https -cr 2 -mi 3

2. Analyze pcaps:

python3.9 pcap_parse.py --dir examples/pcaps/ -rv routeviews_file -an asnames_file --summary -o examples/analyzed_output.csv 

Russing CenTrace from your machine may place you at risk if you use it within a highly censoring regime. CenTrace takes actions that try to trigger censoring middleboxes multiple times, and try to interfere with the functioning of the middlebox. Therefore, please exercice caution while using the tool, and understand the risks of running CenTrace before using it on your machine. Please refer to our paper for more information.

The fuzzing measurement data from the study in our paper can be found here.

If you use the CenTrace tool or data, please cite the following publication:

@inproceedings{sundararaman2022network,<br>
title = {Network Measurement Methods for Locating and Examining Censorship Devices},<br>
author = {Sundara Raman, Ram and Wang, Mona and Dalek, Jakub and Mayer, Jonathan and Ensafi, Roya},<br>
booktitle={In ACM International Conference on emerging Networking EXperiments and Technologies (CoNEXT)},<br>
year={2022}

Censorship measurements are constanlt improving to adapting to the changing censorship landscape, and we need the help of the community to improve CenTrace and keep it updated! We welcome any and all contributions. Please feel free to open an Issue, Pull Request, or send us an email.

This repository is released under the GNU General Public License (see LICENSE).

Email addresses: [email protected], [email protected], [email protected], [email protected], [email protected], and [email protected]

Ram Sundara Raman

Mona Wang