• Capture the Signal' backend tools and template challenge
  • Challenge Structure
  • Development workflow
  • Running the Backend
  • Docker Images
  • Deployment on AWS

To get started and create a new edition of the CTS, it's advisable to create a separate repo or branch to keeps things clean.

$ cp -R . /some/path/cts-EVENT_NAME
$ cd /some/path/cts-EVENT_NAME
$ git init

and continue from there. If you prefer working with branches, go with a new branch!

This repository is intended for the team that runs the Capture the Signal, not for release before each contest, unless you want to spoil the fun 😉

It contains the code to run the RF-over-IP server, in a dockerized fashion (one challenge per container). Each challenge can be customized for each competition without rebuilding each docker image (although it'd take only a few seconds to do).

The cts-tools repository contains instructions and material that can be handed out to the participants, yet only to the participants.

The challenges/ folder in the present repository contains the challenge files, each in the following structure:

• cts-signal_<N>:
  • bomb/ contains the GNURadio flowgraph
    • assets/ for any static file that you need to ship with your signal
    • requirements.pip should you need signal-specific Python dependencies
    • main.sh is the main that will be launched to run the signal
    • signal.grc is the main flowgraph
    • Makefile is used to compile the flowgraph into Python code signal.py (this should not be checked into the repository)
    • signal.cfg is the configuration file referenced by the signal
  • README.md please be nice, document your challenge

To create new signals, we suggest re-using existing ones. After all, as long as you keep the same structure, it's just another GNURadio flowgraph to edit!

1. Make a copy of a signal that is known to work

   $ cp -R cts-signal_0 cts-signal_<N>
   $ cd cts-signal_<N>

2. Work on your signal.grc (e.g., using GNURadio Companion) and bare in mind that everything should be self contained within the signal_<N> sub-folder.
3. Test that your signal works well in GNURadio.

Just as easy as:

$ docker-compose up -d              # bring up ALL signals
$ docker-compose ps
$ docker-compose logs -f signal_0   # attach to signal_0 stdout

$ docker-compose up signal_0        # bring up one signal and do not detach

Now you can test it by pointing it to the right virtual frequency (i.e., port).

All challenges develope so far can run on the capturethesignal/cts-base image, which is based on capturethesignal/gnuradio-mini-docker. Both are hosted on the Docker Hub public registry:

• docker.com/u/capturethesignal

but can be built locally if needed: check the docker/ subfolder and the phretor/gnuradio-mini-docker repository.

We've always been using AWS to deploy our CTS backends, but of course feel free to use whatever platform you prefer, and please keep this just as a reference. If you have enough time and are willing to share, the community would be enormously grateful to anyone who will send us a pull request with a Terraform script 😉

• Computing

  • Streaming RF over IP challenges
    • 1 m5a.4xlarge instance size it depending on how many challenges/contestants will be receiving the streamed signals
      • we suggest to deploy this in any of the public sub-networks, with all ports open
      • have Docker and Docker Compose installed
      • install AWS efs-utils to mount the /var/challenges EFS, to which you'll git clone this repository, and/or any other challenges that you're willing to run
      • when AWS ECS will support port ranges, this instance could be replaced by a bunch of properly sized ECS tasks/containers
  • Score board (based on CTFd)
    • 1 Relational Database Service (RDS) database instance
      • create an initial database named ctfd
      • note the endpoint in the DATABASE_URL variable below
      • has to support JSON data types: we use MariaDB >= 10.4.18
      • we haven't had any success with using Amazon Aurora although it should support JSON data types
    • 1 ElastiCache Redis instance
      • note the endpoint in the REDIS_URL below
    • 1 Elastic File System (EFS) file system for persistent storage
      • 1 EFS access point for the uploads (e.g., /var/uploads)
      • 1 EFS access point for the logs (e.g., /var/log/CTFd)
      • 1 EFS access point for the challenges
    • 1 ECS (Elastic Container Service) Fargate cluster
      • augment the default IAM role to include access to EFS
      • 1 task definition
        • 1 container pointing to the ctfd/ctfd Docker Image (or, feel free to use ours capturethesignal/CTFd)
          • mount /var/uploads and /var/log/CTFd into the container and define at least these variables
          • ACCESS_LOG = -
          • ERROR_LOG = -
          • DATABASE_URL = mysql+pymysql://admin:CHANGEME@RDS_ENDPOINT.amazonaws.com/ctfd
          • LOG_FOLDER = /var/log/CTFd
          • UPLOAD_FOLDER = /var/uploads
          • MAIL_USERNAME = YOUR_AWS_SES_SMTP_USER
          • MAIL_PASSWORD = YOUR_AWS_SES_SMTP_PASS
          • MAIL_PORT = 587
          • MAIL_SERVER = YOUR_AWS_SES_SMTP_HOST
          • MAIL_TLS = true
          • MAIL_USEAUTH = true
          • MAILFROM_ADDR = [email protected]
          • REDIS_URL = redis://ELASTICACHE_ENDPOINT.cache.amazonaws.com:6379
          • REVERSE_PROXY = true
          • SECRET_KEY = CHANGEME
          • WORKERS = 4
          • more info at: https://docs.ctfd.io/docs/deployment/configuration/#server-level-configuration
        • 1 service to run 1 instance of the task definition above
          • the service needs to be associated a Security Group with 8000/tcp inbound rule allowed
          • the service will receive HTTP requests from the ALB and will forward them to port 8000
          • any time you'll restart or change the service, AWS ECS will re-configure the ALB automatically, so you won't need to change anything public facing
  • Accessing the infrastructure
    • 1 micro instance to debug, test, monitor, just in case
      • we suggest to deploy this in any of the private sub-networks, with only port 22 open
      • make this accessible from the outside via a TCP/IP network load balancer

• Networking (use this CloudFormation template)

  • 1 VPC (Virtual Private Cloud)
  • 1 Internet Gateway
  • 2 NAT Gateways
  • 2 Private sub-networks
  • 2 Public sub-networks
  • route tables
  • 1 Application Load Balancer (ALB) to the scoreboard (use HTTPS if you can, ACM SSL certificates are free)
  • 1 TCP/IP load balancer to the EC2 instance(s)
  • (recommended) host your domain on Route 53 for ease of maintenance/integration
  • make sure that you create enough security groups (SGs) and that machines/containers can reach each other, including (but not limited to):
    • the EFS instance should have a SG configured with an inbound rule that allows traffic to NFS port (2049) from
      • the 2 EC2 instances
      • the ECS container
    • the RDS instance should have a SG configured with an inbound rule that allows traffic to NFS port (2049) from the ECS container
    • the Redis instance should have a SG configured with an inbound rule that allows traffic to Redis port (6379) from the ECS container
    • the ECS task should be associated to a SG configured with inbound rules to allow traffic to port 8000/tcp (HTTP) from the ALB's SG

We're almost certain we've missed something 😇