It’s critical for any app managing the flow of cryptocurrency to architect their app to follow security best-practices. Cryptocurrency-enabled apps are significant targets for malicious actors in the sense they enable the attacker to realize immediate monetary gain from exploits. The following checklist offers guidance on the most common vulnerabilities. Even if every piece of advice is followed, security is not guaranteed. Web security is constantly evolving, which warrants a certain degree of paranoia.
Ensure TLS enabled (Letsencrypt allows you to do this for free). Redirect http to https where necessary. This ensures that Man in the Middle attacks cannot occur, and sensitive data is securely transferred between the client and browser. Learn how to get an SSL certificate for free here.
If you don’t have SSL/TLS enabled, stop everything and do this first.
Most web frameworks have a configuration file or extensions where you may specify your CSP policy, and the headers will be auto-generated for you. For example, see Helmet for Node.js.
This would have prevented the Blackwallet Hack.
This is an HTTP header that tells the browser that all future connections to a particular site should use HTTPS. To implement this, add the header to your website. Some web frameworks have this built in, like Django!
This would have prevented the MyEtherWallet DNS hack.
In an ideal world, you don’t have to store much sensitive data. If you must, tread carefully. There are many strategies in storing sensitive data; start by ensuring sensitive data is encrypted using a proven cipher like AES-256, and stored separately from application data and always pick an AEAD mode. Any communication between the application server and secret server should be in a private network and / or authenticated via HMAC. Your cipher strategy will change based on whether you will be sending the ciphertext over the wire multiple times. Finally, back up any encryption keys you may use offline, and store them only in-memory in your app.
Consult a good cryptographer and read up on best practices. A good place to start is looking into the documentation of your favorite web framework.
Rolling your own crypto is a bad idea. Always use tried and tested libraries. A good example is [NaCl](https://en.wikipedia.org/wiki/NaCl_(software)).
Attackers often need to spend some time exploring your website for unexpected or overlooked behavior. Examining logs defensively can help you catch on to what their trying to achieve and ensure you’re protected. At the least, you can block their IP, or automate blocking based on suspicious behavior you unearth.
Finally, it is worth setting up error reporting (e.g. Sentry): Oftentimes, people trigger strange bugs when they are trying to hack things.
If you have logins for users, it is critical that your authentication system is built securely. Of course, the best way to do this is to use something off the shelf. Both Ruby on Rails and Django have robust, built-in authentication schemes.
Many JSON web token implementations are poorly done, so ensure the library you use is audited.
Hash passwords with a time-tested scheme. The winner of the last password hashing contest was Argon2. Balloon Hashing is also worth looking into.
Strongly prefer 2FA, and require U2F or TOTP 2FA for sensitive actions.
2FA is really important. Email accounts are usually not very secure. Having a second factor of authentication ensures that users who accidentally stay logged on, or have their password guessed are still protected.
Finally, require strong passwords. Common and short passwords can easily be brute forced. Dropbox has a great open source tool that gauges password strength fairly quickly, making it usable for user interactions.
Denial of service attacks are usually accomplished by overloading your web servers with traffic. To mitigate this risk, rate limit traffic from IPs and browser fingerprints. Sometimes people will use proxies to bypass IP rate-limiting. In the end, malicious actors can always find ways to spoof their identity, so the surest way to block DOS attacks are to implement proof of work checks in your client, or use a managed service like Cloudflare.
Attackers will often scan your ports, and see if you were negligent and left any open. Services like Heroku do this for you. Read about how to enable this on AWS here.
Phishing attacks will thwart any well-formed security infrastructure. Have clear policies published on your website, and articulate them to users when they sign up (you will never ask for their password, etc.). Sign messages to your users. Prompt users to check the domain of the website they are on.
Use a tool like Snyk to scan your third party client libraries for vulnerabilities. Make sure you keep your third-party libraries up-to-date -- oftentimes upgrades are triggered by security exploits.
You can use Mozilla Observatory to check your HTTP security as well.
Most modern web and mobile frameworks handle both CSRF protection and SQL injections. Ensure CSRF protection enabled, and that you are using a database ORM instead of running raw SQL based on user input. For example, see what Ruby on Rails documentation says about SQL injections.
We hope this guide was useful! It is by no means comprehensive, but it's a good place to start if you haven’t paid attention to security yet. Remember, security is only as strong as its weakest link. All of this is pointless if you have bad passwords and hackers can guess your AWS password.