AppSecSchool

Demystifying JSON Web Tokens (JWT): Practical Tips to Secure Your Application

JSON Web Tokens, popularly known as JWTs, are a staple in modern authentication systems. However, many developers might not be utilizing them in the safest way possible. Let's unpack some critical, practical tips that can substantially bolster your application security.

JWT Best Practices

1. Key Rotation

Typically, a JWT validation in your codebase might look something like this:

if jwt.verify(secret, token)
  return true
else
  return false
end

However, consider the following modification to introduce support for key or secret rotation:

if jwt.verify(secret, token)
  return true
elsif jwt.verify(previous_secret, token)
  return true
else
  return false
end

The simple addition ensures that even if you have to rotate your secrets, there's no need for a synchronized change across all applications using it.

2.Ensure Secret Strength

Always verify the robustness of your secret. Ensure that your secret meets a minimum size requirement to prevent possible vulnerabilities.

if secret.size < 32
  puts "Secret too small"
  exit
end

3. Logging Verification Failures

Generate logs for token verification failures. This practice will allow faster detection of issues and potential attack vectors.

if jwt.verify(secret, token)
  return true
else
  log.error("Invalid token!:"+token)
  return false
end

4. Specify the JWT Algorithm

Explicitly mention the algorithm when verifying the JWT to prevent issues like the None algorithm or Algorithm confusion attacks.

if jwt.verify(secret, token, 'HS256')
  return true
else
  return false
end

5. Monitor Signature Verification

Implement a monitoring script that checks signature verification daily. Acquire a JWT, modify the payload (while retaining the header and signature), and submit this altered token. Ensure your application produces an error, and the monitoring script should validate this response.

6. Token Expiry

Every JWT should have an expiration. Implement it using either the exp (expiry) or iat (issued at) claims. It's a fundamental security measure to ensure tokens aren't valid indefinitely.

Note: You should never sign a token without specifying an expiry.

Wrapping Up

These six pointers are foundational yet often overlooked in ensuring robust application security around JWTs. Adopting these practices will set you on the path to more secure app implementations. Remember, it's often the straightforward measures that render the most significant impact.