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Insecurely generated token - JWT

Need​

Secure generation and management of tokens for user creation service

Context​

  • Usage of Scala for building scalable and high-performance applications
  • Usage of javax.crypto.spec.SecretKeySpec for generating secret keys in cryptography
  • Usage of pdi.jwt.Jwt for JWT (JSON Web Token) authentication and authorization
  • Usage of JwtAlgorithm for handling JSON Web Tokens (JWT) in PDI (Pentaho Data Integration)
  • Usage of pdi.jwt.JwtClaim for handling and validating JWT claims

Description​

Non compliant code​

import javax.crypto.spec.SecretKeySpec
import pdi.jwt.{Jwt, JwtAlgorithm, JwtClaim}

val key = "weakKey" // weak key used for signing the token
val claim = JwtClaim("""{"user":"username"}""") // payload

val token = Jwt.encode(claim, key, JwtAlgorithm.HS256) // encoding the token

The above code snippet is a simple example of how a JSON Web Token (JWT) might be generated in a Scala backend application using the Play framework.

The key used for signing the token ("weakKey") is weak and can be easily guessed or brute-forced by an attacker. This makes the JWT insecure, as an attacker who knows the signing key can forge tokens, modify token parameters such as the expiration date, and consume the service as if they were a legitimate user.

The payload of the JWT is a JSON string containing the username of the user. This information is encoded into the token using the Jwt.encode() method, along with the weak key and the HS256 algorithm.

The HS256 algorithm is a symmetric algorithm, meaning the same key is used for both signing the token and verifying it. This increases the risk associated with the key being compromised, as an attacker with the key can both create and verify tokens.

In addition, the key is hardcoded into the application, which is a bad practice. Keys should be stored securely and not exposed in the code.

Steps​

  • Generate a strong and secure key for signing the token
  • Use a secure cryptographic algorithm for signing the token
  • Ensure the token payload does not contain sensitive information
  • Implement proper token validation and verification mechanisms
  • Regularly rotate the signing key to enhance security

Compliant code​

import java.security.SecureRandom
import javax.crypto.KeyGenerator
import javax.crypto.spec.SecretKeySpec
import pdi.jwt.{Jwt, JwtAlgorithm, JwtClaim}

// Generate a strong and secure key for signing the token
val keyGen = KeyGenerator.getInstance("HmacSHA256")
val secureRandom = new SecureRandom()
keyGen.init(secureRandom)
val secretKey = keyGen.generateKey()
val key = new SecretKeySpec(secretKey.getEncoded, "HmacSHA256")

// Ensure the token payload does not contain sensitive information
val claim = JwtClaim("""{"user":"username"}""") // payload

// Use a secure cryptographic algorithm for signing the token
val token = Jwt.encode(claim, key.getEncoded, JwtAlgorithm.HS256) // encoding the token

The above code fixes the vulnerability by generating a strong and secure key for signing the token. It uses the KeyGenerator class to generate a secret key for the HmacSHA256 algorithm. The SecureRandom class is used to generate a random number that is used to initialize the key generator.

The payload of the token does not contain any sensitive information. It only contains the username of the user.

The token is then encoded using the Jwt.encode method. The HS256 algorithm is used for signing the token, which is a secure cryptographic algorithm.

The signing key should be regularly rotated to enhance security. This can be done by generating a new key at regular intervals and replacing the old key with the new one.

The token should also be properly validated and verified before it is used. This can be done by using the Jwt.validate and Jwt.decode methods.

References​

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