JSON Web Tokens (JWT) are a popular way to securely transmit information between parties. They are often used for authentication and information exchange in web applications. One important aspect of JWTs is the algorithm used to sign them.However, choosing and understanding these algorithms is critical for security.
This blog explains the three most commonly discussed algorithms in JWT: HS256, RS256, and the infamous None algorithm.
Mastering in JSON Web Token ( JWT )
What is a JWT Token?
Before we dive into the algorithms, let’s quickly understand what a JWT is. A JWT (JSON Web Token) is like a digital passport. It’s a small piece of data that proves who you are and what you’re allowed to do. When you log in to a website, the server gives you this token. Every time you make a request (like viewing your profile or accessing your dashboard), you show this token to prove your identity.
JWT token contains three parts:
- Header: This part contains information about how the token is signed, including the algorithm used.
- Payload: This part contains the claims or the information you want to share.
- Signature: This part is created by combining the header and payload, then signing it with a secret key or a private key.
HS256: HMAC with SHA-256
HS256 stands for HMAC (Hash-based Message Authentication Code) using the SHA-256 hashing algorithm. It is a symmetric algorithm, which means the same secret key is used for both signing and verifying the token.
How does it work?
- Signing: When a JWT is created, the header and payload are combined and signed using the secret key. This creates a unique signature.
- Verification: When the token is received, the server uses the same secret key to verify the signature. If it matches, the token is valid.
Pros and Cons:
- Pros:
- Simple to implement.
- Fast because it uses a single secret key.
- Cons:
- If the secret key is compromised, anyone can create valid tokens.
- Not suitable for scenarios where multiple parties need to verify the token.
When to Use HS256:
- Good for Simple Systems: Ideal for scenarios where only one server handles both signing and verification since the same key is used for both.
RS256: RSA Signature with SHA-256:
RS256 uses RSA (Rivest-Shamir-Adleman) for signing the JWT. It is an asymmetric algorithm, which means it uses a pair of keys: a private key for signing and a public key for verification.
How does it work?
- Signing: The server creates a JWT and signs it with its private key. This signature is unique to the token.
- Verification: The recipient can verify the token using the server’s public key. If the signature matches, the token is valid.
Pros and Cons:
- Pros:
- More secure because the private key is never shared.
- ✅ High Security: Even if the public key is leaked, tokens can’t be forged since the private key remains secret.
- Multiple parties can verify the token using the public key.
- Cons:
- Slower than HS256 due to the complexity of RSA.
- Requires key management to handle the public and private keys.
When to Use RS256:
- Distributed Systems: Perfect for systems with multiple servers or services. For example, if one service issues tokens (using the private key) and others verify them (using the public key).
Key Differences Between HS256 and RS256:
None Algorithm:
The “None” algorithm means that the JWT is not signed at all. This is not recommended for production use, as it does not provide any security.
eyJhbGciOiJub25lIn0.eyJ1c2VyX2lkIjoxLCJyb2xlIjoiYWRtaW4ifQ.How does it work?
- No Signing: The JWT is created without a signature. Anyone can create a token and claim it is valid. The token look like this:
eyJhbGciOiJub25lIn0.eyJ1c2VyX2lkIjoxLCJyb2xlIjoiYWRtaW4ifQ.The last part of the JWT (the signature) is empty.
- Verification: Since there is no signature, any token can be accepted as valid.
Pros and Cons:
- Pros: Very simple and fast.
- Cons: No security at all. Anyone can create a token, leading to potential misuse.
When to Choose Which Algorithm?
- HS256
:- Use when you control both token creation and verification on the same server.
- Keep the secret key private and long enough (e.g., 256 bits).
- RS256:
- Use in distributed systems where different servers or services need to verify tokens.
- Protect the private key securely and distribute the public key as needed.
- None:
- Avoid completely in production. It’s only meant for specific test scenarios.
Understanding the different algorithms used in JWTs is crucial for building secure applications. HS256 is simple and fast but less secure if the secret key is compromised. RS256 offers better security with its asymmetric approach but requires more resources and key management. The None algorithm should be avoided in any secure application.
When choosing an algorithm, consider your application’s security needs and the complexity you are willing to manage. Always prioritize security to protect your users and their data!