How do you choose the right jwt signing algorithm and key size?

1 Symmetric vs Asymmetric Algorithms

JWT signing algorithms can be classified into two categories: symmetric and asymmetric.

Symmetric algorithms use the same secret key to sign and verify the tokens, while asymmetric algorithms use a pair of public and private keys. The public key can be shared with anyone, but the private key must be kept secret and secure. Symmetric algorithms are faster and simpler, but they require you to share the secret key with all the parties involved, which can pose a risk of compromise.

Asymmetric algorithms are more secure and scalable, but they are slower and more complex, and they require you to manage the public and private keys properly.

2 Common JWT Signing Algorithms

The most common JWT signing algorithms are HMAC, RSA, and ECDSA.

HMAC stands for Hash-based Message Authentication Code, and it is a symmetric algorithm that uses a hash function and a secret key to generate a signature.

RSA stands for Rivest-Shamir-Adleman, and it is an asymmetric algorithm that uses a public and private key pair to generate and verify a signature.

ECDSA stands for Elliptic Curve Digital Signature Algorithm, and it is also an asymmetric algorithm that uses a public and private key pair, but based on elliptic curve cryptography.

Each algorithm has its own strengths and weaknesses, depending on your security requirements, performance needs, and compatibility issues.

4 How to Generate and Store the Keys

Once you have chosen the JWT signing algorithm and key size, you need to generate and store the keys properly. For symmetric algorithms like HMAC, you can use a random number generator or a secure password generator to create a secret key, and store it in a safe and encrypted place, such as a vault or a configuration file. You should also rotate the secret key periodically, and avoid sharing it with anyone who does not need it.

For asymmetric algorithms like RSA and ECDSA, you can use a tool or a library to generate a public and private key pair, and store them in separate locations. You should keep the private key as secret and secure as possible, and only use it to sign the tokens. You should distribute the public key to anyone who needs to verify the tokens, such as your clients or servers.

5 How to Test and Validate the Tokens

Finally, you need to test and validate the tokens that you sign and verify with your chosen JWT signing algorithm and key size. Use a tool or a library to encode and decode the tokens, and check their header, payload, and signature sections. You can also use a tool or a website to validate the tokens online, and see if they match your expected values and claims.

You should also test the tokens for different scenarios, such as expiration, revocation, tampering, and replay attacks, and see how your algorithm and key size handle them. Monitor and audit the tokens for any anomalies or breaches, and report and resolve them as soon as possible.