The comparison of Keys.secretKeyFor and Keys.hmacShaKeyFor

Before going the comparison see other related blogs related the JWT.

Related blog list:

• How Keys.secretKeyFor() works ?
• How Keys.hmacShaKeyFor() works ?
• JWT tokens in Java using the jjwt-api version 0.11.5 in Eclipse

Here's the comparison of Keys.secretKeyFor and Keys.hmacShaKeyFor presented in a clear table format:

Feature	Keys.secretKeyFor(SignatureAlgorithm algorithm)	Keys.hmacShaKeyFor(byte[] keyBytes)
Functionality	Generates a new, secure, random secret key based on the provided algorithm.	Creates a Key object from the provided raw byte array of a secret key.
Input	SignatureAlgorithm enum (e.g., HS256, HS512).	A byte[] representing the raw bytes of the secret key.
Key Generation	Yes, it actively creates a new secret key.	No, it uses an existing secret key provided as input.
Key Source	Internally generated using a secure random number generator.	Externally provided by the user/application.
Key Length	Ensures the generated key meets the minimum security requirements for the algorithm.	Relies on the length of the provided byte array; insufficient length throws an error.
Randomness	High, as it uses a cryptographically secure random source.	Depends entirely on the randomness of the input byte array.
Convenience	Very convenient for quickly obtaining a secure key without prior setup.	Requires the secret key bytes to be available beforehand.
Primary Use Case	Development, simple setups, or when a temporary key is acceptable.	Production environments, using persistent and managed secret keys.
Security Focus	Ensuring a secure key is generated.	Ensuring a provided key is used correctly and is of sufficient strength.

Regarding which is best and secure:

Aspect	Keys.secretKeyFor	Keys.hmacShaKeyFor (with secure key management)
Security	Secure if the generated key is handled carefully (less control over origin).	More robust security due to control over key generation and management.
Control	Less direct control over the key's origin and lifecycle.	Greater control over key generation, storage, and rotation.
Persistence	Not ideal for persistent keys across application restarts.	Designed for using persistent keys loaded from secure storage.
Production Use	Generally not recommended for long-term production use.	Recommended for production when combined with secure key management.

In essence:

• Keys.secretKeyFor is great for quickly getting a secure key generated within your application.
• Keys.hmacShaKeyFor is the preferred method for production when you have a strategy for generating, storing, and managing your secret key securely outside of the immediate function call. It gives you more control and allows for persistent keys.

The security of Keys.hmacShaKeyFor heavily relies on how you obtain and manage the byte[] you provide to it. If you use a strong, randomly generated key stored securely, it's the more robust and secure option for production.