JWT Encoder/Decoder
Encode, decode, and verify JSON Web Tokens (JWT) with support for multiple algorithms
About JSON Web Tokens
JSON Web Token (JWT) is an open standard (RFC 7519) that defines a compact and self-contained way for securely transmitting information between parties as a JSON object. This information can be verified and trusted because it is digitally signed.
Key concepts in JWT:
- Header: Contains the type of token and the signing algorithm being used.
- Payload: Contains the claims. Claims are statements about an entity (typically, the user) and additional data.
- Signature: Used to verify that the sender of the JWT is who it says it is and to ensure that the message wasn't changed along the way.
- Signing Algorithms: Different algorithms provide different security characteristics and require different types of keys.
Security Note: JWTs can be either signed, encrypted or both. If a token is signed, but not encrypted, everyone can read its contents, but when you don't know the private key, you cannot change it. Otherwise, the receiver will notice that the signature won't match anymore.
JWT Algorithm Comparison
Different JWT signing algorithms offer varying levels of security, performance, and key management requirements. Here's a comparison of the algorithms available in this tool:
| Algorithm | Type | Key Type | Security Level | Best For |
|---|---|---|---|---|
| HS256 | HMAC with SHA-256 | Symmetric | High | Simple applications where the same party issues and verifies tokens |
| HS384 | HMAC with SHA-384 | Symmetric | Very High | Applications requiring higher security than HS256 |
| HS512 | HMAC with SHA-512 | Symmetric | Very High | Applications requiring maximum security with HMAC |
| RS256 | RSA with SHA-256 | Asymmetric | High | Distributed systems where token issuer and verifier are different parties |
| RS384 | RSA with SHA-384 | Asymmetric | Very High | Applications requiring higher security than RS256 |
| RS512 | RSA with SHA-512 | Asymmetric | Very High | Applications requiring maximum security with RSA |
| ES256 | ECDSA with SHA-256 | Asymmetric | High | Mobile applications where token size and computational efficiency matter |
| ES384 | ECDSA with SHA-384 | Asymmetric | Very High | Applications requiring higher security than ES256 with ECDSA |
| ES512 | ECDSA with SHA-512 | Asymmetric | Very High | Applications requiring maximum security with ECDSA |
Example: Using JWT in Authentication
Here's a common flow for using JWTs in authentication:
- User logs in with credentials (username/password)
- Server verifies credentials and generates a JWT containing user identity and permissions
- Server sends the JWT to the client
- Client stores the JWT (typically in local storage or as a cookie)
- Client includes the JWT in the Authorization header for subsequent requests
- Server validates the JWT signature and grants access based on the claims in the payload
This stateless authentication mechanism is widely used in modern web applications, especially in microservices architectures.
JWT Implementation Examples
Here are examples of how to implement JWT encoding and decoding in different programming languages:
Best Practices for JWT Implementation
- Always use strong, randomly generated keys for signing
- Set appropriate expiration times for tokens
- Include standard claims (iat, exp, sub) when applicable
- Validate all claims on the server side
- Use HTTPS for token transmission
- Consider token refresh mechanisms for long-lived sessions
- Implement proper error handling for token validation
Common JWT Libraries
- JavaScript/Node.js: jsonwebtoken, jose
- Python: PyJWT, python-jose
- Java: jjwt, java-jwt
- PHP: firebase/php-jwt
- Go: golang-jwt/jwt
- Ruby: jwt gem
- C#: System.IdentityModel.Tokens.Jwt