JWT RS256 Generator

HS256 (HMAC-SHA256) uses a single shared secret that both the issuer and verifier must know — if the secret leaks, anyone can forge tokens. RS256 (RSA-SHA256) uses an asymmetric key pair: the server signs with a private key, and anyone can verify with the corresponding public key. This means you can publish your public key (e.g., as a JWKS endpoint) so third parties can verify tokens without ever seeing the private key. RS256 is preferred for public APIs and multi-service architectures.

Use RS256 or ES256 when: (1) multiple services need to verify tokens without sharing a secret, (2) you expose a public JWKS endpoint so external systems can validate tokens, (3) you need stronger non-repudiation guarantees, or (4) your security policy mandates asymmetric cryptography. ES256 (ECDSA P-256) is preferred over RS256 for new systems — it produces shorter signatures and is faster to verify. HS256 is fine for single-service setups where only your own backend verifies tokens.

RS256 uses RSA key pairs in PEM format. The private key starts with '-----BEGIN RSA PRIVATE KEY-----' (PKCS#1) or '-----BEGIN PRIVATE KEY-----' (PKCS#8). The public key starts with '-----BEGIN PUBLIC KEY-----'. Generate a 2048-bit or 4096-bit key pair with: openssl genrsa -out private.pem 2048 and openssl rsa -in private.pem -pubout -out public.pem. Most JWT libraries also accept JWKS (JSON Web Key Sets) format — use a library like node-jose or python-jose to convert. Never embed private keys in client-side code.

Keep payloads small — JWTs are sent on every request. Use short claim names (sub, iss, aud, exp, iat, jti) for standard data. Always include exp (expiration) — short-lived tokens (15 min to 1 hour) reduce the window for misuse. Include jti (JWT ID) if you need revocation support. Use aud to scope tokens to specific services, preventing token reuse across APIs. Avoid storing sensitive data (passwords, full PII) in claims — the payload is Base64url-encoded but not encrypted. If you need confidentiality, use JWE (JSON Web Encryption) instead of plain JWT.