JJWT (io.jsonwebtoken)

Datos y las comprobaciones que los respaldan

Nada de lo que sigue está copiado de la documentación. La comprobación content/libraries/verify/jjwt/run.sh ejecutó JJWT (io.jsonwebtoken) 0.13.0 en la imagen de contenedor maven:3.9.16-eclipse-temurin-25 el 20 de octubre de 2026; la página debe coincidir con lo que imprimió, y cada dato cita esas líneas.

• Algoritmos JWS

  HS256HS384HS512RS256RS384RS512PS256PS384PS512ES256ES384ES512EdDSA

  Con HS, RS, PS y ES de 256/384/512 y EdDSA se firmó y se verificó; ES256K, Ed25519 y Ed448 no están en Jwts.SIG.

  Registrado por la comprobación

  fact jws-algorithms = HS256, HS384, HS512, RS256, RS384, RS512, PS256, PS384, PS512, ES256, ES384, ES512, EdDSA
  evidence jws-algorithms: ES256K: not in Jwts.SIG
  evidence jws-algorithms: Ed25519: not in Jwts.SIG
  evidence jws-algorithms: Ed448: not in Jwts.SIG

• Codificación de la firma ES256

  raw

  Las firmas ES256 son 64 bytes de r‖s en bruto.

  Registrado por la comprobación

  fact jws-ecdsa-encoding = raw

• Firma DER dentro de un JWS

  rejected

  Una firma ES256 codificada en DER falla con Provided signature is 576 bits (72 bytes) but ES256 signatures must be exactly 512 bits (64 bytes).

  Registrado por la comprobación

  fact jws-der-signature = rejected
  evidence jws-der-signature: SignatureException: Unable to verify Elliptic Curve signature using provided ECPublicKey: Provided signature is 576 bits (72 bytes) but ES256 signatures must be exactly 512 bits (64 bytes) per [RFC 7518, Section 3.4 (validation)](https://www.rfc-editor.org/rfc/rfc7518.html#section-3.4).

• Lista de algoritmos permitidos

  from-key

  La clave de verificación determina el algoritmo: un token RS256 contra una clave pública EC falló con UnsupportedJwtException.

  Registrado por la comprobación

  fact jwt-algorithm-allowlist = from-key
  evidence jwt-algorithm-allowlist: RS256 token, verifyWith(EC public key): UnsupportedJwtException: The parsed JWT indicates it was signed with the 'RS256' signature algorithm, but the provided sun.security.ec.ECPublicKeyImpl key may not be used to verify RS256 signatures.  Because the specified key reflects a specific and expected algorithm, and the JWT does not reflect this algorithm, it is likely that the JWT was not expected and therefore should not be trusted.  Another possibility is that the parser was provided the incorrect signature verification key, but this cannot be assumed for security reasons.

• Tokens sin firma (alg none)

  opt-in

  parseSignedClaims rechaza los tokens sin firmar; Jwts.parser().unsecured() con parseUnsecuredClaims los lee.

  Registrado por la comprobación

  fact jwt-alg-none = opt-in
  evidence jwt-alg-none: parseSignedClaims with the EC key: UnsupportedJwtException: Unsecured JWSs (those with an 'alg' (Algorithm) header value of 'none') are disallowed by default as mandated by https://www.rfc-editor.org/rfc/rfc7518.html#section-3.6. If you wish to allow them to be parsed, call the JwtParserBuilder.unsecured() method, but please read the security considerations covered in that method's JavaDoc before doing so. Header: {alg=none, typ=JWT}
  evidence jwt-alg-none: parser().unsecured().parseUnsecuredClaims: verified

• Clave pública usada como secreto HMAC

  rejected

  Un token HS256 con el texto PEM como clave se rechazó contra la clave pública EC, pero se verificó con Keys.hmacShaKeyFor(pemBytes).

  Registrado por la comprobación

  fact jwt-hmac-public-key = rejected
  evidence jwt-hmac-public-key: verifyWith(EC public key): UnsupportedJwtException: The parsed JWT indicates it was signed with the 'HS256' signature algorithm, but the provided sun.security.ec.ECPublicKeyImpl key may not be used to verify HS256 signatures.  Because the specified key reflects a specific and expected algorithm, and the JWT does not reflect this algorithm, it is likely that the JWT was not expected and therefore should not be trusted.  Another possibility is that the parser was provided the incorrect signature verification key, but this cannot be assumed for security reasons.
  evidence jwt-hmac-public-key: verifyWith(Keys.hmacShaKeyFor(PEM bytes)): verified

• Curva cotejada con alg

  enforced

  Firmar ES256 con una clave P-384 falla: the 'ES256' algorithm requires EC Keys with 256 bits.

  Registrado por la comprobación

  fact jwt-ecdsa-curve-check = enforced
  evidence jwt-ecdsa-curve-check: SignatureException: Unable to compute ES256 signature. Cause: The provided Elliptic Curve signing key size (aka order bit length) is 384 bits (48 bytes), but the 'ES256' algorithm requires EC Keys with 256 bits (32 bytes) per [RFC 7518, Section 3.4](https://www.rfc-editor.org/rfc/rfc7518.html#section-3.4).

• Desfase de reloj predeterminado

  0s

  Sin tolerancia de desfase de reloj por defecto: se rechazó un token caducado 3 segundos antes.

  Registrado por la comprobación

  fact jwt-clock-skew = 0s

• Claim de caducidad obligatorio

  no

  Un token sin exp se analizó correctamente.

  Registrado por la comprobación

  fact jwt-exp-required = no

• Secreto HMAC corto

  rejected

  Keys.hmacShaKeyFor rechazó una clave de 16 bytes con WeakKeyException.

  Registrado por la comprobación

  fact jwt-hmac-short-secret = rejected
  evidence jwt-hmac-short-secret: Keys.hmacShaKeyFor(16 bytes): WeakKeyException: The specified key byte array is 128 bits which is not secure enough for any JWT HMAC-SHA algorithm.  The JWT JWA Specification (RFC 7518, Section 3.2) states that keys used with HMAC-SHA algorithms MUST have a size >= 256 bits (the key size must be greater than or equal to the hash output size).  Consider using the Jwts.SIG.HS256.key() builder (or HS384.key() or HS512.key()) to create a key guaranteed to be secure enough for your preferred HMAC-SHA algorithm.  See https://tools.ietf.org/html/rfc7518#section-3.2 for more information.

Uso

import io.jsonwebtoken.Claims;
import io.jsonwebtoken.Jwts;
import java.security.KeyPair;
import java.util.Date;

public class Usage {
    public static void main(String[] args) {
        KeyPair pair = Jwts.SIG.ES256.keyPair().build();
        String token = Jwts.builder()
            .subject("user-42")
            .issuer("https://auth.example.com")
            .expiration(new Date(System.currentTimeMillis() + 600_000))
            .signWith(pair.getPrivate(), Jwts.SIG.ES256)
            .compact();

        // The key decides which algorithms are acceptable; require iss and exp explicitly
        // and allow some clock skew (the default is none).
        Claims claims = Jwts.parser()
            .verifyWith(pair.getPublic())
            .requireIssuer("https://auth.example.com")
            .clockSkewSeconds(30)
            .build()
            .parseSignedClaims(token)
            .getPayload();
        System.out.println("sub: " + claims.getSubject() + ", has exp: " + (claims.getExpiration() != null));
    }
}