JJWT (io.jsonwebtoken)

Os fatos e as verificações por trás deles

Nada abaixo foi copiado da documentação. A verificação content/libraries/verify/jjwt/run.sh executou JJWT (io.jsonwebtoken) 0.13.0 na imagem de contêiner maven:3.9.16-eclipse-temurin-25 em 20 de outubro de 2026; a página precisa corresponder ao que a verificação imprimiu, e cada fato lista essas linhas.

• Algoritmos JWS

  HS256HS384HS512RS256RS384RS512PS256PS384PS512ES256ES384ES512EdDSA

  Assinatura e verificação funcionaram com HS, RS, PS e ES em 256/384/512 e com EdDSA; ES256K, Ed25519 e Ed448 não estão em Jwts.SIG.

  Registrado pela verificação

  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

• Codificação da assinatura ES256

  raw

  As assinaturas ES256 são 64 bytes de r‖s brutos.

  Registrado pela verificação

  fact jws-ecdsa-encoding = raw

• Assinatura DER dentro de um JWS

  rejected

  Uma assinatura ES256 codificada em DER falha com Provided signature is 576 bits (72 bytes) but ES256 signatures must be exactly 512 bits (64 bytes).

  Registrado pela verificação

  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

  A chave de verificação determina o algoritmo: um token RS256 verificado com uma chave pública EC falhou com UnsupportedJwtException.

  Registrado pela verificação

  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 sem assinatura (alg none)

  opt-in

  parseSignedClaims rejeita tokens sem assinatura; Jwts.parser().unsecured() com parseUnsecuredClaims os lê.

  Registrado pela verificação

  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

• Chave pública usada como segredo HMAC

  rejected

  Um token HS256 que usava o texto PEM como chave foi rejeitado com a chave pública EC, mas foi verificado com Keys.hmacShaKeyFor(pemBytes).

  Registrado pela verificação

  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 conferida com o alg

  enforced

  Assinar ES256 com uma chave P-384 falha: the 'ES256' algorithm requires EC Keys with 256 bits.

  Registrado pela verificação

  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).

• Tolerância padrão de diferença de relógio

  0s

  Sem tolerância para diferença de relógio por padrão: um token expirado três segundos antes foi rejeitado.

  Registrado pela verificação

  fact jwt-clock-skew = 0s

• Claim de expiração obrigatória

  no

  Um token sem exp foi analisado com sucesso.

  Registrado pela verificação

  fact jwt-exp-required = no

• Segredo HMAC curto

  rejected

  Keys.hmacShaKeyFor rejeitou uma chave de 16 bytes com WeakKeyException.

  Registrado pela verificação

  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));
    }
}