How to avoid KeyLengthException when using Spring OAuth2 Resource Server and a symmetric key

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So I'm working on a Resource Server (a Spring Boot app), and I would like to leverage the goodies of Spring Security OAuth2 Resource Server library.

The problem I'm facing right now is that the Authorization Server (another Spring Boot app) signs JWTs with a symmetric key, that was set to a pretty short string a long time ago, and I that cannot change.

I tried this, following the Spring Security documentation:

@EnableWebSecurity
public class SecurityConfiguration extends WebSecurityConfigurerAdapter {

    @Override
    protected void configure(HttpSecurity http) throws Exception {
        http
                .authorizeRequests(authorize -> authorize
                        .anyRequest().permitAll())
                .oauth2ResourceServer(OAuth2ResourceServerConfigurer::jwt);
    }
    
    @Bean
    public JwtDecoder jwtDecoder(@Value("${jwt.secret-key}") String secretKey) {
        return NimbusJwtDecoder
                .withSecretKey(new SecretKeySpec(secretKey.getBytes(StandardCharsets.UTF_8), "HS512"))
                .macAlgorithm(MacAlgorithm.HS512)
                .build();
    }
}

But I get the following error:

Caused by: com.nimbusds.jose.KeyLengthException: The secret length must be at least 256 bits
at com.nimbusds.jose.crypto.impl.MACProvider.<init>(MACProvider.java:118) ~[nimbus-jose-jwt-9.10.1.jar:9.10.1]
at com.nimbusds.jose.crypto.MACVerifier.<init>(MACVerifier.java:168) ~[nimbus-jose-jwt-9.10.1.jar:9.10.1]
at com.nimbusds.jose.crypto.MACVerifier.<init>(MACVerifier.java:81) ~[nimbus-jose-jwt-9.10.1.jar:9.10.1]
at com.nimbusds.jose.crypto.MACVerifier.<init>(MACVerifier.java:113) ~[nimbus-jose-jwt-9.10.1.jar:9.10.1]
at com.nimbusds.jose.crypto.factories.DefaultJWSVerifierFactory.createJWSVerifier(DefaultJWSVerifierFactory.java:100) ~[nimbus-jose-jwt-9.10.1.jar:9.10.1]
at com.nimbusds.jwt.proc.DefaultJWTProcessor.process(DefaultJWTProcessor.java:364) ~[nimbus-jose-jwt-9.10.1.jar:9.10.1]
at com.nimbusds.jwt.proc.DefaultJWTProcessor.process(DefaultJWTProcessor.java:303) ~[nimbus-jose-jwt-9.10.1.jar:9.10.1]
at org.springframework.security.oauth2.jwt.NimbusJwtDecoder.createJwt(NimbusJwtDecoder.java:154) ~[spring-security-oauth2-jose-5.5.3.jar:5.5.3]
... 61 common frames omitted

From what I can see the MACProvider that generates this exception is not configurable and the key length required cannot be relaxed. Is there any way around this?

Thanks

EDIT:

Tried the suggestion of padding the key with 0s like so:

@Bean
public JwtDecoder jwtDecoder(@Value("${jwt.secret-key}") String secretKey) {
    var key = secretKey.getBytes(StandardCharsets.UTF_8);
    var paddedKey = Arrays.copyOf(key, 128);
    return NimbusJwtDecoder
            .withSecretKey(new SecretKeySpec(paddedKey, "HS512"))
            .macAlgorithm(MacAlgorithm.HS512)
            .build();
}

but now I'm getting the following exception:

com.nimbusds.jose.proc.BadJWSException: Signed JWT rejected: Invalid signature
    at com.nimbusds.jwt.proc.DefaultJWTProcessor.process(DefaultJWTProcessor.java:378) ~[nimbus-jose-jwt-9.10.1.jar:9.10.1]
    at com.nimbusds.jwt.proc.DefaultJWTProcessor.process(DefaultJWTProcessor.java:303) ~[nimbus-jose-jwt-9.10.1.jar:9.10.1]
    at org.springframework.security.oauth2.jwt.NimbusJwtDecoder.createJwt(NimbusJwtDecoder.java:154) ~[spring-security-oauth2-jose-5.5.3.jar:5.5.3]
    at org.springframework.security.oauth2.jwt.NimbusJwtDecoder.decode(NimbusJwtDecoder.java:137) ~[spring-security-oauth2-jose-5.5.3.jar:5.5.3]
    at org.springframework.security.oauth2.server.resource.authentication.JwtAuthenticationProvider.getJwt(JwtAuthenticationProvider.java:97) ~[spring-security-oauth2-resource-server-5.5.3.jar:5.5.3]
    at org.springframework.security.oauth2.server.resource.authentication.JwtAuthenticationProvider.authenticate(JwtAuthenticationProvider.java:88) ~[spring-security-oauth2-resource-server-5.5.3.jar:5.5.3]
    at org.springframework.security.authentication.ProviderManager.authenticate(ProviderManager.java:182) ~[spring-security-core-5.5.3.jar:5.5.3]
    at org.springframework.security.oauth2.server.resource.web.BearerTokenAuthenticationFilter.doFilterInternal(BearerTokenAuthenticationFilter.java:130) ~[spring-security-oauth2-resource-server-5.5.3.jar:5.5.3]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.3.12.jar:5.3.12]
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:336) ~[spring-security-web-5.5.3.jar:5.5.3]
    at org.springframework.security.oauth2.client.web.OAuth2AuthorizationRequestRedirectFilter.doFilterInternal(OAuth2AuthorizationRequestRedirectFilter.java:178) ~[spring-security-oauth2-client-5.5.3.jar:5.5.3]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.3.12.jar:5.3.12]
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:336) ~[spring-security-web-5.5.3.jar:5.5.3]
    at org.springframework.security.web.authentication.logout.LogoutFilter.doFilter(LogoutFilter.java:103) ~[spring-security-web-5.5.3.jar:5.5.3]
    at org.springframework.security.web.authentication.logout.LogoutFilter.doFilter(LogoutFilter.java:89) ~[spring-security-web-5.5.3.jar:5.5.3]
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:336) ~[spring-security-web-5.5.3.jar:5.5.3]
    at org.springframework.security.web.csrf.CsrfFilter.doFilterInternal(CsrfFilter.java:117) ~[spring-security-web-5.5.3.jar:5.5.3]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.3.12.jar:5.3.12]
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:336) ~[spring-security-web-5.5.3.jar:5.5.3]
    at org.springframework.security.web.header.HeaderWriterFilter.doHeadersAfter(HeaderWriterFilter.java:90) ~[spring-security-web-5.5.3.jar:5.5.3]
    at org.springframework.security.web.header.HeaderWriterFilter.doFilterInternal(HeaderWriterFilter.java:75) ~[spring-security-web-5.5.3.jar:5.5.3]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.3.12.jar:5.3.12]
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:336) ~[spring-security-web-5.5.3.jar:5.5.3]
    at org.springframework.security.web.context.SecurityContextPersistenceFilter.doFilter(SecurityContextPersistenceFilter.java:110) ~[spring-security-web-5.5.3.jar:5.5.3]
    at org.springframework.security.web.context.SecurityContextPersistenceFilter.doFilter(SecurityContextPersistenceFilter.java:80) ~[spring-security-web-5.5.3.jar:5.5.3]
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:336) ~[spring-security-web-5.5.3.jar:5.5.3]
    at org.springframework.security.web.context.request.async.WebAsyncManagerIntegrationFilter.doFilterInternal(WebAsyncManagerIntegrationFilter.java:55) ~[spring-security-web-5.5.3.jar:5.5.3]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.3.12.jar:5.3.12]
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:336) ~[spring-security-web-5.5.3.jar:5.5.3]
    at org.springframework.security.web.FilterChainProxy.doFilterInternal(FilterChainProxy.java:211) ~[spring-security-web-5.5.3.jar:5.5.3]
    at org.springframework.security.web.FilterChainProxy.doFilter(FilterChainProxy.java:183) ~[spring-security-web-5.5.3.jar:5.5.3]
    at org.springframework.web.filter.DelegatingFilterProxy.invokeDelegate(DelegatingFilterProxy.java:358) ~[spring-web-5.3.12.jar:5.3.12]
    at org.springframework.web.filter.DelegatingFilterProxy.doFilter(DelegatingFilterProxy.java:271) ~[spring-web-5.3.12.jar:5.3.12]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189) ~[tomcat-embed-core-9.0.54.jar:9.0.54]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162) ~[tomcat-embed-core-9.0.54.jar:9.0.54]
    at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:100) ~[spring-web-5.3.12.jar:5.3.12]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.3.12.jar:5.3.12]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189) ~[tomcat-embed-core-9.0.54.jar:9.0.54]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162) ~[tomcat-embed-core-9.0.54.jar:9.0.54]
    at org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:93) ~[spring-web-5.3.12.jar:5.3.12]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.3.12.jar:5.3.12]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189) ~[tomcat-embed-core-9.0.54.jar:9.0.54]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162) ~[tomcat-embed-core-9.0.54.jar:9.0.54]
    at org.springframework.boot.actuate.metrics.web.servlet.WebMvcMetricsFilter.doFilterInternal(WebMvcMetricsFilter.java:96) ~[spring-boot-actuator-2.5.6.jar:2.5.6]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.3.12.jar:5.3.12]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189) ~[tomcat-embed-core-9.0.54.jar:9.0.54]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162) ~[tomcat-embed-core-9.0.54.jar:9.0.54]
    at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:201) ~[spring-web-5.3.12.jar:5.3.12]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.3.12.jar:5.3.12]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189) ~[tomcat-embed-core-9.0.54.jar:9.0.54]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162) ~[tomcat-embed-core-9.0.54.jar:9.0.54]
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:197) ~[tomcat-embed-core-9.0.54.jar:9.0.54]
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:97) ~[tomcat-embed-core-9.0.54.jar:9.0.54]
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:540) ~[tomcat-embed-core-9.0.54.jar:9.0.54]
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:135) ~[tomcat-embed-core-9.0.54.jar:9.0.54]
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92) ~[tomcat-embed-core-9.0.54.jar:9.0.54]
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:78) ~[tomcat-embed-core-9.0.54.jar:9.0.54]
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:357) ~[tomcat-embed-core-9.0.54.jar:9.0.54]
    at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:382) ~[tomcat-embed-core-9.0.54.jar:9.0.54]
    at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65) ~[tomcat-embed-core-9.0.54.jar:9.0.54]
    at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:895) ~[tomcat-embed-core-9.0.54.jar:9.0.54]
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1722) ~[tomcat-embed-core-9.0.54.jar:9.0.54]
    at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) ~[tomcat-embed-core-9.0.54.jar:9.0.54]
    at org.apache.tomcat.util.threads.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1191) ~[tomcat-embed-core-9.0.54.jar:9.0.54]
    at org.apache.tomcat.util.threads.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:659) ~[tomcat-embed-core-9.0.54.jar:9.0.54]
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) ~[tomcat-embed-core-9.0.54.jar:9.0.54]
    at java.base/java.lang.Thread.run(Thread.java:834) ~[na:na]

EDIT2:

The source generates the JWT like so (using io.jsonwebtoken 0.9.1 library):

private String generateToken(Map<String, Object> claims, String username) {

    Header header = Jwts.header();
    header.setType("JWT");

    String jti = UUID.randomUUID().toString();
    Date now = new Date(System.currentTimeMillis());

    return Jwts.builder()
            .setClaims(claims)
            .setHeader((Map<String, Object>) header)
            .setSubject(username)
            .setIssuedAt(now)
            .setIssuer("issuer")
            .setId(jti)
            .signWith(SignatureAlgorithm.HS512, secret)
            .compact();
}

EDIT3:

Solution:

@Bean
public JwtDecoder jwtDecoder(@Value("${jwt.secret-key}") String secretKey) {
    var key = TextCodec.BASE64.decode(secretKey);
    var paddedKey = key.length < 128 ? Arrays.copyOf(key, 128) : key;
    return NimbusJwtDecoder
            .withSecretKey(new SecretKeySpec(paddedKey, "HS512"))
            .macAlgorithm(MacAlgorithm.HS512)
            .build();
}
spring-boot oauth-2.0 spring-security java
1 Answers

it looks like that ,HMAC, if the secret length is shorter than the block size of hash algorithm it would pad the secret with zeros.

and according to this

Block size: the size of the data block the underlying hash algorithm operates upon. For SHA-256, this is 512 bits, for SHA-384 and SHA-512, this is 1024 bits.

Output length: the size of the hash value produced by the underlying hash algorithm. For SHA-256, this is 256 bits, for SHA-384 this is 384 bits, and for SHA-512, this is 512 bits.

the block size of SHA-512 is 128 bytes.

I suggest that if the source used HS512 algorithm try to pad the secret with zeros to see if it works or not. if you have Guava library in your class path:

Bytes.ensureCapacity(secretKey.getBytes(StandardCharsets.UTF_8), 128, 0);

ensureCapacity method source code:

  public static byte[] ensureCapacity(byte[] array, int minLength, int padding) {
    Preconditions.checkArgument(minLength >= 0, "Invalid minLength: %s", minLength);
    Preconditions.checkArgument(padding >= 0, "Invalid padding: %s", padding);
    return array.length < minLength ? Arrays.copyOf(array, minLength + padding) : array;
  }

Edit 2:

first try to decode the secret to base 64

byte[] decodedBytes = Base64.decodeBase64(secret)

then add padding and use it in your decoder(if the size of the decodedBytes is less than 128):

Arrays.copyOf(decodedBytes, 128);

I did the following test and everything was ok:

  private String generateToken(Map<String, Object> claims, String username) {

    Header header = Jwts.header();
    header.setType("JWT");

    String jti = UUID.randomUUID().toString();
    Date now = new Date(System.currentTimeMillis());

    return Jwts.builder()
        .setClaims(claims)
        .setHeader((Map<String, Object>) header)
        .setSubject(username)
        .setIssuedAt(now)
        .setIssuer("issuer")
        .setId(jti)
        .signWith(SignatureAlgorithm.HS512, "asdf")
        .compact();
  }

  public JwtDecoder jwtDecoder() {
  // base64 decoder from org.apache.tomcat.util.codec.binary.Base64;
    byte[] key = Base64.decodeBase64("asdf");
   // var key = "asdf".getBytes(StandardCharsets.UTF_8);
    var paddedKey = Arrays.copyOf(key, 128);
    return NimbusJwtDecoder
        .withSecretKey(new SecretKeySpec(paddedKey, "HS512"))
        .macAlgorithm(MacAlgorithm.HS512)
        .build();
  }

and used it like:

Main s = new Main();
String token = s.generateToken(new HashMap<>(), "hatef");
JwtDecoder decoder = s.jwtDecoder();
System.out.println(decoder.decode(token));

Edit 3:

OP reported in comments:

it worked with io.jsonwebtoken.impl.TextCodec.BASE64.decode(secretKey) instead of org.apache.tomcat.util.codec.binary.Base64.decodeBase64(secretKey), with the latter i still had a com.nimbusds.jose.proc.BadJWSException

user_78381690
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