diff --git a/modules/cybercore-core/src/main/java/br/com/cybercore/signer/core/security/NonceManager.java b/modules/cybercore-core/src/main/java/br/com/cybercore/signer/core/security/NonceManager.java
index bb3d85b..646e9f0 100644
--- a/modules/cybercore-core/src/main/java/br/com/cybercore/signer/core/security/NonceManager.java
+++ b/modules/cybercore-core/src/main/java/br/com/cybercore/signer/core/security/NonceManager.java
@@ -10,6 +10,8 @@ import java.util.concurrent.ConcurrentHashMap;
  */
 public class NonceManager {
 
+    public static final Duration DEFAULT_CLOCK_SKEW = Duration.ofSeconds(30);
+
     private final Duration windowDuration;
     private final ConcurrentHashMap<String, Instant> usedNonces = new ConcurrentHashMap<>();
 
@@ -21,6 +23,34 @@ public class NonceManager {
         this(Duration.ofSeconds(120));
     }
 
+    /**
+     * Valida um timestamp de requisição em relação ao relógio local, considerando a janela
+     * de validade e uma margem segura de clock skew (tolerância a desvio de relógio entre cliente e agente).
+     *
+     * @param requestTimestamp Instant da requisição informado pelo cliente.
+     * @param clockSkew Tolerância de tolerância a skew de relógio.
+     * @return {@code true} se o timestamp estiver na faixa válida permitida.
+     */
+    public boolean isTimestampValid(Instant requestTimestamp, Duration clockSkew) {
+        if (requestTimestamp == null) {
+            return false;
+        }
+        Duration skew = clockSkew != null ? clockSkew : DEFAULT_CLOCK_SKEW;
+        Instant now = Instant.now();
+        Instant earliestAllowed = now.minus(windowDuration).minus(skew);
+        Instant latestAllowed = now.plus(skew);
+
+        return !requestTimestamp.isBefore(earliestAllowed) && !requestTimestamp.isAfter(latestAllowed);
+    }
+
+    public boolean isTimestampValid(Instant requestTimestamp) {
+        return isTimestampValid(requestTimestamp, DEFAULT_CLOCK_SKEW);
+    }
+
+    public Duration getWindowDuration() {
+        return windowDuration;
+    }
+
     /**
      * Tenta registrar um nonce.
      *
diff --git a/modules/cybercore-core/src/test/java/br/com/cybercore/signer/core/security/NonceManagerTest.java b/modules/cybercore-core/src/test/java/br/com/cybercore/signer/core/security/NonceManagerTest.java
index 4a59247..969ba92 100644
--- a/modules/cybercore-core/src/test/java/br/com/cybercore/signer/core/security/NonceManagerTest.java
+++ b/modules/cybercore-core/src/test/java/br/com/cybercore/signer/core/security/NonceManagerTest.java
@@ -28,4 +28,84 @@ class NonceManagerTest {
         assertThat(manager.registerNonce(null)).isFalse();
         assertThat(manager.registerNonce("   ")).isFalse();
     }
+
+    @Test
+    @DisplayName("Deve permitir apenas 1 registro concorrente simultâneo para o mesmo nonce")
+    void shouldBeThreadSafeUnderHighConcurrency() throws Exception {
+        NonceManager manager = new NonceManager();
+        String identicalNonce = "shared-race-nonce-" + java.util.UUID.randomUUID();
+        int threads = 30;
+
+        java.util.concurrent.ExecutorService executor = java.util.concurrent.Executors.newFixedThreadPool(threads);
+        java.util.concurrent.CountDownLatch startLatch = new java.util.concurrent.CountDownLatch(1);
+        java.util.concurrent.atomic.AtomicInteger successes = new java.util.concurrent.atomic.AtomicInteger(0);
+        java.util.concurrent.atomic.AtomicInteger rejections = new java.util.concurrent.atomic.AtomicInteger(0);
+
+        java.util.List<java.util.concurrent.Future<?>> futures = new java.util.ArrayList<>();
+        for (int i = 0; i < threads; i++) {
+            futures.add(executor.submit(() -> {
+                try {
+                    startLatch.await();
+                    boolean registered = manager.registerNonce(identicalNonce);
+                    if (registered) {
+                        successes.incrementAndGet();
+                    } else {
+                        rejections.incrementAndGet();
+                    }
+                } catch (InterruptedException e) {
+                    Thread.currentThread().interrupt();
+                }
+            }));
+        }
+
+        startLatch.countDown();
+        for (java.util.concurrent.Future<?> f : futures) {
+            f.get();
+        }
+        executor.shutdown();
+
+        assertThat(successes.get()).isEqualTo(1);
+        assertThat(rejections.get()).isEqualTo(threads - 1);
+        assertThat(manager.activeNonceCount()).isEqualTo(1);
+    }
+
+    @Test
+    @DisplayName("Deve validar timestamp com tolerância a clock skew (passado recente e pequeno futuro)")
+    void shouldValidateTimestampWithClockSkew() {
+        NonceManager manager = new NonceManager(Duration.ofSeconds(60));
+        java.time.Instant now = java.time.Instant.now();
+
+        // Timestamp atual é válido
+        assertThat(manager.isTimestampValid(now)).isTrue();
+
+        // 10 segundos no passado (dentro da janela de 60s) é válido
+        assertThat(manager.isTimestampValid(now.minusSeconds(10))).isTrue();
+
+        // 20 segundos no futuro (dentro do clock skew de 30s) é tolerado
+        assertThat(manager.isTimestampValid(now.plusSeconds(20))).isTrue();
+
+        // 100 segundos no passado (fora de 60s + 30s = 90s) é rejeitado
+        assertThat(manager.isTimestampValid(now.minusSeconds(100))).isFalse();
+
+        // 60 segundos no futuro (além do skew de 30s) é rejeitado
+        assertThat(manager.isTimestampValid(now.plusSeconds(60))).isFalse();
+
+        // Nulo é rejeitado
+        assertThat(manager.isTimestampValid(null)).isFalse();
+    }
+
+    @Test
+    @DisplayName("Deve limpar nonces expirados além da janela configurada")
+    void shouldCleanupExpiredNonces() throws Exception {
+        NonceManager manager = new NonceManager(Duration.ofMillis(50));
+        manager.registerNonce("temporary-nonce");
+        assertThat(manager.activeNonceCount()).isEqualTo(1);
+
+        Thread.sleep(70);
+        manager.cleanupExpired();
+        assertThat(manager.activeNonceCount()).isEqualTo(0);
+
+        // Após expirar e ser limpo, pode ser aceito novamente
+        assertThat(manager.registerNonce("temporary-nonce")).isTrue();
+    }
 }