diff --git a/property-guard-spring-boot-starter/src/main/java/cn/org/codecrafters/propertyencryptor/PropertyGuard.java b/property-guard-spring-boot-starter/src/main/java/cn/org/codecrafters/propertyencryptor/PropertyGuard.java
new file mode 100644
index 0000000..c1d95ef
--- /dev/null
+++ b/property-guard-spring-boot-starter/src/main/java/cn/org/codecrafters/propertyencryptor/PropertyGuard.java
@@ -0,0 +1,96 @@
+/*
+ * Copyright (C) 2023 CodeCraftersCN.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package cn.org.codecrafters.propertyencryptor;
+
+import cn.org.codecrafters.devkit.utils.AesUtil;
+import org.springframework.boot.SpringApplication;
+import org.springframework.boot.env.EnvironmentPostProcessor;
+import org.springframework.boot.env.OriginTrackedMapPropertySource;
+import org.springframework.core.env.ConfigurableEnvironment;
+import org.springframework.core.env.MapPropertySource;
+import org.springframework.core.env.SimpleCommandLinePropertySource;
+
+import java.util.HashMap;
+import java.util.Optional;
+
+/**
+ * PropertyEncryptor is a utility class designed for encrypting configuration
+ * information in Spring Boot applications.
+ * <p>
+ * Spring Boot applications often need to store sensitive configuration details
+ * such as database passwords, API keys, etc. To ensure that these sensitive
+ * pieces of information are not exposed, developers can utilize the
+ * {@code PropertyGuard} class to encrypt and store them within configuration
+ * files.
+ * <p>
+ * <b>Usage</b>
+ * In {@code application.yml} or {@code application.properties}:
+ * <pre>
+ *     # original
+ *     app.example-properties=Sample Value
+ *
+ *     # encrypted with key 3856faef0d2d4f33
+ *     app.example-properties=pe:t4YBfv8M9ZmTzWgTi2gJqg==
+ * </pre>
+ * Then, add the command line arguments like {@code --pe.key=3856faef0d2d4f33}.
+ * <p>
+ * This class is extracted from <a href="https://baomidou.com/pages/e0a5ce/"
+ * >MyBatis-Plus</a>.
+ *
+ * @author hubin@baomidou
+ * @see org.springframework.boot.env.EnvironmentPostProcessor
+ */
+public class PropertyGuard implements EnvironmentPostProcessor {
+
+    /**
+     * Process the encryption environment variables.
+     *
+     * @param environment the environment to post-process
+     * @param application the application to which the environment belongs
+     */
+    @Override
+    public void postProcessEnvironment(ConfigurableEnvironment environment, SpringApplication application) {
+        // Get the key for encryption from command line.
+        var encryptionKey = "";
+        for (var ps : environment.getPropertySources()) {
+            if (ps instanceof SimpleCommandLinePropertySource source) {
+                encryptionKey = source.getProperty("pe.key");
+                break;
+            }
+        }
+
+        if (Optional.ofNullable(encryptionKey).map((key) -> !key.isEmpty()).orElse(false)) {
+            var map = new HashMap<String, Object>();
+            for (var propertySources : environment.getPropertySources()) {
+                if (propertySources instanceof OriginTrackedMapPropertySource source) {
+                    for (var name : source.getPropertyNames()) {
+                        if (source.getProperty(name) instanceof String str) {
+                            if (str.startsWith("pe:")) {
+                                map.put(name, AesUtil.decrypt(str.substring(3), encryptionKey));
+                            }
+                        }
+                    }
+                }
+            }
+            // Put the decrypted data into environment variables, and made them at top-level.
+            if (!map.isEmpty()) {
+                environment.getPropertySources().addFirst(new MapPropertySource("custom-encrypt", map));
+            }
+        }
+    }
+}
diff --git a/property-guard-spring-boot-starter/src/main/resources/META-INF/spring.factories b/property-guard-spring-boot-starter/src/main/resources/META-INF/spring.factories
new file mode 100644
index 0000000..dcdcd64
--- /dev/null
+++ b/property-guard-spring-boot-starter/src/main/resources/META-INF/spring.factories
@@ -0,0 +1 @@
+org.springframework.boot.env.EnvironmentPostProcessor=cn.org.codecrafters.propertyencryptor.PropertyGuard
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