Feat: 암호화 키 제공자 인터페이스 및 구현체 추가

- AES/CBC/PKCS7Padding 암호화 방식 사용

Author: wjdrjs00

core/security/src/main/java/com/threegap/bitnagil/security/AndroidKeyProvider.kt

@@ -0,0 +1,41 @@
+package com.threegap.bitnagil.security
+
+import android.security.keystore.KeyGenParameterSpec
+import android.security.keystore.KeyProperties
+import java.security.KeyStore
+import javax.crypto.KeyGenerator
+import javax.crypto.SecretKey
+
+class AndroidKeyProvider : KeyProvider {
+    private val keyStore =
+        KeyStore
+            .getInstance("AndroidKeyStore")
+            .apply { load(null) }
+
+    override fun getKey(): SecretKey {
+        val existingKey = keyStore.getEntry(KEY_ALIAS, null) as? KeyStore.SecretKeyEntry
+        return existingKey?.secretKey ?: createKey()
+    }
+
+    private fun createKey(): SecretKey {
+        return KeyGenerator.getInstance(ALGORITHM).apply {
+            init(
+                KeyGenParameterSpec.Builder(
+                    KEY_ALIAS,
+                    KeyProperties.PURPOSE_ENCRYPT or KeyProperties.PURPOSE_DECRYPT,
+                ).setBlockModes(BLOCK_MODE)
+                    .setEncryptionPaddings(PADDING)
+                    .setRandomizedEncryptionRequired(true)
+                    .setUserAuthenticationRequired(false)
+                    .build(),
+            )
+        }.generateKey()
+    }
+
+    companion object {
+        private const val KEY_ALIAS = "bitnagil_auth_token"
+        private const val ALGORITHM = KeyProperties.KEY_ALGORITHM_AES
+        private const val BLOCK_MODE = KeyProperties.BLOCK_MODE_CBC
+        private const val PADDING = KeyProperties.ENCRYPTION_PADDING_PKCS7
+    }
+}

core/security/src/main/java/com/threegap/bitnagil/security/KeyProvider.kt

@@ -0,0 +1,7 @@
+package com.threegap.bitnagil.security
+
+import javax.crypto.SecretKey
+
+interface KeyProvider {
+    fun getKey(): SecretKey
+}