[Feature/#9] AuthToken 암복호화 로직 구현

app/build.gradle.kts

@@ -16,6 +16,7 @@ dependencies {
     implementation(projects.core.datastore)
     implementation(projects.core.designsystem)
     implementation(projects.core.network)
+    implementation(projects.core.security)
     implementation(projects.data)
     implementation(projects.domain)
     implementation(projects.presentation)

core/security/.gitignore

@@ -0,0 +1 @@
+/build

core/security/build.gradle.kts

@@ -0,0 +1,11 @@
+plugins {
+    alias(libs.plugins.bitnagil.android.library)
+}
+
+android {
+    namespace = "com.threegap.bitnagil.security"
+}
+
+dependencies {
+    testImplementation(libs.androidx.junit)
+}

core/security/proguard-rules.pro

@@ -0,0 +1,21 @@
+# Add project specific ProGuard rules here.
+# You can control the set of applied configuration files using the
+# proguardFiles setting in build.gradle.
+#
+# For more details, see
+#   http://developer.android.com/guide/developing/tools/proguard.html
+
+# If your project uses WebView with JS, uncomment the following
+# and specify the fully qualified class name to the JavaScript interface
+# class:
+#-keepclassmembers class fqcn.of.javascript.interface.for.webview {
+#   public *;
+#}
+
+# Uncomment this to preserve the line number information for
+# debugging stack traces.
+#-keepattributes SourceFile,LineNumberTable
+
+# If you keep the line number information, uncomment this to
+# hide the original source file name.
+#-renamesourcefileattribute SourceFile

core/security/src/main/AndroidManifest.xml

@@ -0,0 +1,4 @@
+<?xml version="1.0" encoding="utf-8"?>
+<manifest xmlns:android="http://schemas.android.com/apk/res/android">
+
+</manifest>

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/Crypto.kt

@@ -0,0 +1,32 @@
+package com.threegap.bitnagil.security
+
+import javax.crypto.Cipher
+import javax.crypto.spec.IvParameterSpec
+
+class Crypto(
+    private val keyProvider: KeyProvider,
+    private val transformation: String = "AES/CBC/PKCS7Padding",
+) {
+    fun encrypt(bytes: ByteArray): ByteArray {
+        val cipher = Cipher.getInstance(transformation)
+        cipher.init(Cipher.ENCRYPT_MODE, keyProvider.getKey())
+        val iv = cipher.iv
+        val encrypted = cipher.doFinal(bytes)
+        return iv + encrypted
+    }
+
+    fun decrypt(bytes: ByteArray): ByteArray {
+        val cipher = Cipher.getInstance(transformation)
+        require(bytes.size >= cipher.blockSize) {
+            INVALID_INPUT_TOO_SHORT_MSG
+        }
+        val iv = bytes.copyOfRange(0, cipher.blockSize)
+        val data = bytes.copyOfRange(cipher.blockSize, bytes.size)
+        cipher.init(Cipher.DECRYPT_MODE, keyProvider.getKey(), IvParameterSpec(iv))
+        return cipher.doFinal(data)
+    }
+
+    companion object {
+        private const val INVALID_INPUT_TOO_SHORT_MSG = "[ERROR] 복호화할 수 없는 입력입니다."
+    }
+}

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
+}

core/security/src/test/java/com/threegap/bitnagil/security/CryptoTest.kt

@@ -0,0 +1,122 @@
+package com.threegap.bitnagil.security
+
+import org.junit.Assert.assertEquals
+import org.junit.Assert.assertNotEquals
+import org.junit.Assert.assertThrows
+import org.junit.Test
+import javax.crypto.BadPaddingException
+import javax.crypto.KeyGenerator
+import javax.crypto.SecretKey
+
+class CryptoTest {
+    private class FakeKeyProvider : KeyProvider {
+        private val key: SecretKey =
+            KeyGenerator
+                .getInstance("AES")
+                .apply { init(128) }
+                .generateKey()
+
+        override fun getKey(): SecretKey = key
+    }
+
+    private val crypto =
+        Crypto(
+            keyProvider = FakeKeyProvider(),
+            transformation = "AES/CBC/PKCS5Padding",
+        )
+
+    @Test
+    fun `암호화 후 복호화하면 원래 데이터와 같아야 한다`() {
+        // given
+        val original = "테스트 데이터".toByteArray()
+
+        // when
+        val encrypted = crypto.encrypt(original)
+        val decrypted = crypto.decrypt(encrypted)
+
+        // then
+        assertEquals(String(original), String(decrypted))
+    }
+
+    @Test
+    fun `같은 데이터를 암호화해도 결과는 달라야 한다`() {
+        // given
+        val input = "같은 입력".toByteArray()
+
+        // when
+        val encrypted1 = crypto.encrypt(input)
+        val encrypted2 = crypto.encrypt(input)
+
+        // then
+        assertNotEquals(encrypted1.toList(), encrypted2.toList())
+    }
+
+    @Test
+    fun `입력값이 너무 짧은 경우 IllegalArgumentException이 발생해야 한다`() {
+        // given
+        val invalid = ByteArray(4) { 0x00 }
+
+        // when & then
+        assertThrows(IllegalArgumentException::class.java) {
+            crypto.decrypt(invalid)
+        }
+    }
+
+    @Test
+    fun `빈 바이트 배열 암호화 시 예외가 발생하지 않아야 한다`() {
+        val input = ByteArray(0)
+        val encrypted = crypto.encrypt(input)
+        val decrypted = crypto.decrypt(encrypted)
+        assertEquals(String(input), String(decrypted))
+    }
+
+    @Test
+    fun `IV 일부가 조작된 경우 복호화하면 원래 데이터와 달라야 한다`() {
+        // given
+        val original = "iv 테스트".toByteArray()
+        val encrypted = crypto.encrypt(original)
+        encrypted[0] = encrypted[0].inc()
+
+        // when
+        val decrypted = crypto.decrypt(encrypted)
+
+        // then
+        assertNotEquals(String(original), String(decrypted))
+    }
+
+    @Test
+    fun `암호화된 데이터가 조작된 경우 복호화 실패해야 한다`() {
+        // given
+        val original = "데이터 조작".toByteArray()
+        val encrypted = crypto.encrypt(original)
+        encrypted[encrypted.lastIndex] = encrypted.last().inc()
+
+        // when & then
+        assertThrows(BadPaddingException::class.java) {
+            crypto.decrypt(encrypted)
+        }
+    }
+
+    @Test
+    fun `다른 키로 복호화하면 실패해야 한다`() {
+        // given
+        val original = "다른 키 테스트".toByteArray()
+        val encrypted = crypto.encrypt(original)
+
+        val otherKeyProvider =
+            object : KeyProvider {
+                override fun getKey(): SecretKey {
+                    val keyGen = KeyGenerator.getInstance("AES")
+                    keyGen.init(128)
+                    return keyGen.generateKey()
+                }
+            }
+
+        val otherCrypto = Crypto(otherKeyProvider, "AES/CBC/PKCS5Padding")
+
+        // when & then
+        assertThrows(BadPaddingException::class.java) {
+            otherCrypto.decrypt(encrypted)
+        }
+    }
+}

settings.gradle.kts

@@ -28,6 +28,7 @@ include(":app")
 include(":core:datastore")
 include(":core:designsystem")
 include(":core:network")
+include(":core:security")
 include(":data")
 include(":domain")
 include(":presentation")