Feat: 암호화/복호화 기능을 위한 Crypto 클래스 추가

- 테스트 코드 추가

Author: wjdrjs00

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

@@ -0,0 +1,25 @@
+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)
+        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)
+    }
+}

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

@@ -0,0 +1,113 @@
+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.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 `잘못된 데이터로 복호화를 시도하면 예외가 발생해야 한다`() {
+        // given
+        val invalid = ByteArray(4) { 0x00 }
+
+        // when & then
+        assertThrows(Exception::class.java) {
+            crypto.decrypt(invalid)
+        }
+    }
+
+    @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(Exception::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(Exception::class.java) {
+            otherCrypto.decrypt(encrypted)
+        }
+    }
+}