Securing Data in KMP: Cross-Platform Encryption Strategies for Local Storage

This project explores encryption techniques for securing local data in Kotlin Multiplatform (KMP) projects, focusing on cross-platform strategies. It demonstrates how to handle sensitive information on both Android and iOS by leveraging platform-specific encryption libraries like CoreCrypto for iOS and Cipher & Keystore for Android. The goal is to achieve seamless data security without sacrificing cross-platform flexibility.

Libraries Used

• KOIN - For dependency injection
• DATASTORE - For local storage
• Keystore - to store cryptographic keys in a container
• CoreCrypto- for cryptographic operations in iOS
• Cipher - to perform encryption and decryption operations using various algorithms (such as AES, RSA, and DES)

Encryption in Shared Module

composeApp/src/commonMain/kotlin/com/kmp/encryption/utils/EncryptionManager.kt

This is an interface that defines the encryption and decryption methods.

interface EncryptionManager {
    suspend fun encrypt(plainText: String) : ByteArray
    suspend fun decrypt(cipherText: ByteArray): String
}

Their implementation is done in the native Android & iOS modules

• Android Module: composeApp/src/androidMain/kotlin/com/kmp/encryption/utils/AndroidEncryptionManager.kt
• iOS Module: composeApp/src/iosMain/kotlin/com/kmp/encryption/IosEncryptionManager.kt

Local Storage in Shared Module

composeApp/src/commonMain/kotlin/com/kmp/encryption/utils/DataStoreManager.kt

This is a class that uses dataStore to store/retrieve data locally. DataStore is instantiated in the native Android and iOS modules through Koin.

• Android Module: composeApp/src/androidMain/kotlin/com/kmp/encryption/di/AppModule.android.kt

single<DataStore<Preferences>> {
        val context = get<Context>()
        PreferenceDataStoreFactory.createWithPath(produceFile = {
            context.filesDir.resolve(DATASTORE_PREF_FILENAME).absolutePath.toPath()
        })
    }

• iOS Module : composeApp/src/iosMain/kotlin/com/kmp/encryption/di/AppModule.ios.kt

single<DataStore<Preferences>> {
        PreferenceDataStoreFactory.createWithPath(
            produceFile = {
                val directory = NSFileManager.defaultManager.URLForDirectory(
                    directory = NSDocumentDirectory,
                    inDomain = NSUserDomainMask,
                    appropriateForURL = null,
                    create = false,
                    error = null
                )

                val filePath = requireNotNull(directory).path()+"/$DATASTORE_PREF_FILENAME"
                filePath.toPath()
            }
        )
    }

Presentation slides for this project are available here