Get EncryptedSharedPreferences

SharedPreferencesUtils.kt

//
// Get EncryptedSharedPreferences and handle restore of accidentallly
// backuped file that we can no longer decrypt. If the master key provided
// is not able to decrypt the shared preferences, the file will be recreated.
// 
// Tested with "androidx.security:security-crypto:1.1.0-alpha06"
//

package pl.rynkowski.platform_utils

import android.content.Context
import android.content.SharedPreferences
import androidx.security.crypto.EncryptedSharedPreferences
import androidx.security.crypto.MasterKey
import java.security.KeyStore
import timber.log.Timber

private const val appMasterKeyAlias = "custom_master_key"

fun Context.getMasterKey(): MasterKey {
    val keystore = KeyStore.getInstance("AndroidKeyStore")
    keystore.load(null)
    val masterKeyAlias =
        if (keystore.isKeyEntry(appMasterKeyAlias)) appMasterKeyAlias
        else MasterKey.DEFAULT_MASTER_KEY_ALIAS
    return MasterKey.Builder(this, masterKeyAlias)
        .setKeyScheme(MasterKey.KeyScheme.AES256_GCM)
        .build()
}

fun Context.getEncryptedSharedPreferences(filename: String): SharedPreferences {
    val masterKey = getMasterKey()
    // Return the shared preferences if we can
    val sharedPreferences = getEncryptedSharedPreferencesOrNull(filename, masterKey)
    return sharedPreferences ?: run {
        // otherwise delete and try again
        Timber.w("Cannot retrieve preferences encrypted with current master key. Deleting and recreating.")
        deleteSharedPreferences(filename)
        return getEncryptedSharedPreferencesOrThrow(filename, masterKey)
    }
}

fun Context.getEncryptedSharedPreferencesOrNull(filename: String, key: MasterKey): SharedPreferences? =
    try {
        getEncryptedSharedPreferencesOrThrow(filename = filename, key = key)
    } catch (e: Exception) {
        null
    }

fun Context.getEncryptedSharedPreferencesOrThrow(filename: String, key: MasterKey): SharedPreferences =
    EncryptedSharedPreferences.create(
        this,
        filename,
        key,
        EncryptedSharedPreferences.PrefKeyEncryptionScheme.AES256_SIV,
        EncryptedSharedPreferences.PrefValueEncryptionScheme.AES256_GCM,
    )

fun Context.getSharedPrefs(filename: String, encrypted: Boolean = false): SharedPreferences =
    if (encrypted) {
        getEncryptedSharedPreferences(filename)
    } else {
        getSharedPreferences(filename, Context.MODE_PRIVATE)
    }