A SharedPreferences wrapper implementation with encryption/decryption, using CipherHelper implementation.

SecureSharedPreferences.kt

import android.content.SharedPreferences

/**
 * A [android.content.SharedPreferences] wrapper that helps easy reading/writing values.
 *
 * @author Francesco Jo(nimbusob@gmail.com)
 * @since 22 - Mar - 2018
 */
class SecureSharedPreferences(private val sharedPref: SharedPreferences) {
    fun contains(key: String) = sharedPref.contains(key)

    fun get(key: String, defaultValue: Boolean): Boolean = getInternal(key, defaultValue)

    fun get(key: String, defaultValue: Int): Int = getInternal(key, defaultValue)

    fun get(key: String, defaultValue: Long): Long = getInternal(key, defaultValue)

    fun get(key: String, defaultValue: String): String = getInternal(key, defaultValue)

    /**
     * Client codes must handle ClassCastException by their own at the call site if happens.
     */
    private fun <T : Any> getInternal(key: String, defaultValue: T): T {
        val str = sharedPref.getString(key, "")
        if (str.isNullOrEmpty()) {
            return defaultValue
        }
        val value = AndroidCipherHelper.decrypt(str)

        @Suppress("PlatformExtensionReceiverOfInline", "UNCHECKED_CAST", "IMPLICIT_CAST_TO_ANY")
        return when(defaultValue) {
            is Boolean -> value.toBoolean()
            is Int     -> value.toInt()
            is Long    -> value.toLong()
            is String  -> value
            else -> throw IllegalArgumentException("defaultValue only could be one of these types: Boolean, Int, Long, String")
        } as T
    }

    fun put(key: String, value: Boolean) = putInternal(key, value)

    fun put(key: String, value: Int) = putInternal(key, value)

    fun put(key: String, value: Long) = putInternal(key, value)

    /**
     * Due to the encryption layer limitations, input value must be shorter than [CipherHelper.KEY_LENGTH_BIT] bytes.
     */
    fun put(key: String, value: String) = putInternal(key, value)

    private fun putInternal(key: String, value: Any?) {
        try {
            sharedPref.edit().run({
                if (value == null) {
                    remove(key)
                } else {
                    putString(key, AndroidCipherHelper.encrypt(value.toString()))
                }

                apply()
            })
        } catch (e: Throwable) {
            e.printStackTrace()
        }
    }

    companion object {
        fun wrap(sharedPref: SharedPreferences) = SecureSharedPreferences(sharedPref)
    }
}