Password based encryption

PBESpec.kt

import android.security.keystore.KeyProperties
import java.security.SecureRandom
import java.security.spec.KeySpec
import javax.crypto.SecretKey
import javax.crypto.SecretKeyFactory
import javax.crypto.spec.PBEKeySpec
import javax.crypto.spec.SecretKeySpec

// Source - https://medium.com/@hayk.mkrtchyan8998/shedding-light-on-android-encryption-android-crypto-api-part-2-cipher-147ff4411e1d

/**
 * A symmetric encryption key can be generated from the passphrase by
 * using the Password Based Key Derivation Function version 2 (PBKDF2).
 * @param password - The passphrase to generate the key from
 * @param keyLength - The length of the key to generate (i.e. 128, 192 or 256-bit AES key)
 */
fun generateStrongAESKey(password: CharArray, keyLength: Int): SecretKey {
    //Initialize objects and variables for later use
    val iterationCount = 10000
    val saltLength = keyLength / 8

    //Generate the salt
    val salt = generateRandomSalt(saltLength)
    val keySpec: KeySpec = PBEKeySpec(password, salt, iterationCount, keyLength)

    val keyFactory = SecretKeyFactory.getInstance("PBKDF2WithHmacSHA1")
    val keyBytes = keyFactory.generateSecret(keySpec).encoded
    return SecretKeySpec(keyBytes, KeyProperties.KEY_ALGORITHM_AES)
}

fun generateRandomSalt(saltLength: Int): ByteArray {
    val random = SecureRandom()
    val salt = ByteArray(saltLength)
    random.nextBytes(salt)
    return salt
}