Flutter / Dart : Avoid storing password in plain text

Question

I am using Dart mailer in Flutter and there is a comment that says:

How you use and store passwords is up to you. Beware of storing passwords in plain.

Is there any way to hash the password? How can I avoid storing it in plain text?

Answer 1

It is generally not a good idea to store passwords in plain text anywhere. The way you handle passwords, though, depends on the platform.

Flutter

The flutter_secure_storage package uses Keychain on iOS and KeyStore on Android to store passwords (or tokens).

// Create storage
final storage = FlutterSecureStorage();

// Read secret 
String value = await storage.read(key: key);

// Write secret 
await storage.write(key: key, value: value);

Note that for Android the min API is 18.

Dart Server

If you are making a server, it is even more important not to store the user passwords in plain text. If the server is compromised, the attacker would have access to all of the passwords, and many users use the same password on multiple accounts.

It would be best to hand the authentication over to Google or Facebook or some other trusted third party by using OAuth2. However, if you are doing your own authorization, you should hash the passwords with a salt and save the hash, not the password itself. This makes it more difficult for an attacker to get the user passwords in case the server is compromised.

A basic implementation (but see comment below) could use the crypto package by the Dart Team.

// import 'package:crypto/crypto.dart';
// import 'dart:convert';

var password = 'password123';
var salt = 'UVocjgjgXg8P7zIsC93kKlRU8sPbTBhsAMFLnLUPDRYFIWAk';
var saltedPassword = salt + password;
var bytes = utf8.encode(saltedPassword);
var hash = sha256.convert(bytes);

Save the salt and the hash. Discard the password. Use a different salt for every user.

To make brute forcing the hashes more difficult, you can also check out the dbcrypt package.

Answer 2

If you want to hash

Use the password_hash package. Their example code is very easy to use:

var generator = new PBKDF2();
var salt = Salt.generateAsBase64String();
var hash = generator.generateKey("mytopsecretpassword", salt, 1000, 32);

Store both the hash and the salt, and you can verify someone else's password attempt by running the generator.generateKey function using their password and the saved salt.

What you actually want

If you're trying to automatically login, you of course need the original password, not a hash. You have a couple options

1. If the device that will have your app installed is safe, as in it is some company-owned device that has to be logged into by an employee, then have it in plaintext. It doesn't matter. As any company's security policy should be, you must make sure that hard drives are wiped before disposing of electronics (And make sure that no one can stroll in and take the iPad or whatever it is).

2. If unknown people outside of your organization will be installing your app, you will have to have them login and use their email, or have an API open that will send emails on their behalf (To prevent spamming from your email). The app would sent a POST to that API to send an email. If you had the plaintext password in the application, they could find it on their device, and abuse it.

Answer 3

This response comes late, but here is my approach to storing and using a password for sending emails to recipients using mailer in Flutter. I hope it helps anyone facing this issue.

First I downloaded the crypton package. Then I created a separate dart file where I handle everything related to sending mails, I called it mailer. In this file is where I specify the password, encrypts it using crypton, and use send the email using the decrypted password.

Below is the code of my mailer.dart file:

import 'dart:io';
import 'package:flutter/material.dart';
import 'package:mailer/mailer.dart';
import 'package:mailer/smtp_server.dart';
import 'package:intl/intl.dart';
import 'package:crypton/crypton.dart';

class Mailer {
  //the variable below we use to encrypt and decrypt the password
  RSAKeypair _rsaKeypair = RSAKeypair.fromRandom();
  //Below we set the password as a private variable
  String _password = 'mySecurePassword';
  
  //We set an encrypted variable that will store the encrypted password;
  String _encrypted;

  //The function below sets the encrypted variable by assigning it the encrypted value of the password
  void setEncrypt () {
    _encrypted = _rsaKeypair.publicKey.encrypt(_password);
  }

  //The function below is responsible for sending the email to the recipients and it is what we call when we want to send an email   
  emailSender({@required String emailRecipient, @required List<String> paths}) async {
    //We call the setEncrypt() function to assign the correct value to the encrypted variable
    setEncrypt();
    String username = 'email@email.com';
    //We asign the decrypted value of encrypted to the password we provide to the smtpServer 
    String password = _rsaKeypair.privateKey.decrypt(_encrypted);

    //The rest of sending an email is the same.

    final smtpServer = gmail(username, password);
    // Use the SmtpServer class to configure an SMTP server:
    // final smtpServer = SmtpServer('smtp.domain.com');
    // See the named arguments of SmtpServer for further configuration
    // options.

    // Create our message.
    Message message = Message()
      ..from = Address(username, 'Your name')
      ..recipients.add(emailRecipient)
      ..ccRecipients.addAll(['secondEmail@email.com'])
      ..subject = 'Date: ${DateFormat('dd/MM/yyyy').format(DateTime.now())}'
      ..text = 'This is the plain text.\nThis is line 2 of the text part.'
      ..html = "<h1>Hi:</h1>\n<p>This is some html</p>\n<p>Greetings, mailer.dart</p>";

    for (String path in paths) {
      message
        ..attachments.add(
          FileAttachment(
            File(
              path,
            ),
          ),
        );
    }
    var connection = PersistentConnection(smtpServer);

    // Send the first message
    await connection.send(message);

    // send the equivalent message
    //await connection.send(equivalentMessage);

    // close the connection
    await connection.close();
  }
}

This was my approach to solving the issue of storing passwords as plain text for sending emails using the mailer package or any package with a similar purpose.