Hardware-backed security

fortran77 · December 19, 2018, 3:54am

Most newer Android devices, and all newer Apple mobile devices, and many desktop machines, provide hardware-backed key management and encryption. This should be used when available. The hardware will store keys and will enforce rate limits on brute-force cracking attempts. Then even a weak password or a 4-digit PIN can provide relatively high security.

kspearrin · December 19, 2018, 5:17pm

The Android Keystore and iOS Keychain is already used… ?

fortran77 · December 20, 2018, 8:11pm

I searched the source code on github and didn’t find any suitable hits. Maybe I was using the wrong search strings. Sorry about that.

itsbruce · December 31, 2018, 4:46am

Same API calls either way, so it’s not going to be obvious unless the code calls something like keyInfo.isInsideSecureHardware() and does something special. Or calls getEncoded() on a private key and does something with the result - because that would be a null value if the device has a Trusted Execution Environment, since you can’t take private keys out of it.

But if you look at the significant part of the code…

github.com

bitwarden/mobile/blob/master/src/Android/Services/AndroidKeyStoreStorageService.cs

using Java.Security;
using Javax.Crypto;
using Android.OS;
using Bit.App.Abstractions;
using System;
using Android.Security;
using Javax.Security.Auth.X500;
using Java.Math;
using Android.Security.Keystore;
using Android.App;
using Plugin.Settings.Abstractions;
using Java.Util;
using Javax.Crypto.Spec;
using Android.Preferences;

namespace Bit.Android.Services
{
    public class AndroidKeyStoreStorageService : ISecureStorageService
    {
        private const string AndroidKeyStore = "AndroidKeyStore";

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… none of that is happening. The code is just passing objects around. On a device with a TEE, the objects are just holding references to the private key and the crypto operations (cipher.doFinal()) are actually executed within the TEE by the KeyMaster module. But that’s a layer underneath the KeyStore API and happens transparently to the calling code.

fortran77 · December 31, 2018, 2:19pm

It’s very kind of you to explain in detail. Thanks.