Darth Null’s Ramblings

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Hello! I'm David Schuetz.
This is where I ramble about...stuff.

More Mobile Malware Melodrama

A few days ago I commented on the iOS malware situation. One might sum it up as “fanboys smugly assert there is no iOS malware; anti-fanboys smugly point to this list as proof that the fanboys are idiots.”

Then not three days later, American Banker posted an article about Svpeng, an existing trojan that’s been making the rounds in Russia and is now hitting US users.

What I found most interesting about that article is this: Not once do they mention the platforms affected by the malware. Hell, even the Kaspersky press release is coy about it, only using the word “Android” once, and that in their formal name for the trojan (Trojan-Banker.AndroidOS.Svpeng.a). This trojan seems to have been out for almost a year, but now that it’s hitting US users, Kaspersky is putting on a full-court press in the…er…press… (I should really steer clear of sports analogies). Predictably, I’ve had customers anxiously asking about the trojan, and whether they or their customers should be concerned.

A quick Google search on the trojan’s name nets 1 scan and 1 summary report from Virus Total, and 9 (mostly breathless) news reports about this horrible new scourge that the banks can’t do anything about. Most of these seem to be regurgitated press releases or wire reports, with no useful details at all. And, again, most of these don’t mention what platforms the malware attacks.

So what does this thing actually do? I found a mention on Emerging Threats from January, and some more details from Kaspersky from last November, but thus far, it’s damned near impossible to figure out just how this spreads, let alone how to block it.

What I wish Kaspersky had put in their press release (which would’ve percolated to many of the hundreds of articles simply repeating their information) was:

and so on.

If the folks discovering, naming, and alerting the public about the malware (Kaspersky), and the relevant industry-specific press (American Banker) can’t explain the problem in useful terms, should we really be surprised when mainstream press can’t do any better? (also, 10:1 this is on all the morning shows by the end of the week). Which means that soon, everybody will be asking about it, and worried about their data (and their money).

I’m just afraid that very few of us will be able to answer those worries with anything approaching a useful response.

Memory Pressure, Capacity Limits, and Ubiquitous Computing

One of the things I was most looking forward to with my new iPhone 5S was faster switching between applications. It seemed like my 4S always took 5-10 seconds to toggle between two programs, even simple apps. Jumping from Angry Birds to YouTube (to see what I’m doing wrong) and back again was agonizing.

Unfortunately, though the 5S is significantly faster, switching has in some ways become worse. The slowest reloads are faster, but I feel like I need full reloads more frequently. I’m convinced this is simply due to memory usage. Many applications (especially those with lots of full retina artwork) are taking the device to its RAM limits. No amount of new processor power can mask the fact that there’s just not enough memory in the device.

So it occurred to me a while ago — what if Apple can come up with a good way to load a program in memory in small chunks? Last year at WWDC, they showed off all kinds of processor and OS tricks to make OS X as power-efficient as possible. Could they do something similar for memory?

Rather than loading an entire application into memory at once, could iOS offer a way to let programmers break their apps into smaller chunks that are loaded only when needed? Kind of like the time-based grouping of operations in OS X, only focused on memory rather than CPU usage. Why should the code for managing app settings be in memory while the user is off shooting zombies? Do you really need chart generation code when we’re just editing text in a word processor?

If we’re able to do something like this, then all kinds of new things suddenly become possible. The oft-rumored “side by side” application usage could be a possibility, for one. I’m not sure that’d work otherwise, as the apps just seem to need too much RAM. Of course, Apple could double the memory in the devices, but then apps would just expand to fill that size as well.

Another thing that might then be possible is sort of an “iTunes Match” for applications. The OS would keep frequently used applications on the device at all times, but only “install” rarely used apps on demand. If you’re only downloading bits of an app at a time, as needed, then this might actually be feasible.

It’s interesting in a way — some time ago, there was talk about “Just In Time” delivery of applications over the internet. It’s possible this was part of the promise of Java — I may have blocked the precise origins of the concept from my memory. I distinctly remember thinking at the time, hell no, if I buy an application I want a copy of it locally, all the time. That I wouldn’t trust that I’d be able to retrieve my applications over the net like that.

Well, guess what? We skipped right over JIT applications and put all our data in the cloud instead. Kind of funny, when I think about it.

As long as I’m rampantly speculating (on the day that WWDC opens, no less — I really should get these thoughts out when they happen and not months later…), let’s take this line of thinking to its logical, yet absurd, conclusion. If all our data is on the cloud, and if all our apps can be downloaded from the cloud on demand…why do we even need “our own” iPads? Just authenticate yourself to the iPad, and boom!, it looks like your iPad, with all your apps and data coming down when you ask for them. Done using the iPad? Sign out, and boom! again, all the data’s gone.

Of course, Apple has not shown any indication that they want to follow the concept of “logins” on an iPad, but it’s an interesting thought anyway. Go to Starbucks, borrow one of their store iPads, work with it as if it’s your own, then log out and leave it for the next user. Apple’s already toyed with some of this, as you can configure an OS X machine to allow guests to log in using Apple IDs (though it’s obviously not doing this data / application magic at all). Also, something akin to this was always hoped for with NeXT machines (though in that case, you’d carry your computing world around on a 256MB magneto-optical disk, which was damned cool for 1988).

I understand that this sort of change would be difficult to achieve, and possibly impossible in practice. But it’s certainly interesting to think of. And, putting aside crazy ideas about “logging in” to a friend’s iPad and replicating your entire environment on the fly, I still think that something like this would be very useful (and may even be required) for making apps much more responsive, especially when switching between applications.

And we could even use the iWatch and BTLE for seamless authentication!

Making Tunnelblick + Google Authenticator Easier to Use

I’ve been occasionally using a VPN that requires a Google Authenticator code to connect. I say “occasionally” because it’s a pain to use — I have to launch Tunnelblick (the VPN client I’m using on my Mac), then get the VPN password out of my password manager and paste it in, then open my phone, launch Google Authenticator, and enter the displayed tokencode next to my password.

It’s not horrible — but it’s awkward enough that I find myself looking for ways to avoid using this particular connection. Then the other day, a co-worker suggested using a script to dump the credentials into the VPN config on the fly and re-launch. And so, my lunchtime project was decided for me.

Tunnelblick won’t let you write credentials to the configuration file, but it will happily pull them from the OS X Keychain. So now I just need to find a library to write to the keychain. Turns out that’s easy, too — there’s a command at /usr/bin/security that does exactly what I need. Now I just need to make it look pretty.

And that’s what I’ve got now: “gtb” — Google(auth) + TunnelBlick. This script:

  1. For setup:
    1. Prompts you for your base VPN password and Google Authenticator Key
    2. Writes them to the keychain
  2. For normal use:
    1. Reads the password and key from the keychain
    2. Computes the current Google Authenticator tokencode
    3. Writes to the keychain entry Tunnelblick uses for the VPN password
    4. Launches Tunnelblick and opens the selected VPN

Delighted (or maniacal, your choice) laughter is left as the responsibility of the user.

How does it work? Well (after setup) the first thing we need to do is read the data from the keychain. For a Tunnelblick VPN called “MyVPN” this can be done with the aforementioned security command:

$ /usr/bin/security find-generic-password -gs Tunnelblick-Auth-MyVPN -a auth-data
keychain: "/Users/dschuetz/Library/Keychains/login.keychain"
class: "genp"
    0x00000007 <blob>="Tunnelblick-Auth-MyVPN"
    0x00000008 <blob>=<NULL>
    "cdat"<timedate>=0x32303134303533303134313430355A00  "20140530141405Z\000"
    "mdat"<timedate>=0x32303134303533303134313834385A00  "20140530141848Z\000"


The important bit is the last line, where the “secret” stored in the keychain entry lives (it’s always called “password,” no matter what you store there). My script reads that entry, splits on the ‘:’ into google_key and vpn_password fields, and then goes on to compute the tokencode.

Google Authenticator uses a system called the Time-based One-time Password Algorithm, or TOTP for short. Basically, it:

  1. Treats the key string as a Base-32 string and decodes it into a binary key
  2. Computes the current timestamp, based on the UNIX epoch, to a 30-second accurracy (that is, the timestamp number will increment by 1 every 30 seconds).
  3. Computes the HMAC-SHA1 of (key, timestamp)
  4. Reads the last byte of the resultant HMAC digest, and uses the lowermost 4 bits of that character to select an index into the digest
  5. Reads the four bytes from the digest, beginning with the index, as the base for the token
  6. Strips the most-significant bit off that 4-byte word and reduces the result (using modulo arithmetic) to a 6-digit number
  7. Returns the number (padded with leading zeroes if necessary)

One interesting problem I ran into: The Google key was 22 letters long (after stripping spaces). All the examples I could find online showed only 16 letter keys, but clearly this longer key worked fine in the iPhone application. However, it wouldn’t work in my script — I kept getting errors in the Base-32 decoding. Padding the string with additional “A”s worked — so my script takes the provided key string and tries that until it produces a valid Base-32 decoding.

There’s a great library that does all this on github (thanks, Tom Jaskowski), but I simply extracted the part that I cared about and incorporated it directly into the script. Here’s what it looks like in Python:

def get_totp_token(key_str):
    key = base64.b32decode(key_str)       # the authentication key
    num = int(time.time()) // 30          # epoch time to 30 sec
    msg = struct.pack('>Q', num)          # pack into a binary thing

  # take a SHA1 HMAC of key and binary-packed time value
    digest = hmac.new(key, msg, hashlib.sha1).digest()

  # last 4 bits of the digest tells us which 4 bytes to use
    offset = ord(digest[19]) & 15
    token_base = digest[offset : offset+4]

  # unpack that into an integer and strip it down
    token_val = struct.unpack('>I', token_base)[0] & 0x7fffffff
    token = token_val % 1000000

    return "%06d" % token                 # pad with leading zeroes

Once the tokencode has been computed, it’s appended to the base password, and written back into the keychain using security:

/usr/bin/security add-generic-password -U -s Tunnelblick-Auth-MyVPN -a password -w myVPNPassword123456

Then we use a little Applescript magic to launch the right VPN connection in Tunnelblick:

echo 'Tell app "Tunnelblick" to connect "MyVPN"' | osascript

…and that’s it!

Security of Keychain Items

A quick note on the keychain items themselves. The security application, by default, can access these items without prompting the user for their password. This means that, if you leave your desktop unlocked, anyone could walk up and extract the VPN credentials with a couple quick command line calls. So it’s best to open up the Keychain Access application, find the VPN’s “password” and “auth-data” entries, and secure them. Do this by removing the “security” application from the list of apps which can access the data at all times. (Leave Tunnelblick authorized to read the ‘password’ entry so it can launch more smoothly). You’ll also want to set the “Ask for Keychain Password” flag. Then, when you run the script, the Keychain will prompt you for your login password (to access the auth-data entry), and after that everything will happen magically without further intervention.

If you’d prefer to not store the Google Authenticator credentials in the keychain (but rely on the Google Auth app on your phone, for example), then enter “none” when settng up the Google Authenticator key, and the script will prompt for the current tokencode when it is run. Otherwise, technically, we’re kind of eliminating the “2” from “2-Factor” authentication.

I’ve posted the entire script as a gist on Github. I hope people find it useful, but remember, this is a hack written over lunch one day (and cleaned up during free moments over a couple days following). It might work perfectly for you. It might not work at all.

The basic concept should be applicable to other situations — I’d bet it could be changed to work with Viscosity (or other Mac VPN clients), or with other OTP codes, with minimal effort. But I use Tunnelblick, so that’s all it supports at the moment.


Inadvertent OS X Mail Loading of Images in SPAM


I just noticed an interesting bug. I got a SPAM email (which I fortunately get far fewer of today because of SpamHero). As I usually do when a SPAM leaks through, I forwarded it to SpamHero so they can use it to improve their filters.

Less than a minute after forwarding the email, I received another copy of virtually the same SPAM. Dutifully, I forwarded it again, but this time I noticed something strange: Though the Mail application identified the email as SPAM (and thus refused to load embedded images), the email as incorporated into the forwarding message window did load the images.

Inconsistent avoidance of SPAM images

It’s a commonly-repeated security recommendation that one shouldn’t load images by default when reading email, especially for suspicious messages, as the URLs for those images may be used for multiple potentially nefarious purposes. For one, they could use that to verify “Yes, this email address worked!” and then send more SPAM your way. Obviously we don’t want that to happen.

The irony is that the very act of forwarding the message to the filtering service may in fact be hurting, rather than helping. In this case, the URL was exactly the same in both emails, and didn’t appear to be uniquely created to help track which messages were successfully delivered.

Unfortuantely, I’m not sure there’s an easy way to prevent this from happening (other than Apple changing the app’s behavior).

Apple ID Madness


One of the reasons I was so excited to get an iPhone a few years back was because of contact management. For years (from 1997 until about 2010) I carried around a Palm Pilot, which had reasonably good tools to synchronize data between the mobile device and my computer. Then I got a “modern” cell phone, which could do text messaging and everything, and setting up data syncing with that was….nearly impossible. But the iPhone, well, most of the time it works just fine.

But then Andrea got an iPhone as well. So now we needed to share contacts and calendar information between both of us. So how do you do that?

Hello, Mobile Me!

Goodbye, Mobile Me! (now it’s iCloud)

This worked out pretty well for a while — we simply used the same iCloud account on both our iPhones (and later, iPad), and now any contact added to one device appeared on all the others instantly. It also synced to our laptop and desktop systems. Yay!

But then Apple introduced FaceTime (2010) and iMessage (2011), which both used your Apple ID as an address. So now we needed to have individual iCloud accounts as well. This is actually pretty easy to set up, though there are a few important limits to keep in mind.

First, only one account can be the “primary” iCloud account on a device. This account will have a few additional features beyond what additional (shared or private) iCloud accounts get. All iCloud storage (key/value data from games, for example, or Keynote documents saved to iCloud, or iCloud backups and iCloud keychains) are associated only with the primary account. Also, Photo Streams, saved Safari bookmarks and Passbook passes will only synchronize among devices with the same primary iCloud account. Finally (and this changed with iOS 7) the Find My iPhone feature only works with the primary iCloud account. So you won’t be able to use a single family account to track the location of every device in the family.

Most of those limits are fairly reasonable (though the Find My iPhone limit is still a bit annoying). So how do you set this up?

On an iOS device, launch the Settings application, and go to iCloud. On OS X, the same settings are found in System Preferences, also under iCloud. This is where you will enter your primary iCloud account information. If you don’t already have an Apple ID, you can configure one here, or it may be easier to create that from the desktop by going to appleid.apple.com. Once the account has been set up, select which features you want to use. I use just about everything except Keychain, Backups, and Mail (most people will probably have a dedicated email account separate from iCloud).

You’ll probably want to enable this same iCloud account for the other “personal” features on iOS (and OS X, where appropriate): iMessage, FaceTime, and Game Center.

Now that you have your personal iCloud account configured, you need to create a shared account for the family. Go back to appleid.apple.com and create a new account, then on iOS go to Settings: Mail, Contacts and Calendars (or System Preferences: Internet Accounts on OS X) and enter that account as a new iCloud account. Select which features you’d like to share (we share Contacts, Calendars, Reminders, and Notes), repeat on all devices which need access, and that’s it!

Many accounts gives much flexibility

Well, almost. Because now we’re at the point where all three of our kids are capable of sending messages to one another. And to do that, they need to know everyone’s email addresses, too. No problem, just add them to the shared account!

Well, almost. Except that there’s no way to connect to an iCloud account as a “read only” user. So there’s the (somewhat real) chance that they might accidentally delete one (or more, or most) contacts from the system. This is easily solved with a “kids” iCloud account. It’s just like the main family account, but it’s shared only between the kids’ devices, and if they accidentally delete things, well, that’s not a huge deal. We also stripped out all contacts except immediate family and close relatives (‘cause we also don’t want them texting “POOOOOPY BUTTTT!!!!!” to our friends…)

And, finally, all these iCloud accounts are separate from accounts for the iTunes Music Store (and App store and stores for Videos and iBooks). That’s separate, and currently shared across all our devices for Application and media purchases, though we’re running into some issues there as well (that’ll be another blog post).

So now we have something that looks like this:

Lots of accounts

A couple of problems remain:

Overall, though, this arrangement has worked pretty well for a couple of years now. It’s quite a bit different from how we synchronized contacts between Outlook an a Palm Pilot 1000, and I’m quite glad for the progress we’ve made.

It’s time to (re)start.

Wow, I haven’t posted here in nearly a year. For a while last year, I was experimenting with a second blog where I could post quick little blurbs, links to interesting current events, but that never really took hold. I think part of it was it was just too much of a pain to post the little things. Plus, I don’t know, somehow I just got busy or somehting last summer.

So now it’s time to start again. I’ve changed over the blog system to something simpler than the WordPress system I was using before — Marco Arment’s Second Crack. It’s cleaner, a lot simpler, a whole lot faster, and also lets me easily publish things like slides, papers, or other media. It’s also got a simple applet that I can use to post “link posts,” and I’ll try again to start pulling out interesting looking things for comment.

Unlike WordPress, this site won’t have comments (I never got many anyway), nor does it have a “subscription” option (for the 3 or 4 people who received copies of posts in email). A RSS feed is available, and hopefuly I’ll have automatic tweeting of stories working as well.

Soon, hopefully, I’ll be able to put up a writeup of the 2014 DBIR puzzle (which I and Alex Pinto won first place on as a team!), and then maybe I’ll look for other puzzles which I haven’t written up yet, and talk slides which haven’t been posted. I’ll also keep hacking the Second Crack engine (I’ve got a short list of features I’d like to add).

So for the few of you who read the silly things I’ve posted here, thanks for reading, and hopefully soon you’ll have more content to wade through. :)