June 2013

PRISM logo

My post about how a central claim of the PRISM story turns out not to be true has drawn a wide range of comments. There’s one particular kind of comment I’d like to address here: the idea that, even if what I said was true, it was a mere technical detail and is not important in the larger story. (Here’s one such response.)

If the original claim about PRISM had been true, it would have had major implications for how we understand power and the nature of our political world.

The idea that the importance of a fact (or an error) would correlate to the number and familiarity of the words required to explain it is wrong. Just because life would be easier for reporters and readers if that were the case doesn’t make it the case. Sometimes, a thing is important even though it requires new words or concepts in order to be explained. This is one of those times. The number of syllables involved in causing a misunderstanding has no relationship to the significance of that misunderstanding.

Remember George W. Bush’s famous 16 words? “The British government has learned that Saddam Hussein recently sought significant quantities of uranium from Africa.” Those were just 16 words. The importance of the lie is unrelated to its length.

Greenwald and MacAskill did not lie. They simply misunderstood something. But what they misunderstood was very, very important. The issue in the PRISM reporting apparently arose because Greenwald and MacAskill misunderstood the meaning of this label on an NSA slide:

“Collection directly from the servers of these U.S. Service Providers: Microsoft, Yahoo, Google, Facebook, PalTalk, AOL, Skype, YouTube, Apple”

When the leaks first appeared, only two things really stood out as news, especially to the tech community — news in the sense of being something we fundamentally didn’t know before: the massive scale of phone call logs collection, and the claim that the NSA could “directly and unilaterally seize the communications off the companies’ servers” (referring to online services companies, not phone companies).

The latter claim about “directly and unilaterally” seizing communications from company servers was the more shocking one. This is partly because it was about data, not just metadata. But it was also because it meant that people we thought we knew — in many cases, people we’d worked with — had been hiding something big, something that, unlike (say) receiving and acting on National Security Letters, we didn’t think the law required them to hide and that we would not expect could be successfully hidden for long. It meant that not only did the system not work the way we thought it worked, it wasn’t even built the way we thought it was built. The moment I first read that quote, I straightened in my chair. If this is true, I thought, then we’re living in a very different place from the one we imagined.

The quote is from Glenn Greenwald’s and Ewan MacAskill’s original article in The Guardian on June 6th:

…defenders of the FAA argued that a significant check on abuse would be the NSA’s inability to obtain electronic communications without the consent of the telecom and internet companies that control the data. But the Prism program renders that consent unnecessary, as it allows the agency to directly and unilaterally seize the communications off the companies’ servers.

Looking at that text, what would you think it means? (Go ahead and read it in context in the original article, just to be sure.)

The most natural interpretation of “directly” and “unilaterally” — really, the only interpretation the authors could expect, given the context — is that the NSA could get anything it wants directly from the servers of major online services companies, without asking the company first (hence “unilaterally”). In other words, the companies’ lawyers don’t have a chance to review the request and push back. It means a monopolar world in which even commercial services are essentially an arm of the government, instead of a multipolar world where, even though the government may be heavy-handed, there are still competing pressures, negotiations, and compromises — a world where the possibility of saying “no” still exists.

The scarier, monopolar interpretation was the one reacted to by the very next person the article quotes, Jameel Jaffer, the director of the ACLU’s Center for Democracy:

“It’s shocking enough just that the NSA is asking companies to do this… The NSA is part of the military. The military has been granted unprecedented access to civilian communications.

This is unprecedented militarisation of domestic communications infrastructure. That’s profoundly troubling to anyone who is concerned about that separation.”

Glenn Greenwald and Ewen MacAskill say nothing to correct Jaffer’s interpretation. As the authors of the piece, and therefore the people who chose to quote Jaffer’s reaction in the first place, one can only assume that the reason they did not correct Jaffer’s interpretation is that they did not think Jaffer misunderstood.

Eventually, I, along with many others looking at the primary source materials and other sources, realized that Greenwald and MacAskill had overstated this part of the case — the NSA does not have direct, unilateral access. It doesn’t have a secret route around company lawyers. It doesn’t have engineers planted in senior positions in every major online service company (or at least if it does, the documents leaked so far do not contain evidence of that).

Instead, what’s going on is, more or less, what we thought was going on, just with more abuse and less restraint on the government side. That’s serious, but it’s comprehensibly serious, not “Oops, I guess we live in the shadowy power of the Deep State after all” serious. The true situation is one that can still respond to popular pressure and political dissatisfaction.

I think it’s clear by now that what I (and Mark Jaquith and Rick Perlstein) wrote is right as far as the facts are concerned. For some other analyses that have come out since then supporting the claim that there is not direct and unilateral access, see Ashkan Soltani, and Declan McCullagh at CNET, and Hunter Walker’s piece at Talking Points Memo, especially the quote from Ben Adida of Mozilla, and the New York Times (despite the misleading title on the piece, its content confirms the less alarmist interpretation).

So why do I care?

Adapting a comment I made in reply to a reader of the earlier post:

The big picture is about understanding the true dynamics of the world we live in, so we can decide how to act and what is most important to focus on. The picture Greenwald originally painted is, more or less, one of government-dominated oligopoly in which basically all the big players sat down at the same table and agreed to play by the NSA’s rules. I don’t think that was an accurate picture. I see instead multiple power bases, with some degree of internal dissent within each organization (including even the NSA and the FISA courts, but much more so within the companies), and on important issues even open dissent between actors. Yes, there’s a lot of coercion and compromise, and there is no doubt that some companies hand over more than they should without asking enough questions — but they don’t all do that. Of course we shouldn’t be happy that the average person’s most immediate choice is which big protector(s) to grant conditional trust to. But as I said in response to someone else in a blog comment, it’s not like Russia and North Korea are the same thing (and the U.S. is neither). There are meaningful differences among surveillance states, and understanding the kind you live in is important if you’re trying to figure out which risks to take for what goals.

This is a more complex picture than the one Greenwald painted, but if it is a truer one, then the paths available for resisting a surveillance state are quite different than they would be in a more monolithic situation. Do you take to the streets, or do you file lawsuits? If the latter, then against whom, a company or the government? (I don’t mean to suggest these are the only options; they’re just examples.)

Hence the importance of people understanding that the government does not do unmediated “direct” and “unilateral” collection from the servers of all major private-sector online service companies. How realistic was that idea ever? What U.S. company, that originated as a mass-market services company and not as a government contractor, would agree to give government IT staff unfettered access to its live-data servers? The business risk would be incredible, the risk of public embarrassment incredible… the proposition just doesn’t make sense to me. It never passed the smell test.

People in the U.S. following this story are trying to figure out what kind of country they live in, because after all, there are countries where the companies wouldn’t have a choice about granting that kind of access. If Glenn Greenwald succeeds in persuading U.S. readers that they live in one of those countries, and he is wrong, then he will unintentionally help to erode the feeling of collective empowerment and of individual rights that is crucial for resisting further encroachment.

That’s why I care.

Addenda: One critic’s claim that I “repackaged” Mark Jaquith’s (very fine) post isn’t true. I wrote the bulk of my post before finding out about Jaquith’s; when I saw Jaquith’s, I thought it expressed the problem very well and I decided to point to it (and restructured my post accordingly). Also, though I am a Fellow at the New America Foundation, I had no awareness (until some commenters on my original post mentioned it) that NAF receives Gates or Schmidt money. Anyway, the funding for my work with NAF doesn’t come from those sources. Though the place the funding does come from won’t assuage those critics, since it’s the Open Internet Tools Project, which is largely funded by the U.S. State Department. To reiterate: the views expressed on this blog are my own and are not influenced by nor attributable to the New America Foundation, the Open Internet Tools Project, or any other organization. Finally, Mark Jaquith has updated his post to account for Greenwald’s response. I think Mark’s analysis of that response (search for the phrase “Update: Greenwald response”) is very good, and have nothing to add except a big +1.

PRISM logo

Over and over we’ve read that Gen. Keith Alexander, the head of the NSA, claimed that its massive surveillance program has prevented “dozens” of terrorist attacks. Journalists are careful to report this claim as simply what Alexander said, not as a fact itself — we’re responsible journalists, far too wise in the ways of the world to believe something just because someone in the Administration said it! We know better than that.

Except that he didn’t say it. At least as far as I can tell — if anyone knows of a source for the claim other than the below, please let me know. So far, the only source I’m aware of is the exchange with Sen. Patrick Leahy referred to here.

What Gen. Alexander said was subtly but signicantly different, and he’s probably not surprised to see it being misinterpreted in the NSA’s favor right now. We shouldn’t look to the NSA for a correction on this, but do note that Alexander was careful not to lie. No doubt he would lie, if he had too, but this time we did the work for him.

(Not to take undue credit: this discrepancy was pointed out to me by a friend who prefers to remain unattributed. Later a mutual friend pointed us to this post, which has the quotes and the analysis and the video link. I’m really just repeating what that post has already pointed out.)

First of all, Gen. Alexander never said “dozens of attacks”. The dozens he referred to were dozens of call records that contributed to the discovery or disruption of… something, something he calls “events” (apparently elsewhere he’s only talked about two actual attacks disrupted; I don’t have the source for that, but if you do please leave it in the comments).

Watch how this works:

Gen. Keith Alexander: “…it’s dozens of terrorist events that these have helped prevent.”

Sen. Patrick Leahy: “OK, so dozens? Now we collect millions and millions and millions of records through 215, but dozens of them have proved crucial, critical, is that right?”

Gen. Keith Alexander: “For both here and abroad, in disrupting or contributing to the disruption of terrorist attacks.”

Sen. Patrick Leahy: “Out of those millions, dozens have been critical?”

Gen. Keith Alexander: “That’s correct.”

Fascinating. He didn’t say “dozens of attacks”. He does, at first, after a long and clearly thoughtful pause (see the video below), say “dozens of events” once. What’s an “event”? If you disrupt a terrorist meeting, that’s an event. If you disrupt a terrorist eating dinner, is that an event? Maybe. I don’t know. But I do know that when someone in national security wants to defend their work, they use the word “attacks”. Attacks are what matter. When they use the much weaker word “events”, it is not an accident — it is because the stronger word is not available.

Sen. Leahy then gives him the opening to subtly switch the subject to the call records, rather than the events or attacks or whatever they are. Whether Leahy did that by accident or not I don’t know either. But Alexander gratefully takes Leahy’s pivot, to the extent of avoiding even having an explicit subject in his next two sentences — he just grabs Leahy’s antecedent like a life raft and rides it the rest of the way.

He never said dozens of attacks. He very carefully did not say dozens of attacks.

Satisfied that he didn’t say dozens of attacks?

Now let’s look at some headlines:

NSA: ‘Dozens of attacks’ prevented by snooping (The Register)

NSA chief: Surveillance has stopped dozens of potential attacks (Chicago Tribune)

NSA head: Surveillance program prevented dozens of terrorist attacks (Salon)

Alexander: Phone Collection Has Prevented ‘Dozens’ of Attacks (Democracy Now)

And just today I saw it in the New York Times too:

In a robust defense of the phone program, General Alexander said that it had been critical in helping to prevent “dozens of terrorist attacks” both in the United States and abroad…

Current score:

Experienced Washington NSA directors:   1  
Experienced Washington Senators:   N/A  
Experienced Washington journalists:   0  

Here’s that video:

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[Note: This post now uses the phrase “collect-then-select”, instead of “collect-then-analyze”, which wasn’t quite as accurate. Other than that, and adding the references at the end, I’ve made no changes. There is a redirection in place from the old URL.]

One notion that keeps surfacing in the ongoing PRISM leak is that intelligence services have started collecting vast amounts of data just to store for potential later use under a specific warrant. In other words, they want to have it all easily at hand for when they’re actually investigating someone and need to discover that person’s contacts, social network, travel patterns, consumer habits, etc.

For the actual investigation, so the claim goes, they’ll obtain warrants as needed, even if the initial collection was unwarranted — in other words, the collection phase can skate by without a warrant, because even though they have the data they haven’t actually looked at it yet, so no one’s rights are being violated. Then later when they do look at it, they make sure they have a warrant.

This sounds sane, or at least like a good-faith attempt to abide by some kind of legal framework while still getting the job done… until you think about it:

A low-level systems administrator just leaked thousands of top-secret documents. How can they guarantee that your data is safe, even if it’s supposedly just being stored and not analyzed?

This point is understandably hard for intelligence services to acknowledge. No one wants to think about their system’s failure modes. But if you’re collecting and storing private data about millions of citizens, failure modes become not merely important, but a dominant consideration.

Legal protections are designed with failure modes in mind. We cannot guarantee that our systems operate as designed; we can at best hope. This is why “collect then select” is a problem. It’s not because the data is hurting anyone by sitting idly in a storage facility, unexamined by humans or machines. It’s because you can’t be sure it’s really idle. If a conscience-stricken 29 year old can leak thousands of top-secret documents to a journalist, a more mercenary employee — or perhaps just one whose family is being threatened by some very interested party — can access your data and make it available to someone else. This risk is inherent in the centralized collection and storage of the data. By collecting it, the intelligence services have created another route of vulnerability for private information about you. I’m sure they’re doing their best to protect it, but in the long run, their best probably won’t be enough.

Anyway, as Moxie Marlinspike eloquently argues, we should all have something to hide.


I’ve seen the “collect-then-select” notion described in many places. The three I was able to dig up after the fact are all from the New York Times:

Disclosures on N.S.A. Surveillance Put Awkward Light on Previous Denials:

“Right now we have a situation where the executive branch is getting a billion records a day, and we’re told they will not query that data except pursuant to very clear standards,” Mr. Sherman said. “But we don’t have the courts making sure that those standards are always followed.”

N.S.A. Chief Says Phone Record Logs Halted Terror Threats:

Analysts can look at the domestic calling data only if there is a reason to suspect it is “actually related to Al Qaeda or to Iran,” she said, adding: “The vast majority of the records in the database are never accessed and are deleted after a period of five years. To look at or use the content of a call, a court warrant must be obtained.”

ACLU Files Lawsuit Seeking to Stop the Collection of Domestic Phone Logs:

Timothy Edgar, a former civil liberties official on intelligence matters in the Bush and Obama administrations who worked on building safeguards into the phone log program, said the notion underlying the limits was that people’s privacy is not invaded by having their records collected, but only when a human examines them.

That same article goes on to make another important point about why collect-then-select is problematic:

Moreover, while use of the database is now limited to terrorism, history has shown that new government powers granted for one purpose often end up applied to others. An expanded search warrant authority justified by the Sept. 11 attacks, for example, was used far more often in routine investigations like suspected drug, fraud and tax offenses.

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[Update 2013-06-13: See Rick Perlstein’s piece about this on The Nation’s blog. Glenn Greenwald later responded here.]

Mark Jaquith’s post The PRISM Details Matter is spot-on. Glenn Greenwald has misunderstood a key technical fact, one that removes the most explosive charge in the whole scoop. And for some reason, Greenwald refuses to correct it.

The crucial question is:

Are online service companies giving the government fully automated access to their data, without any opportunity for review or intervention by company lawyers?

Greenwald essentially says yes, they are. Yet nothing leaked so far indicates that this is the case, and the companies all vehemently deny it. They say they have humans in the chain. The information leaked so far supports this claim or is at least consistent with it.

It looks like Greenwald & co simply misunderstood an NSA slide, most likely because they don’t have the technical background to know that “servers” is a generic word and doesn’t necessarily mean the same thing as “the main servers on which a company’s customer-facing services run”. The “servers” mentioned in the slide are just lockboxes used for secure data transfer. They have nothing to do with the process of deciding which requests to comply with — they’re just a means of securely & efficiently delivering information once a company has decided to do so.

As Jaquith emphasizes, this is not merely a pedantic point. This is central to the story, and as far as I can tell, Greenwald continues to misunderstand and thus misrepresent it. It’s an epic botch in an important story :-(.

An email I sent to some friends yesterday, about this exact same point:

  From: Karl Fogel
  To: <undisclosed recipients>
  Subject: Re: Cowards | Uncrunched
  Date: Mon, 10 Jun 2013 14:18:57 -0500
  One of the above wrote:
  >Since the topic has taken over part of my morning, thought I'd share: 
  I read this post when it came out, yeah.  I think it's mostly wrong.
  What is described here is just a delivery mechanism.  *If* you're a
  company that's complying with government requests for data (and not all
  requests are abusive or unreasonable) a lockbox is a perfectly sensible
  way to do it.
  Sure, the lockbox may run on a server that belongs to the company, but
  this is not the same as -- indeed, is *totally unrelated to* -- giving
  the government direct access to your servers, the servers that are
  related to the actual service you provide as part of your business,
  which is how far too many bloggers are portraying it.
  Uncrunched quotes Claire Cain Miller approvingly:
    "While handing over data in response to a legitimate FISA request is a
    legal requirement, making it easier for the government to get the
    information is not."
  What?  This makes no sense.  The lockbox may or may not make it easier
  for the government, but it sure makes it easier for the *company* to
  securely hand over data while lowering the risk of some unauthorized
  third party gaining access.  If you're going to comply, might as well do
  it responsibly and without increasing the compliance burden on yourself.
  What the hell are the companies supposed to do?  Put the data on a
  CD-ROM and mail it to Fort Meade?
  It's not like there aren't legitimate things to complain about here.  I
  don't understand why Uncrunched is wasting time with non-problems.

At the end of the post is a list of updates about new client-side betrayals I’ve noticed since this was first written in mid-2013.

A shorter and less technical version of this article was published in the Slate / New America Foundation “Future Tense” series in January 2014:

Privacy Apps Like Snapchat Make a Promise They Can’t Keep

Message on phone screen promises to self destruct.  Really.

Some apps are making an impossible promise, one that these days might really matter to people. The promise is this:

“You can control the copies of data you send to other people.”

You can’t. It’s not even possible in principle. If an app promises that you can send people email messages, photos, audio recordings, or videos that will “self-destruct” or “can only be viewed for a limited time controlled by you” or “can only be viewed by people you approve”, just smile and back away slowly.

These promises all depend on client-side betrayal. That is, they depend on a device obeying commands from someone other than its owner. For example, a smartphone that does what the phone manufacturer — or mobile carrier — wants it to do, instead of what its owner asks.

Now, it’s true that some devices actually do practice client-side betrayal. This is one of the reasons I don’t own a Kindle.

But when you send someone a message or a photo, how can you be sure they’re using a device that will betray them? You can’t. You can’t count on their device serving your goals instead of theirs.

You might think apps only make such promises for platforms where they can count on the recipient’s device being of the betraying sort. But app designers can never know for sure that the necessary betrayal will occur as required. To start with, many apps run on Android devices, after all. The Android operating system is open source (admittedly on a very long release cycle, with various manufacturer-specific proprietary divergences along the way, but still, in the long run it is open source). A sufficiently motivated user could modify their Android device such that every frame written to the screen or every sound written to the speakers is recorded to the SD storage card. That video may have self-destructed as advertised, but that doesn’t really matter if there’s a perfectly good copy still sitting in permanent storage. Heck, while we’re at it, why even believe the deletion happened at all? An Android user could modify the OS-level delete system call to not actually delete, but rather move the file over to an easily-accessible holding area from which recent items can be rescued if the user decides they’re interesting enough. (This is not so different from how most OS delete calls work already. Feeling safer yet?)

Everything I said about Android above applies to any open source operating system: GNU/Linux, Firefox Mobile OS, all of them.

If the user controls her operating system, then she controls her data, period. And open source means users do control their operating systems. They don’t necessarily have to know how to program, they just have to know how to hire people who can program — just as they don’t have to know how internal combustion engines work to hire a mechanic to fix their car.

Open source means no client-side betrayal, at least for people who care enough to avoid it.

Anyway, even without open source operating systems, the recipient can still save it old school: just point another camera-enabled device at the screen and take a picture.

Who’s depending on client-side betrayal?

Full disclaimer: I first started noticing this trend through my work with OpenITP, but the opinions here are entirely my own. The users and developers OpenITP works with are people who need to be able to take privacy promises seriously; as a result, I’ve become more sensitive to those promises than I used to be. When someone makes a promise that conflicts with my technical understanding of how the digital world works, I start asking questions.

Here is a partial list of apps that have caused me to ask questions lately (emphases added):


“You can delete your message from the receivers phone.”

“Be confident sending private information and pictures. You have control over your messages, when you delete a sent message it will be removed from the receivers phone and images are not sharable unless you make them so.”


“Privly makes it possible for you to control your data after posting it across the internet. You can post to Facebook without allowing Facebook access to your communications, you can even unsend emails…”

[Update: Priv.ly improved their language after this post was originally published; the claims on their web site seem to be much more accurate now.]

Snapchat (from their blog):

“Deleting Snaps From the Recipient’s Device”

“After a snap has been opened, the temporary copy of it is deleted from the device’s storage. We try to make this happen immediately, sometimes it might take a minute or two. The files are deleted by sending a ‘delete’ instruction to the phone’s file system. This is the normal way that things are usually deleted on computers and phones — we don’t do anything special (like ‘wiping’).

Extra Details

While an unopened snap is being stored on the device, it’s not impossible to circumvent the Snapchat app and access the files directly. This isn’t something we support or encourage and in most cases it would involve jailbreaking or ‘rooting’ the phone and voiding its warranty. If you’re trying to save a snap, it would be easier (and safer) to just take a screenshot or take a picture with another camera.

Also, if you’ve ever tried to recover lost data after accidentally deleting a drive or maybe watched an episode of CSI, you might know that with the right forensic tools, it’s sometimes possible to retrieve data after it has been deleted. So… you know… keep that in mind before putting any state secrets in your selfies :)”


“sender-based control over who can read messages, where and for how long”

“[Wickr can] send text messages, videos, documents that self-destruct — all encrypted, and it exceeds NSA top-level encryption on the device before it goes out on network with a key that only you have.” (Founder Nico Sell quoted in Silicon Beat.)

Hush Box:

“Secure, self-destructing email.”

(I don’t know anything more about this one; there’s no further explanation on the page, beyond the above.)

Silent Text:

“Self-Destruct any message, file, photo, video or voice recording with our timed Burn Notice.”

[Note: I added this one on 2013-09-04, long after this post originally appeared, because I ran across this article.]


The Confide app turned out to be a kind of Greatest Hits of impossible privacy promises:

“Messages disappear after they’re read, ensuring all of your communication remains private, confidential and always off the record.”

“…we alert you if a screenshot is attempted.”

“Get alerted when your message is read.”

“…allows you to speak freely, without a risk of what you say being forwarded on or permanently stored…”

“We alert you (and the recipient) if the recipient attempts to take a screen shot.”

And my personal favorite: “Notify me about Confide for Android.”

[Note: added this one on 2014-01-09, after this post originally appeared, thanks to this article.]


Google's 'Export options disabled' popup.

Google Spreadsheets and presumably Google Docs in general offer the document owner an “Export options disabled” mode. Someone with whom the document has been shared will see this message if they try to download a copy of the document they’re viewing in their browser: “The owner has disabled options to download, print, or copy for commenters and viewers on this file. Learn more. Google is assuming a certain amount of cooperation from the user’s web browser. That assumption cannot be relied on in general; although presently most user’s browsers are by default cooperating with Google in this regard, they may not always do so (a sufficiently motivated user could change the situation right now, in fact — no new technological developments are necessary, just a little work under the hood of the browser).

Confusing the Threat Models

What these promises have in common is that they confuse two very different threat models. One is the scenario where you’re communicating with an ally — someone who, as far as you know, has no intent to do you harm, though they could do so by accidentally re-sharing something. The other is the scenario where you’re communicating with a stranger or with someone who might actively intend you harm.

The “Extra Details” section in the Snapchat marketing quote above is a particularly good example of this confusion. Somewhere between the first and second sentences, they subtly switch whom they’re addressing. This first sentence is clearly to the sender:

“While an unopened snap is being stored on the device, it’s not impossible to circumvent the Snapchat app and access the files directly.”

Then suddenly they switch to talk to the recipient…

“This isn’t something we support or encourage and in most cases it would involve jailbreaking or ‘rooting’ the phone and voiding its warranty. If you’re trying to save a snap, it would be easier (and safer) to just take a screenshot or take a picture with another camera.”

…then just as suddenly they switch back, still without any explicit acknowledgement that they’re talking to two different parties with possibly different interests:

Also, if you’ve ever tried to recover lost data after accidentally deleting a drive or maybe watched an episode of CSI, you might know that with the right forensic tools, it’s sometimes possible to retrieve data after it has been deleted. So… you know… keep that in mind before putting any state secrets in your selfies :)”

That middle portion, where they talk to the recipient, could be translated to “For our sake, please don’t interfere with the process of your device betraying you.” Recipients in the first threat model will cooperate; those in the second threat model won’t.

Ultimately, these apps aren’t really about security and privacy. They’re about convenience in situations where dependable privacy isn’t a requirement. An app that deletes a photo after showing it to your friend for six seconds is just a convenience for everyone involved. It makes things easier for both parties: Hah hah, look at this picture of me stuffing a hundred dollar bill into his sock while he pours a margarita down my throat! Wasn’t it a great vacation? Wish you were there. No need to worry about deleting this photo; it’ll take care of itself. See you Tuesday at the office.

That’s fine, if that’s all you wanted. But the vast majority of people who read the marketing around these apps will take them at their word. Wow, I can send an email that self destructs immediately after the recipient is done reading it? That’s great! It’s like attorney-client privilege without the expensive law degree. Where do I sign up?

People don’t think about threat models. They think about features and promises. If the app says it does X, they believe it does X.

The trouble is, problem recipients are not evenly distributed across all the pictures and emails and videos one sends. The problem recipients are concentrated in the sensitive items, because the temptation to be a problem recipient is highest exactly for the things a sender would most want deleted. Or as the great saying has it (attributed to both George Orwell and Paul Fussell): “What someone doesn’t want you to publish is journalism; all else is publicity.”

Most people who come to my front door are honest, but the lock on the door is not for them. Promises of client-side cooperation are pointless, from the sender’s point of view, if they are most likely to be circumvented by those most tempted to harm the sender in the first place.

One more example, just to drive the point home.

Some mass email services — “mass email” is not a euphemism for spam, by the way; these services are tremendously useful, helping legitimate organizations run their announcement email lists, etc — promise to tell you how many recipients have opened the email you sent.

“Whuh-huuuh-whaaat??” I thought to myself, when I first heard about this. How on earth can anyone else know whether I’ve opened up an email, let alone whether I’ve read it? My mailreading software does not send signals to third parties when I open messages. That would be an incredible betrayal of my trust.

And yet there are these services, promising exactly that. Here’s Mailchimp (the quotes below are from their Features page and their Reports Overview page):

MailChimp’s free reports tell you who’s opening, clicking, and coming back for more…

Our interactive graphs show you how many emails were delivered, how many people opened your email

Opens by Location: See where in the world your subscribers are located and track engagement by country.

A/B Split Testing People who A/B test their email campaigns get 11% better open rates and 17% more clicks…

It turns out — surprise! — that they’re depending on client-side betrayal, of course.

These days, most people are reading mail in their browser, using one of the online services like Hotmail, etc, or in some other network-enabled email client. And when those email clients get an email that includes an image, they will (in some cases) display images by default — even if the image content isn’t embedded inside the email, but rather is merely linked to from the mail and has to be fetched (at the time the message is opened) from somewhere out on the Internet.

So what these services do is include a tiny image, just one pixel large and, if possible, the same color as the message’s background color. But they don’t include that pixel directly in the mail. Instead, they keep it on their own servers, at a URL unique to that particular message. When the recipient opens the message, their mailreader fetches all the images, even the tiny & invisible ones, and it is by receiving the request for the image at that unique URL that the upstream service knows the mail has been opened.

Some browser-based mailreading services have image display turned off by default, which avoids this betrayal. Google’s Gmail was one of them, until recently, but they have started transitioning to showing images by default, and their notice about the changeover explicitly warns users that this will allow some senders to know whether a mail has been opened. I’m not sure about the other services (if anyone knows, please leave a note in the comments).

Possibly Mailchimp talks about that somewhere, though I didn’t see it if so. The part that I saw just tells senders that Mailchimp can determine the “open rate” for the emails they send out. If Mailchimp has statistics on what percentage of email users set images to display by default — thus making themselves vulnerable to at least one kind of client-side betrayal — that would be very interesting; I don’t know if they do.

It turns out there’s a history here.

I showed an early draft of this post to my friend Jeff Ubois, and he instantly thought of who had covered this ground already. There’s a 2009 book by Viktor Mayer-Schönberger called Delete: The Virtue of Forgetting in the Digital Age; I haven’t read it, but the discussion with Jeff made me wish I had. There’s also an article by US Federal District Judge James Rosenbaum called In Defense of the delete Key”, published in the law journal The Green Bag, about how the Delete key doesn’t actually delete (as I touched on earlier).

Client-side betrayal can have consequences both social and legal. Phrases Jeff tossed out include “inadvertent waiver rule” and “spoliation of evidence”. The sender’s request to delete may still be considered an expression of intent, and that can be legally useful under certain circumstances. Pity about that photo appearing on the front page of the New York Times, but at least it won’t be admissible in court because you tried to ensure the recipients would delete it. That’s some comfort, anyway.

So here’s my promise to you:

If you send me something in digital form, you cannot count on me — or my devices — deleting all my copies of it unless I explicitly tell you they’re gone. The copies I receive from you will continue to exist as long as I want them to, and whether I share them with others is entirely a matter of social conventions and of honor, not of technical enforcement from your side. You also can’t be certain that I have not read an email you sent; you can be certain I have read it if I say I have, or if I reply to it.

But really, these are just the same promises the rest of the Internet makes. If someone thinks otherwise, it means they’re depending on client-side betrayal by your devices — but it’s up to you, not them, whether that betrayal happens.

Or as my friend Jim Blandy puts it: “It’s my computer, damn it!”


Updates since original post, in reverse chronological order:

2021-05-31 Hey, I don’t want to make a federal case of it or anything — okay, sorry, couldn’t resist — but Snapchat’s inability to actually control other people’s copies of images has now led all the way to the U.S. Supreme Court, in Mahanoy Area School District v. B.L.: “The case arose after Brandi Levy … a student at Mahanoy Area High School in Mahanoy City, Pennsylvania, posted an angry, profane Snapchat message from an off-campus location upon learning near the end of the 2016–17 school year that she had not earned a place on the school’s varsity cheerleading squad for the next season. A screenshot of the self-deleting message was saved [by another student] and seen by school officials, who suspended the student from cheerleading for the next year, on the grounds that she had signed and was subject to a school district policy prohibiting such speech on social media.”

2020-09-29 Philippe at Missive writes about how they decided to abandon read-tracking (a classic use of client-side betrayal) for their email-sending service, though he still seems to have a very limited view of what constitutes “abuse” of that misfeature.

2019-11-04 Thanks to the EFF for pointing out this creative proposal for client-side betrayal: client-side scanning for forbidden content. I can’t even… I just can’t even. This idea is so bad in so many different ways that I’m going to give up trying to describe it and say that if you’re suffering from a shortage of bemused outrage today, you should go read their post about it.

2019-08-13: A pretty extreme example: it turns out that getting deplatformed from Apple’s online services breaks all your Apple-controlled devices. Who could ever have seen this coming?

2019-07-30: Some web publishers rely on client-side betrayal to support their N-free-articles-before-paywall model, and will have to change now that browser makers have (finally) started favoring user control and privacy. The linked article does a decent job of explaining the issue.

2019-03-20: The newly-announced Gmail Confidential Mode relies completely on client-side betrayal. Their announcement ignores the question of how they can make these kinds of confidentiality promises for email (hint: they can’t). Email is one of the least-centralized services on the Internet. Senders know nothing about the software receivers use. Either Google can’t keep the promises they’re making, or this isn’t actually email and they should stop calling it that. It’s striking how they frame the situation of users who don’t use Google-controlled products to read email — note especially the second sentence below:

“Note: Although confidential mode helps prevent the recipients from accidentally sharing your email, it doesn’t prevent recipients from taking screenshots or photos of your messages or attachments. Recipients who have malicious programs on their computer may still be able to copy or download your messages or attachments.”

Do they mean “malicious programs” like… any non-Google-controlled mailreading software? E.g., Mozilla Thunderbird, or Emacs Gnus, or any of the other non-Google mailreading software listed here?

Finally, see also this Tutanota blog post about Gmail’s so-called confidential mode.

2016-10-12: Kudos to Open Whisper Systems for honesty in advertising. They’ve implemented a new “disappearing messages” feature in their Signal app, but their announcment of the feature is completely up front about what situations it’s good for. The second paragraph spells it out:

“Disappearing messages are a way for you and your friends to keep your message history tidy. They are a collaborative feature for conversations where all participants want to automate minimalist data hygiene, not for situations where your contact is your adversary — after all, if someone who receives a disappearing message really wants a record of it, they can always use another camera to take a photo of the screen before the message disappears.”

2015-09-13: An almost too-good-to-be-true laundry list of client-side betrayals may be found in this post about the service & free software at canarytokens.org.

2014-10-11: So that thing I predicted in this post — the thing where people hack their client-side software to defeat Snapchat’s so-called protections — has now happened. See also this story, which is also really about client-side betrayal even though it at first looks like it’s about a server-side security issue.

2014-05-08: It’s nice to see that the New York Times — and the U.S. Federal Trade Commission! — have caught up with this problem: Off the Record In a Chat App? Don’t Be Sure: Case Against Snapchat Tells Users to Beware. (Compare it with this rather less skeptical earlier story in the Times from February 2013.)

For a more general examination of the importance of people having control over the hardware and software they use, see Neha Narula’s excellent piece Who Really Owns Your Phone? from January 2013.