Is iMessage secure? The good, the bad, and the complicated

Is iMessage secure? The good, the bad, and the complicated

Last week, researchers from QuarksLab gave a presentation at HITBSecConf2013 on the security of iMessage. The researchers sought to investigate claims made by Apple that nobody but the sender and receiver could read iMessage data thanks to their use of end-to-end encryption. While the researchers discovered that they were able to intercept and decrypt iMessages, Apple was quick to respond insisting iMessages infrastructure is not set up for that type of interception. So which is it? Is iMessage secure or not?

Details published on the research cover two kinds of scenarios. The first scenarios is one where a malicious attacker is able to intercept, decrypt, and manipulate iMessages between two users. The researchers properly point out, multiple times, that this attack has "strong requirements". An attacker must be able to acquire both parties private keys (in one type of scenario), impersonate two separate Apple servers, redirect the victims' traffic to those servers, and install a certificate for their own CA on the users' devices. Is this possible? Absolutely, and the researchers even published a YouTube video demonstrating the attack. It is probable? No. While the attack is reproducible in an environment where you control and have full access to the devices you're attacking, it becomes tremendously more difficult when you're talking about targeting people in the wild.

The second scenario the researchers discuss, which is slightly more worrisome, though probably not freak-out worthy, is one where Apple could intercept and decrypt iMessage between two users. With Apple, there's no need for an attacker to install their own trusted CA on a victim's device because Apple already has a CA that is trusted by iOS devices. Apple doesn't need to impersonate any servers because they're the ones running the actual servers. This also means Apple doesn't need to redirect the victims' traffic since it's already in the middle of it. Finally, Apple owns the server that assigns the encryption keys. This means that, from a cryptography standpoint, Apple possesses everything necessary to read iMessages between its users.

Apple issued a response to the research, saying that iMessage is not architected in a way that would allow such an attack to take place:

The research discussed theoretical vulnerabilities that would require Apple to re-engineer the iMessage system to exploit it, and Apple has no plans or intentions to do so.

While theoretically Apple has all the pieces necessary to intercept iMessages, their stance is that technologically their system is not set up in a way that would allow for that. While Apple could be lying about this, the damage that would be caused to their reputation if it was discovered that they were lying doesn't seem like it would be worth the risk. If Apple had a backdoor for reading iMessages, it seems more likely that they simply would have stayed quiet back in June, rather than going on record with a voluntary statement insisting they can't read iMessages. With the number of large tech companies that we now know the NSA taps into data from, Apple would have had nothing to lose by staying quiet about the whole thing, but they have a lot to lose from lying.

Moreover, whether you trust Apple or not, trust them to do what's in their own self-interest. If iMessage is proven to be exploitable in a way Apple has denied, it will harm their business. That's not in Apple's self-interest.

The research raises an interesting point though, which is that, if the NSA wanted to, from a cryptographic standpoint, there is nothing stopping them from requiring Apple go give them access to people's messages. The NSA could coerce Apple into re-engineering the iMessage system to allow for such eavesdropping. With that in mind, it would be nice to see Apple come up with a stronger key infrastructure, or perhaps as a start just sharing more information about their current system.

Another change some people have been proposing is certificate pinning. Ironically, a lack of certificate pinning is what allowed the researchers to analyze iMessage's traffic; the closed protocol which Apple has been scrutinized for not publishing more details on. If Apple had employed certificate pinning, iMessage would not have accepted the researchers' self-signed certificates that they were using on their fake iMessage servers. Certificate pinning would also prevent a malicious attacker from installing their own CA on a victims' devices, in turn preventing them from intercepting iMessage traffic. This would increase security in terms of an outside attacker, which as we already discussed, is a fairly unlikely scenario, but wouldn't change anything about Apple's potential ability to intercept messages. It could be argued that Apple should do this from a security standpoint, but still does not address the bigger concern.

For now, it really comes down to a question of whether or not you should use iMessage. The researchers gave an accurate assessment:

MITM attacks on iMessage are unpractical to the average hacker, and the privacy of iMessage is good enough for the average user.

If the informations being exchanged are sensitive to the point that you don’t want any government agencies to look into them, don’t. It's important to remember that iMessage was introduced as a replacement for SMS, which isn't encrypted at all and can be easily spoofed. The importance of security shouldn't be downplayed, but in the context of text messaging, iMessage continues to be more secure than SMS.

As users, we are left trying to find the right balance of convenience and security. iMessage offers the security of encrypting messaging, but sacrifices some security with the convenience of transparent encryption. Apple could implement a system where a sender and receiver confirm their keys with each other before beginning messaging, but of course this would reduce convenience. If you currently have a need to transmit highly sensitive information that you can't risk the NSA or other three-letter acronyms from seeing, iMessage isn't the best choice and really never was. For the other 99.9% of iOS users, iMessage remains a convenient messaging solution and there's not much need to worry about your communications becoming compromised.

Have something to say about this story? Leave a comment! Need help with something else? Ask in our forums!

Nick Arnott

Security editor, breaker of things, and caffeine savant. QA at POSSIBLE Mobile. Writes on about QA & security, and as @noir on Twitter about nothing in particular.

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Reader comments

Is iMessage secure? The good, the bad, and the complicated


For many people it doesn't matter one jot what Apple says. The only people that know exactly how the iMessage system is engineered is Apple and they are not going to tell anyone whether they do have access though I am inclined to believe that regardless of whether they can or cannot the fact remains that they, like the rest of the world, don't give one iota about anyone elses messaging, who to or contents of the messages.

Though there are too many people that live a miserable Paranoid existence with tin foil hats and worrying that the bogey man waiting round every corner and believing that somewhere there is a government spook trying to find out what they are doing. These are probably the same people preparing for the end of the world and living in underground tunnels.

If anyone wants to find out what's in my messages then they can ask me, I'll tell them exactly the contents of my messages sent and received. Nothing to hide and nothing to worry about.

Of course there are probably those that believe that they are important and that everyone wants to know about their lives but enough about the Kardashians loll

Apple's technical denial simply does not add up. There is no need for a "rearchitecture" when they have access to the ID of the sender, the ID of the recipient, and both sets of encryption keys for each, especially when they very essence of iMessage is to relate those data points to deliver messages quickly. Perhaps they would need to put together a secondary step in their pipeline, and maybe even a UI to make it easier on an internal snoop, but that hardly constitutes a few weekends' work, much less a rearchitecture.

More importantly, the article should at least note before taking Apple's statement at face value that Apple is part of a trade group that formally recommended CISPA to Congress, saying:

"we commend the (Congressional) committee for providing liability protections to companies participating in voluntary information-sharing."

If Apple *cannot* spy on users's data, it is curious they would contribute to petitioning Congress on a bill to offer protection for companies to do exactly that at the government's request.

If Apple's system truly is engineered to disallow such interception, it would be a *HUGE* competitive advantage for Apple, and they could corner the entire business market by trumpeting this as a security feature Google and Microsoft lack. That they do not leads inescapably to the conclusion that they can, or, if you are feeling *really* charitable towards Apple, that they unilaterally reserve the right to "voluntarily share" with governements.

That does not mean Apple is any more or less trustworthy than any other intermediary, however. Google, Microsoft, and all the US carriers angle for the same protections:

After ^THIS^ , all I hear is crickets. LoL The incessant paranoia regarding one's personal text messages is a riot! Unless you are on the NSA hit list, you have nothing to worry about. SMH

Ah, the old "nothing to hide" gambit, where the NSA only takes in limited information from black-mustachioed twirling villains. Of course, they limit their targets, they even say so!

Oh, except that the head of the NSA had to apologize for directly lying to the very Congressional groups that are supposed to oversee them.

But surely they still have a very limited hit list, like you say. Terrorists only.

...or people of interest to the DEA, which has been using NSA-collected data

...or happen to be dating somebody in the NSA

...or people who happen to have a cloud-based address book

...or French nationals

...or Brazilian nationals

...or the President of Mexico

...or the head of a telco that refuses to grant NSA access to customer information

These are not fantasies - I tried to pick quotes from left- and right-wing sources to show it is not partisan outrage at work here. These all already happened, with express approval from the FISA court, where the NSA is allowed to present evidence, but no other side may contest.

But these examples will not sway you, because you somehow think our government has a default right to invade your personal life, when our entire Constitution was built around limiting government's powers, and the 4th, 5th, and 10th, 11th, and 14th Amendments all specifically written to further cement those protections. Your attitude is typically un-American, all the more sad because it is most often espoused by people who consider themselves some strain of patriot.

Former Supreme Court Justice Brandeis called "the right to be let alone" our most precious right , that ought to be secured against invasion except for some compelling reason of public welfare. For 216 years, the government was supposed to present a case before granting itself such extraordinary powers. In the last decade, people like you are willing to cede as much as ordinary.


First, let me commend you on you ability to "Google"! Your examples are not only spot on but shows how reprehensible and invasive a society we have become. Second, I have no qualms regarding SCJ Brandeis's comment. Not only do I concur with his words, I can only wish they could be enforced more stringently. We live in a society that is given the ability to print or speak what we wish, whether it be valid or not. You will find that in the Constitution under freedom of speech. But PLEASE ... Before you ASSume that I am one that has become someone "willing to cede", walk a mile in my shoes, for you will find that I proudly served this county in order for you to have the right to speak your mind, NOT verbally berate with narcissistic accusations derived from pompous drivel. IF anybody feels the need to intercept my messages, they will find that I need a half gallon of coffee cream and I have a vet appointment for my puppy in December. Hardly worth the effort in my opinion. are so close to the point here:

"I can only wish they could be enforced more stringently"

But do not grasp that the *reason* they are not enforced is because the apathy of people about their right to privacy means there is no political cost to any such invasion.

And yes, when you allow that "IF people see the need to intercept" your messages, that they can, then you are in fact ceding that they have the unilateral right to do so.

Unfortunately the deaths of more than 2400 people on September 11th inadvertently gave the politicians the "excuse" needed for the unilateral invasion. In no way, shape or form was I involved with the voting process regarding the Patriot Act and the bill gave a lot of citizens a false sense of security. Believe me, If there was a way to back pedal in time twenty years or more, I would gladly make that return trip!

I certainly have no quarrel with the concept that spying, and other unsavory actions, can be necessary for national defense. In that sense, we are pretty close. I also agree with your statement that 9/11 gave politicians an excuse for unilaterally invading citizen privacy. Also like you, I do not cheer the Patriot Act.

It seems like our main difference is that I hold out the naive hope that if people stop resigning themselves to the necessity and inevitability of these invasions (which, and I apologize if I misinterpreted your earlier words, but it certainly seemed to me you have done), and instead put pressure on their elected representatives to demand accountability for those unelected agencies and to enforce citizens' rights as enumerated in that Constitution and its amendments, that we the people could rollback, not the actual tragedy, but at least some of the self-inflicted wounds that followed.

"Apathy" is the hammer hitting the nail on the head. Most Americans don't take the time to understand the ramifications. "So what if they see my text saying 'LOL' to my friend". But you're correct. That they have the ability to do so with seemingly no restrictions, provides them the inferred right to do so everywhere else too. Call me paranoid, but the more the government collects on what people are saying, the better the opportunity to control messages. Yes, I did just finish reading 1984. Scares the bejesus outta me.

No electronic communication is secure. It will be that way until iOS 107 can send quantum iMessages.

Inspiring news for iPad, iPhone and Mac customers is that the Apple has engaged two-stage check for some of its quirks. This certainly incorporates an extra security while keeping your records being hacked.