Entries Tagged "Facebook"

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Facebook Fingerprinting Photos to Prevent Revenge Porn

This is a pilot project in Australia:

Individuals who have shared intimate, nude or sexual images with partners and are worried that the partner (or ex-partner) might distribute them without their consent can use Messenger to send the images to be “hashed.” This means that the company converts the image into a unique digital fingerprint that can be used to identify and block any attempts to re-upload that same image.

I’m not sure I like this. It doesn’t prevent revenge porn in general; it only prevents the same photos being uploaded to Facebook in particular. And it requires the person to send Facebook copies of all their intimate photos.

Facebook will store these images for a short period of time before deleting them to ensure it is enforcing the policy correctly, the company said.

At least there’s that.

More articles.

EDITED TO ADD: It’s getting worse:

According to a Facebook spokesperson, Facebook workers will have to review full, uncensored versions of nude images first, volunteered by the user, to determine if malicious posts by other users qualify as revenge porn.

Posted on November 9, 2017 at 6:23 AMView Comments

Technology to Out Sex Workers

Two related stories:

PornHub is using machine learning algorithms to identify actors in different videos, so as to better index them. People are worried that it can really identify them, by linking their stage names to their real names.

Facebook somehow managed to link a sex worker’s clients under her fake name to her real profile.

Sometimes people have legitimate reasons for having two identities. That is becoming harder and harder.

Posted on October 13, 2017 at 6:57 AMView Comments

WhatsApp Security Vulnerability

Back in March, Rolf Weber wrote about a potential vulnerability in the WhatsApp protocol that would allow Facebook to defeat perfect forward secrecy by forcibly change users’ keys, allowing it — or more likely, the government — to eavesdrop on encrypted messages.

It seems that this vulnerability is real:

WhatsApp has the ability to force the generation of new encryption keys for offline users, unbeknown to the sender and recipient of the messages, and to make the sender re-encrypt messages with new keys and send them again for any messages that have not been marked as delivered.

The recipient is not made aware of this change in encryption, while the sender is only notified if they have opted-in to encryption warnings in settings, and only after the messages have been re-sent. This re-encryption and rebroadcasting effectively allows WhatsApp to intercept and read users’ messages.

The security loophole was discovered by Tobias Boelter, a cryptography and security researcher at the University of California, Berkeley. He told the Guardian: “If WhatsApp is asked by a government agency to disclose its messaging records, it can effectively grant access due to the change in keys.”

The vulnerability is not inherent to the Signal protocol. Open Whisper Systems’ messaging app, Signal, the app used and recommended by whistleblower Edward Snowden, does not suffer from the same vulnerability. If a recipient changes the security key while offline, for instance, a sent message will fail to be delivered and the sender will be notified of the change in security keys without automatically resending the message.

WhatsApp’s implementation automatically resends an undelivered message with a new key without warning the user in advance or giving them the ability to prevent it.

Note that it’s an attack against current and future messages, and not something that would allow the government to reach into the past. In that way, it is no more troubling than the government hacking your mobile phone and reading your WhatsApp conversations that way.

An unnamed “WhatsApp spokesperson” said that they implemented the encryption this way for usability:

In WhatsApp’s implementation of the Signal protocol, we have a “Show Security Notifications” setting (option under Settings > Account > Security) that notifies you when a contact’s security code has changed. We know the most common reasons this happens are because someone has switched phones or reinstalled WhatsApp. This is because in many parts of the world, people frequently change devices and Sim cards. In these situations, we want to make sure people’s messages are delivered, not lost in transit.

He’s technically correct. This is not a backdoor. This really isn’t even a flaw. It’s a design decision that put usability ahead of security in this particular instance. Moxie Marlinspike, creator of Signal and the code base underlying WhatsApp’s encryption, said as much:

Under normal circumstances, when communicating with a contact who has recently changed devices or reinstalled WhatsApp, it might be possible to send a message before the sending client discovers that the receiving client has new keys. The recipient’s device immediately responds, and asks the sender to reencrypt the message with the recipient’s new identity key pair. The sender displays the “safety number has changed” notification, reencrypts the message, and delivers it.

The WhatsApp clients have been carefully designed so that they will not re-encrypt messages that have already been delivered. Once the sending client displays a “double check mark,” it can no longer be asked to re-send that message. This prevents anyone who compromises the server from being able to selectively target previously delivered messages for re-encryption.

The fact that WhatsApp handles key changes is not a “backdoor,” it is how cryptography works. Any attempt to intercept messages in transmit by the server is detectable by the sender, just like with Signal, PGP, or any other end-to-end encrypted communication system.

The only question it might be reasonable to ask is whether these safety number change notifications should be “blocking” or “non-blocking.” In other words, when a contact’s key changes, should WhatsApp require the user to manually verify the new key before continuing, or should WhatsApp display an advisory notification and continue without blocking the user.

Given the size and scope of WhatsApp’s user base, we feel that their choice to display a non-blocking notification is appropriate. It provides transparent and cryptographically guaranteed confidence in the privacy of a user’s communication, along with a simple user experience. The choice to make these notifications “blocking” would in some ways make things worse. That would leak information to the server about who has enabled safety number change notifications and who hasn’t, effectively telling the server who it could MITM transparently and who it couldn’t; something that WhatsApp considered very carefully.

How serious this is depends on your threat model. If you are worried about the US government — or any other government that can pressure Facebook — snooping on your messages, then this is a small vulnerability. If not, then it’s nothing to worry about.

Slashdot thread. Hacker News thread. BoingBoing post. More here.

EDITED TO ADD (1/24): Zeynep Tufekci takes the Guardian to task for their reporting on this vulnerability. (Note: I signed on to her letter.)

EDITED TO ADD (2/13): The vulnerability explained by the person who discovered it.

This is a good explanation of the security/usability trade-off that’s at issue here.

Posted on January 17, 2017 at 6:09 AMView Comments

Hijacking Someone's Facebook Account with a Fake Passport Copy

BBC has the story. The confusion is that a scan of a passport is much easier to forge than an actual passport. This is a truly hard problem: how do you give people the ability to get back into their accounts after they’ve lost their credentials, while at the same time prohibiting hackers from using the same mechanism to hijack accounts? Demanding an easy-to-forge copy of a hard-to-forge document isn’t a good solution.

Posted on July 7, 2016 at 1:27 PMView Comments

Facebook Using Physical Location to Suggest Friends

This could go badly:

People You May Know are people on Facebook that you might know,” a Facebook spokesperson said. “We show you people based on mutual friends, work and education information, networks you’re part of, contacts you’ve imported and many other factors.”

One of those factors is smartphone location. A Facebook spokesperson said though that shared location alone would not result in a friend suggestion, saying that the two parents must have had something else in common, such as overlapping networks.

“Location information by itself doesn’t indicate that two people might be friends,” said the Facebook spokesperson. “That’s why location is only one of the factors we use to suggest people you may know.”

The article goes on to describe situations where you don’t want Facebook to do this: Alcoholics Anonymous meetings, singles bars, some Tinder dates, and so on. But this is part of Facebook’s aggressive use of location data in many of its services.

BoingBoing post.

EDITED TO ADD: Facebook backtracks.

Posted on June 28, 2016 at 6:56 AMView Comments

Mass Surveillance Silences Minority Opinions

Research paper: Elizabeth Stoycheff, “Under Surveillance: Examining Facebook’s Spiral of Silence Effects in the Wake of NSA Internet Monitoring“:

Abstract: Since Edward Snowden exposed the National Security Agency’s use of controversial online surveillance programs in 2013, there has been widespread speculation about the potentially deleterious effects of online government monitoring. This study explores how perceptions and justification of surveillance practices may create a chilling effect on democratic discourse by stifling the expression of minority political views. Using a spiral of silence theoretical framework, knowing one is subject to surveillance and accepting such surveillance as necessary act as moderating agents in the relationship between one’s perceived climate of opinion and willingness to voice opinions online. Theoretical and normative implications are discussed.

No surprise, and something I wrote about in Data and Goliath:

Across the US, states are on the verge of reversing decades-old laws about homosexual relationships and marijuana use. If the old laws could have been perfectly enforced through surveillance, society would never have reached the point where the majority of citizens thought those things were okay. There has to be a period where they are still illegal yet increasingly tolerated, so that people can look around and say, “You know, that wasn’t so bad.” Yes, the process takes decades, but it’s a process that can’t happen without lawbreaking. Frank Zappa said something similar in 1971: “Without deviation from the norm, progress is not possible.”

The perfect enforcement that comes with ubiquitous government surveillance chills this process. We need imperfect security­ — systems that free people to try new things, much the way off-the-record brainstorming sessions loosen inhibitions and foster creativity. If we don’t have that, we can’t slowly move from a thing’s being illegal and not okay, to illegal and not sure, to illegal and probably okay, and finally to legal.

This is an important point. Freedoms we now take for granted were often at one time viewed as threatening or even criminal by the past power structure. Those changes might never have happened if the authorities had been able to achieve social control through surveillance.

This is one of the main reasons all of us should care about the emerging architecture of surveillance, even if we are not personally chilled by its existence. We suffer the effects because people around us will be less likely to proclaim new political or social ideas, or act out of the ordinary. If J. Edgar Hoover’s surveillance of Martin Luther King Jr. had been successful in silencing him, it would have affected far more people than King and his family.

Slashdot thread.

EDITED TO ADD (4/6): News article.

Posted on March 29, 2016 at 12:58 PMView Comments

Possible Government Demand for WhatsApp Backdoor

The New York Times is reporting that WhatsApp, and its parent company Facebook, may be headed to court over encrypted chat data that the FBI can’t decrypt.

This case is fundamentally different from the Apple iPhone case. In that case, the FBI is demanding that Apple create a hacking tool to exploit an already existing vulnerability in the iPhone 5c, because they want to get at stored data on a phone that they have in their possession. In the WhatsApp case, chat data is end-to-end encrypted, and there is nothing the company can do to assist the FBI in reading already encrypted messages. This case would be about forcing WhatsApp to make an engineering change in the security of its software to create a new vulnerability — one that they would be forced to push onto the user’s device to allow the FBI to eavesdrop on future communications. This is a much further reach for the FBI, but potentially a reasonable additional step if they win the Apple case.

And once the US demands this, other countries will demand it as well. Note that the government of Brazil has arrested a Facebook employee because WhatsApp is secure.

We live in scary times when our governments want us to reduce our own security.

EDITED TO ADD (3/15): More commentary.

Posted on March 15, 2016 at 6:17 AMView Comments

Sidebar photo of Bruce Schneier by Joe MacInnis.