Tag Archives: metadata

The Insecurity of Photo Cropping

Post Syndicated from Bruce Schneier original https://www.schneier.com/blog/archives/2023/02/the-insecurity-of-photo-cropping.html

The Intercept has a long article on the insecurity of photo cropping:

One of the hazards lies in the fact that, for some of the programs, downstream crop reversals are possible for viewers or readers of the document, not just the file’s creators or editors. Official instruction manuals, help pages, and promotional materials may mention that cropping is reversible, but this documentation at times fails to note that these operations are reversible by any viewers of a given image or document.

[…]

Uncropped versions of images can be preserved not just in Office apps, but also in a file’s own metadata. A photograph taken with a modern digital camera contains all types of metadata. Many image files record text-based metadata such as the camera make and model or the GPS coordinates at which the image was captured. Some photos also include binary data such as a thumbnail version of the original photo that may persist in the file’s metadata even after the photo has been edited in an image editor.

Interview with Signal’s New President

Post Syndicated from Bruce Schneier original https://www.schneier.com/blog/archives/2022/10/interview-with-signals-new-president.html

Long and interesting interview with Signal’s new president, Meredith Whittaker:

WhatsApp uses the Signal encryption protocol to provide encryption for its messages. That was absolutely a visionary choice that Brian and his team led back in the day ­- and big props to them for doing that. But you can’t just look at that and then stop at message protection. WhatsApp does not protect metadata the way that Signal does. Signal knows nothing about who you are. It doesn’t have your profile information and it has introduced group encryption protections. We don’t know who you are talking to or who is in the membership of a group. It has gone above and beyond to minimize the collection of metadata.

WhatsApp, on the other hand, collects the information about your profile, your profile photo, who is talking to whom, who is a group member. That is powerful metadata. It is particularly powerful—and this is where we have to back out into a structural argument ­ for a company to collect the data that is also owned by Meta/Facebook. Facebook has a huge amount, just unspeakable volumes, of intimate information about billions of people across the globe.

It is not trivial to point out that WhatsApp metadata could easily be joined with Facebook data, and that it could easily reveal extremely intimate information about people. The choice to remove or enhance the encryption protocols is still in the hands of Facebook. We have to look structurally at what that organization is, who actually has control over these decisions, and at some of these details that often do not get discussed when we talk about message encryption overall.

I am a fan of Signal and I use it every day. The one feature I want, which WhatsApp has and Signal does not, is the ability to easily export a chat to a text file.

Bunnie Huang’s Plausibly Deniable Database

Post Syndicated from Bruce Schneier original https://www.schneier.com/blog/archives/2022/02/bunnie-huangs-plausibly-deniable-database.html

Bunnie Huang has created a Plausibly Deniable Database.

Most security schemes facilitate the coercive processes of an attacker because they disclose metadata about the secret data, such as the name and size of encrypted files. This allows specific and enforceable demands to be made: “Give us the passwords for these three encrypted files with names A, B and C, or else…”. In other words, security often focuses on protecting the confidentiality of data, but lacks deniability.

A scheme with deniability would make even the existence of secret files difficult to prove. This makes it difficult for an attacker to formulate a coherent demand: “There’s no evidence of undisclosed data. Should we even bother to make threats?” A lack of evidence makes it more difficult to make specific and enforceable demands.

[…]

Precursor is a device we designed to keep secrets, such as passwords, wallets, authentication tokens, contacts and text messages. We also want it to offer plausible deniability in the face of an attacker that has unlimited access to a physical device, including its root keys, and a set of “broadly known to exist” passwords, such as the screen unlock password and the update signing password. We further assume that an attacker can take a full, low-level snapshot of the entire contents of the FLASH memory, including memory marked as reserved or erased. Finally, we assume that a device, in the worst case, may be subject to repeated, intrusive inspections of this nature.

We created the PDDB (Plausibly Deniable DataBase) to address this threat scenario. The PDDB aims to offer users a real option to plausibly deny the existence of secret data on a Precursor device. This option is strongest in the case of a single inspection. If a device is expected to withstand repeated inspections by the same attacker, then the user has to make a choice between performance and deniability. A “small” set of secrets (relative to the entire disk size, on Precursor that would be 8MiB out of 100MiB total size) can be deniable without a performance impact, but if larger (e.g. 80MiB out of 100MiB total size) sets of secrets must be kept, then archived data needs to be turned over frequently, to foil ciphertext comparison attacks between disk imaging events.

I have been thinking about this sort of thing for many, many years. (Here’s my analysis of one such system.) I have come to realize that the threat model isn’t as simple as Bunnie describes. The goal is to prevent “rubber-hose cryptanalysis,” simply beating the encryption key out of someone. But while a deniable database or file system allows the person to plausibly say that there are no more keys to beat out of them, the perpetrators can never be sure. The value of a normal, undeniable encryption system is that the perpetrators will know when they can stop beating the person — the person can undeniably say that there are no more keys left to reveal.

Law Enforcement Access to Chat Data and Metadata

Post Syndicated from Bruce Schneier original https://www.schneier.com/blog/archives/2021/12/law-enforcement-access-to-chat-data-and-metadata.html

A January 2021 FBI document outlines what types of data and metadata can be lawfully obtained by the FBI from messaging apps. Rolling Stone broke the story and it’s been written about elsewhere.

I don’t see a lot of surprises in the document. Lots of apps leak all sorts of metadata: iMessage and WhatsApp seem to be the worst. Signal protects the most metadata. End-to-end encrypted message content can be available if the user uploads it to an unencrypted backup server.

EDITED TO ADD (12/13): Here’s a more legible copy of the text.