A Few Thoughts on Cryptographic Engineering

Some random thoughts about crypto. Notes from a course I teach. Pictures of my dachshunds.

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Attack of the week: Voice calls in LTE

I haven’t written an “attack of the week” post in a while, and it’s been bumming me out. This is not because there’s been a lack of attacks, but mostly because there hasn’t been an attack on something sufficiently cryptographically exciting that it can rouse me out of my blogging torpor. But today brings a beautiful attack called ReVoLTE, on...

A few thoughts about Signal’s Secure Value Recovery

Over the past several months, Signal has been rolling out a raft of new features to make its app more usable. One of those features has recently been raising a bit of controversy with users. This is a contact list backup feature based on a new system called Secure Value Recovery, or SVR. The SVR feature allows Signal to upload your contacts into Signal’s...

Does Zoom use end-to-end encryption?

TL;DR: It’s complicated. Yesterday Zoom (the videoconferencing company, not the defunct telecom) put out a clarification post describing their encryption practices. This is a nice example of a company making necessary technical clarifications during a difficult time, although it comes following widespread criticism the company received over their previous,...

EARN IT is a direct attack on end-to-end encryption

Yesterday a bipartisan group of U.S. Senators introduced a new bill called the EARN IT act. On its face, the bill seems like a bit of inside baseball having to do with legal liability for information service providers. In reality, it represents a sophisticated and direct governmental attack on the right of Americans to communicate privately. I can’t...

What is the random oracle model and why should you care? (Part 5)

This is part five of a series on the Random Oracle Model.  See here for the previous posts: Part 1: An introductionPart 2: The ROM formalized, a scheme and a proof sketchPart 3: How we abuse the ROM to make our security proofs workPart 4: Some more examples of where the ROM is used About eight years ago I set out to write a very informal piece on...

On client-side media scanning

A few weeks ago, U.S. Attorney General William Barr joined his counterparts from the U.K. and Australia to publish an open letter addressed to Facebook. The Barr letter represents the latest salvo in an ongoing debate between law enforcement and the tech industry over the deployment of end-to-end (E2E) encryption systems — a debate that will soon be...

How safe is Apple’s Safe Browsing?

This morning brings new and exciting news from the land of Apple. It appears that, at least on iOS 13, Apple is sharing some portion of your web browsing history with the Chinese conglomerate Tencent. This is being done as part of Apple’s “Fraudulent Website Warning”, which uses the Google-developed Safe Browsing technology as the back end. This feature...

Looking back at the Snowden revelations

Edward Snowden recently released his memoirs. In some parts of the Internet, this has rekindled an ancient debate: namely, was it all worth it? Did Snowden’s leaks make us better off, or did Snowden just embarass us and set back U.S. security by decades? Most of the arguments are so familiar that they’re boring at this point. But no matter how many...

How does Apple (privately) find your offline devices?

At Monday’s WWDC conference, Apple announced a cool new feature called “Find My”. Unlike Apple’s “Find my iPhone“, which uses cellular communication and the lost device’s own GPS to identify the location of a missing phone, “Find My” also lets you find devices that don’t have cellular support or internal GPS — things like laptops, or (and Apple has...

Attack of the week: searchable encryption and the ever-expanding leakage function

A few days ago I had the pleasure of hosting Kenny Paterson, who braved snow and historic cold (by Baltimore standards) to come talk to us about encrypted databases. Kenny’s newest result is with first authors Paul Grubbs, Marie-Sarah Lacharité and Brice Minaud. It isn’t so much about building encrypted databases, as it is about the risks of building...

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