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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Is Telegram really an encrypted messaging app?
25 Aug 2024 | original ↗

This blog is reserved for more serious things, and ordinarily I wouldn’t spend time on questions like the above. But much as I’d like to spend my time writing about exciting topics, sometimes the world requires a bit of what Brad Delong calls “Intellectual Garbage Pickup,” namely: correcting wrong, or mostly-wrong ideas that spread unchecked …...

Is Telegram really an encrypted messaging app?
25 Aug 2024 | original ↗

This blog is reserved for more serious things, and ordinarily I wouldn’t spend time on questions like the above. But much as I’d like to spend my time writing about exciting topics, sometimes the world requires a bit of what Brad Delong calls “Intellectual Garbage Pickup,” namely: correcting wrong, or mostly-wrong ideas that spread unchecked …...

A quick post on Chen’s algorithm
16 Apr 2024 | original ↗

Update (April 19): Yilei Chen announced the discovery of a bug in the algorithm, which he does not know how to fix. This was independently discovered by Hongxun Wu and Thomas Vidick. At present, the paper does not provide a polynomial-time algorithm for solving LWE. If you’re a normal person — that is, a person … Continue reading A quick post on...

A quick post on Chen’s algorithm
16 Apr 2024 | original ↗

Update (April 19): Yilei Chen announced the discovery of a bug in the algorithm, which he does not know how to fix. This was independently discovered by Hongxun Wu and Thomas Vidick. At present, the paper does not provide a polynomial-time algorithm for solving LWE. If you’re a normal person — that is, a person … Continue reading A quick post on...

Attack of the week: Airdrop tracing
11 Jan 2024 | original ↗

It’s been a while since I wrote an “attack of the week” post, and the fault for this is entirely mine. I’ve been much too busy writing boring posts about Schnorr signatures! But this week’s news brings an exciting story with both technical and political dimensions: new reports claim that Chinese security agencies have developed … Continue reading...

Attack of the week: Airdrop tracing
11 Jan 2024 | original ↗

It’s been a while since I wrote an “attack of the week” post, and the fault for this is entirely mine. I’ve been much too busy writing boring posts about Schnorr signatures! But this week’s news brings an exciting story with both technical and political dimensions: new reports claim that Chinese security agencies have developed … Continue reading...

To Schnorr and beyond (part 2)
30 Nov 2023 | original ↗

This post continues a long, wonky discussion of Schnorr signature schemes and the Dilithium post-quantum signature. You may want to start with Part 1. In the previous post I discussed the intuition behind Schnorr signatures, beginning with a high-level design rationale and ending with a concrete instantiation. As a reminder: our discussion began...

To Schnorr and beyond (part 2)
30 Nov 2023 | original ↗

This post continues a long, wonky discussion of Schnorr signature schemes and the Dilithium post-quantum signature. You may want to start with Part 1. In the previous post I discussed the intuition behind Schnorr signatures, beginning with a high-level design rationale and ending with a concrete instantiation. As a reminder: our discussion began...

To Schnorr and beyond (Part 1)
6 Oct 2023 | original ↗

Warning: extremely wonky cryptography post. Also, possibly stupid and bound for nowhere. One of the hardest problems in applied cryptography (and perhaps all of computer science!) is explaining why our tools work the way they do. After all, we’ve been gifted an amazing basket of useful algorithms from those who came before us. Hence it’s …...

To Schnorr and beyond (Part 1)
6 Oct 2023 | original ↗

Warning: extremely wonky cryptography post. Also, possibly stupid and bound for nowhere. One of the hardest problems in applied cryptography (and perhaps all of computer science!) is explaining why our tools work the way they do. After all, we’ve been gifted an amazing basket of useful algorithms from those who came before us. Hence it’s …...

Some rough impressions of Worldcoin
21 Aug 2023 | original ↗

Recently a reader wrote in and asked if I would look at Sam Altman’s Worldcoin, presumably to give thoughts on it from a privacy perspective. This was honestly the last thing I wanted to do, since life is short and this seemed like an obvious waste of it. Of course a project devoted to literally … Continue reading Some rough impressions...

Some rough impressions of Worldcoin
21 Aug 2023 | original ↗

Recently a reader wrote in and asked if I would look at Sam Altman’s Worldcoin, presumably to give thoughts on it from a privacy perspective. This was honestly the last thing I wanted to do, since life is short and this seemed like an obvious waste of it. Of course a project devoted to literally … Continue reading Some rough impressions...

On Ashton Kutcher and Secure Multi-Party Computation
11 May 2023 | original ↗

Back in March I was fortunate to spend several days visiting Brussels, where I had a chance to attend a panel on “chat control“: the new content scanning regime being considered by the EU Commission. Among various requirements, this proposed legislation would mandate that client-side scanning technology be incorporated into encrypted text...

On Ashton Kutcher and Secure Multi-Party Computation
11 May 2023 | original ↗

Back in March I was fortunate to spend several days visiting Brussels, where I had a chance to attend a panel on “chat control“: the new content scanning regime being considered by the EU Commission. Among various requirements, this proposed legislation would mandate that client-side scanning technology be incorporated into encrypted text...

PRFs, PRPs and other fantastic things
8 May 2023 | original ↗

A few weeks ago I ran into a conversation on Twitter about the weaknesses of applied cryptography textbooks, and how they tend to spend way too much time lecturing people about Feistel networks and the boring details of AES. Some of the folks in this conversation suggested that instead of these things, we should be … Continue reading PRFs, PRPs...

PRFs, PRPs and other fantastic things
8 May 2023 | original ↗

A few weeks ago I ran into a conversation on Twitter about the weaknesses of applied cryptography textbooks, and how they tend to spend way too much time lecturing people about Feistel networks and the boring details of AES. Some of the folks in this conversation suggested that instead of these things, we should be … Continue reading PRFs, PRPs...

Book Review: Red Team Blues
24 Apr 2023 | original ↗

As a rule, book reviews are not a thing I usually do. So when I received an out-of-the-blue email from Cory Doctorow last week asking if I would review his latest book, Red Team Blues, it took a minute to overcome my initial skepticism. While I’m a fan of Cory’s work, this is a narrow/nerdy … Continue reading Book Review: Red Team Blues →

Book Review: Red Team Blues
24 Apr 2023 | original ↗

As a rule, book reviews are not a thing I usually do. So when I received an out-of-the-blue email from Cory Doctorow last week asking if I would review his latest book, Red Team Blues, it took a minute to overcome my initial skepticism. While I’m a fan of Cory’s work, this is a narrow/nerdy … Continue reading Book Review: Red Team Blues →

Remarks on “Chat Control”
23 Mar 2023 | original ↗

On March 23 I was invited to participate in a panel discussion at the European Internet Services Providers Association (EuroISPA). The focus of this discussion was on recent legislative proposals, especially the EU Commission’s new “chat control” content scanning proposal, as well as the future of encryption and fundamental rights. These are the...

Remarks on “Chat Control”
23 Mar 2023 | original ↗

On March 23 I was invited to participate in a panel discussion at the European Internet Services Providers Association (EuroISPA). The focus of this discussion was on recent legislative proposals, especially the EU Commission’s new “chat control” content scanning proposal, as well as the future of encryption and fundamental rights. These are the...

Why encrypted backup is so important
7 Dec 2022 | original ↗

You might have seen the news today that Apple is announcing a raft of improvements to Macs and iOS devices aimed at improving security and privacy. These include FIDO support, improvements to iMessage key verification, and a much anticipated announcement that the company is abandoning their plans for (involuntary) photo scanning. While every...

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