David Cash

Computer Science Professor at University of Chicago. Researcher in cryptography and computer security. I use multiplicative notation for cryptographic groups.

[David Cash @cdavidcash]

For anyone following at home, the answer is that an index-calculus type attack is possible. See https://t.co/eAoMlck1wc

[David Cash @cdavidcash]

Hi Crypto-Twitter,

Can anyone explain the rationale of the padding string (PS) in PKCS#1 v1.5 RSA signatures? Is there an attack if we simply pad with all zeros (i.e. just sign the bare digest)? Do the FF bytes just give us a warm fuzzy feeling?

Sincerely,
stumped instructor

[David Cash @cdavidcash]

@matthew_d_green Parts of Chicago have had big problems. There was a week in June when we didn't get mail at all.

[David Cash @cdavidcash]

@ChrisPeikert Is it because you need to require that exactly two edges intersect at each vertex? Or exclude donut-like shapes and disconnected regions or something?

[David Cash @cdavidcash]

@bertkaufman Worth watching to the very end!

[David Cash @cdavidcash]

@stochastician Growing up (80s/90s), talking on the phone was actually better than talking in person sometimes. It felt like latency on the phone was less than latency across a room.

[David Cash @cdavidcash]

@LindellYehuda @matthew_d_green Indeed. I'm grateful that crypto has the IACR to help with this rather being stuck with the ACM and IEEE.

[Ross Anderson @rossjanderson]

Here are some problems with private contact tracing. We should not give policymakers the false hope that they can avoid hard choices: https://t.co/HYq9DzuIK6

[David Cash @cdavidcash]

@stochastician Indeed... the IT is generally great here, but occasionally there's a wart or two.

And Hi! I think you can see at least two CS people and one physics person that you know from your place.

[David Cash @cdavidcash]

@feamster @UChicago The south half of Washington Park has been especially beautiful this past month!

[David Cash @cdavidcash]

@stochastician FTA: #1 is "Prioritize your customers by profitability" :)

[David Cash @cdavidcash]

@LindellYehuda @koeppelmann I think this is a thing, called group testing (https://t.co/fVBx9xVdHF). I recall that the hardness of some version of the problem implies PKE.

[David Cash @cdavidcash]

@mvaria Are you really claiming your system is "Taming the Coronavirus"?

[David Cash @cdavidcash]

@matthew_d_green Bonus points for ones without threat models or any input from public health people.

[David Cash @cdavidcash]

@secparam But by god they won't use the random oracle model!

[David Cash @cdavidcash]

@matthew_d_green Maybe a primer on practical lightweight crypto?

[David Cash @cdavidcash]

@LindellYehuda @nikitab I think many accept "smaller than inverse exponential" as "exponential", especially when it comes to tail bounds.

[David Cash @cdavidcash]

@GarbledCircus If I have time, I also hope to make an assignment to forge a cert that verifies under an (old) vulnerable version of openssl (https://t.co/sXzxUgUOei).

In general, exposing students to the reality ASN.1 and C implementation issues has a lot of education value.

[David Cash @cdavidcash]

@GarbledCircus For the next fall I plan to develop a problem based on https://t.co/t1WcKHykMX and another on the old bad deterministic implementation Miller-Rabin. Both require a good understanding of the basic number theory.