jdewerd (u/jdewerd) - Readit News

jdewerd commented on AMD adds RF-sampling data converters to Versal adaptive SoCs (2024) electronicsweekly.com/new... · Posted by u/teleforce

hkwerf · 7 months ago

Yes, I have seen versal, in particular in defense and satcom. However, in just that field, I have also never seen an RFSoC.

I've seen lots of integrated RF transceivers that were tightly coupled to the FPGAs, but not shared on the same SoC.

jdewerd · 7 months ago

Is that because defense doesn't like them or is it because (non-wartime) defense moves on geological timescales and these are "new"?

jdewerd commented on Benchmarking RSA Key Generation words.filippo.io/dispatch... · Posted by u/mfrw

af3d · 8 months ago

Iterating over some huge search space in an essentially sequential manner is generally not going to be nearly performant as simply selecting an odd number at random. You could try using a generating polynomial instead such as f(x) = x^2 + x + 41 but even that isn't going to help much in the long run. (There are Diophantine equations which one day may prove useful for generating random primes however AFAICT finding efficient solutions is still currently considered a hard problem.)

jdewerd · 8 months ago

Yes, but the more we mix sieve rejection into candidate selection the more we complicate the rule of thumb. "Reject even numbers as prime candidates" is probably OK to leave as an exercise for the reader, as is the equivalent "round every candidate to odd" optimization. The point about random vs sequential is well taken, though, and it doesn't complicate the rule of thumb, so I changed it.

jdewerd commented on Benchmarking RSA Key Generation words.filippo.io/dispatch... · Posted by u/mfrw

rainsford · 8 months ago

It's been a while since I've looked at the literature on RSA prime generation, but I seem to remember that picking a random starting point and iterating until you find a prime is discouraged because primes aren't evenly distributed so key generation timing could reveal some information about your starting point and eventual prime choice.

I'm not sure how realistic of an issue this is given the size of the primes involved. Even if an attacker can extract sensitive enough timing information to figure out exactly how many iterations were required to find a 1024 bit prime from a 1204 bit random starting point, I'm not aware of a good way to actually find either value. You do also introduce a bias since you're more likely to select prime numbers without a close neighbor in the direction you are iterating from, but again I'm not sure how practical an attack on this bias would be.

Still, to avoid any potential risk there I seem to remember best practice being to just randomly generate numbers of the right size until you find a prime one. With the speed of modern RNGs, generating a fresh number each time vs iterating doesn't seem like a significant penalty.

jdewerd · 8 months ago

Yes, excellent point! I originally omitted this detail for simplicity, but on reflection I don't think it actually achieved much in the way of simplifying the rule so I changed it to reflect reality. Thanks for pointing that out.

EDIT: the rush of people offering up sieve optimizations is pushing me back towards formulating the rule of thumb on a consecutive block of numbers, since it makes it very clear that these are not included, rather than implicitly or explicitly including some subset of them (implicit is bad because opacity, explicit is bad because complexity).

jdewerd commented on Benchmarking RSA Key Generation words.filippo.io/dispatch... · Posted by u/mfrw

jdewerd · 8 months ago

> The prime-counting function approximation tells us there are Li(x) primes less than x, which works out[5] to one prime every 354 odd integers of 1024 bits.

Rule of thumb: Want a 1024-bit prime? Try 1024 1024-bit candidates and you'll probably find one. Want a 4096-bit prime? Try 4096 4096-bit candidates and you'll probably find one.

The approximate spacing of primes around p is ln(p), so ln(2^1024) = 1024*ln(2), and ln(2)=0.693 so if you are willing to absorb 0.693 into your rule of thumb as a safety margin you get the delightfully simple rule of thumb above. Of course, you'll still want to use a sieve to quickly reject numbers divisible by 2, 3, 5, 7, etc, and this easily rejects 90% of numbers, and then do a Fermat primality test on the remainders (which if you squint is sort of like "try RSA, see if it works"), and then do Miller-Rabin test to really smash down the probability that your candidate isn't prime. The probabilities can be made absurdly small, but it still feels a bit scandalous that the whole thing is probabilistic.

EDIT: updated rule of thumb to reflect random candidate choice rather than sequential candidate choice.

jdewerd commented on Jimmy Carter has died washingtonpost.com/obitua... · Posted by u/gkolli

bdndndndbve · 8 months ago

FDR doesn't make the cut?

jdewerd · 8 months ago

Oh, he only busted the Great Depression, won WWII, built half of the infrastructure that we keep kicking the expiration date on, and negotiated 80% of the beneficial fine print in your employment contract. Don't you think he could have done a bit more?

My list would be: 1. FDR, 2. Carter, 3. Teddy. Carter because he sacrificed his career to fix inflation (Republican attempts to rewrite history notwithstanding), and Teddy because he wasn't merely an excellent man with excellent politics, but also because whenever present-day Republicans try to claim the man without claiming his politics I can turn it into a teachable moment, and putting him on a list with the other two is the perfect bait.

jdewerd commented on US could ban TP-Link routers over hacking fears: report nypost.com/2024/12/18/bus... · Posted by u/esaym

nottorp · 9 months ago

There's that nagging feeling that they're not concerned about security but banning anything that works well, is inexpensive and isn't made by an US company...

Anecdote: once I bought the cheapest router I could find online. The idea was to test connecting to a crap AP. Unfortunately the cheapest was a TP-Link and it worked absolutely perfectly, ruining my test plan.

jdewerd · 9 months ago

I love cheap and reliable TP-Link routers as much as the next guy, but it's definitely also a security issue. The CCP almost certainly has a backdoor. Maybe a respectable one in the form of an undisclosed bug or the ability to lean on an update provider, but the point stands: it's absolutely a security issue and denying this is cope.

Routers are going to be a bit more expensive and a bit less reliable for a while. We'll live.