Author Archives: jspilman

Open Letter to The Atlantic

Dear Robinson and Alexis,

Thank you for your article today on the COVID positivity rate over time. [1] Good data is hard to come by, but proper interpretation of the meager data we have is almost non-existent.

I believe we will study the 2020 COVID-19 epidemic for decades, but perhaps not for the reason you suspect. We will study it as an abject failure of epidemiology; a failure to define and execute a scientifically proven method to accurately estimate a virus’s crucial properties and characteristics in the face of totally obvious and predictable testing shortfalls and biases.

It seems like everyone today is an armchair epidemiologist. Perhaps because the basic concepts are truly quite approachable. Whether we are discussing IFR, CFR, Ro, or Rt… these variables give us a fairly easy to grasp handle on how quickly should we expect a virus to spread, how much we should worry if we catch it, and what measures would be appropriate to take in curbing the spread. And yet, experts have constantly lead us far afield of reality in estimating these absolutely crucial factors.

This is why I took keen interest in your article today discussing attempts to establish prevalence, and another piece of news, being the antibody study out of Santa Clara. [2]

It should be obvious to everyone that a virus for which no pre-existing surveillance networks exist, for which no pre-existing testing assays exist, for which no human has innate immunity, which spreads easily between humans, and for which asymptomatic cases are numerous if not the overwhelming majority… it should be immediately obvious that the number of reported cases for such a virus will dramatically lag the number of actual cases. The Santa Clara study out today estimates that testing has failed to detect on the order of 98 – 99.9% of positive cases (undercounting by 50x – 85x).

This is actually tremendously good news. While the WHO irresponsibly and incorrectly pushed a “CFR” of 3.4% in China [3], what we are dealing with is, in fact, a virus that can be very dangerous to a slim minority of people (80%+ of fatalities reporting 3 or more co-morbitities) but where in the vast majority of cases is mild or even totally asymptomatic. Every day now we see new data which point to the overall IFR of COVID-19 to be closer to 0.3%, making it, despite uproarious objections to the contrary, roughly on par with a bad flu season.

The implication for the public health response is impossible to under-state. As we finally discover and come to terms with the fact that the prevalence of COVID-19 in metropolitan populations is likely 3-5%, and quickly approaching 10%, we can finally admit that containment is impossible, and mitigation is fruitless. The only reachable end-point is, as it is every flu season, herd immunity.

What we have control of is one key variable, which is how quickly we approach the point of herd immunity, the effect of which will be to provide innate suppression of the Ro or viral spread. In this case, the herd immunity threshold that will confer this benefit is roughly 65% exposed, given the baseline estimates Ro of SARS-CoV-2 (for lower Ro, a lower herd immunity threshold is needed to innately slow transmission in the general population). So while we appear to be roughly 1/6th the way there numerically, luckily, on a time-scale, this whole ordeal is more than half over.

All that is left, then, is to dispel this peculiar internet-meme turned national health policy that is “flattening the curve”. The premise of spreading out the time scale of infections to allow more health-care-hours available per hospitalized patient can sometimes make sense depending on the hospitalization rate, the available resources, and the effective treatment modalities.

But here’s the rub. After hearing so much about ventilators and PPE, the stark truth is this; The vast majority of healthcare worker are already exposed and immune, as antibody testing of frontline workers will soon demonstrate, making extensive PPE use essentially unnecessary. More sobering, is that 80 – 90% of patients which are ventilated have died. [4] The primary intervention has proven not only to be ineffective, but actively lethal. It’s almost maddening to consider that flattening the curve in such an environment actually kills more patients than it saves.

It will take some time for everyone to come to grips with this new data and viewpoint, but I hope it will start happening quickly, based on articles like yours.

A virus for which the only proven effective treatments are extremely scalable and moderate (non-invasive oxygen therapy and frequent repositioning), for which the vast majority of people infected will never even know they had it unless tested… calls for the immediate and complete re-opening of our economy. Literally trillions of dollars are on the line, and 20% of all workers stand unemployed, until the narrative on this disease can come to terms with the facts of COVID-19 as they have finally become readily apparent.

I hope that you will continue to report on these crucial epidemiological factors and continue to explain how to interpret them as new data becomes available, as it will help shift the narrative and ultimately help re-open our economy sooner, saving countless lives and livelihoods

Discovering a New FizzBuzz – The Cheryl Birthday Problem

If you haven’t heard about the Cheryl Birthday Problem, it’s a cute little teaser and worth taking a look. Now I just saw this lovely post about how to Solve the Cheryl Birthday Problem with Prolog. I thought it might be neat to solve it in SQL!

The interesting thing about the problem is the peculiar way the problem is worded. I happen to like the wording quite a bit, and I think teasing out the meaning is most of the fun;

Albert and Bernard have just met Cheryl. “When is your birthday?” Albert asked Cheryl. Cheryl thought for a moment and said, “I won’t tell you, but I’ll give you some clues”. She wrote down a list of ten dates:

  • May 15, May 16, May 19
  • June 17, June 18
  • July 14, July 16
  • August 14, August 15, August 17

“One of these is my birthday,” she said.

Cheryl whispered in Albert’s ear the month, and only the month, of her birthday. To Bernard, she whispered the day, and only the day. “Can you figure it out now?” she asked Albert.

  • Albert: “I don’t know when your birthday is, but I know Bernard doesn’t know, either.”
  • Bernard: “I didn’t know originally, but now I do.”
  • Albert: “Well, now I know, too!”

When is Cheryl’s birthday?

Our first step is setting up the problem;

CREATE TABLE #Birthdays (Month int, Day int)
INSERT INTO #Birthdays VALUES (5, 15), (5, 16), (5, 19),
(6, 17), (6, 18), (7, 14), (7, 16), (8, 14), (8, 15), (8, 17)
-- (10 row(s) affected)

The trick is in reducing the dialog between Albert and Bernard into a process of elimination. Albert knows the month, and Bernard knows the day. Obviously Albert can’t possibly know the date, because every month has at least two potential dates when it could be Cheryl’s birthday. But there are two months with unique days, namely May 19 and June 18. If the answer was either of those, then Bernard would know off the bat. Therefore when Albert lets on that he knows that Bernard doesn’t know, that’s our first clue. Albert knows it’s a month where none of the possible days are unique. Or to flip the logic so we can do the test one step at a time, we will delete any Month which has a Day which is unique;

--I know Bernard doesn't know
--a.k.a Delete any months which have unique days
DELETE FROM #Birthdays
WHERE [Month] IN (SELECT MIN([Month]) FROM #Birthdays GROUP BY [Day] HAVING COUNT(1) = 1)
-- (5 row(s) affected)

The syntax of MIN([Month]) in the sub-query is something I’ve always seen as a failing of SQL. The COUNT(1)=1 means there can only ever possibly be a single record in each group. The query analyzer should know that, and let us directly access columns outside the aggregator without a warning in these cases. Or perhaps at least, provide an ONLY() hinting function to make the code easier to read! Anyway, back to the problem at hand…

The next clue is that Bernard tells us that now he knows the date. In other words, in the remaining set of dates, the day must be unique. Again, to flip the logic, we will delete any day which is not unique;

--Bernard didn't know originally but now he knows
--a.k.a Bernard's day must be unique in the resulting table
DELETE FROM #Birthdays
WHERE [Day] IN (SELECT [Day] FROM #Birthdays GROUP BY [Day] HAVING COUNT(1) > 1)
-- (2 row(s) affected)

Finally, now Albert also knows the right answer. This is the same deletion as above, except now we will delete any month which is not unique;

--Now Albert knows
--a.k.a Albert's month must be unique in the resulting table
DELETE FROM #Birthdays
WHERE [Month] IN (SELECT [Month] FROM #Birthdays GROUP BY [Month] HAVING COUNT(1) > 1)
-- (2 row(s) affected)

And now we simply print our result:

SELECT * FROM #Birthdays
Month       Day
----------- -----------
7           16
(1 row(s) affected)

I’m sure there are more direct ways to achieve the result in SQL, but this seems like the best match to how I actually worked through the solution step by step. Maybe we’ve found a more entertaining replacement for FizzBuzz! It would be interesting to code this instead as a set of nested SELECT statements, or perhaps using only a sequence of JOINS. Of course any Turing complete language can make easy work of Cheryl’s trickery, and as long as there’s cake for everyone at the end, I wouldn’t mind seeing more of Cheryl in future coding screens.

The Value of a Low Valuation

Business Insider analyzed a leaked email between Evan Spiegel (CEO of Snapchat) and Mitch Lasky, a Board member of Snapchat (Partner at Benchmark Capital). The email was leaked as part of the Sony hack, because the CEO of Sony, Michael Lynton, is also on the Board of Snapchat. Snapchat lost a lot of sensitive emails in the Sony breach because of that connection.

One interesting topic for that Board discussion was Snapchat’s Section 409A valuation. The IRS requires paying taxes as restricted stock vests (or up front if you so-elect) based on the fair market value of the stock. Or, if options, based on the intrinsic + time-value of the options. So maintaining a low common stock valuation becomes a crucial exercise if you want to actually be able to issue any meaningful number of shares to your employees.

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The Self-Hosting Moonshot

Self-hosting an app may provide some unique advantages, like scalability and privacy, but it comes at a cost. There’s a huge usability gap in the setup cost. Users expect the web to ‘just work’ and don’t want the cognitive load of ‘configuring’ or managing something. So the self-hosted app has to “feel” like a local app, and nothing more. From the user perspective, the back-end is “weightless”.

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The Future of Bitcoin Escrow

Bitcoin has a built-in functionality, called CHECKMULTISIG, where you can require two or more private keys in order to spend a transaction. There are an incredible number of ways you could theoretically use CHECKMULTISIG, but the most obvious use case is a secure escrow functionality. A quick glance at the history of Bitcoin powered services over the last 3 years shows how much the community could benefit from better ways to escrow payments.

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How Lavabit Will Win on Appeal

There’s something missing from the arguments being set forth in the Lavabit appeal, and I think it opens a gaping hole in the government’s case. This case actually isn’t about encryption keys at all, and I think refocusing the argument will give the appeals court the “out” they’re looking for to decide in Lavabit’s favor without actually deciding the issue of whether the government can compel production of SSL keys.

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US Response Missing in Egyptian Government’s Mass Killings of Protesters

I just read this NY Times article on the mass killings in Egypt, and I highly recommend you take the time to read it: http://www.nytimes.com/2013/08/15/world/middleeast/egypt.html?pagewanted=all&_r=0

This is incredibly disturbing on so many levels. I haven’t been keeping up to speed on current events in Egypt as much as now I think I should, so this was eye opening and I think a must-read. There is too much in the article to try quoting specific parts or recapping it; I think you just need to read the source, especially if you’re not up to speed.

There are so many thoughts and questions that this brings to mind… and I hope we can at least drive some critical discussion following these events.

CERT Advisory on DNS Amplification Offers Little Hope

CERT released an advisory today on DNS Amplification Attacks.  These attacks are nothing new; in fact dealing with this kind of load is business as usual for the Tier1/2 providers. But I was surprised with how little apparently CERT has to offer in the way of advice to thwart the attacks.

Open Letter to Flightfox

Hey guys,

I think your company is great, but haven’t had a chance to use you yet. How many people (myself included) are in the same boat?

I read about your latest music festival contest on HN. Maybe that’s ‘Mission Accomplished’ for you already. But I think you should consider running a different kind of contest. I think it comes down to: What market are you targeting with multicontinental music festivals? I can’t quite figure out if you only book multi-continent ’round-the-world’ flights, or if you’re up for more run of the mill business trips and family vacations?  Do you just do the flight, or can you do the hotel accommodations as well? What about something like flights to Europe plus hotel and train travel between countries?

How about running a contest a few more of us could relate to.  Show us how great you could be at planning a budget trip for a family of 4 with kids of different ages. That would solve an immediate problem for a lot of people, not just some sexy corner case. A quality budget experience when kids are involved means no hostels, no campgrounds (unless that’s the whole point), and age appropriate attractions. I’m sure your experts could justify the ‘finders fee’ with some of the great trips they could cook up!

I think part of the problem is I don’t understand what your target market actually is. It doesn’t click who exactly you are trying to serve. It’s the difference between me taking the time to learn about your ‘system’ and maybe even trying it out, and just ‘doing it the old way’.

 

 

SRP vulnerability when using a 256-bit modulus

Note to reader: This SRP vulnerability applies only if a 256-bit modulus is being used. For example, in Blizzard’s Battle.net 2 protocol, the modulus is 1024-bit [1].

In my prior blog post, I explained how an attacker can use a dictionary attack to try to guess users’ passwords based on the recent Blizzard data breach, where they were using SRP to store the passwords. Some readers have pointed out, it is significantly slower to dictionary attack SRP than raw SHA1, so SRP at least protects users who have chosen strong / random passwords. However, depending on the bit-length of the modulus, there may be an improved technique which could allow significantly faster attacks.

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