# Evan A. Sultanik, Ph.D.

Evan's First Name @ Sultanik .com

Chief Scientist
Digital Operatives, LLC

Drexel University College of Computing & Informatics
Department of Computer Science

## Lenticrypt: a Provably Plausibly Deniable Cryptosystem

### or, This Picture of Cats is Also a Picture of Dogs

Back in 2009, I wrote about a thought experiment on how to subvert copyright law via plausible deniability. A couple years ago I expanded on that thought experiment by proposing a seedling idea on how to accomplish it via cryptography. Since then, I've slowly been developing that seedling into a functioning proof-of-concept, which has culminated in the creation of the Lenticrypt project:

Lenticrypt can generate a single ciphertext file such that different plaintexts are generated depending on which key is used for decryption:

$python lenticrypt.py -e key1 plaintext1 -e key2 plaintext2 -o output.enc$ python lenticrypt.py -d key1 output.enc | diff - plaintext1 -s
Files - and plaintext1 are identical

## Streams Data Processing Workshop

### A Presentation Introducing Distributed Combinatorial Optimization

I will be presenting a talk introducing distributed combinatorial optimization at the Streams Data Processing Workshop tomorrow. Here are the slides:

Handouts for the talk are also available, here.

## Sushi Elitism

### Three reasons why you've probably never had an authentic sushi experience.

There are a number of myths and misconceptions surrounding both the creation and consumption of sushi that I'd I think are important enough to devote an entire blog entry toward their clarification.

Proper sushi has a small amount of wasabi applied to the underside of the fish. Some people claim that "it is to prevent parasites" (via the natural anticeptic properties of the wasabi), but I find this explanation a bit dubious (I would think that the wasabi would have to be uniformly applied to the entire fish to have any measurable effect). The wasabi is really there to add flavor. In really high-end sushi restaurants in Japan, for example, it is relatively uncommon for the guest to be served a mound of grated wasabi; that's the sushi equivalent to serving an un-tossed caesar salad with the dressing on the side. Instead, the chef applies the perfect amount of wasabi to each piece of sushi. Some chefs will not even serve soy sauce, instead individually brushing on the sauce on each piece. If wasabi is served separately from the fish, it is generally also considered bad form to mix it with the soy sauce (as is commonly done in the US).

So, why might you have never seen this before at your local sushi joint?

1. It takes more time/skill/effort to do it properly.
2. Many sushi restaurants in the US do not have properly trained sushi chefs. In fact, in most areas of the country with little or no Japanese population, don't be surprised if your sushi chef is a Salvadorian who learned from the Oaxacan who learned from the Korean owner of the restaurant. Not that there's anything wrong with that; one of my favorite sushi places is run by an Indonesian. Just keep in mind that the people making you your sushi may have never experienced the "real thing" themselves.
3. "Real," fresh wasabi is very rare and expensive. Most of the stuff that is used in the US is basically horseradish paste plus food coloring. Restaurants that can both procure and afford to use the real stuff will want to use it sparingly; they wouldn't want to waste it by putting a mound of it on each plate. Therefore, they might be more inclined to use the "proper" technique.

Here is a video in which you can see famous chef Naomichi Yasuda using wasabi inside the sushi. It all happens very quickly, but you can clearly see him dip into the bin of wasabi, rub it on the underside of the fish, and then apply the fish to the rice. Here is another video in which Anthony Bourdain explains the "rules" of high-end sushi eating, while dining at the super-famous and super-expensive Sukiyabashi Jiro (the proprietor of which is actually designated as a "living treasure" by the Japanese government). That second video shows the chef brushing on the soy sauce, and the general lack of both soy and wasabi on the plates.

And on to the matter of chopsticks. Some purists claim that you're not supposed to use them, instead using your hands. I've been to Japan, and it really varies by the type of establishment. Here is my take on it: I think it really depends on the formality of the restaurant. In the more formal places, they won't serve any separate wasabi or soy (only gari) and they'll give you a small moist towel (in addition to the oshibori) that you are supposed to use to clean your fingers between pieces of sushi, under the expectation that you will use your hands. If they don't give a towel to clean your fingers, then I think it is acceptable to use chopsticks.

When I say "high-end", I mean a place that specializes in just sushi. In Japan, these places are usually tiny, consisting of only a bar. Each sushi chef services at most 5 customers at a time. Each chef is supported by perhaps one apprentice (who might prepare some of the seafood) and several other apprentices in the kitchen whose primary job is to prepare the rice. Sushi is all about the rice, after all; an apprentice will spend the better part of the first decade of his training just learning how to cook the rice, before even touching any seafood. That's why most casual restaurants in Japan (e.g., izakaya) will forego even serving sushi, instead offering preparations that require less skill/training (e.g., sashimi).

## Will eating late at night make you fat?

### TL;DR: No.

Despite awkwardness caused by his recent rants on the topics of modern cooking techniques and more recently fandom, Alton Brown is still one of my favorite sources of culinary quotes. One of which, related to nutrition, is

In keeping with my recent posts' unintentional gastronomic theme [1,2], I am going to dedicate this post to debunking a myth related to the above quote. I claim that there is no bad time to eat, only bad eating habits. Specifically, I'd like to dispell the common misconception that the time of one's meal alone can affect weight gain.

I recall hearing a story on NPR a year or two ago about a study which specifically tried to test the claim that eating late at night is unhealthy. The study concluded that there was absolutely no correlation between the proximity of mealtime to sleep and weight gain, other than the fact that people tend to choose to eat more unhealthy foods late at night. I can't seem to find a reference to that study, however, so I am going to have to do some research myself. Right. Lets get stuck in.

The majority of our food is actually digested during sleep, so the common argument that "eating late at night is bad because our metabolism [slows or shuts down] during sleep" is incorrect. With that said, there is a correlation between night eating, low self-esteem, reduced daytime hunger, and weight loss among people who are already obese or prone to obesity, however, this correlation does not necessarily imply causation (i.e., the act of eating a late meal does not necessarily provoke these conditions). It may simply be the case that the types of foods that people prefer to eat late at night are less healthy. There is still much debate on the subject, however, many scientists agree that meal frequency, as opposed to time, is one of the best predictors for weight gain. For example, the time between meals is highly correlated to one's waist size. This makes some intuitive sense, since eating more, smaller meals will help regulate insulin levels, and spikes in insulin levels (which can be caused by large meals and/or large gaps in time between meals) have been linked to weight gain.

A newer study followed the eating and sleeping patterns of 52 subjects over one week. They found a correlation between "late sleepers" (i.e., people who go to sleep late and wake up late) and high body mass index, and that eating after 8pm was associated with higher body mass index. A relatively recent New York Times article summarizing the results of the study makes the further claim that eating late at night leads to weight gain, however, I disagree with that claim on the grounds that correlation does not imply causation. In fact, the original study noted:

Late sleepers consumed more calories at dinner and after 8:00 PM, had higher fast food, full-calorie soda and lower fruit and vegetable consumption.

Therefore, I think the results of the study can be interpreted to mean that there is a correlation between eating/sleeping late and a poor diet.

Furthermore back in 2006, the same research team conducted a study on monkeys in which they were fed a diet similar to the average (i.e., high-fat) diet common in the USA. The only variable was the time of day that the monkeys were fed. With all else remaining constant, the researchers found no correlation between weight gain and time of feeding.

It was really interesting to see that the monkeys who ate most of their food at night were no more likely to gain weight than monkeys who rarely ate at night. This suggests that calories cause weight gain no matter when you eat them.

While I'm on a roll here, let me quickly dispel yet another myth. I know many people that adhere to the strict "calorie-in/calorie-out" nutritional theory. This seems particularly popular among mathy/engineering types. The idea is that if your body burns fewer calories than what it takes in through food then it will gain weight. This theory, in general, is fallacious. The body doesn't necessarily consume all of the calories of the food we stick down our throats. The time between meals will, in effect, affect the way one's body "decides" to digest the food. Furthermore, as this study and others like it suggest, not all types of calorie sources are equal when it comes to how the body processes them!

In conclusion, if you're overweight, it's not necessarily legitimate to blame your late-night eating schedule. You can't even blame your high calorie diet (only the types of calories you choose to eat).