From Nand To Dinner - CEST August 2020

# .title.alex[From Nand to Dinner]
      ## .subtitle.alex[A Midsummer Night’s Talk]

Lisa '[lislis](https://lislis.de/)' Passing

[CEST - Aug 2020](https://clojureverse.org/t/new-online-meetup-clojure-european-summer-time/6018/9)

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### I've been getting into hardware recently.

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.link[[//twitter.com/daisyowl/status/841802094361235456](https://twitter.com/daisyowl/status/841802094361235456)]

.hidden[Screenshot of a tweet by @daisyowl saying "If you ever code something that  'feels like a hack but it works', just remember that a CPU is literally a rock we tricked into thinking"]

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## How did we trick a rock into thinking?

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## What makes Silicon cool?

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It will from strong bonds with other Si atoms, sharing electrons to achieve 8 Valence electrons.]

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.half[
      Through introducing impurities in the silicon, we can alter its conductivity (This is called **doping**).]

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.half[
      Through introducing impurities in the silicon, we can alter its conductivity (This is called **doping**).

**Phosphorus** (*P*, 5 Valence electrons) will introduce an extra electron (n-type).]

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.half[
      Through introducing impurities in the silicon, we can alter its conductivity (This is called **doping**).

**Phosphorus** (*P*, 5 Valence electrons) will introduce an extra electron (n-type).

**Boron** (*B*, 3 Valence electrons) will introduce a gap (p-type).]

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Aaand what?

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# MOSFET

**M**etal-**O**xide-**S**emiconductor **F**ield-**E**ffect **T**ransistor

A switch (or amplifier) without any mechanical parts.

- FET proposed and patented in 1925, but no working device

- 17 years later the patent ran out and people started working on a working device

- 1959 working MOSFET invented at Bell Labs

- Kickstarted the information age revolution!

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      ## Transistors replaced vacuum tubes]

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## Abstractions!

Current (or lack of) gives us logic states,

transistors give us logic gates NOT, AND, OR

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## From Nand to Tetris

There is a book for that!

https://www.nand2tetris.org/

And a video playlist

https://www.youtube.com/playlist?list=PL8dPuuaLjXtNlUrzyH5r6jN9ulIgZBpdo

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# XOR

Input A | Input B | Output
      --------|--------|-----
      0  | 0 | 0
      0  | 1 | 1
      1  | 0 | 1
      1  | 1 | 0

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## The Dining Cryptographers Problem pt1

“Three cryptographers gather around a table for dinner.

The waiter informs them that the meal has been paid for by someone, who could be one of the cryptographers or the National Security Agency (NSA).

The cryptographers respect each other's right to make an anonymous payment, but want to find out whether the NSA paid.

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## The Dining Cryptographers Problem pt2

“So they decide to execute a two-stage protocol.

In the first stage, every two cryptographers establish a shared one-bit secret, say by tossing a coin behind a menu so that only two cryptographers see the outcome in turn for each two cryptographers.

Suppose, for example, that after the coin tossing, cryptographer A and B share a secret bit 1, A and C share 0, and B and C share 1.

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## The Dining Cryptographers Problem pt3
      “In the second stage, each cryptographer publicly announces a bit, which is:

- if they didn't pay for the meal, the exclusive OR (XOR) of the two shared bits they hold with their two neighbours,
      - if they did pay for the meal, the opposite of that XOR.

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## The Dining Cryptographers Problem pt4

“Supposing none of the cryptographers paid, then A announces 1 ⊕ 0 = 1, B announces 1 ⊕ 1 = 0, and C announces 0 ⊕ 1 = 1.

On the other hand, if A paid, she announces ¬ ( 1 ⊕ 0 ) = 0.

The three public announcements combined reveal the answer to their question. One simply computes the XOR of the three bits announced.

If the result is 0, it implies that none of the cryptographers paid (so the NSA must have paid the bill).

Otherwise, one of the cryptographers paid, but their identity remains unknown to the other cryptographers.”

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# DC-networks

- Anonymous communication networks with unconditional sender and recipient untraceability

- Though simple and elegant, there are limitations

- Collisions, eg when 2 cryptographers paid

- Disruption, eg malicious messages

- Complexity, eg pairwise shared secrets

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# DC-networks

There is further research and prototypes available!

- [Paper on implementing DC as protocol](https://fahrplan.events.ccc.de/congress/2007/Fahrplan/attachments/981_ccc-paper.pdf)

- [Paper on Verdict](https://dedis.cs.yale.edu/dissent/papers/verdict-abs/)

- [Paper on Dissent](https://dedis.cs.yale.edu/dissent/)

- [Herbivore](http://www.cs.cornell.edu/people/egs/herbivore/documentation.html)

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## I think DC solves a real life problem.

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      Did someone in your group pay for your drinks, or some rando?

(While respecting everyone's right to make an anonymous payment)

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### I've been getting into hardware recently.

And I build a device for that.

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.no-bullets[
      - 📧 mail@lislis.de
      - 🐘 [@lislis@toot.cat](https://toot.cat/@lislis)
      - 🐙 || 🦊 lislis
      - 📽 [//lislis.de/talks/nand-to-dinner](https://lislis.de/talks/nand-to-dinner)
      - 💽 [//github.com/lislis/nsaoryou](https://github.com/lislis/nsaoryou)]