## A Shallow Dive into Private-Key Encryptions

We have the illusion that, as long as the key exchange was done securely, Private-Key, also known as Symmetric Cryptography, is solidly safe; if we ever introduce Public-Key or Asymmetric Cryptography to exchange private keys, then we are unbreakable.…

## Maurice Wilkins & DNA

Maurice Wilkins was one of the key scientists involved in the discovery and verification of the structure of DNA. Wilkins began investigating DNA after working on radar screens and the Manhattan Project during World War II. Like many scientists, he was worried the Nazis could develop nuclear weapons, and was…

## Oysters Bring Sea to Chicago

This is a translated version. Read the original one by Ent. In 1954, biologist F.A. Brown dug a batch of oysters from the Connecticut Shore. Knowing the oysters’ tide-relating behaviour, the biorhythm researcher brought them to an underground aquarium in Chicago thousands of miles away, hoping for a new…

## 【笔记】简单数论函数集合

Intro 咕了一年的集合。NOIp 内容。 （实际上只讲了两个函数） 常见数论函数 $\epsilon(n)=[n=1]$$1(n)=1$$id_k(n)=n^k$$I(n)=id_1(n)=n$$\sigma_k(n)=\sum\limits_{d|n}d^k$$\varphi(n)$$\mu(n)$ 欧拉函数 $\varphi(n)$ Definition $\varphi(n)$ 等于小于等于 $n$ 且与 $n$ 互质的正整数个数，即 \varphi(…