# Using math to decrypt messages

Alright. If you’ve been watching videos online, you might have heard about cryptography, which is where you encrypt messages using certain “ciphers”. There’s many ciphers that can be used, such as the Caesar Cipher, the Polyalphabetic Cipher, the Polybius Square, and many others. Cryptography has been a very important part of history, dating all the way back to 1900 BC, when unusual hieroglyphic writing was discovered in an Egyptian tomb.

Now, how would we decrypt these encryptions?

The first and simplest cipher is the Caesar Cipher. Named after Gaius Julius Caesar, this cipher involves shifting every letter in the message a certain number of times, which is determined by the key, chosen before the message is sent. The best way to decrypt this is to simply test out every key, since there are really only 26 possible keys, from A to Z.

The next cipher is the Polyalphabetic Cipher. This cipher involves using a word as a key instead of one letter, which increases the number of encrypted messages, but the only problem is the repetition. To decrypt a Polyalphabetic Cipher, only the key’s length is needed. For example, if the key is a word with five letters (e.g. “SNAKE”), you could find the letter frequency of the letters, and comparing different frequencies can give results.

The Polybius Square is a very simple method of encryption. It takes every letter from A to Y and it turns it into a pair of numbers, ranging from 1 to 5 (or 0 to 4 in some cases). It’s very simple, as the grid is usually in either row to row, column to column or spiral, and even if the number scheme is YX instead of XY, they can easily be tested.

Now we get to the first interesting one. The Playfair Cipher is a rather interesting one, as you need a cipher word to encrypt the message, but it’s very complicated. You place the word at the top of the 5 by 5 grid, with repeated letters being removed. For example, the word “example” would become “exampl”, and “chocolate” would become “cholate”. Next, the encryptions use pairs of letters, and every two letters are plotted on the graph, with the other two corners becoming the new letters. This cipher is extremely difficult to crack, but with enough trial and error, this cipher may be decrypted, with an emphasis on the may. It is very improbable, and

The most secure cipher, however, is the one-time pad. This monster of a cipher is as unbreakable as a 100-meter wall of titanium, and even better, impossible. The reason why the one-time pad is so secure is because the original message could be anything, and the key could be anything. For a 20-letter message, even with just letters, there are almost 2*10^28 possible combinations, which is 20 octillion. Even for five digits, there are 11.8 million possible combinations. Even if we were limited to the letters A-J (10 letters), that’s 100,000 combinations, which is possible, but very time consuming. Even then, we wouldn’t be able to determine which combination of letters is the correct one.

This is why the one-time pad is so good, but you have to be careful. If a key is repeated, the intercepted messages now share a feature, and by using an extremely fast program and maybe a supercomputer, a one-time pad (in this case, it’s a two-time pad) cipher can be decrypted. It may take a long time, but it could be achieved.

Cryptography has an extremely wide range of ciphers, independent of whether or not they are secure. Huk pm fvb jhu ylhk aopz, aohur fvb zv tbjo mvy ylhkpun hss aol dhf aoyvbno. Aopz wvza avvr tl h jvuzpklyhisf svun aptl, huk aohur fvb zv tbjo.

This post was one of my hardest posts I’ve ever written, and it feels so good to finally get it out. Thank you for supporting me to this day (to my 10 followers, and those non-followers that are somehow reading this), and I will see you… in two weeks.

Or before. I don’t know.

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