When I was in fifth grade, my friend and I developed a code where we replaced each letter of the alphabet with a number. We were able to write to each other in secret and if anyone were to ever find our notes, they wouldn’t be able to decode it. Our ability to communicate without anyone understanding what we were writing was a lot of fun.
With the ever-growing data footprint and its exchange globally through the usage of the internet, the protection of data and privacy has become very important to many people. Cryptography plays a crucial role in communication, maintenance and management of information.
The word “cryptography” is made up of ‘crypto’ (secret) and ‘graph’ (writing). The algorithm to convert plain text to a text that no one can understand is called ‘cipher.’ Encryption is when a piece of text or set of numbers is converted into another piece of text/set of numbers that no one understands and the reverse of this is called decryption. When each letter in the alphabet is encrypted according to a letter that is, let’s say, 10 letters away, it is called the Caesar Cipher, or shifter. In this example, A would equal K, B would equal L, C would equal M, and so on, and once you get to Q, which is equal to Z, you start over, with R equaling A, S equaling B, etc. This type of cryptography is easy to decipher.
When each letter is simply replaced with another letter, it is called the Substitution Cipher. To decode this, one must first understand the English language. “E” is the most common letter used in English. So, if someone was looking at a set of encrypted text and the most common letter was, for example, “B,” the person could try to replace every “B” with “E” and use common letters that way.
Columnar Transposition Cipher is when each character of a sentence is written in a grid left to right. There is a keyword given and with each letter, there is a number corresponding with the letter and these numbers are put in alphabetical order. For example, if our keyword was “BANANA,” our corresponding numbers would be ‘1’ for the first “A,” ‘2’ for the second “A,” ‘3’ for the third “A,” ‘4’ for the “B,” ‘5’ for the first “N” and ‘6’ for the second “N.” Since the keyword has 6 letters, our grid has 6 columns. Now let’s say that our sentence is “BANANAS TASTE GOOD.” We would put each letter in a box in the grid from left to right, top to bottom. Since our sentence has 16 letters and there are 6 columns, our last row is going to have 2 blank spaces. We can just put an “X” in the leftover boxes. Now, we look at the letter that corresponds with ‘1’ which would be “A.” Under “A” are the letters “A,” “T” and “O.” Under ‘2’ (the second “A”) are the letters “A,” “S” and “D.” Under ‘3’ are the letters “A,” “E” and “X.” Once we get all the letters under the corresponding numbers, our encrypted code will look like this: ATO / ASD / AEX / BSG / NAO / NTX with the slash marks indicating a new column. Removing the slash marks, our final encrypted code will look something like this: ATOAS DAEXB SGNAO NTX and for someone to decode the encrypted text, they would need the keyword (you can even scramble it to make it harder for them).
The Enigma Rotor provides an encryption method of shifting the substitution key for every character in the text. For example, the Enigma Roto can have AAAA translated into PEZK. Criss-crossing the wires and rotating rotors in different ways provides a large number of combinations, which makes it even harder to decrypt. With the arrival of computers, encryption technologies use the help of software, making it stronger. IBM, a computer hardware company, came up with the Data Encryption Standard (DES) in 1977, defining the technology to encrypt and protect things like passwords and personal identifiers. It used binary keys that were 56 bits (making it 2 to the 56th power, or 2 multiplied by itself 56 times) long to encrypt. It resulted in 72 Quadrillion (72 * 1015) combinations. At that time, it was not possible to crack this using the available computing resources.
In 2001, the Advanced Encryption Standard (AES) was published. This encryption standard is designed on larger binary key sizes (128 bits, 192 bits, 256 bits) to make any attacks futile. AES divides data into 16-byte blocks and applies a series of permutations and other complex mathematical operations to encrypt the text. The reason for not going to a much higher binary key size is to make it secure without compromising the performance.
Encryption and decryption use different techniques based upon the way the keys are exchanged. If the encrypting keys are sent to the recipient over the internet, there is a risk of being intercepted. This problem is answered with the help of public keys and private keys. This can be explained with the example of lockers. Let’s say Person A wants to deliver a piece of information to Person B without anyone else getting to it. Person A can slip the piece of information by using a public key and opening a hole in Person B’s locker. No outsider can get the piece of information Person A delivered because their hands are too big to fit inside the hole and also, they don’t have Person B’s private key. Person B can use their private key to open their entire locker and get the piece of information. This is mathematically done by the One Way function (aka the mode function). The Diffie-Hellman key exchange is based upon this, where the secret exponent (basically the private key) of the sender and the receiver are used for encryption and decryption. This is an example of Symmetric Encryption.
Asymmetric Encryption is where a pair of keys is used to encrypt and decrypt. If Key A encrypts the message, Key B is used to decrypt, if Key B encrypts the message, Key A is used to decrypt. (Which means, in Symmetric Encryption, Key A is used to decrypt and encrypt and Key B does not exist.) This is used to create a matching key pair, keeping one key public and making another a secret (or private). This technique is used in the famous RSA (named after its inventors Ronald Rivest, Leonard Shamir and Adi Adleman [RSA is also known as Rivest-Shamir-Adleman]) technology.
Cryptography plays a key role in keeping us safe when we browse the internet, exchange emails, shop online, undergo credit card transactions, keeping our online school assignments private, keeping our school records private and basically everything.
Vaageesha Das is a 10th grader at Morgantown High School. Today’s information comes from: https://www.youtube.com/watch?v=jhXCTbFnK8o; https://en.wikipedia.org/wiki/Diffie%E2%80%93Hellman_key_exchange; https://en.wikipedia.org/wiki/RSA_(cryptosystem); https://crypto.interactive-maths.com/columnar-transposition-cipher.html.
