Cryptography

Monoalphabetic ciphers use a set of rules to replace each letter with another consistently, making them susceptible to brute force attacks that try every kind of replacement. While more complex ciphers can transform text in less obvious ways, because certain letters are used more often than others, an analysis of letter frequency may reveal patterns that help uncover the rules that make up a cipher.

From the Greek word for "hidden writing," scytales were batons around which a long strip of leather or parchment was wrapped before messages were written. Recipients needed a scytale of the correct width to encircle received ribbons and reveal the message. Members of the Navajo Nation created a code that remained unbroken throughout its use in World War II.

This tool provides users with customizable protocols, including Caesar, Affine, and Vigenère ciphers, to hide messages in transformed text and convert them back into legible formats. Mechanisms are also available to convert text into other communication languages, such as Morse code and URL encoding.

Using settings selected from a series of rotors and a plugboard that let operators swap letters with any of their choosing, the machine lit up the output letter for each letter typed. While this system could generate messages requiring any of 150 quintillion potential keys, the machine's reflector never encrypted a letter as itself, providing an entry point for exploiting the system.

Made by American artist Jim Sanborn, the sculpture consists of copper plates engraved with messages written with the 26 letters of the Latin alphabet and question marks. The last of the four messages was decrypted in 2025, but the piece remains of interest to cryptoanalysts.

Established by the National Institute of Standards and Technology in 2001, the protocol transforms plaintext into ciphertext using multiple rounds of processing, including substitution, transposition, and mixing. Larger keys undergo more rounds to produce 16-byte blocks of scrambled data, with 256-bit AES keys taking 3.31 × 10⁵⁶ years to decrypt via brute force.

This form of asymmetric cryptography uses mathematical functions that rely on the product of two large prime numbers. Because traditional computers struggle to factor such products, obtaining the private keys needed to decrypt messages becomes effectively impossible. This security can be reinforced with larger prime numbers, though this makes encryption more computationally taxing.

In 1994, Peter Shor introduced an algorithm that showed a quantum computer could efficiently factor the product of two very large prime numbers, undermining the mathematics that makes RSA so secure. While using larger keys can delay the decryption time of quantum computers, this solution increases the time it takes to encrypt data, which may become impractical.

Seeing the potential of this technology, some governments and malicious actors have already started storing encrypted data, in the hopes that quantum computers within the next 10 to 20 years will be able to decrypt it. As of 2022, the National Institute of Standards and Technology has selected four algorithms for inclusion in a quantum-resistant encryption standard.

Published in 1977 by Whitfield Diffie and Martin Hellman, the system involves two parties combining each of their unique private keys with a public key using a mathematical function. The combinations are exchanged and mixed to establish a common key to third party can determine. The Diffie-Hellman system underlies the encryption protocols for internet traffic.