Cryptography

Cryptography, or cryptology, is the practice and study of techniques for secure communication even when others try to interfere. It involves creating and analyzing ways to keep messages private, so only the right people can read them. Today, cryptography uses ideas from mathematics, computer science, information security, and other fields to protect information.

Before modern times, cryptography mainly meant encryption—changing readable information into confusing text that only certain people could change back. With the invention of machines in World War II and the rise of computers, these methods became more complex. They now have many uses, from online shopping to keeping passwords safe.

Modern cryptography relies heavily on mathematical theory and computer science. Special methods are designed to be very hard to break, using problems that currently cannot be solved quickly even with powerful computers. While some systems can theoretically be broken, they are considered secure because it would take too much time and effort. This balance between security and practicality is what makes modern cryptography so important in our digital world.

Terminology

The word "cryptograph" was first used in the 19th century in a story by Edgar Allan Poe called "The Gold-Bug". The word comes from Greek, where "crypton" means hidden and "grapho" means to write.

Cryptography is about making messages secret. Encryption changes normal text, called plaintext, into secret text, called ciphertext. To read the secret text again, you need a key – a special secret word or number. There are two main types of systems: symmetric, where the same key locks and unlocks the message, and asymmetric, where a public key locks the message and a private key unlocks it. Asymmetric systems are often used to share a key safely before using a faster symmetric system.

History

Main article: History of cryptography

Cryptography is the practice of creating and studying ways to send secret messages. Long ago, people used simple tricks to hide what they were writing, like switching letters or moving them around. One famous example is the Caesar cipher, used by Julius Caesar, where he shifted each letter three places forward in the alphabet.

Over time, people invented more clever ways to hide messages, such as using special wheels or machines. During World War II, teams worked hard to break codes used by enemies. Today, cryptography helps keep information safe on the internet and in computers, using math to protect secrets.

Modern cryptography

Claude Shannon helped create modern cryptography in the middle of the last century. His work used math to keep messages safe. Before this, cryptography studied language patterns. Now, it uses many parts of math, like number theory and information theory.

Today, cryptography protects all kinds of data, not just words. Computers help us make stronger codes and hide information in text, pictures, or other forms. Scientists also study how quantum physics might change future security.

Symmetric-key cryptography

Symmetric-key cryptography uses one key for both sending and receiving messages. This was the only kind of encryption until 1976. There are two types: block ciphers, which work on pieces of data, and stream ciphers, which create a steady flow of key data. Examples are the Advanced Encryption Standard (AES) for block ciphers and RC4 for stream ciphers.

Public-key cryptography

Public-key cryptography uses two keys: a public key anyone can see and a private key only the owner keeps. This helps manage keys in big networks. The idea started in 1976 by Whitfield Diffie and Martin Hellman. A common method is the RSA algorithm, made by Ronald Rivest, Adi Shamir, and Len Adleman.

Cryptographic hash functions

Cryptographic hash functions change any input into a fixed-size output, making it hard to know the original data. They help check if data is real. Examples are SHA-1 and the newer SHA-2 family, with SHA-3 being made to improve safety.

Cryptanalysis

Cryptanalysis studies ways to find weak spots in cryptographic systems. Some methods, like the one-time pad, are thought to be unbreakable when used right. Attacks can come from studying encrypted messages or mistakes in using encryption.

Cryptographic primitives

Cryptographic primitives are basic tools with certain security features. They help build more complex systems, called cryptosystems, which do things like secure messaging or digital signatures.

Cryptosystems

Cryptosystems mix primitives to create safe functions. Examples include RSA for encryption and digital signatures, and systems for safe online payments. These systems often need talk between several parties to stay secure.

Lightweight cryptography

Lightweight cryptography is made for devices with little power, like those in the Internet of Things (IoT). Algorithms such as Ascon and SPECK are built to meet these tough needs while keeping data safe.

Applications

Main category: Applications of cryptography

Cryptography helps keep information safe on the internet. It protects messages and data so only the right people can read them. Many websites use special codes, called encryption, to keep information private. For example, when you visit a website that starts with "https://", it uses encryption to keep your data safe.

Cryptography is also important for keeping passwords secret. Computers change passwords into a special code instead of storing them as they are. This way, even if someone tries to look at the password, they cannot read it. Some computer programs use encryption to protect all the data on a computer’s hard drive.

Cryptography plays a big role in cryptocurrency and new ways of managing money online. It helps make sure that only the right people can access and spend money. As technology grows, scientists are working on new ways to keep information safe even from very powerful computers called quantum computers.

Main article: Cybersecurity

Legal issues

See also: Cryptography laws in different nations

Cryptography is important for keeping secrets safe, but this can sometimes cause problems for police and government agencies. Because cryptography helps protect privacy, there have been many discussions about how it should be used and controlled.

In some countries, there are rules about using cryptography. For example, France used to have strict rules, but these have changed. Places like China and Iran still need special permission to use it. The United States allows cryptography for people to use at home but has talked a lot about sending it to other countries. In the past, the U.S. government watched the export of cryptography very closely because it was important for safety. As the Internet grew, these rules became looser, and today many people use strong cryptography every day with tools like web browsers and email.

Main article: Export of cryptography

Main article: Digital rights management

See also: Clipper chip

Main article: Key disclosure law