Cryptography

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Cryptography is the practice and study of techniques for secure communication in the presence of adversaries. It involves constructing and analyzing protocols that prevent third parties from reading private messages. Modern cryptography intersects disciplines of mathematics, computer science, and electrical engineering. Core concepts include encryption, decryption, ciphers, and keys. Cryptography is used in digital signatures, secure web browsing (HTTPS), authentication, and blockchain technologies.

History

The earliest known use of cryptography is in non-standard hieroglyphs carved in ancient Egypt. The Greeks used the 0, a transposition cipher. Around 100 BC, Julius Caesar employed the 1, a simple substitution cipher shifting letters by three places. During the Renaissance, polyalphabetic ciphers like the 2 emerged. The development of radio communications in the 20th century led to mechanical cipher machines, most notably the German 3. Allied cryptanalysts, including Alan Turing, successfully broke Enigma, contributing to the birth of modern computing.

The post-war era saw the publication of Claude Shannon’s Communication Theory of Secrecy Systems (1949), which laid the mathematical foundations of cryptography. In 1976, Whitfield Diffie and Martin Hellman introduced 0. Shorty after, the 1 algorithm was developed, enabling secure key exchange over insecure channels. The late 20th century brought the 2 (AES), adopted by the U.S. government.

Modern Cryptography

Modern cryptographic systems fall into two broad categories: 0s (e.g., AES, ChaCha20) where the same key is used for encryption and decryption, and 1s (e.g., RSA, elliptic-curve cryptography) using a public–private key pair. Cryptographic hash functions (e.g., SHA-256) and digital signatures are also essential for data integrity and non-repudiation. The field continues to evolve with the advent of quantum computing, which threatens many current public-key schemes, driving research into 2.