Ciphers All

A cipher is an algorithm or mathematical function used to encrypt plaintext into an unreadable format (ciphertext) and decrypt it back again. Unlike a “code,” which replaces whole words or phrases with secret symbols, a cipher operates on the level of individual letters, bits, or small blocks of data.

Historically, all ciphers are built using two foundational operations: substitution (replacing characters) and transposition (scrambling their order). Fundamental Types of Classical Ciphers

Before computers, people used pen-and-paper “classical ciphers” to protect communications. They fall into a few primary categories defined by the American Cryptogram Association: 1. Substitution Ciphers

These replace letters with other letters, numbers, or symbols while keeping the original sequence intact.

Secret Language: Cryptography & Secret Codes | Exploratorium