Encryption
Ancient

One of the earliest forms of encryption is symbol replacement, which was first found in the tomb of Khnumhotep II, who lived in 1900 BC Egypt. Symbol replacement encryption is “non-standard,” which means that the symbols require a cipher or key to understand. This type of early encryption was used throughout Ancient Greece and Rome for military purposes. One of the most famous military encryption developments was the Caesar cipher, which was a system in which a letter in normal text is shifted down a fixed number of positions down the alphabet to get the encoded letter. A message encoded with this type of encryption could be decoded with the fixed number on the Caesar cipher.

Around 800 AD, Arab mathematician Al-Kindi developed the technique of frequency analysis – which was an attempt to systematically crack ciphers, including the Caesar cipher. This technique looked at the frequency of letters in the encrypted message to determine the appropriate shift. This technique was rendered ineffective after the creation of the polyalphabetic cipher, described by Al-Qalqashandi (1355–1418) and Leon Battista Alberti (in 1465), which incorporated different sets of languages. In order for frequency analysis to be useful, the person trying to decrypt the message would need to know which language the sender chose.
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