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5.  In cryptography, ciphertext is the result of
encryption performed on plaintext using an
algorithm, called a cipher.

6. Cryptography began thousands of
years ago.
Early 20th century, the invention
of complex mechanical and
electromechanical machines.

7. Throughout history, the need for secrecy
has been important.
Abu Yusuf Ya’qub ibn e Ishaaq Al-Kindi was
the first to De-Cipher an encrypted
message.

8. Historical pen and paper ciphers used in the past are sometimes
known as classical ciphers. They include:
Substitution cipher: the units of plaintext are replaced with
ciphertext (Caesar cipher)
Transposition cipher: the ciphertext is a permutation of the
plaintext (Rail fence cipher)
Polyalphabetic substitution cipher: a substitution cipher using
multiple substitution alphabets (Vigenère cipher and Enigma
machine)
Permutation cipher: a transposition cipher in which the key is
a permutation
Private-key cryptography (symmetric key algorithm): the same
key is used for encryption and decryption
Public-key cryptography (asymmetric key algorithm): two
different keys are used for encryption and decryption