Autokey Ciphers Group Members Talha Zameer Fiaz Ashraf

Autokey Ciphers

Group Members: • • Talha Zameer Fiaz Ashraf M. Bilal Umair Minhas Hammad Hassan Zeeshan Shabbir Mubashar Hassan

What is AUTOKEY Chiper? ? • An autokey cipher (also known as the autoclave cipher) is a cipher which incorporates the message (the plaintext) into the key.

History • The Autokey Cipher is almost identical to the Vigenère Cipher – only it’s more secure • It was first invented by Girolamo Cardano and was made more secure by Vigenère(The Vigenère cipher is a method of encrypting alphabetic text by using a series of different Caesar ciphers based on the letters of a keyword )

Encryption • Start by choosing plain text and a keyword of any length • Write the keyword over the plain text, and then immediately after the keyword, begin writing the plain text Key: RESTAURANTMEET Plaintext: MEETMEFORLUNCH

Encryption II • After you assign a keyword to all of the plain text, you are going to need a tabula recta.

Encryption III • In order to encrypt plain text, you locate the row with the first letter to be encrypted, and the column with the first letter of the key. The letter where the line and column cross is the ciphertext letter

Example • Key: RESTAURANTMEET • Plaintext: MEETMEFORLUNCH Cipher letter = D Continue this for the rest of the message.

Example, cont. • You should now have this encrypted text: Key: RESTAURANTMEET Plaintext: MEETMEFORLUNCH Ciphertext: DIWMMYWOEEGRGA • Now, if someone gave you the message “DIWMMYWOEEGRGA”, would you know how to decrypt it?

Decryption • Assuming the buddy who sent you the secret message likes you, he probably message sent you the keyword, too. • With a key of RESTAURANT and ciphertext DIWMMYWOEEGRGA, find the key characters in the top-column header and the ciphertext characters in the table

Example, Cont. Key: R ESTAURANTMEET Ciphertext: D IWMMYWOEEGRGA Plaintext = M Repeat! The secret message: “Meet me for lunch”.

Why Study Cryptanalysis? • Study of cryptanalysis gives insight into all aspects of crypto • Gain insight into attacker’s mindset – “black hat” vs “white hat” mentality • Cryptanalysis is more fun than cryptography – Cryptographers are boring – Cryptanalysts are cool • But cryptanalysis is hard.