Classical Ciphers Cryptography Lecture 1 Chantilly Academy Poorvi
- Slides: 15
Classical Ciphers Cryptography Lecture 1: Chantilly Academy Poorvi Vora Department of Computer Science George Washington University
Cryptography Why might one need cryptography? 9/16/2020 Chantilly Academy Crypto Lecture 1: Spring 07 2
What is a cryptosystem? A cryptosystem consists of: • • • All messages: called plaintext All encrypted messages: called ciphertext A set of all keys A procedure for encryption A procedure for decryption 9/16/2020 Chantilly Academy Crypto Lecture 1: Spring 07 3
Caesar Cipher A B C D E F G H I J d m n e f g h i j k l K AN EYE FOR AN EYE dq hbh iru dq hbh Trivial to break 9/16/2020 Chantilly Academy Crypto Lecture 1: Spring 07 5
Shift Cipher Key A B C D E F 0 a b c d e f 1 b c d e f g 2 c d e f g h 3 d e f g h i 4 e f g h i j 9/16/2020 Chantilly Academy Crypto Lecture 1: Spring 07 6
Encrypt your own messages • Choose a key • Choose a short message for the person to your right. • Use the scratch paper to encrypt the message using the table and the key • Write the encrypted message on one side of an index card. Write the key you used on the other. • Give it to the person. 9/16/2020 Chantilly Academy Crypto Lecture 1: Spring 07 7
Decrypt your messages • If you got a message, decrypt it, using the key and the table • If not, decrypt: rfym nx httq using key: 5 9/16/2020 Chantilly Academy Crypto Lecture 1: Spring 07 8
Vigenère Cipher The key used for each symbol is different. For example: AN EYE FOR AN EYE BA BA BLACK SHEEP (Here: A=0, B=1, C=2, etc. ) bn fyf qot k…. 9/16/2020 Chantilly Academy Crypto Lecture 1: Spring 07 9
Vigenère Cipher on bits 01011101 message 9/16/2020 Chantilly Academy Crypto Lecture 1: Spring 07 10
Encrypt with Vigenère Cipher Use a coin to generate the bits of the key. Encrypt the following string: 01001011 Encrypted message on index card, key on back, pass it to person next to you 9/16/2020 Chantilly Academy Crypto Lecture 1: Spring 07 11
Decrypt the message given to you using the key on the back of the card 9/16/2020 Chantilly Academy Crypto Lecture 1: Spring 07 12
HW Assignment Decrypt the following texts: – etarq tqemu encrypted using the shift cipher – hjko me rtds encrypted using the Vigenère Cipher One is impossible to break without knowing the key. Which one? Why? 9/16/2020 Chantilly Academy Crypto Lecture 1: Spring 07 13
Permutation Cipher x 1 2 3 4 5 (x) 3 2 5 1 4 x 1 2 3 4 5 -1(x) Encrypt: canwegohomenow 9/16/2020 Chantilly Academy Crypto Lecture 1: Spring 07 14
Special Permutation Cipher perhaps the oldest known cipher classisboringtoday ciidlsnaabgysotrsrox What was the permutation? History 9/16/2020 Chantilly Academy Crypto Lecture 1: Spring 07 15
- Poorvi vora
- Roger strittmatter
- Cryptography techniques
- 01:640:244 lecture notes - lecture 15: plat, idah, farad
- Guide to codes and ciphers
- Modern symmetric key ciphers
- Is playfair cipher monoalphabetic
- Modern block cipher in cryptography
- Random alphabet chart
- Des
- Traditional ciphers
- Kasiski examination
- Atbash code
- Use rail fence cipher. pt:- "meet me at the park"
- Drive ppt
- Lucifer cipher