AMITY UNIVERSITY ONLINE
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This document provides an overview of cryptography concepts including: - A brief history of cryptography from substitution ciphers to the Enigma machine. - Cryptography uses algorithms and keys to encrypt plaintext into ciphertext and decrypt ciphertext back to plaintext. - Symmetric and asymmetric cryptography use different algorithms like the Caesar cipher or public/private key pairs to secure communications.
AMITY UNIVERSITY ONLINE
- 1. CYBER SECURIT Lecture – 8 Faculty Name : Professor Seema Sahai
- 2. Cryptography
- 3. Objectives • Describe the history of cryptography • Describe symmetric and asymmetric cryptography algorithms • Explain public key infrastructure (PKI) • Describe possible attacks on cryptosystems
- 4. Understanding Cryptography Basics • Cryptography is the process of converting plaintext into cipher text – Plaintext: readable text (also called clear text) – Cipher text: unreadable or encrypted text • Cryptography is used to hide information from unauthorized users • Decryption is the process of converting cipher text back to plaintext
- 5. History of Cryptography • Substitution cipher – Replaces one letter with another letter based on a key – Example: Julius Caesar’s Cipher • Used a key value of 3 • ABCDEFGHIJKLMNOPQRSTUVWXYZ • DEFGHIJKLMNOPQRSTUVWXYZABC
- 6. History of Cryptography (continued) • Cryptanalysis studies the process of breaking encryption algorithms • When a new encryption algorithm is developed, cryptanalysts study it and try to break it – Or prove that it is impractical to break it (taking much time and many resources)
- 7. Enigma • Used by the Germans during World War II – Replaced letters as they were typed – Substitutions were computed using a key and a set of switches or rotors – Image from Wikipedia
- 8. Steganography • The process of hiding data in plain view in pictures, graphics, or text – Example: changing colors slightly to encode individual bits in an image • The image on the left contains the image on the right hidden in it
- 9. Algorithms • An algorithm is a mathematical function or program that works with a key • Security comes from – A strong algorithm—one that cannot be reversed without the key – A key that cannot be found or guessed
- 10. Keys (not in textbook) • A sequence of random bits – The range of allowable values is called a key space • The larger the keys pace, the more secure the key – 8-bit key has 28 = 256 values in keys pace – 24-bit key has 224 = 16 million values – 56-bit key has 256 = 7 x 1016 values – 128-bit key has 2128 = 3 x 1038 values