1. Cryptography The science of writing in secret code

2. The Science of Writing In Secret Code Cryptography is an ancient art - first documented use of cryptography in writing dates back to circa 1900 B.C. when an Egyptian scribe used non-standard hieroglyphs in an inscription New forms of cryptography came soon after the widespread development of computer communications

3. Secure Communication Crypto is the secure communication in the presence of third parties (adversaries) Generally: about constructing and analyzing protocols that overcome such adversaries MAIN GOAL: SECURITY!

4. DISCIPLINES Modern crypto intersects disciples of Math, Computer Science, and Electrical Engineering APPLICATIONS: ATM cards, computer passwords, electronic commerce, etc. Related to various aspects in information security such as data confidentiality, data integrity, authentication

5. Specific Security Requirements Authentication: process of proving one’s identity Privacy/confidentiality: ensuring that no one can read the message except the intended receiver Integrity: assuring the intended receiver that the original message has not been altered in any way Non-repudiation: mechanism to prove that sender really sent the message

6. Cryptographic Schemes Initial unencrypted date is referred to as plaintext It is then encrypted into ciphertext Then decrypted into usable plaintext PLAINTEXTCIPHERTEXTPLAINTEXT

7. Types of Cryptography Secret Key Cryptography (SKC) Public Key Cryptography (PKC) Hash Functions

8. Crypto

9. SECRET KEY ENCRYPTION Also known as private key & symmetric key

10. Secret Key Encryption

11. PUBLIC KEY ENCRYPTION

12. Public Key Encryption

13. Why Three? Each scheme is optimized for some specific applications Secret Key Cryptography is suited for encrypting messages as it provides privacy and confidentiality Public Key Cryptography is ideal for non- repudiation and user authentication Hash functions ensure data integrity

14. Caesar Cipher Roman ruler Julius Caesar used a very simple cipher for secret communication Involves the use of a “displacement” concept Caesar cipher is the simplest to solve, since there are only 25 possible combinations

15. Caesar Cipher Outside wheel: The Alphabet Inner wheel: can be rotated so that any letter on one wheel can be aligned with any letter on the other wheel - The inner wheel becomes the key

16. CAESAR CIPHER

17. A lock is only as strong as its weakest link