Cryptography Dr. X.

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Presentation transcript:

Cryptography Dr. X

Outline What is cryptography? Ceasar Cipher Public key cryptography

What is cryptography? Cryptography or cryptology (from Greek κρυπτός kryptós, "hidden, secret"; and γράφειν graphein, "writing", or -λογία -logia, "study", respectively[1]) is the practice and study of techniques for secure communication in the presence of third parties called adversaries. (from Wikipedia) https://www.khanacademy.org/computing/computer- science/cryptography/crypt/v/intro-to-cryptography

Types of cryptography Symmetric: encryption methods in which both the sender and receiver share the same key Ex. Ceasar Cipher What are the pros and cons? Asymmetric/public key: the public key may be freely distributed, while its paired private key must remain secret. In a public-key encryption system, the public key is used for encryption, while the private or secret key is used for decryption. Diffie-Hellman RSA

Terminology Key Public Private Encryption key Cipher Plain text

One time pad https://www.khanacademy.org/computing/computer- science/cryptography/crypt/v/one-time-pad What are the pros and cons of this type of encryption?

Public key encryption

Public key encryption Choose p = 3 and q = 11 Compute n = p * q = 3 * 11 = 33 Public key is (e, n) => (7, 33) Private key is (d, n) => (3, 33) The encryption of m = 2 is c = 27 % 33 = 29 The decryption of c = 29 is m = 293 % 33 = 2

Modulo Operation % Remainder of division Ex. 5 % 4 = 1 If I was trying to divide 5 with 4, 4 can fit in 5 once and the remainder is 1 Practice: 100 % 3 35 % 4 18 % 19

Crypto exercise Symmetric key cryptography with Ceasar cipher Asymmetric key crypto with RSA

Why do we need cryptography? Internet is an open medium Confidentiality Integrity…