Cryptography Survey.

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Presentation transcript:

Cryptography Survey

Problem: How would you send a message over an unsecure communication channel? NECACELTAS

Problem: How would you play poker over the internet?

Cryptography vocabulary Plaintext-preencryption text Ciphertext-text after it has the encryption Encryption-function from plain text to ciphertext Decryption-function from ciphertext to plaintext Key- object which allows encryption/decryption

Caesar’s Cipher NECACELTAS

Caesar’s Cipher RIGEGIPAEX

Substitute each letter with the one 4 ahead in the alphabet. This can augmented by allowing various shifts How is it cracked? Try every key

Substitution How is it cracked? a b c d e f g h i j k l m n o p q r s t u v w x y z t h o m a s j e f r n b c d g i k l p q u v w x y z Letter Frequency a 8.167% b 1.492% c 2.782% d 4.253% e 12.702% f 2.228% g 2.015% h 6.094% i 6.966% j 0.153% k 0.772% l 4.025% m 2.406% n 6.749% o 7.507% p 1.929% q 0.095% r 5.987% s 6.327% t 9.056% u 2.758% v 0.978% w 2.360% x 0.150% y 1.974% z 0.074% How is it cracked?

Vigenere Cipher theanswerstotheexam facadefacadefacadef Letter Frequency a 8.167% b 1.492% c 2.782% d 4.253% e 12.702% f 2.228% g 2.015% h 6.094% i 6.966% j 0.153% k 0.772% l 4.025% m 2.406% n 6.749% o 7.507% p 1.929% q 0.095% r 5.987% s 6.327% t 9.056% u 2.758% v 0.978% w 2.360% x 0.150% y 1.974% z 0.074% facadefacadefacadef yhgaqwbetswsyhgeaer How is it cracked?

One time pad theanswerstotheexam theveryverysecretke moivrjuzvjrgxjviqkq How is it cracked?

Claude Shannon Decided that the security of the system should depend only on the key Proved that one-time-pad with random key is completely secure

Early 20th Century “Gentlemen don't read each other's mail.”

Symmetric Key

Asymmetric key

RSA plaintext: t encryption key: n, e decryption key: n, d

RSA Choose large primes p and q. Let n=pq

Example of RSA

Suppose we want to encrypt 5

Signing documents I’m Spartacus I’m Spartacus

Signing documents I’m Spock (I’m Spock)^d mod n ((I’m Spock)^d mod n)^e mod n I’m Spock

RSA How is it cracked?

AES Symmetric encryption process used in most transactions Approved by NSA for “Top Secret” documents

The Future Quantum Cryptography

Typical Transaction Give me the Amazon key Here it is, signed by us Lets use this AES key

Mental Poker What do we need?

Mental Poker Agree upon a set of strings to represent the deck

Mental Poker Player 1 encrypts every card with key A and shuffles Player 2 encrypts every card with key B and shuffles

Mental Poker Player 1 decrypts key A from all the cards and encrypts each one with a distinct key (A1,A2 etc) Player 2 decrypts key B from all the cards and encrypts each one with a distinct key (B1,B2 etc)

Mental Poker When Player 1 agrees that Player 2 should be able to see a card, they hand over the appropriate key