# Cryptography Flashcards

1

Q

Caesar cipher

A

Encrypt with x + 3

Decrypt with x - 3

2

Q

Vigenere cipher

A

Given vector responding to keyword eg. ABC is 123

Then

Hello = 8,5,11,11,14

Goes to

8+1, 5+2, 11+3, 11+1, 14+2

9,7,14,12,16

3

Q

In RSA one chooses

A

- 2 large primes p != q to form n=pq
- 2<=e<=φ(n) such that gcd(e, φ(n)) = 1

-compute 2<=s<=φ(n) such that es = 1 mod(φ(n))

e is encryption s is decryption

4

Q

Public key in RSA

A

k^{p} = (n,e)

5

Q

RSA secret key

A

K^{s} = (n,s)

6

Q

RSA encryption function

A

7

Q

RSA decryption function

A

8

Q

RSA plaintext and cipher text alphabets

A

9

Q

RSA key space

A

10

Q

Prove

A

11

Q

To send plaintext, RSA

A

-Compute c = m^{e} mod(n)

Where m is message

12

Q

To decipher c, RSA

A

Compute (by FLT and Euler’s Theorem)

13

Q

Quick way to calculate φ(n) for RSA

A

Φ(n) = (p-1)(q-1) where pq=n (primes p!=q)

14

Q

Basic principle

A

15

Q

Proof of basic principle

A