Cryptography

Simon Schug

May 2020

Introduction

What is Cryptography?

Cryptography is the art & science of keeping messages secure 🔒️

Crypto + Graphy = Secret + Writing
  • Plaintext: The secret message.
  • Ciphertext: The encrypted message.
  • Encryption: Disguising a message to hide its contents.
  • Decryption: The process of turning ciphertext back into plaintext.

Who needs Encryption?

👩‍⚕️️🕵‍👩‍💻️👮️🏦️ 

Everyone.

What can it be used for?

Cryptography is not only used for sending secret messages.

  • Privacy / Confidentiality ✉️
  • Authentication 🗝️
  • Anonymity 🕵‍
  • Signature / Certification 🔏️

Mass Surveillance

“If you have nothing to hide, you have nothing to fear.”

crypto-wars

Governments are trying to limit access to cryptography.

Cypherpunks

We the Cypherpunks are defending our privacy with cryptography.

lightsaber

NSA

Quiz-Time!

Classical Ciphers

Caesar Cipher caesar

Julius Caesar used a form of substitution cipher
to send messages to his troops.

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
D E I K O R S T W Y C

Cipher Wheel

Make your own Caesar cipher 🖌️

Permutation Cipher

permutation

Can you decipher the message in this challenge?

Vigenère Cipher

alphabet-circle

T19 H7 E4 S18 E4 C2 R17 E4 T19 M12 E4 S18 S18 A0 G6 E4
P15 A0 S18 S18 W22 O14 R17 D3 P15 A0 S18 S18 W22 O14 R17 D3
I H

Cryptanalysis

Code

A code is a system of rules to convert information (letters, sounds, images) into another form of representation.

01011100010101001 10100011011010110 01101100101010001 00001101001011101

qr-code

barcode

Fingerprint Challenge

fingerprint

Can you hack the password in this challenge?

  • How many combinations are there?
  • Come up with a strong password that you can easily remember
  • How strong is it? Check it

Breaking the Caesar Cipher

We have intercepted an encrypted message. Can you decrypt it?

Ogo qgm sjw s hjwllq kesjl zsucwj

letter-frequency

Quiz Time

Modern Cryptography

Public-key Cryptography

Modern cryptosystems make heavy use of public key algorithms.

public-private-key

Key Exchange

The Diffie–Hellman key exchange algorithm allows to securely exchange keys over a public channel.

Diffie-Hellman

Contact Tracing