The secrets of cryptography

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The Secrets of Cryptography Christopher Riley PHP South Coast, 2016 1

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Introduction

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Cryptography is HARD 2

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Historic ciphers

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The ceasar shift

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The ceasar shift 3

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The substitution cipher

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The substitution cipher 4

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The substitution cipher: possible keys 403,291,461,126,605,635,584,000,000 5

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The substitution cipher: statistics 6

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The substitution cipher: frequency analysis 7

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Vigenère cipher

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The Vigenère cipher 8

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The Vigenère cipher 9

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The Vigenère cipher 10

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Breaking the Vigenère cipher

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Breaking The Vigenère cipher 11

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Breaking The Vigenère cipher 12

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Enigma

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Enigma 13

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Enigma 14

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Breaking Enigma 15

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Modern ciphers

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Modern cryptography • Confidentiality 16

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Modern cryptography • Confidentiality • Key exchange 17

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Modern cryptography • Confidentiality • Key exchange • Identity 18

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Modern cryptography • Confidentiality • Key exchange • Identity • Authentication 19

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Modern cryptography • Confidentiality • Key exchange • Identity • Authentication • Random number generation 20

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Symmetric ciphers

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Stream ciphers

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A5/1

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A5/1: implementation diagram 21

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A5/1: register clocking 22

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Stream cipher weaknesses • Keys must not be reused 23

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Stream cipher weaknesses • Keys must not be reused • Easy for an attacker to modify a message 24

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Stream cipher weaknesses • Keys must not be reused • Easy for an attacker to modify a message • Hard to partially decrypt messages 25

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Block ciphers

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AES

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AES: 1 round • Substitute Bytes • Shift Rows • Mix Columns • Add Round Key 26

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AES: Substitute Bytes 27

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AES: Shift Rows 28

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AES: Mix Columns 29

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AES: Add Round Key 30

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Modes of operation

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ECB

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ECB 31

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ECB: the ECB penguin 1By Larry Ewing [email protected] with The GIMP 32

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CBC

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CBC 33

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CTR

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CTR 34

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GCM

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GCM 35

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Asymetric ciphers

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Public key cryptography

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RSA

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RSA • (me)d ≡ m (mod n) 36

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RSA • (me)d ≡ m (mod n) • c ≡ me (mod n) 37

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RSA • (me)d ≡ m (mod n) • c ≡ me (mod n) • cd ≡ (me)d ≡ m (mod n) 38

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Identity verification

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RSA: Message signatures • (md)e ≡ m (mod n) • s ≡ md (mod n) • se ≡ (md)e ≡ m (mod n) 39

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Implementing Cryptography

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Implementing Cryptography • Don’t 40

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Implementing Cryptography • Don’t • Use existing implementations 41

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Implementing Cryptography • Don’t • Use existing implementations • Bring in an expert 42

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Implementing Cryptography in PHP

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Implementing Cryptography in PHP • Halite + libsodium • https://github.com/paragonie/halite 43

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Implementing Cryptography in PHP • Halite + libsodium • https://github.com/paragonie/halite • Defuse PHP encryption • https://github.com/defuse/php-encryption 44

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Further reading • Simon Singh - The code book • http://simonsingh.net/The_Black_Chamber 45

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Further reading • Simon Singh - The code book • http://simonsingh.net/The_Black_Chamber • Bruce Schneier • https://www.schneier.com 46

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Further reading • Simon Singh - The code book • http://simonsingh.net/The_Black_Chamber • Bruce Schneier • https://www.schneier.com • https://github.com/gilfether/phpcrypt 47

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Thanks • @giveupalready • https://github.com/carnage • https://joind.in/talk/d31d1 48

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Cipher Challenge • The cipher challenge is now closed, but if you want to have a go anyway, the main text is now here • http://tiny.cc/0qq6by • @phpyorkshire 49