Secure Communication over insecure network

Slide 1

Slide 1 text

SECURE COMMUNICATION HOW OUR LIVES DEPEND ON CRYPTOGRAPHY TEJAS BUBANE TUESDAY TALKS AT CYBRILLA

Slide 2

Slide 2 text

No content

Slide 3

Slide 3 text

Communication?

Slide 4

Slide 4 text

! Communication?

Slide 5

Slide 5 text

" ! Communication?

Slide 6

Slide 6 text

" ! Communication?

Slide 7

Slide 7 text

" ! Communication?

Slide 8

Slide 8 text

Secure? " ! Communication?

Slide 9

Slide 9 text

Secure? " ! #$ Communication?

Slide 10

Slide 10 text

Secure? " ! #$ 1. Conﬁdentiality Communication?

Slide 11

Slide 11 text

Secure? " ! #$ 1. Conﬁdentiality 2. Identity Communication?

Slide 12

Slide 12 text

PROBLEM 1

Slide 13

Slide 13 text

PROBLEM 1

Slide 14

Slide 14 text

PROBLEM 1

Slide 15

Slide 15 text

PROBLEM 1

Slide 16

Slide 16 text

PROBLEM 1

Slide 17

Slide 17 text

PROBLEM 1

Slide 18

Slide 18 text

PROBLEM 1

Slide 19

Slide 19 text

PROBLEM 1

Slide 20

Slide 20 text

PROBLEM 1 Man in the middle attack

Slide 21

Slide 21 text

PROBLEM 1 Man in the middle attack Incorrect identity

Slide 22

Slide 22 text

PROBLEM 2

Slide 23

Slide 23 text

PROBLEM 2

Slide 24

Slide 24 text

PROBLEM 2

Slide 25

Slide 25 text

PROBLEM 2

Slide 26

Slide 26 text

PROBLEM 2

Slide 27

Slide 27 text

PROBLEM 2

Slide 28

Slide 28 text

PROBLEM 2

Slide 29

Slide 29 text

PROBLEM 2 Eavesdropping attack

Slide 30

Slide 30 text

PROBLEM 2 Eavesdropping attack No Secrecy

Slide 31

Slide 31 text

E(text, key) = cipher D(cipher, key) = text cipher

Slide 32

Slide 32 text

E(text, key) = cipher D(cipher, key) = text cipher Symmetric Key Cryptography

Slide 33

Slide 33 text

E(text, key) = cipher D(cipher, key) = text cipher Symmetric Key Cryptography 1.Caesar Cipher (44 BC)

Slide 34

Slide 34 text

E(text, key) = cipher D(cipher, key) = text cipher Symmetric Key Cryptography 1.Caesar Cipher (44 BC) CYBRILLA => FBEULOOD

Slide 35

Slide 35 text

E(text, key) = cipher D(cipher, key) = text cipher Symmetric Key Cryptography 1.Caesar Cipher (44 BC) CYBRILLA => FBEULOOD 2. Vigenère Cipher (1553)

Slide 36

Slide 36 text

E(text, key) = cipher D(cipher, key) = text cipher Symmetric Key Cryptography 1.Caesar Cipher (44 BC) CYBRILLA => FBEULOOD 2. Vigenère Cipher (1553) Plaintext: ATTACKATDAWN Key: LEMONLEMONLE Ciphertext: LXFOPVEFRNHR

Slide 37

Slide 37 text

No content

Slide 38

Slide 38 text

No content

Slide 39

Slide 39 text

No content

Slide 40

Slide 40 text

No content

Slide 41

Slide 41 text

Enigma machine

Slide 42

Slide 42 text

Enigma machine Bombe

Slide 43

Slide 43 text

Enigma machine Bombe

Slide 44

Slide 44 text

E(text, pubkey) = cipher D(cipher, privkey) = text pubkey hello! cipher

Slide 45

Slide 45 text

E(text, pubkey) = cipher D(cipher, privkey) = text pubkey Public Key Cryptography hello! cipher

Slide 46

Slide 46 text

Identity Certificate Binds Identity with public key OS/Mozilla Root certificates Browser verifies signature, matches URL

Slide 47

Slide 47 text

SSL/TLS •SSL (Netscape, 1995) •TLS 1.0 (IETF 1999) •TLS 1.1 (2006) •TLS 1.2 (2008) •TLS 1.3 (2018) Cryptographic Protocol

Slide 48

Slide 48 text

TLS Handshake

Slide 49

Slide 49 text

TLS Handshake

Slide 50

Slide 50 text

ClientHello TLS Handshake Nc

Slide 51

Slide 51 text

ClientHello ServerHello TLS Handshake Nc Ns

Slide 52

Slide 52 text

ClientHello ServerHello ServerCertiﬁcate TLS Handshake Public Key (pk) Nc Ns

Slide 53

Slide 53 text

ClientHello ServerHello ServerCertiﬁcate ServerHelloDone TLS Handshake Public Key (pk) Nc Ns

Slide 54

Slide 54 text

ClientHello ServerHello ServerCertiﬁcate ServerHelloDone TLS Handshake Public Key (pk) kbs, ksb counter mk = RSA(pmk, Nc, Ns) Nc Ns

Slide 55

Slide 55 text

ClientHello ServerHello ServerCertiﬁcate ServerHelloDone ClientKeyExchange PreMasterSecret = Enc(pmk) TLS Handshake Public Key (pk) kbs, ksb counter mk = RSA(pmk, Nc, Ns) Nc Ns

Slide 56

Slide 56 text

ClientHello ServerHello ServerCertiﬁcate ServerHelloDone ClientKeyExchange PreMasterSecret = Enc(pmk) TLS Handshake Public Key (pk) kbs, ksb counter mk = RSA(pmk, Nc, Ns) Nc Ns kbs, ksb counter mk = RSA(pmk, Nc, Ns

Slide 57

Slide 57 text

ClientHello ServerHello ServerCertiﬁcate ServerHelloDone ClientKeyExchange PreMasterSecret = Enc(pmk) Finished Encrypted ChangeCipherSpec TLS Handshake Public Key (pk) kbs, ksb counter mk = RSA(pmk, Nc, Ns) Nc Ns kbs, ksb counter mk = RSA(pmk, Nc, Ns

Slide 58

Slide 58 text

ClientHello ServerHello ServerCertiﬁcate ServerHelloDone ClientKeyExchange PreMasterSecret = Enc(pmk) Finished Encrypted ChangeCipherSpec Decrypt TLS Handshake Public Key (pk) kbs, ksb counter mk = RSA(pmk, Nc, Ns) Nc Ns kbs, ksb counter mk = RSA(pmk, Nc, Ns

Slide 59

Slide 59 text

ClientHello ServerHello ServerCertiﬁcate ServerHelloDone ClientKeyExchange PreMasterSecret = Enc(pmk) ChangeCipherSpec Finished Encrypted ChangeCipherSpec Decrypt Finished Encrypted TLS Handshake Public Key (pk) kbs, ksb counter mk = RSA(pmk, Nc, Ns) Nc Ns kbs, ksb counter mk = RSA(pmk, Nc, Ns

Slide 60

Slide 60 text

No content

Slide 61

Slide 61 text

What now?

Slide 62

Slide 62 text

What now? ‣Client & Server both have has ksb, kbs

Slide 63

Slide 63 text

What now? ‣Client & Server both have has ksb, kbs ‣Use symmetric key encryption (AES) for all further communications

Slide 64

Slide 64 text

What now? ‣Client & Server both have has ksb, kbs ‣Use symmetric key encryption (AES) for all further communications ‣Why not use public key everywhere?

Slide 65

Slide 65 text

What now? ‣Client & Server both have has ksb, kbs ‣Use symmetric key encryption (AES) for all further communications ‣Why not use public key everywhere? ‣Public key encryption is slow - use it for key exchange (handshake) and use fast symmetric encryption thereafter

Slide 66

Slide 66 text

No content

Slide 67

Slide 67 text

How secure?

Slide 68

Slide 68 text

How secure? RSA based on prime factorization problem. 768 RSA = 1500 CPU years (2yrs realtime on many hundreds of computers) We use 1024/2048 bits RSA.

Slide 69

Slide 69 text

How secure? RSA based on prime factorization problem. 768 RSA = 1500 CPU years (2yrs realtime on many hundreds of computers) We use 1024/2048 bits RSA. AES with a 128 bit key requires storing 288 bits of data = 38 trillion terabytes of space > all the data stored on all the computers on the planet in 2016.