Secure Communication over insecure network

A look at the land of Cryptography and how it affects our online life. We won't be diving into cryptography algorithms - instead we will treat them as “black boxes” - and see how they fit together given the right input. A bird's eye look at TLS handshake.

Mostly requires just logical thinking of how all these different pieces fit together.

Transcript

1. SECURE COMMUNICATION HOW OUR LIVES DEPEND ON CRYPTOGRAPHY TEJAS BUBANE TUESDAY TALKS AT CYBRILLA
3. Communication?
4. ! Communication?
5. " ! Communication?
6. " ! Communication?
7. " ! Communication?
8. Secure? " ! Communication?
9. Secure? " ! #$ Communication?
10. Secure? " ! #$ 1. Confidentiality Communication?
11. Secure? " ! #$ 1. Confidentiality 2. Identity Communication?
12. PROBLEM 1
13. PROBLEM 1
14. PROBLEM 1
15. PROBLEM 1
16. PROBLEM 1
17. PROBLEM 1
18. PROBLEM 1
19. PROBLEM 1
20. PROBLEM 1 Man in the middle attack
21. PROBLEM 1 Man in the middle attack Incorrect identity
22. PROBLEM 2
23. PROBLEM 2
24. PROBLEM 2
25. PROBLEM 2
26. PROBLEM 2
27. PROBLEM 2
28. PROBLEM 2
29. PROBLEM 2 Eavesdropping attack
30. PROBLEM 2 Eavesdropping attack No Secrecy
31. E(text, key) = cipher D(cipher, key) = text cipher
32. E(text, key) = cipher D(cipher, key) = text cipher Symmetric Key Cryptography
33. E(text, key) = cipher D(cipher, key) = text cipher Symmetric Key Cryptography 1.Caesar Cipher (44 BC)
34. E(text, key) = cipher D(cipher, key) = text cipher Symmetric Key Cryptography 1.Caesar Cipher (44 BC) CYBRILLA => FBEULOOD
35. E(text, key) = cipher D(cipher, key) = text cipher Symmetric Key Cryptography 1.Caesar Cipher (44 BC) CYBRILLA => FBEULOOD 2. Vigenère Cipher (1553)
36. 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
41. Enigma machine
42. Enigma machine Bombe
43. Enigma machine Bombe
44. E(text, pubkey) = cipher D(cipher, privkey) = text pubkey hello! cipher
45. E(text, pubkey) = cipher D(cipher, privkey) = text pubkey Public Key Cryptography hello! cipher
46. Identity Certificate Binds Identity with public key OS/Mozilla Root certificates Browser verifies signature, matches URL
47. SSL/TLS •SSL (Netscape, 1995) •TLS 1.0 (IETF 1999) •TLS 1.1 (2006) •TLS 1.2 (2008) •TLS 1.3 (2018) Cryptographic Protocol
48. TLS Handshake
49. TLS Handshake
50. ClientHello TLS Handshake Nc
51. ClientHello ServerHello TLS Handshake Nc Ns
52. ClientHello ServerHello ServerCertificate TLS Handshake Public Key (pk) Nc Ns
53. ClientHello ServerHello ServerCertificate ServerHelloDone TLS Handshake Public Key (pk) Nc Ns
54. ClientHello ServerHello ServerCertificate ServerHelloDone TLS Handshake Public Key (pk) kbs, ksb counter mk = RSA(pmk, Nc, Ns) Nc Ns
55. ClientHello ServerHello ServerCertificate ServerHelloDone ClientKeyExchange PreMasterSecret = Enc(pmk) TLS Handshake Public Key (pk) kbs, ksb counter mk = RSA(pmk, Nc, Ns) Nc Ns
56. 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
57. 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
58. 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
59. 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
61. What now?
62. What now? ‣Client & Server both have has ksb, kbs
63. What now? ‣Client & Server both have has ksb, kbs ‣Use symmetric key encryption (AES) for all further communications
64. What now? ‣Client & Server both have has ksb, kbs ‣Use symmetric key encryption (AES) for all further communications ‣Why not use public key everywhere?
65. 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
67. How secure?
68. 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.
69. 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.
71. Trust CAs
72. Trust CAs Trust IETF
73. Trust CAs Thanks! Trust IETF