### SlideShare for iOS

by Linkedin Corporation

FREE - On the App Store

- Total Views
- 5,068
- Views on SlideShare
- 4,997
- Embed Views

- Likes
- 3
- Downloads
- 239
- Comments
- 1

https://acconline.austincc.edu | 41 |

https://bb.csueastbay.edu | 19 |

https://blackboard.bsu.edu | 10 |

https://twitter.com | 1 |

Uploaded via SlideShare as Adobe PDF

© All Rights Reserved

- 1. Alice & Bob Public key cryptography 101 DPC Uncon - May 2011 Amsterdam - Netherlands ‣ http://joind.in/3466Friday, May 20, 2011
- 2. Who am I? Joshua Thijssen (32) Senior Software Engineer @ Enrise Development in PHP, Python, Perl, C, Java.... Blogs: http://www.adayinthelifeof.nl http://www.enrise.com/blog Email: joshua@enrise.com Twitter: @jaytaphFriday, May 20, 2011
- 3. What are we discussing? ‣ An introduction into public key encryption ‣ But ﬁrst of all... ‣ Who are Alice and Bob???Friday, May 20, 2011
- 4. Terminology (1)Friday, May 20, 2011
- 5. Terminology (1) Meet Alice, and Bob.Friday, May 20, 2011
- 6. Terminology (2) Fictional characters who are representing either side of the (communication) line. Person A(lice) is sending a message to person B(ob).Friday, May 20, 2011
- 7. Terminology (3) http://labs.google.com/sets?hl=en&q1=plaintext&q2=ciphertext&q3=cipher&q4=deterministic&q5=rsa&btn=Large+Set http://www.wordle.net/createFriday, May 20, 2011
- 8. Encryption history Before we look at good encryptions, let’s take a look at some bad ones...http://www.ﬂickr.com/photos/wwworks/4612188594/sizes/m/in/photostream/Friday, May 20, 2011
- 9. Encryption history (1) “algorithm”: A = 1, B = 2, C = 3, ...., Z = 26 ‣ SUBSTITUTION SCHEMEFriday, May 20, 2011
- 10. Encryption history (1) “algorithm”: A = 1, B = 2, C = 3, ...., Z = 26 Encrypted message: 12,1,13,5 ‣ SUBSTITUTION SCHEMEFriday, May 20, 2011
- 11. Encryption history (1) “algorithm”: A = 1, B = 2, C = 3, ...., Z = 26 Encrypted message: 12,1,13,5 = L,A,M,E ‣ SUBSTITUTION SCHEMEFriday, May 20, 2011
- 12. Encryption history (2) “algorithm”: A = (A + key) mod 26, B = (B + key) mod 26 .... Z = (Z + key) mod 26 or: m = m + k mod 26 ‣ CAESAREAN CIPHERFriday, May 20, 2011
- 13. Encryption history (2) “algorithm”: A = (A + key) mod 26, B = (B + key) mod 26 .... Z = (Z + key) mod 26 or: Message: L A M E m = m + k mod 26 ‣ CAESAREAN CIPHERFriday, May 20, 2011
- 14. Encryption history (2) “algorithm”: A = (A + key) mod 26, B = (B + key) mod 26 .... Z = (Z + key) mod 26 or: Message: L A M E m = m + k mod 26 Ciphertext (key=1): M B N F ‣ CAESAREAN CIPHERFriday, May 20, 2011
- 15. Encryption history (2) “algorithm”: A = (A + key) mod 26, B = (B + key) mod 26 .... Z = (Z + key) mod 26 or: Message: L A M E m = m + k mod 26 Ciphertext (key=1): M B N F Ciphertext (key=-1): K Z L D ‣ CAESAREAN CIPHERFriday, May 20, 2011
- 16. Encryption history (2) “algorithm”: A = (A + key) mod 26, B = (B + key) mod 26 .... Z = (Z + key) mod 26 or: Message: L A M E m = m + k mod 26 Ciphertext (key=1): M B N F Ciphertext (key=-1): K Z L D Ciphertext (key=26): L A M E ‣ CAESAREAN CIPHERFriday, May 20, 2011
- 17. Encryption history (2) “algorithm”: A = (A + key) mod 26, B = (B + key) mod 26 .... Z = (Z + key) mod 26 or: Message: L A M E m = m + k mod 26 Ciphertext (key=1): M B N F Ciphertext (key=-1): K Z L D Ciphertext (key=26): L A M E Ciphertext (key=0): L A M E ‣ CAESAREAN CIPHERFriday, May 20, 2011
- 18. Encryption history (2) “algorithm”: A = (A + key) mod 26, B = (B + key) mod 26 .... Z = (Z + key) mod 26 or: Message: L A M E m = m + k mod 26 Ciphertext (key=1): M B N F Ciphertext (key=-1): K Z L D Ciphertext (key=26): L A M E Ciphertext (key=0): L A M E Ciphertext (key=13):Y N Z R (ROT13) ‣ CAESAREAN CIPHERFriday, May 20, 2011
- 19. Encryption history (3) ‣ FLAWS IN THESE CIPHERSFriday, May 20, 2011
- 20. Encryption history (3) ‣ Key is too easy to guess. ‣ FLAWS IN THESE CIPHERSFriday, May 20, 2011
- 21. Encryption history (3) ‣ Key is too easy to guess. ‣ Key has to be send to Bob. ‣ FLAWS IN THESE CIPHERSFriday, May 20, 2011
- 22. Encryption history (3) ‣ Key is too easy to guess. ‣ Key has to be send to Bob. ‣ Deterministic. ‣ FLAWS IN THESE CIPHERSFriday, May 20, 2011
- 23. Encryption history (3) ‣ Key is too easy to guess. ‣ Key has to be send to Bob. ‣ Deterministic. ‣ Prone to frequency analysis. ‣ FLAWS IN THESE CIPHERSFriday, May 20, 2011
- 24. Frequency Analysis (1)Friday, May 20, 2011
- 25. Frequency Analysis (1) ‣ The usage of every letter in the English (or any other language) can be represented by a percentage.Friday, May 20, 2011
- 26. Frequency Analysis (1) ‣ The usage of every letter in the English (or any other language) can be represented by a percentage. ‣ ‘E’ is used 12.7% of the times in english texts, the ‘Z’ only 0.074%.Friday, May 20, 2011
- 27. Frequency Analysis (2) Once upon a midnight dreary, while I pondered, weak and weary, Over many a quaint and curious volume of forgotten lore— While I nodded, nearly napping, suddenly there came a tapping, As of some one gently rapping—rapping at my chamber door. "Tis some visitor," I muttered, "tapping at my chamber door— Only this and nothing more." Ah, distinctly I remember, it was in the bleak December, And each separate dying ember wrought its ghost upon the floor. Eagerly I wished the morrow;—vainly I had sought to borrow From my books surcease of sorrow—sorrow for the lost Lenore— For the rare and radiant maiden whom the angels name Lenore— Nameless here for evermore. And the silken sad uncertain rustling of each purple curtain Thrilled me—filled me with fantastic terrors never felt before; So that now, to still the beating of my heart, I stood repeating "Tis some visitor entreating entrance at my chamber door— Some late visitor entreating entrance at my chamber door;— This it is and nothing more." ‣ EDGAR ALLAN POE: THE RAVENhttp://www.gutenberg.org/cache/epub/14082/pg14082.txtFriday, May 20, 2011
- 28. Frequency Analysis (3) A small bit of text can result in differences, but still there are some letters we can deduce.. ‣ “THE RAVEN”, FIRST PARAGRAPHFriday, May 20, 2011
- 29. Frequency Analysis (3) A small bit of text can result in differences, but still there are some letters we can deduce.. ‣ “THE RAVEN”, FIRST PARAGRAPHFriday, May 20, 2011
- 30. Frequency Analysis (4) We can deduce almost all letters just without even CARING about the crypto algorithm used. ‣ “THE RAVEN”, ALL PARAGRAPHSFriday, May 20, 2011
- 31. Encryption algorithms (1) ‣ SYMMETRICAL ALGORITHMSFriday, May 20, 2011
- 32. Encryption algorithms (1) ‣ Previous examples were symmetrical encryptions. ‣ SYMMETRICAL ALGORITHMSFriday, May 20, 2011
- 33. Encryption algorithms (1) ‣ Previous examples were symmetrical encryptions. ‣ Same key is used for both encryption and decryption. ‣ SYMMETRICAL ALGORITHMSFriday, May 20, 2011
- 34. Encryption algorithms (1) ‣ Previous examples were symmetrical encryptions. ‣ Same key is used for both encryption and decryption. ‣ Good symmetrical encryptions: AES, Blowﬁsh, (3)DES ‣ SYMMETRICAL ALGORITHMSFriday, May 20, 2011
- 35. Encryption algorithms (2) ‣ THE PROBLEM WITH SYMMETRICAL ALGORITHMSFriday, May 20, 2011
- 36. Encryption algorithms (2) ‣ How do we send over the key securely? ‣ THE PROBLEM WITH SYMMETRICAL ALGORITHMSFriday, May 20, 2011
- 37. Encryption algorithms (2) ‣ How do we send over the key securely? ‣ O hai egg, meet chicken. ‣ THE PROBLEM WITH SYMMETRICAL ALGORITHMSFriday, May 20, 2011
- 38. Public key encryption Another encryption method: asymmetrical encryption or public key encryption. ‣ FINALLY, WE HAVE ARRIVED...Friday, May 20, 2011
- 39. Public key encryption (1) Two keys instead of one: public key - available for everybody. Can be published on your blog. private key - For your eyes only!Friday, May 20, 2011
- 40. Public key encryption (2) ‣ USES 2 KEYS INSTEAD OF ONE: A KEYPAIRhttp://upload.wikimedia.org/wikipedia/commons/f/f9/Public_key_encryption.svgFriday, May 20, 2011
- 41. Public key encryption (3) It is NOT possible to decrypt the message with same key that is used to encrypt. but We can encrypt with either key.Friday, May 20, 2011
- 42. Public key encryption (4) ‣ MULTIPLE APPLICATIONS FOR PUBLIC KEY ENCRYPTIONFriday, May 20, 2011
- 43. Public key encryption (4) ‣ Can be used for encrypting data. ‣ MULTIPLE APPLICATIONS FOR PUBLIC KEY ENCRYPTIONFriday, May 20, 2011
- 44. Public key encryption (4) ‣ Can be used for encrypting data. ‣ Can be used for data validation and authentication (signing). ‣ MULTIPLE APPLICATIONS FOR PUBLIC KEY ENCRYPTIONFriday, May 20, 2011
- 45. Symmetrical vs Asymmetrical (1) Symmetrical Asymmetrical ✓ quick. ✓ no need to send over the ✓ not resource intensive. (whole) key. ✓useful for small and large ✓ can be used for encryption messages. and validation (signing). ✗ need to send over the key ✗ very resource intensive. to the other side. ✗ only useful for small messages.Friday, May 20, 2011
- 46. Symmetrical vs Asymmetrical (2) Use symmetrical encryption for the (large) message and encrypt the key used with an asymmetrical encryption method.Friday, May 20, 2011
- 47. Symmetrical vs Asymmetrical (3) Hybrid ✓ quick ✓ not resource intensive ✓ useful for small and large messages ✓ safely exchange key dataFriday, May 20, 2011
- 48. Symmetrical vs Asymmetrical (3) Hybrid ✓ quick ✓ not resource intensive ✓ useful for small and large messages ✓ safely exchange key data +Friday, May 20, 2011
- 49. Symmetrical vs Asymmetrical (3) Hybrid ✓ quick ✓ not resource intensive ✓ useful for small and large messages ✓ safely exchange key data + = http://www.zastavki.com/pictures/1152x864/2008/Animals_Cats_Small_cat_005241_.jpgFriday, May 20, 2011
- 50. How does it work? We will focus on the popular RSA, but there are other algorithms as well: DH, DSS(DSA) etc...Friday, May 20, 2011
- 51. How does it work? (1) Public key encryption works on the premise that it is practically impossible to refactor a large number back into 2 separate prime numbers.Friday, May 20, 2011
- 52. How does it work? (1) Public key encryption works on the premise that it is practically impossible to refactor a large number back into 2 separate prime numbers. Prime number is only divisible by 1 and itself: 2, 3, 5, 7, 11, 13, 17, 19 etc...Friday, May 20, 2011
- 53. How does it work? (2)Friday, May 20, 2011
- 54. How does it work? (2) ‣ There is no proof that it’s impossible to refactor quickly (all tough it doesn’t look plausible)Friday, May 20, 2011
- 55. How does it work? (2) ‣ There is no proof that it’s impossible to refactor quickly (all tough it doesn’t look plausible) ‣ Brute-force decrypting is always lurking around (quicker machines, better algorithms).Friday, May 20, 2011
- 56. How does it work? (2) ‣ There is no proof that it’s impossible to refactor quickly (all tough it doesn’t look plausible) ‣ Brute-force decrypting is always lurking around (quicker machines, better algorithms). ‣ Good enough today != good enough tomorrow.Friday, May 20, 2011
- 57. How does it work? (3) (it’s 13 and 17 btw)Friday, May 20, 2011
- 58. How does it work? (3) “large” number: 221 (it’s 13 and 17 btw)Friday, May 20, 2011
- 59. How does it work? (3) “large” number: 221 but we cannot calculate its prime factors without brute force. There is no “formula” (like e=mc 2) (it’s 13 and 17 btw)Friday, May 20, 2011
- 60. Math example ‣ LET’S DO SOME MATHFriday, May 20, 2011
- 61. Math example This is mathness!Friday, May 20, 2011
- 62. Math example No, this is RSAAAAAAAAFriday, May 20, 2011
- 63. Math exampleFriday, May 20, 2011
- 64. Math example ‣ p = (large) prime number ‣ q = (large) prime number (but not too close to p) ‣ n = p . q (= bit length of the rsa-key) ‣ φ = (p-1) . (q-1) (the φ thingie is called phi) ‣ e = gcd(e, φ) = 1 ‣ d = e^-1 mod φ ‣ public key = tuple (n, e) ‣ private key = tuple (n, d)Friday, May 20, 2011
- 65. Math exampleFriday, May 20, 2011
- 66. Math example Step 1: select primes P and Q ‣ P = ? | Q = ? | N = ? | Phi = ? | e = ? | d = ?Friday, May 20, 2011
- 67. Math example Step 1: select primes P and Q ‣ P = 11 ‣ P = ? | Q = ? | N = ? | Phi = ? | e = ? | d = ?Friday, May 20, 2011
- 68. Math example Step 1: select primes P and Q ‣ P = 11 ‣ Q=3 ‣ P = ? | Q = ? | N = ? | Phi = ? | e = ? | d = ?Friday, May 20, 2011
- 69. Math example Step 2: calculate N and Phi ‣ P = 11 | Q = 3 | N = ? | Phi = ? | e = ? | d = ?Friday, May 20, 2011
- 70. Math example Step 2: calculate N and Phi ‣ N = P . Q = 11 . 3 = 33 ‣ P = 11 | Q = 3 | N = ? | Phi = ? | e = ? | d = ?Friday, May 20, 2011
- 71. Math example Step 2: calculate N and Phi ‣ N = P . Q = 11 . 3 = 33 ‣ Phi = (11-1) . (3-1) = 10 . 2 = 20 ‣ P = 11 | Q = 3 | N = ? | Phi = ? | e = ? | d = ?Friday, May 20, 2011
- 72. Math example Step 3: ﬁnd e ‣ P = 11 | Q = 3 | N = 33 | Phi = 20 | e = ? | d = ?Friday, May 20, 2011
- 73. Math example Step 3: ﬁnd e ‣ e = 3 (Fermat prime: 3, 17, 65537) ‣ P = 11 | Q = 3 | N = 33 | Phi = 20 | e = ? | d = ?Friday, May 20, 2011
- 74. Math example Step 3: ﬁnd e ‣ e = 3 (Fermat prime: 3, 17, 65537) ‣ gcd(e, phi) = 1 ==> gcd(3, 20) = 1 ‣ P = 11 | Q = 3 | N = 33 | Phi = 20 | e = ? | d = ?Friday, May 20, 2011
- 75. Math example Step 4: ﬁnd d ‣ P = 11 | Q = 3 | N = 33 | Phi = 20 | e = 3 | d = ?Friday, May 20, 2011
- 76. Math example Step 4: ﬁnd d ‣ Extended Euclidean Algorithm gives 7 ‣ P = 11 | Q = 3 | N = 33 | Phi = 20 | e = 3 | d = ?Friday, May 20, 2011
- 77. Math example Step 4: ﬁnd d ‣ Extended Euclidean Algorithm gives 7 ‣ brute force: (e.d mod n = 1) ‣ P = 11 | Q = 3 | N = 33 | Phi = 20 | e = 3 | d = ?Friday, May 20, 2011
- 78. Math example Step 4: ﬁnd d ‣ Extended Euclidean Algorithm gives 7 ‣ brute force: (e.d mod n = 1) 3 . 1 = 3 mod 20 = 3 3 . 6 = 18 mod 20 = 18 3 . 2 = 6 mod 20 = 6 3 . 7 = 21 mod 20 = 1 3 . 3 = 9 mod 20 = 9 3 . 8 = 24 mod 20 = 4 3 . 4 = 12 mod 20 = 12 3 . 9 = 27 mod 20 = 7 3 . 5 = 15 mod 20 = 15 ‣ P = 11 | Q = 3 | N = 33 | Phi = 20 | e = 3 | d = ?Friday, May 20, 2011
- 79. Math example ‣ P = 11 | Q = 3 | N = 33 | Phi = 20 | e = 3 | d = 7Friday, May 20, 2011
- 80. Math example That’s it: ‣ P = 11 | Q = 3 | N = 33 | Phi = 20 | e = 3 | d = 7Friday, May 20, 2011
- 81. Math example That’s it: ‣ public key = (n, e) = (33, 3) ‣ P = 11 | Q = 3 | N = 33 | Phi = 20 | e = 3 | d = 7Friday, May 20, 2011
- 82. Math example That’s it: ‣ public key = (n, e) = (33, 3) ‣ private key = (n, d) = (33, 7) ‣ P = 11 | Q = 3 | N = 33 | Phi = 20 | e = 3 | d = 7Friday, May 20, 2011
- 83. Math example The actual math is much more complex since we use very large numbers, but it all comes down to these (relatively simple) calculations..Friday, May 20, 2011
- 84. Encrypting & decrypting Encrypting a message: c = me mod n Decrypting a message: m = cd mod nFriday, May 20, 2011
- 85. Encrypting & decrypting (1) Encrypting a message: private key = (n,d) = (33, 7): m = 13, 20, 15, 5 13^7 mod 33 = 7 20^7 mod 33 = 26 15^7 mod 33 = 27 5^7 mod 33 = 14 c = 7, 26, 27,14Friday, May 20, 2011
- 86. Encrypting & decrypting (2) Decrypting a message: public key = (n,e) = (33, 3): c = 7, 26, 27, 14 7^3 mod 33 = 13 26^3 mod 33 = 20 27^3 mod 33 = 15 14^3 mod 33 =5 m = 13, 20, 15, 5Friday, May 20, 2011
- 87. Encrypting & decrypting (3)Friday, May 20, 2011
- 88. Encrypting & decrypting (3) ‣ A message is an “integer”, not a block of data.Friday, May 20, 2011
- 89. Encrypting & decrypting (3) ‣ A message is an “integer”, not a block of data. ‣ A message must be between 2 and n-1.Friday, May 20, 2011
- 90. Encrypting & decrypting (3) ‣ A message is an “integer”, not a block of data. ‣ A message must be between 2 and n-1. ‣ Deterministic, so we must use a padding scheme to make it non-deterministic.Friday, May 20, 2011
- 91. Encrypting & decrypting (4) ‣ Public Key Cryptography Standard #1 ‣ Pads data with (random) bytes up to n bits in length (v1.5 or OAEP/v2.x). ‣ Got it ﬂaws and weaknesses too. Always use the latest available version (v2.1) ‣ http://www.rsa.com/rsalabs/node.asp?id=2125Friday, May 20, 2011
- 92. Encrypting & decrypting (5) Data = 4E636AF98E40F3ADCFCCB698F4E80B9F The encoded message block, EMB, after encoding but before encryption, with random padding bytes shown in green: 0002257F48FD1F1793B7E5E02306F2D3228F5C95ADF5F31566729F132AA12009 E3FC9B2B475CD6944EF191E3F59545E671E474B555799FE3756099F044964038 B16B2148E9A2F9C6F44BB5C52E3C6C8061CF694145FAFDB24402AD1819EACEDF 4A36C6E4D2CD8FC1D62E5A1268F496004E636AF98E40F3ADCFCCB698F4E80B9F After RSA encryption, the output is: 3D2AB25B1EB667A40F504CC4D778EC399A899C8790EDECEF062CD739492C9CE5 8B92B9ECF32AF4AAC7A61EAEC346449891F49A722378E008EFF0B0A8DBC6E621 EDC90CEC64CF34C640F5B36C48EE9322808AF8F4A0212B28715C76F3CB99AC7E 609787ADCE055839829E0142C44B676D218111FFE69F9D41424E177CBA3A435B ‣ PKCS#1 (v1.5) IN ACTION http://www.di-mgt.com.au/rsa_alg.html#pkcs1schemesFriday, May 20, 2011
- 93. Implementations of public keys in real life http://farm4.static.ﬂickr.com/3538/3420164047_09ccc14e29.jpgFriday, May 20, 2011
- 94. Web communication public key encryption in Web communications (aka: I never use my credit card for internet purchases. It’s not safe. Instead, I gave it to the waiter who walked away with it into the kitchen for 5 minutes..)Friday, May 20, 2011
- 95. Web communication (1) Welcome to 1991: HTTP is plaintext. Everybody can be trusted. This page is under construction, here’s a photo of my cat and a link to geocities. ‣ BACK IN TIMEFriday, May 20, 2011
- 96. Web communication (2) ‣ BUT NOW...Friday, May 20, 2011
- 97. Web communication (2) ‣ Free WiFi everywhere ‣ BUT NOW...Friday, May 20, 2011
- 98. Web communication (2) ‣ Free WiFi everywhere ‣ Trafﬁc snooping ‣ BUT NOW...Friday, May 20, 2011
- 99. Web communication (2) ‣ Free WiFi everywhere ‣ Trafﬁc snooping ‣ Authorization: Basic? (yes,VERY basic) ‣ BUT NOW...Friday, May 20, 2011
- 100. Web communication (3) ‣ USING HTTPSFriday, May 20, 2011
- 101. Web communication (3) ‣ HTTP encapsulated by TLS (previously SSL). ‣ USING HTTPSFriday, May 20, 2011
- 102. Web communication (3) ‣ HTTP encapsulated by TLS (previously SSL). ‣ More or less: an encryption layer on top of http. ‣ USING HTTPSFriday, May 20, 2011
- 103. Web communication (3) ‣ HTTP encapsulated by TLS (previously SSL). ‣ More or less: an encryption layer on top of http. ‣ Hybrid encryption. ‣ USING HTTPSFriday, May 20, 2011
- 104. Web communication (4)Friday, May 20, 2011
- 105. Web communication (4) ‣ Actual encryption methodology is decided by the browser and the server (highest possible encryption used).Friday, May 20, 2011
- 106. Web communication (4) ‣ Actual encryption methodology is decided by the browser and the server (highest possible encryption used). ‣ Symmetric encryption (AES-256, others)Friday, May 20, 2011
- 107. Web communication (4) ‣ Actual encryption methodology is decided by the browser and the server (highest possible encryption used). ‣ Symmetric encryption (AES-256, others) ‣ But both sides needs the same key, so we have the same problem as before: how do we send over the key?Friday, May 20, 2011
- 108. Web communication (5)Friday, May 20, 2011
- 109. Web communication (5) ‣ Key is exchanged in a public/private encrypted communication.Friday, May 20, 2011
- 110. Web communication (5) ‣ Key is exchanged in a public/private encrypted communication. ‣ Which public key?Friday, May 20, 2011
- 111. Web communication (5) ‣ Key is exchanged in a public/private encrypted communication. ‣ Which public key? ‣ It is stored inside the server’s SSL certiﬁcateFriday, May 20, 2011
- 112. Web communication (6) ‣ “GLOBAL” HTTPS HANDSHAKEFriday, May 20, 2011
- 113. Web communication (6) ‣ Browser sends over its encryption methods. ‣ “GLOBAL” HTTPS HANDSHAKEFriday, May 20, 2011
- 114. Web communication (6) ‣ Browser sends over its encryption methods. ‣ Server decides which one to use. ‣ “GLOBAL” HTTPS HANDSHAKEFriday, May 20, 2011
- 115. Web communication (6) ‣ Browser sends over its encryption methods. ‣ Server decides which one to use. ‣ Server send certiﬁcate(s). ‣ “GLOBAL” HTTPS HANDSHAKEFriday, May 20, 2011
- 116. Web communication (6) ‣ Browser sends over its encryption methods. ‣ Server decides which one to use. ‣ Server send certiﬁcate(s). ‣ Client sends “session key” encrypted by the public key found in the server certiﬁcate. ‣ “GLOBAL” HTTPS HANDSHAKEFriday, May 20, 2011
- 117. Web communication (6) ‣ Browser sends over its encryption methods. ‣ Server decides which one to use. ‣ Server send certiﬁcate(s). ‣ Client sends “session key” encrypted by the public key found in the server certiﬁcate. ‣ Server and client uses the “session key” for symmetrical encryption. ‣ “GLOBAL” HTTPS HANDSHAKEFriday, May 20, 2011
- 118. Web communication (7)Friday, May 20, 2011
- 119. Web communication (7) ‣ Thus: Public/private encryption is only used in establishing a secondary (better!?) encryption.Friday, May 20, 2011
- 120. Web communication (7) ‣ Thus: Public/private encryption is only used in establishing a secondary (better!?) encryption. ‣ SSL/TLS is a separate talk (it’s way more complex as this)Friday, May 20, 2011
- 121. Web communication (7) ‣ Thus: Public/private encryption is only used in establishing a secondary (better!?) encryption. ‣ SSL/TLS is a separate talk (it’s way more complex as this) ‣ http://www.moserware.com/2009/06/ﬁrst-few- milliseconds-of-https.htmlFriday, May 20, 2011
- 122. Email communication public key encryption in Email communication (aka: the worst communication method invented when it comes to privacy or secrecy, except for yelling)Friday, May 20, 2011
- 123. Email communication (2)http://change-your-ip.com/wp-content/uploads/image/nigerian_419_scam.jpghttp://torontoemerg.ﬁles.wordpress.com/2010/09/spam.gifFriday, May 20, 2011
- 124. Email communication (3) ‣ DID YOU EVER SEND/RECEIVE EMAILS LIKE THIS?Friday, May 20, 2011
- 125. Email communication (4)Friday, May 20, 2011
- 126. Email communication (4) ‣ Did Bill really send this email?Friday, May 20, 2011
- 127. Email communication (4) ‣ Did Bill really send this email? ‣ Do we know for sure that nobody has read this email (before it came to us?)Friday, May 20, 2011
- 128. Email communication (4) ‣ Did Bill really send this email? ‣ Do we know for sure that nobody has read this email (before it came to us?) ‣ Do we know for sure that the contents of the message isn’t tampered with?Friday, May 20, 2011
- 129. Email communication (4) ‣ Did Bill really send this email? ‣ Do we know for sure that nobody has read this email (before it came to us?) ‣ Do we know for sure that the contents of the message isn’t tampered with? ‣ We use signing!Friday, May 20, 2011
- 130. Signing (1)Friday, May 20, 2011
- 131. Signing (1) ‣ Signing a message means adding a signature that authenticates the validity of a message.Friday, May 20, 2011
- 132. Signing (1) ‣ Signing a message means adding a signature that authenticates the validity of a message. ‣ Like md5 or sha1, so when the message changes, so will the signature.Friday, May 20, 2011
- 133. Signing (1) ‣ Signing a message means adding a signature that authenticates the validity of a message. ‣ Like md5 or sha1, so when the message changes, so will the signature. ‣ This works on the premise that Alice and only Alice has the private key that can create the signature.Friday, May 20, 2011
- 134. Signing (2) http://en.wikipedia.org/wiki/File:Digital_Signature_diagram.svgFriday, May 20, 2011
- 135. Signing (3)Friday, May 20, 2011
- 136. Signing (3) ‣ GPG / PGP: Application for signing and/or encrypting data (or emails).Friday, May 20, 2011
- 137. Signing (3) ‣ GPG / PGP: Application for signing and/or encrypting data (or emails). ‣ Try it yourself with Thunderbird’s Enigmail extension.Friday, May 20, 2011
- 138. Signing (3) ‣ GPG / PGP: Application for signing and/or encrypting data (or emails). ‣ Try it yourself with Thunderbird’s Enigmail extension. ‣ Public keys can be send / found on PGP- servers so you don’t need to send your keys to everybody all the time.Friday, May 20, 2011
- 139. Signing (4)Friday, May 20, 2011
- 140. Signing (5)Friday, May 20, 2011
- 141. Signing (5)Friday, May 20, 2011
- 142. Signing (5)Friday, May 20, 2011
- 143. Email communication (10) ‣ ADVANTAGES OF SIGNING YOUR MAILFriday, May 20, 2011
- 144. Email communication (10) ‣ Everybody can send emails that ONLY YOU can read. ‣ ADVANTAGES OF SIGNING YOUR MAILFriday, May 20, 2011
- 145. Email communication (10) ‣ Everybody can send emails that ONLY YOU can read. ‣ Everybody can verify that YOU have send the email and that it is authentic. ‣ ADVANTAGES OF SIGNING YOUR MAILFriday, May 20, 2011
- 146. Email communication (10) ‣ Everybody can send emails that ONLY YOU can read. ‣ Everybody can verify that YOU have send the email and that it is authentic. ‣ Why is this not the standard? ‣ ADVANTAGES OF SIGNING YOUR MAILFriday, May 20, 2011
- 147. Email communication (10) ‣ Everybody can send emails that ONLY YOU can read. ‣ Everybody can verify that YOU have send the email and that it is authentic. ‣ Why is this not the standard? ‣ No really, why isn’t it the standard? ‣ ADVANTAGES OF SIGNING YOUR MAILFriday, May 20, 2011
- 148. Email communication (7)Friday, May 20, 2011
- 149. Email communication (8)Friday, May 20, 2011
- 150. Email communication (9) Stupidity trumps everything: Don’t loose your private key(s) (as I did on multiple occasions)http://farm4.static.ﬂickr.com/3231/2783827537_b4d2a5cc9a.jpgFriday, May 20, 2011
- 151. Other applications PGP / GPG (encrypt / decrypt sensitive data) OpenSSH (Secure connection to other systems) IPSEC (VPN tunnels) Software signing ‣ PUBLIC KEY ENCRYPTION IN OTHER FIELDSFriday, May 20, 2011
- 152. Any questions? ‣ FOOTER TEXT http://farm1.static.ﬂickr.com/73/163450213_18478d3aa6_d.jpgFriday, May 20, 2011
- 153. Please rate my talk on joind.in: http://joind.in/3466 ‣ THANK YOU FOR YOUR ATTENTIONFriday, May 20, 2011

Full NameComment goes here.Anando Paul, Sr. Software Engineer at Secure Link Services Ltd | Selise Rockin' Software very nice presentation...Krzysztof Kotowicz, Web security researcher at SecuRing 2 years agodbauckm2 years agomury89Tagspublic key cryptography3 years ago