Oh, you're so random

Transcript

1. None

2. select a random element

3. select a random element ‘tis one is ok.

4. None
5. None

6. Information Theory

7. hard TOPIC Information Theory

8. hard TOPIC dumb SPEAKER + Information Theory

9. 0≤H(X)≤1 where X is a discrete random variable

10. 0≤H(X)≤1 where X is a discrete random variable unpredictable

11. 0≤H(X)≤1 where X is a discrete random variable unpredictable always

    the same
12. None

13. ask a question.

14. None

15. bool is_random(char *bytes, size_t n) { }

16. bool is_random(char *bytes, size_t n) { } AGHHH

17. UNIFORM distribution

18. UNIFORM distribution

19. select a random element array[rand() % array.size]

20. select a random element array[rand() % array.size] UNIFORM distribution

21. select a random element array[rand() % array.size] UNIFORM distribution

22. select a random element array[rand() % array.size] UNIFORM distribution AGHHH

23. This is how you kill the RANDOM pnrg array

24. This is how you kill the RANDOM a pnrg array

25. This is how you kill the RANDOM a pnrg array

26. This is how you kill the RANDOM a a pnrg

    array

27. This is how you kill the RANDOM a a pnrg

    array

28. This is how you kill the RANDOM a a a

    pnrg array

29. This is how you kill the RANDOM a a a

    pnrg array

30. This is how you kill the RANDOM a a a

    pnrg array

31. This is how you kill the RANDOM a a a

    b pnrg array

32. This is how you kill the RANDOM a a a

    b pnrg array

33. This is how you kill the RANDOM a a a

    b b pnrg array

34. This is how you kill the RANDOM a a a

    b b pnrg array

35. This is how you kill the RANDOM a a a

    b b pnrg array

36. This is how you kill the RANDOM a a a

    b b pnrg array

37. how to FIX:

38. how to FIX: 1. Random is hard

39. how to FIX: 1. Random is hard 2. Run away

40. how to FIX: 1. Random is hard 2. Run away

    Math.random() // between 0.0 and 1.0 Javascript

41. how to FIX: 1. Random is hard 2. Run away

42. how to FIX: 1. Random is hard 2. Run away

    prng.rand(5..9) #=> one of [5, 6, 7, 8, 9] prng.rand(5...9) #=> one of [5, 6, 7, 8] Ruby

43. Good.

44. Good. (but I don’t care)

45. None

46. “PRNGs and Hash functions are in the same family of

    algorithms”
47. None

48. hash tables out of nowhere!

49. hash tables out of nowhere! O(1)

50. hash tables out of nowhere! O(1) uniform

51. pathological average data set: O(1)

52. pathological average data set: O(1)

53. pathological average data set: O(1) O(n)

54. ONE fix

55. ONE fix INT_MAX % size == 0

56. collide make them

57. collide make them • Brute force

58. collide make them • Brute force • MITM

59. collide make them • Brute force • MITM • Equivalent

    substrings

60. collide make them • Brute force • MITM • Equivalent

    substrings

61. collide make them • Brute force • MITM • Equivalent

    substrings

62. collide make them • Brute force • MITM • Equivalent

    substrings

63. collide make them • Brute force • MITM • Equivalent

    substrings

64. collide make them • Brute force • MITM • Equivalent

    substrings

65. problem & that’s a

66. problem & that’s a painful comparisons

67. problem & that’s a painful comparisons ~700ms responses

68. MANY fixes

69. MANY fixes (but only one is right)

70. MANY fixes (but only one is right) 1. Limiting request

    size

71. this is bad and you should feel bad! MANY fixes

    (but only one is right) 1. Limiting request size

72. MANY fixes (but only one is right) 2. Changing the

    hash table

73. MANY fixes (but only one is right) 2. Changing the

    hash table (no comment)

74. MANY fixes (but only one is right) 3. Bring back

    the random
75. None

76. “Randomness is too important to be left to chance”

77. Thanks. “Randomness is too important to be left to chance”