Oh, you're so random

Randomness and pink ponies in Codemotion Rome 2012

Transcript

2. select a random element
3. select a random element ‘tis one is ok.
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
13. ask a question.
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)
46. “PRNGs and Hash functions are in the same family of algorithms”
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
76. “Randomness is too important to be left to chance”
77. Thanks. “Randomness is too important to be left to chance”