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Oh, you're so random
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Vicent Martí
March 25, 2012
Programming
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2.5k
Oh, you're so random
Randomness and pink ponies in Codemotion Rome 2012
Vicent Martí
March 25, 2012
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Transcript
None
select a random element
select a random element ‘tis one is ok.
None
None
Information Theory
hard TOPIC Information Theory
hard TOPIC dumb SPEAKER + Information Theory
0≤H(X)≤1 where X is a discrete random variable
0≤H(X)≤1 where X is a discrete random variable unpredictable
0≤H(X)≤1 where X is a discrete random variable unpredictable always
the same
None
ask a question.
None
bool is_random(char *bytes, size_t n) { }
bool is_random(char *bytes, size_t n) { } AGHHH
UNIFORM distribution
UNIFORM distribution
select a random element array[rand() % array.size]
select a random element array[rand() % array.size] UNIFORM distribution
select a random element array[rand() % array.size] UNIFORM distribution
select a random element array[rand() % array.size] UNIFORM distribution AGHHH
This is how you kill the RANDOM pnrg array
This is how you kill the RANDOM a pnrg array
This is how you kill the RANDOM a pnrg array
This is how you kill the RANDOM a a pnrg
array
This is how you kill the RANDOM a a pnrg
array
This is how you kill the RANDOM a a a
pnrg array
This is how you kill the RANDOM a a a
pnrg array
This is how you kill the RANDOM a a a
pnrg array
This is how you kill the RANDOM a a a
b pnrg array
This is how you kill the RANDOM a a a
b pnrg array
This is how you kill the RANDOM a a a
b b pnrg array
This is how you kill the RANDOM a a a
b b pnrg array
This is how you kill the RANDOM a a a
b b pnrg array
This is how you kill the RANDOM a a a
b b pnrg array
how to FIX:
how to FIX: 1. Random is hard
how to FIX: 1. Random is hard 2. Run away
how to FIX: 1. Random is hard 2. Run away
Math.random() // between 0.0 and 1.0 Javascript
how to FIX: 1. Random is hard 2. Run away
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
Good.
Good. (but I don’t care)
None
“PRNGs and Hash functions are in the same family of
algorithms”
None
hash tables out of nowhere!
hash tables out of nowhere! O(1)
hash tables out of nowhere! O(1) uniform
pathological average data set: O(1)
pathological average data set: O(1)
pathological average data set: O(1) O(n)
ONE fix
ONE fix INT_MAX % size == 0
collide make them
collide make them • Brute force
collide make them • Brute force • MITM
collide make them • Brute force • MITM • Equivalent
substrings
collide make them • Brute force • MITM • Equivalent
substrings
collide make them • Brute force • MITM • Equivalent
substrings
collide make them • Brute force • MITM • Equivalent
substrings
collide make them • Brute force • MITM • Equivalent
substrings
collide make them • Brute force • MITM • Equivalent
substrings
problem & that’s a
problem & that’s a painful comparisons
problem & that’s a painful comparisons ~700ms responses
MANY fixes
MANY fixes (but only one is right)
MANY fixes (but only one is right) 1. Limiting request
size
this is bad and you should feel bad! MANY fixes
(but only one is right) 1. Limiting request size
MANY fixes (but only one is right) 2. Changing the
hash table
MANY fixes (but only one is right) 2. Changing the
hash table (no comment)
MANY fixes (but only one is right) 3. Bring back
the random
None
“Randomness is too important to be left to chance”
Thanks. “Randomness is too important to be left to chance”