Upgrade to Pro
— share decks privately, control downloads, hide ads and more …
Speaker Deck
Features
Speaker Deck
PRO
Sign in
Sign up for free
Search
Search
Oh, you're so random
Search
Vicent Martí
March 25, 2012
Programming
14
2.6k
Oh, you're so random
Randomness and pink ponies in Codemotion Rome 2012
Vicent Martí
March 25, 2012
Tweet
Share
More Decks by Vicent Martí
See All by Vicent Martí
Unicorns Die With Bullets Made of Glitter
tanoku
6
560
Threedee Tales From Urban Bohemia
tanoku
3
830
My Mom told me that Git doesn't scale
tanoku
28
1.9k
Intergalactic Javascript Robots from Outer Space
tanoku
273
27k
Ruby is Unlike a Banana
tanoku
97
11k
A talk about libgit2
tanoku
11
1.7k
Other Decks in Programming
See All in Programming
Conquering Massive Traffic Spikes in Ruby Applications with Pitchfork
riseshia
0
150
ネイティブ製ガントチャートUIを作って学ぶUICollectionViewLayoutの威力
jrsaruo
0
130
CSC509 Lecture 01
javiergs
PRO
1
430
The Past, Present, and Future of Enterprise Java
ivargrimstad
0
140
Signals & Resource API in Angular: 3 Effective Rules for Your Architecture @BASTA 2025 in Mainz
manfredsteyer
PRO
0
100
CSC305 Lecture 01
javiergs
PRO
1
400
明日から始めるリファクタリング
ryounasso
0
120
Web技術を最大限活用してRAW画像を現像する / Developing RAW Images on the Web
ssssota
2
1.2k
Go Conference 2025: Goで体感するMultipath TCP ― Go 1.24 時代の MPTCP Listener を理解する
takehaya
7
1.6k
Le côté obscur des IA génératives
pascallemerrer
0
120
CSC509 Lecture 06
javiergs
PRO
0
240
Django Ninja による API 開発効率化とリプレースの実践
kashewnuts
0
970
Featured
See All Featured
It's Worth the Effort
3n
187
28k
RailsConf 2023
tenderlove
30
1.2k
A designer walks into a library…
pauljervisheath
209
24k
Mobile First: as difficult as doing things right
swwweet
224
10k
Balancing Empowerment & Direction
lara
4
680
Become a Pro
speakerdeck
PRO
29
5.5k
Writing Fast Ruby
sferik
629
62k
Optimizing for Happiness
mojombo
379
70k
Performance Is Good for Brains [We Love Speed 2024]
tammyeverts
12
1.2k
個人開発の失敗を避けるイケてる考え方 / tips for indie hackers
panda_program
114
20k
For a Future-Friendly Web
brad_frost
180
9.9k
Navigating Team Friction
lara
189
15k
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”