rfc:improve_predictable_prng_random

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rfc:improve_predictable_prng_random [2017/02/02 03:45] – yohgakirfc:improve_predictable_prng_random [2017/02/03 04:34] – Fix function signature yohgaki
Line 14: Line 14:
 <code php> <code php>
 // We need the same random numbers here // We need the same random numbers here
-mt_srand(1234); +srand(1234); 
 for ($i=0; $i < 10; $i++) { for ($i=0; $i < 10; $i++) {
    // Use my PRNG state    // Use my PRNG state
-   $my_rand[] = mt_rand(); +   $my_rand[] = rand(); 
 } }
  
Line 29: Line 29:
 </code> </code>
  
-**This is not limited to specific request that calls mt_srand($some_value), but applies to consecutive requests.**+**Above code worked as it should. PHP 7.1 broke this code.** Similarly, shuffle()/etc are broken by PHP 7.1. 
 + 
 +<code php> 
 +// We need the same random numbers here 
 +mt_srand(1234);  
 +for ($i=0; $i < 10; $i++) { 
 +   // Use my PRNG state 
 +   $my_rand[] = mt_rand();  
 +} 
 + 
 +// Somewhere later in code AND/OR even other requests 
 + 
 +// We need to shuffle randomly 
 +shuffle($my_random_array); // This is NOT RANDOM at all 
 +</code> 
 + 
 +**These behaviors are not limited to specific request that calls mt_srand($some_value)/srand($some_value), but applies to consecutive requests.**
  
 PHP should have system and user PRNG state to resolve this behavior. PHP should have system and user PRNG state to resolve this behavior.
Line 42: Line 58:
 ==== Rack of Reseeding ==== ==== Rack of Reseeding ====
  
-Reseeding is important for PRNG to mitigate guessed random value. Since MT rand is predictable PRNG, using the same PRNG state allows to guess random value. Current PHP only supports very weak initialization and keeps using the same PRNG state once it is initialized. This behavior makes trivial to guess  MT rand generated random numbers.+Reseeding is important for PRNG to mitigate guessed random value. Since MT rand is predictable PRNG, using the same PRNG state allows to guess next random value easily. Current PHP only supports very weak initialization and keeps using the same PRNG state once it is initialized. This behavior makes trivial to guess  MT rand generated random numbers.
  
 To resolve this issue, PHP should reseed MT rand when state is used certain number of times. To resolve this issue, PHP should reseed MT rand when state is used certain number of times.
Line 70: Line 86:
  
 <code php> <code php>
-  int mt_rand([RandomState $seed_object]) +  int mt_rand([RandomMT $seed_object]) 
-  int mt_rand(int $min, int $max [, RandomState $seed_object]) +  int mt_rand(int $min, int $max [, RandomMT $seed_object]) 
-  int rand([RandomState $seed_object]) +  int rand([Random $seed_object]) 
-  int rand(int $min, int $max [, RandomState $seed_object]) +  int rand(int $min, int $max [, Random $seed_object]) 
-  bool shuffle(array &$arr [, RandomSatate $seed_object]);+  bool shuffle(array &$arr [, Random $seed_object]);
 </code> </code>
  
rfc/improve_predictable_prng_random.txt · Last modified: 2018/03/01 23:13 by carusogabriel

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