rfc:improve_predictable_prng_random
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rfc:improve_predictable_prng_random [2017/02/02 03:41] – yohgaki | rfc:improve_predictable_prng_random [2018/03/01 23:13] (current) – RFC is Under Discussion carusogabriel | ||
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* Date: 2017-02-01 | * Date: 2017-02-01 | ||
* Author: Yasuo Ohgaki < | * Author: Yasuo Ohgaki < | ||
- | * Status: | + | * Status: |
* First Published at: http:// | * First Published at: http:// | ||
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<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; $i++) { | ||
// Use my PRNG state | // Use my PRNG state | ||
- | | + | |
} | } | ||
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</ | </ | ||
- | **This is not limited to specific request that calls mt_srand($some_value), | + | **Above code worked as it should. PHP 7.1 broke this code.** Similarly, shuffle()/ |
+ | |||
+ | <code php> | ||
+ | // We need the same random numbers here | ||
+ | mt_srand(1234); | ||
+ | for ($i=0; $i < 10; $i++) { | ||
+ | // Use my PRNG state | ||
+ | | ||
+ | } | ||
+ | |||
+ | // Somewhere later in code AND/OR even other requests | ||
+ | |||
+ | // We need to shuffle randomly | ||
+ | shuffle($my_random_array); | ||
+ | </ | ||
+ | |||
+ | **These behaviors are not limited to specific request that calls mt_srand($some_value)/ | ||
PHP should have system and user PRNG state to resolve this behavior. | PHP should have system and user PRNG state to resolve this behavior. | ||
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==== 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. | ||
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===== Proposal ===== | ===== Proposal ===== | ||
- | ==== Return PRNG state object from mt_srand()/ | + | ==== Return PRNG random |
<code php> | <code php> | ||
- | | + | |
- | | + | |
</ | </ | ||
- | mt_srand()/ | + | mt_srand()/ |
Note: srand() is alias of mt_rand(). Python initializes MT rand state by string data like this proposal. | Note: srand() is alias of mt_rand(). Python initializes MT rand state by string data like this proposal. | ||
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<code php> | <code php> | ||
- | int mt_rand([RandomState | + | int mt_rand([RandomMT |
- | int mt_rand(int $min, int $max [, RandomState | + | int mt_rand(int $min, int $max [, RandomMT |
- | int rand([RandomState | + | int rand([Random |
- | int rand(int $min, int $max [, RandomState | + | int rand(int $min, int $max [, Random |
- | bool shuffle(array &$arr [, RandomSatate | + | bool shuffle(array &$arr [, Random |
</ | </ | ||
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==== Random object and function ==== | ==== Random object and function ==== | ||
- | Create RandomeInterface, | + | Create RandomeInterface, |
<code php> | <code php> | ||
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public function getBytes(int $length); // Raw bytes | public function getBytes(int $length); // Raw bytes | ||
public function getString(int $length, int $bits = 6); // String [0-9a-zA-Z, | public function getString(int $length, int $bits = 6); // String [0-9a-zA-Z, | ||
- | public function seed($seed = NULL); // No use with CS RNG, return TRUE always. | + | public function seed($seed = NULL); // No use with CS RNG, raise exception. |
- | public function getState(); // Return string representation PRNG state. No use with CS RNG, return NULL. | + | public function getState(); // Return string representation PRNG state. No use with CS RNG, raise exception. |
- | public function setState(string $state); // Set PRNG state. No use with CS RNG, return TRUE always. | + | public function setState(string $state); // Set PRNG state. No use with CS RNG, raise exception. |
- | public function getCount(); // No use with CS RNG, return 0 always. | + | public function getCount(); // No use with CS RNG, raise exception. |
- | public function getReseedCycle(); | + | public function getReseedCycle(); |
- | public function setReseedCycle(int $count); // No use with CS RNG, return TRUE always. | + | public function setReseedCycle(int $count); // No use with CS RNG, raise exception. |
} | } | ||
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public function __construct($seed = NULL) { | public function __construct($seed = NULL) { | ||
$this-> | $this-> | ||
+ | } | ||
+ | |||
+ | private reseed() { | ||
+ | $this-> | ||
+ | if ($this-> | ||
+ | $this-> | ||
+ | $this-> | ||
+ | } | ||
} | } | ||
| | ||
public function getInt($min = NULL, $max = NULL) { | public function getInt($min = NULL, $max = NULL) { | ||
assert($min <= $max); | assert($min <= $max); | ||
+ | $this-> | ||
if ($min && $max) { | if ($min && $max) { | ||
return mt_rand($min, | return mt_rand($min, | ||
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| | ||
public function getBytes(int $length) { | public function getBytes(int $length) { | ||
- | // Return raw random bytes | + | // Return raw random bytes. 3 out of 4 bytes are used not to disclose full PRNG state |
} | } | ||
| | ||
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// Update state by user seed | // Update state by user seed | ||
mt_srand($seed); | mt_srand($seed); | ||
+ | $this-> | ||
} else { | } else { | ||
// Seed by system generated random value | // Seed by system generated random value | ||
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</ | </ | ||
- | uint32_t BG(mt_rand_is_seeded) is used for already seeded flag and counter. | + | uint32_t BG(mt_rand_is_seeded) is used for already seeded flag and counter. |
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mt_srand()/ | mt_srand()/ | ||
- | If users want static random values, they have to use RandomStatus | + | If users want static random values, they have to use Random |
===== Proposed PHP Version(s) ===== | ===== Proposed PHP Version(s) ===== |
rfc/improve_predictable_prng_random.1486006884.txt.gz · Last modified: 2017/09/22 13:28 (external edit)