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  1. In theory, this salt encodes 64 bits of entropy. In practice, the values of
  2. time() and getmypid() are almost predictable and thus very bad choices for
  3. seeding. But let's pretend they are just fine.
  4.  
  5. <?php
  6.  
  7. $seed1 = time(); // quite bad choice of seed
  8. $seed2 = getmypid(); // EVEN WORSE choice of seed (read the manual)
  9. $random = '';
  10.  
  11. mt_srand($seed1);
  12. $random .= random_bits(32);
  13.  
  14. mt_srand($seed2);
  15. $random .= random_bits(32);
  16.  
  17. echo $random;
  18. die;
  19.  
  20. // Counts how many bits are needed to represent $value
  21. function count_bits($value) {
  22.     for($count = 0; $value != 0; $value >>= 1) {
  23.         ++$count;
  24.     }
  25.     return $count;
  26. }
  27.  
  28. // Returns a base16 random string of at least $bits bits
  29. // Actual bits returned will be a multiple of 4 (1 hex digit)
  30. function random_bits($bits) {
  31.     $result = '';
  32.     $accumulated_bits = 0;
  33.     $total_bits = count_bits(mt_getrandmax());
  34.     $usable_bits = intval($total_bits / 8) * 8;
  35.  
  36.     while ($accumulated_bits < $bits) {
  37.         $bits_to_add = min($total_bits - $usable_bits, $bits - $accumulated_bits);
  38.         if ($bits_to_add % 4 != 0) {
  39.             // add bits in whole increments of 4
  40.             $bits_to_add += 4 - $bits_to_add % 4;
  41.         }
  42.  
  43.         // isolate leftmost $bits_to_add from mt_rand() result
  44.         $more_bits = mt_rand() & ((1 << $bits_to_add) - 1);
  45.  
  46.         // format as hex (this will be safe)
  47.         $format_string = '%0'.($bits_to_add / 4).'x';
  48.         $result .= sprintf($format_string, $more_bits);
  49.         $accumulated_bits += $bits_to_add;
  50.     }
  51.  
  52.     return $result;
  53. }
  54.  
Success #stdin #stdout 0.01s 20568KB
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In theory, this salt encodes 64 bits of entropy. In practice, the values of
time() and getmypid() are almost predictable and thus very bad choices for
seeding. But let's pretend they are just fine.

a77915f8393f66d3
https://ideone.com/u4UloT
language:
PHP (php 7.3.5)
created:
12 years ago
visibility:
public

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