Monthly Archives: April 2023

ChatGPT code explanation

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I threw this function:

  protected function get_passphrase_list() {

    // 2023-03-30 jj5 - we cache the generated passphrase list in a static variable so we don't
    // have to constantly regenerate it and because we don't want to put this sensitive data
    // into an instance field. If you don't want the passphrase list stored in a static variable
    // override this method and implement differently.

    static $result = null;

    if ( $result !== null ) { return $result; }

    $secret_list = $this->get_config_secret_list();
    $result = [];

    foreach ( $secret_list as $secret ) {

      $result[] = $this->calc_passphrase( $secret );

    }

    return $result;

  }

into ChatGPT and it said:

This is a protected function that returns a list of passphrases based on a list of secret values obtained from another function, get_config_secret_list(). The passphrases are generated using a method called calc_passphrase().

The function checks if the passphrase list has already been generated by looking at a static variable named $result. If $result is not null, the function returns it. Otherwise, the function generates the passphrase list and stores it in the $result variable.

The reason for caching the passphrase list in a static variable is to avoid having to regenerate it every time the function is called, which can be time-consuming. Additionally, it is considered a security best practice not to store sensitive data, such as passphrases, in instance fields.

If you want to change the way the passphrase list is stored, you can override this method and implement it differently.

PHP preg_match regex fail

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So this happened. Basically the first regex causes preg_match to fail when it tries to process 128KiB ASCII zeros… and 128KiB isn’t really that many zeros. Fortunately the second regex performs much better, PHP runs out of memory before preg_match chokes on that one.

-------------------
Sat Apr 01 13:17:17 [bash:5.1.16 jobs:0 error:0 time:243]
jj5@charm:/home/jj5/desktop/experiment
$ cat base64-regex.php 
<?php

test( '/^(?:[A-Za-z0-9+\/]{4})*(?:[A-Za-z0-9+\/]{2}==|[A-Za-z0-9+\/]{3}=|[A-Za-z0-9+\/]{4})$/' );
test( '/^[a-zA-Z0-9\/+]{2,}={0,2}$/' );

function test( $regex ) {

  echo "testing: $regex\n";

  $n = 0;

  for ( ;; ) {

    $n++;

    echo "n: $n\n";

    $string = str_repeat( '0', pow( 2, $n ) );

    $base64 = base64_encode( $string );

    if ( preg_match( $regex, $base64 ) ) { continue; }

    echo "error at N = $n.\n";

    return;

  }
}

-------------------
Sat Apr 01 13:17:21 [bash:5.1.16 jobs:0 error:0 time:247]
jj5@charm:/home/jj5/desktop/experiment
$ php base64-regex.php 
testing: /^(?:[A-Za-z0-9+\/]{4})*(?:[A-Za-z0-9+\/]{2}==|[A-Za-z0-9+\/]{3}=|[A-Za-z0-9+\/]{4})$/
n: 1
n: 2
n: 3
n: 4
n: 5
n: 6
n: 7
n: 8
n: 9
n: 10
n: 11
n: 12
n: 13
n: 14
n: 15
n: 16
n: 17
error at N = 17.
testing: /^[a-zA-Z0-9\/+]{2,}={0,2}$/
n: 1
n: 2
n: 3
n: 4
n: 5
n: 6
n: 7
n: 8
n: 9
n: 10
n: 11
n: 12
n: 13
n: 14
n: 15
n: 16
n: 17
n: 18
n: 19
n: 20
n: 21
n: 22
n: 23
n: 24
n: 25
n: 26
n: 27
n: 28
n: 29
n: 30
n: 31
n: 32
n: 33
n: 34
n: 35
Killed
-------------------
Sat Apr 01 13:18:21 [bash:5.1.16 jobs:0 error:137 time:307]