The `convert_cry_string()` function is not actually a built-in PHP function as of PHP 8.2. It seems you might be referring to one of these possibilities:PHP 8.PHP 8.1,PHP 8.2,PHP 8.3,and PHP 8.4.1. A custom function you or someone else created2. A function from a specific PHP extension3. A typo for another string conversion function like `convert_uuencode()` or `convert_cyr_string()`

Syntax:<?phpconvert_cyr_string(string $str, string $from, string $to): string?>Parameters:1.`$str`: The string to convert2. `$from`: The source Cyrillic character set (single character)3.`$to`: The target Cyrillic character set (single character)

Character Set Options:`k` - koi8-r`w` - windows-1251`i` - iso8859-5`a` - x-cp866`d` - x-cp866`m` - x-mac-cyrillic

Example:<?php$original = "?????? ???!"; // In Windows-1251 encoding$converted = convert_cyr_string($original, 'w', 'k');echo "Original: " . $original . "\n";echo "Converted to KOI8-R: " . $converted;?>Note

For real cryptographic operations in PHP, you should use proper encryption functions like those in the `openssl` or `sodium` extensions rather than simple transformations like ROT13.