<?php
 
error_reporting(-1);
 
/* Коды для замены букв */
$code = array(
    'а'	=>	'01',    'б'	=>	'02',
    'в'	=>	'03',    'г'	=>	'04',
    'д'	=>	'05',    'е'	=>	'06',
    'ё'	=>	'07',    'ж'	=>	'08',
    'з'	=>	'09',    'и'	=>	'10',
    'й'	=>	'11',    'к'	=>	'12',
    'м'	=>	'13',    'н'	=>	'14',
    'о'	=>	'15',    'р'	=>	'16',
    'с'	=>	'17',    'т'	=>	'18',
    'у'	=>	'19',    'ф'	=>	'20',
    'х'	=>	'21',    'ц'	=>	'22',
    'ч'	=>	'23',    'э'	=>	'24',
    'ю'	=>	'25',    'я'	=>	'27',
    ' '	=>	'28',    'п'	=>	'29',
    'тест' => 'xxx'
);
 
 
$test = 'зашифруем это сообщение и посмотрим что получится тест';
 
$result = strtr($test, $code);
 
echo "$result\n";
 
$decode = array_flip($code);
 
$uncode = strtr($result, $decode);
 
echo $uncode;

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