str_rot13

(PHP 4 >= 4.2.0, PHP 5, PHP 7, PHP 8)

str_rot13 — Perform the rot13 transform on a string

Description

str_rot13(string $string): string

Performs the ROT13 encoding on the string argument and returns the resulting string.

The ROT13 encoding simply shifts every letter by 13 places in the alphabet while leaving non-alpha characters untouched. Encoding and decoding are done by the same function, passing an encoded string as argument will return the original version.

Parameters

string: The input string.

Return Values

Returns the ROT13 version of the given string.

Examples

Example #1 str_rot13() example

<?php

echo str_rot13('PHP 4.3.0'); // CUC 4.3.0

?>

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User Contributed Notes 9 notes

down

shaun ¶

12 years ago

I was reminded again of the desire for a generic str_rot function. Character manipulation loops in PHP are slow compared to their C counterparts, so here's a tuned version of the previous function I posted. It's 1.6 times as fast, mainly by avoiding chr() calls.

<?php
function str_rot($s, $n = 13) {
    static $letters = 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ';
    $n = (int)$n % 26;
    if (!$n) return $s;
    if ($n == 13) return str_rot13($s);
    for ($i = 0, $l = strlen($s); $i < $l; $i++) {
        $c = $s[$i];
        if ($c >= 'a' && $c <= 'z') {
            $s[$i] = $letters[(ord($c) - 71 + $n) % 26];
        } else if ($c >= 'A' && $c <= 'Z') {
            $s[$i] = $letters[(ord($c) - 39 + $n) % 26 + 26];
        }
    }
    return $s;
}
?>

But using strtr() you can get something 10 times as fast as the above :

<?php
function str_rot($s, $n = 13) {
    static $letters = 'AaBbCcDdEeFfGgHhIiJjKkLlMmNnOoPpQqRrSsTtUuVvWwXxYyZz';
    $n = (int)$n % 26;
    if (!$n) return $s;
    if ($n < 0) $n += 26;
    if ($n == 13) return str_rot13($s);
    $rep = substr($letters, $n * 2) . substr($letters, 0, $n * 2);
    return strtr($s, $letters, $rep);
}
?>

This technique is faster because PHP's strtr is implemented in C using a byte lookup table (it has O(m + n) complexity). However, PHP 6 will use Unicode, so I guess(?) strtr will then have to be implemented with a search for each character (O(m * n)). Using strtr might still be faster since it offloads the character manipulation to C rather than PHP, but I don't really know. Take your pick.

Happy coding!

(Benchmark code):

<?php
for ($k = 0; $k < 10; $k++) {
    $s = 'The quick brown fox jumps over the lazy dog.';
    $t = microtime(1);
    for ($i = 0; $i < 1000; $i++) $s = str_rot($s, $i);
    $t = microtime(1) - $t;
    echo number_format($t, 3) . "\n";
}
?>

down

arthur at kuhrmeier dot com ¶

9 years ago

I was writing a function for my website to also rotate numbers, and kept expanding it. I added extra characters, the ability to define the shift in percent, and which type of characters to affect.

<?php
//================================================== STRING ROTATE EXPANDED
function str_shift ($string, $perc=50, $useextra=FALSE, $usedigits=TRUE, $useupper=TRUE, $uselower=TRUE) {
    static $chars = array(
        'lower' => 'abcdefghijklmnopqrstuvwxyz',
        'upper' => 'ABCDEFGHIJKLMNOPQRSTUVWXYZ',
        'digits' => '0123456789',
        'extra' => ',.-()<>%/!"&=;:_[]{}#\\?\'+*',
    );
    settype($perc, 'float');
    if  (!$perc)  return $string;
    $perc = fmod((abs($perc) < 1 ? 100*$perc : $perc), 100);
    if  ($perc < 0)  $perc += 100;
    $use = (is_array($useextra) ? $useextra : array('lower'=>$uselower, 'upper'=>$useupper, 'digits'=>$usedigits, 'extra'=>$useextra));
    foreach ($chars as $type => $letters) {
        if  (!$use[$type])  continue;
        $shift = round(strlen($letters) * $perc / 100);
        $repl = substr($letters, $shift).substr($letters, 0, $shift);
        $string = strtr($string, $letters, $repl);
    }
    return $string;
}

//===== USAGE =====

string str_shift ( string $str [, float $percent [, bool $useextra [, bool $usedigits [, bool $uselower [, bool $useupper] ] ] ] ] )

string str_shift ( string $str [, float $percent [, array $usetypes ] ] )

$usetypes = array('lower'=>bool $uselower, 'upper'=>bool $useupper, 'digits'=>bool $usedigits, 'extra'=>bool $useextra);

//===== EXAMPLES =====

$string = "Peter's 17 pets (incl. 5 hamsters) love Dr Sarah Gibson, DVM!";
echo str_shift($string);
echo str_shift($string, 50, TRUE);
echo str_shift($string, -25, FALSE, FALSE);
echo str_shift($string, 1/3);
echo str_shift($string, 50, array('lower'=>TRUE, 'digits'=>TRUE));
?>

//===== RESULT =====

Crgre'f 62 crgf (vapy. 0 unzfgref) ybir Qe Fnenu Tvofba, QIZ!
Crgre"f 62 crgf [vapy: 0 unzfgref] ybir Qe Fnenu Tvofba; QIZ?
Jynyl'm 17 jynm (chwf. 5 bugmnylm) fipy Xl Mulub Acvmih, XPG!
Yncna'b 40 yncb (rwlu. 8 qjvbcnab) uxen Ma Bjajq Prkbxw, MEV!
Prgre'f 62 crgf (vapy. 0 unzfgref) ybir De Snenu Gvofba, DVM!

1. The basic parameters are the string and the percentage, 50 by default. The next four parameters allow to select which type of characters to process. There is a good reason why I put less common types first, and most obvious last. To activate extra characters you need only 1 additional parameter, otherwise you would need 4 enabling also the obvious types.

2. The definition for the letters and digits is obvious. For the extra characters I chose kind of pairs that make sense when shifted by 50%, e.g. () => [] or & => + etc. Of course you can adjust those characters to anything you like.

3. The first step is to clean the percentage, and also allow "real" floats, e.g. 1/3 for 33.33%. 

4. The next step secures great flexibility when using the function. As described, instead of 4 boolean parameters you can pass 1 array. E.g. the array('upper' => TRUE) will enable the change of uppercase letters only.

5. Finally the function goes through every type and shifts the characters according to the given percentage.

I hope you can use this function and do some fancy stuff with it. Rotating characters doesn't really make sense, but it can be fun.

Arthur :-)

down

peter at NOSPAM jamit dot com ¶

15 years ago

This ROT13 variant is different from my earlier version in that it retains 'ethnicity'. For example, a Chinese text when encrypted will remain Chinese, and the string will not be making sense (the real meaning will be encrypted). Just look at the code and you will understand.

<?php

function unichar2ords($char, $encoding = 'UTF-8') {        
    $char = mb_convert_encoding($char, 'UCS-4', $encoding);
    $val = unpack('N', $char);            
    return $val[1];
    }

function ords2unichar($ords, $encoding = 'UTF-8'){
    $char = pack('N', $ords);
    return mb_convert_encoding($char, $encoding, 'UCS-4');            
    }

function mbStringToArray ($string, $encoding = 'UTF-8') {
    if (empty($string)) return false;
    for ($strlen = mb_strlen($string, $encoding); $strlen > 0; ) {
        $array[] = mb_substr($string, 0, 1, $encoding);
        $string  = mb_substr($string, 1, $strlen, $encoding);
        $strlen  = $strlen - 1;
        }
    return $array;
    }

function unicodeRotN($str, $offset, $encoding = 'UTF-8') {
    $val = '';
    $array = mbStringToArray ($str, $encoding = 'UTF-8');
    $len = count($array);
    for ($i = 0; $i < $len; $i++) {
        $val .= ords2unichar(unichar2ords($array[$i], $encoding) + $offset, $encoding);
        }
    return $val;
    }

// example

$original = '中國是我的家'; // means "China is my home"

$encrypted = unicodeRotN($string, 13); // 为團昼戞皑寃 means "Ñ Ai injustice for the Mission Day" (Google translation)

$decrypted = unicodeRotN($encrypted, -13); // 中國是我的家

?>

down

maximius at gmail dot com ¶

17 years ago

Perhaps someone will find this useful ;)

<?
           function rotN($s, $n){
                $s2 = "";
                for($i = 0; $i < strlen($s); $i++){
                    $char2 = $char = ord($s{$i});
                    $cap = $char & 32;

                    $char &= ~ $cap;
                    $char = $char > 64 && $char < 123 ? (($char - 65 + $n) % 26 + 65) : $char;
                    $char |= $cap;
                    if($char < 65 && $char2 > 64 || ($char > 90 && $char < 97 && ($char2 < 91 || $char2 > 96))) $char += 26;
                    else if($char > 122 && $char2 < 123) $char -= 52;
                    if(strtoupper(chr($char2)) === chr($char2)) $char = strtoupper(chr($char)); else $char = strtolower(chr($char));
                    $s2 .= $char;
                }
                return $s2;
            }
?>
It takes any string, $s, and any ROT value, $n. Just like str_rot13, it's both an encoder and decoder. To decode an encoded string, just pass -$n instead of $n.

down

Chris ¶

6 years ago

A nice, simple way of using rot-n. Allows for a lot of easy customisation, and works quickly. This function uses ASCII characters and values.

<?php

function rotn($val, $n) {
    $min = 0;
    $max = 127;
    $final = '';
    $new_string = str_split($val);
    
    foreach ($new_string as $letter) {
        $current = ord($letter);
        $val = $current+$n;

        if ($val >= $max) {
            $val = $val - $max;
        }

        if ($val <= $min) {
            $val = $val + $min;
        }

        $current = $val;
        $final .= chr($current);
    }

    return $final;
}

echo 'Test 123 (4) -> '.rotn("Test 123", 4).'<br>'; // Xiwx$567
echo 'Test 123 (8) -> '.rotn("Test 123", 8).'<br>'; // \m{|(9:;
echo 'Test 123 (-4) -> '.rotn("Test 123", -4).'<br>'; // Paop-./

$value = rotn("Test 123", 8);
echo 'Test 123 (Reverse [8 then -8]) -> '.rotn($value, -8).'<br>'; // Test 123

?>

down

-1

agente007_1_ at hotmail dot com ¶

9 years ago

/**
SALVAJE COMENTARIO EN ESPAÑOL XD
*/

<?php  

    
$cadena = $_POST['entrada'];

/**convierte en cadena*/
$array = str_split($cadena);

echo $cadena ."<br>";

for ($i=0; $i < count($array); $i++) { 

if( $array[$i] >= "A" &&  $array[$i] <= "M" ){
$letra = ord($array[$i]);
$letra = $letra + 13;
echo chr($letra);
}

if( $array[$i] >= "N" &&  $array[$i] <= "Z" ){
$letra = ord($array[$i]);
$letra = $letra - 13;
echo chr($letra);
}

}

?>

down

-1

devcoder at gmail dot com ¶

6 years ago

My own generic rotN function

<?php
function rotN($string, $n = 13)
{
    $alphabet = join(range('a', 'z'));
    $alen = strlen($alphabet);

    $n %= $alen;
    if($n < 0) {
        $n += $alen;
    }
    if($n == 0) {
        return $string;
    }

    $cycled = substr($alphabet . $alphabet, $n, $alen);
    $alphabet = $alphabet . strtoupper($alphabet);
    $cycled = $cycled . strtoupper($cycled);
    return strtr($string, $alphabet, $cycled);
}
?>

down

-3

electro at whatever dot com ¶

17 years ago

<?php

/**
 * Rotate each string characters by n positions in ASCII table
 * To encode use positive n, to decode - negative.
 * With n = 13 (ROT13), encode and decode n can be positive.
 * 
 * @param string $string
 * @param integer $n
 * @return string
 */
function rotate($string, $n) {
    
    $length = strlen($string);
    $result = '';
    
    for($i = 0; $i < $length; $i++) {
        $ascii = ord($string{$i});
        
        $rotated = $ascii;
        
        if ($ascii > 64 && $ascii < 91) {
            $rotated += $n;
            $rotated > 90 && $rotated += -90 + 64;
            $rotated < 65 && $rotated += -64 + 90; 
        } elseif ($ascii > 96 && $ascii < 123) {
            $rotated += $n;
            $rotated > 122 && $rotated += -122 + 96;
            $rotated < 97 && $rotated += -96 + 122; 
        }
        
        $result .= chr($rotated);
    }
    
    return $result;
}

$enc = rotate('string', 6);
echo "Encoded: $enc<br/>\n";
echo 'Decoded: ' . rotate($enc, -6);

?>

down

-4

arwab at surrealwebs dot com ¶

17 years ago

here's my rot function, it works anyway
<?php
/**
 * preforms the rotation algorithm on the passed in string
 */
function _rot( $str , $dist=13 ){
    if( !is_numeric($dist) || $dist < 0){
        $dist = 13;
    }

    $u_lower =  65; $u_upper =  90;
    $l_lower =  97; $l_upper = 122;
    
    $char_count = ($u_upper - $u_lower) +1;

    while( $dist > $char_count ){
        $dist -= $char_count;
    }

    $newstr = '';
    
    for( $i=0; $i<strlen($str); ++$i){
        $c = ord($str[$i]);

        /*
         * Check if the character is within the bounds of our function (a-zA-z)
         * if not it gets tacked on to the string as is and we move on to the 
         * next one.
         */
        if( $c<$u_lower || $c>$l_upper || ( $c>$u_upper && $c <$l_lower ) ){
            $newstr .= chr($c);
            continue;
        }

        $lower = ( $c<=$u_upper?$u_lower:$l_lower);
        $upper = ( $c<=$u_upper?$u_upper:$l_upper);

        $c += $dist;

        if( $c > $upper){
            $c = (($c - $upper) + ($lower-1));
        }

        $newstr .= chr($c);
    }
    
    return $newstr;
}
?>

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