how i can transpose this program to make the decryption

Question

file name ekripsi.php

<?php
include_once("enc.lib.php");
$plaintext = block('5 TEKNIK DASAR KRIPTOGRAFI','6');
$a = ($plaintext);
echo $a.'<br/>';
?>

file enc.lib.php
<?php
function block($msg,$m)
{
$x=array();
for($i=0;$i<strlen($msg);$i++)
{
$c = $i%$m;
$x[$c] =(isset($x[$c])?$x[$c]:'').substr($msg,$i,1);
}
return join('',$x);
}
?>

Answer 1

it's called cryptography blocking method, the plaintext is divided into blocks consisting of several characters. this is one of the old cryptography techniques.
i dont understand how to make program for decryption.
i made to .php file , the lib and the encrypt

Answer 2

can you write in source code, because i dont really understand , thanks in advance, sorry

Answer 3

can i text you via Facebook, Instagram , whatsapp or others?

Answer 4

can you explain your how the encryption works ? some part doesnt make sense to me

Answer 5

sorry for late answer
i got it, now it make sense to me
its still rough but maybe you can try.
first get the value of textlength%key lets call this leftover, next seperate the block by (textlength-leftover)/key lets call this blocklength. now get block. if the leftover is not 0 then substring the text from 0 to blocklength+1 then reduce left over by 1. then continue and store them in array as a block. now the block are seperated in array all you need to do is arrange them

Answer 6

leftover=text.length%m
blocklen=(text.length-leftover)/m
block=[]
k=0
while i < text.length
j = blocklen
if(leftover>0)
j++
leftover--
if(j>text.length)
j=text.length
block[k++]= text.substring(i,j)
i=j
s=""
for i = 0, i < block[0].length
for j=0, j<block.size
s+=block[j].charat(i)

Answer 7

nice