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1<?php 
2/* 
3* Caesar Decryption In PHP
4* Ceded by Himel
5* On 15th July 2018
6* GitHub Username: Swe-HimelRana
7*/
8
9 function caesarEncrypt($text, $key){
10 	// Checking text if it has space I want to create cipher all world indivusally so that when user will decode it he will get original paragraph with spacing.
11 	$word = explode(" ", $text);
12 	$word = array_map('trim', $word); // I like to remove any space in every word just extra code you can avoid it. (This is my habit :P)
13 	// So that we got our word let's get our key. 
14 
15 	// Key should be numaric Needed a validation 
16 	$encryptionKey = $key;
17 	if(!filter_var($key, FILTER_VALIDATE_INT)){ 
18 		$error =  "Key must be Integer";
19 		 return $error;
20 		 die(); 
21 	}
22
23 	// Let's check key is negative or positive
24 	if($key < 0){
25 		$error = "Please Provide a positive key";
26 		return $error;
27 		die();
28 	}
29 	// Let's chek our text only contain alphabets and space
30	if(ctype_alpha(str_replace(' ', '', $text)) === false){
31 		$error = "Only English Alphabets and Space Please!";
32 		return $error;
33 		die();
34 	}
35 	// Let's convert words to uppercase
36 	 $word = array_map('strtoupper', $word);
37
38 	// Now let's create number of all alphabet
39 	$alphabet = range('A', 'Z');
40
41 	// Now encryption time ..
42 	$decryptedText =array(); // array for storing decrypted alphabets
43
44 	 for ($i=0; $i < count($word) ; $i++) { 
45
46 	 	 for ($j=0; $j < strlen($word[$i]) ; $j++) { 
47 	 	 	// Getting alphabet code
48 	 	     $code = array_search($word[$i][$j], $alphabet);
49            
50 	 	 	$code = $code - $encryptionKey;
51 	 	 	// Getting negative number and  working with We don't allow any nagative code ! :P
52 	 	 	while($code < 0){	 	 	
53 	 	 		$code = 26 + $code; 
54 	 	 	}
55 	 	 	// Getting code to alphabet
56 	 	 	// Before converting let's check if it upper then 25
57 	 	 	while($code > 25){
58 	 	 		// If code upper then 25 get result of code % 26 as code
59 	 	 		$code = intval($code % 26);
60 	 	 		 
61 	 	 	}
62 	 	    
63 	 	 	// Now convert Cipher text and add to array
64 	 	 	array_push($decryptedText, $alphabet[$code]);
65 	 	 }
66 	 	 // Adding Space between every word
67 	 	 array_push($decryptedText, ' ');
68 	 }
69
70 	 $decrypted = implode("", $decryptedText);
71 	 return $decrypted;
72 }
73 
74 // Now take input from url as url encoded 
75 $plainText = urldecode($_GET['text']);
76 $secretKey = urldecode($_GET['key']);
77 // Finally Print result 
78 echo caesarEncrypt($plainText, $secretKey);
79?>