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Php Programming Code Examples

Php > Algorithms Code Examples

PHP Function to EncryptDecrypt a string without a known key

PHP Function to EncryptDecrypt a string without a known key The string itself has his own different key for every character <?PHP FUNCTION ENCRYPT_DECRYPT($Str_Message) { //Function : encrypt/decrypt a string message v.1.0 without a known key $Len_Str_Message=STRLEN($Str_Message); $Str_Encrypted_Message=""; FOR ($Position = 0;$Position<$Len_Str_Message;$Position++){ // long code of the function to explain the algoritm //this function can be tailored by the programmer modifyng the formula //to calculate the key to use for every character in the string. $Key_To_Use = (($Len_Str_Message+$Position)+1); // (+5 or *3 or ^2) //after that we need a module division because can�t be greater than 255 $Key_To_Use = (255+$Key_To_Use) % 255; $Byte_To_Be_Encrypted = SUBSTR($Str_Message, $Position, 1); $Ascii_Num_Byte_To_Encrypt = ORD($Byte_To_Be_Encrypted); $Xored_Byte = $Ascii_Num_Byte_To_Encrypt ^ $Key_To_Use; //xor operation $Encrypted_Byte = CHR($Xored_Byte); $Str_Encrypted_Message .= $Encrypted_Byte; //short code of the function once explained //$str_encrypted_message .= chr((ord(substr($str_message, $position, 1))) ^ ((255+(($len_str_message+$position)+1)) % 255)); } RETURN $Str_Encrypted_Message; } //end function //sample use of the function $Str_Test="This function is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation in any version of the License."."<br>"."This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE."."<br>"."Hello Aitor, Wellcome Home"."<br>"; ECHO $Str_Test."<br>"; $Str_Test2 = ENCRYPT_DECRYPT($Str_Test); ECHO $Str_Test2."<br><br>"; $Str_Test3 = ENCRYPT_DECRYPT($Str_Test2); ECHO "<br>".$Str_Test3."<br>"; ?>