Question

give me a example

Develop a set of functions that will allow you to encrypt a string using a Caesar cipher.

Develop a set of functions that will allow you to decrypt a string using a Caesar cipher.

Develop a set of functions that will help you to solve (break) a Caesar cipher.

Encrypt, Decrypt, Solve in BASIC 1

Encrypt, Decrypt, Solve in Scala (in a procedural manner)

Answer 1

The encryption can be represented using modular arithmetic by first transforming the letters into numbers, according to the scheme, A = 0, B = 1,…, Z = 25. Encryption of a letter by a shift n can be described mathematically as.

(Encryption Phase with shift n)

(Decryption Phase with shift n)

Examples are :

Text : ABCDEFGHIJKLMNOPQRSTUVWXYZ
Shift: 23
Cipher: XYZABCDEFGHIJKLMNOPQRSTUVW

Text : ATTACKATONCE
Shift: 4
Cipher: EXXEGOEXSRGI

Algorithm for Caesar Cipher:

Input:

1. A String of lower case letters, called Text.
2. An Integer between 0-25 denoting the required shift.

Procedure:

• Traverse the given text one character at a time .
• For each character, transform the given character as per the rule, depending on whether we’re encrypting or decrypting the text.
• Return the new string generated.

Encryption and Decryption in scala:

$KEY = "Your KEY";
$IV = "Your IV";
function addpadding($string, $blocksize = 32)
{
    $len = strlen($string);
    $pad = $blocksize - ($len % $blocksize);
    $string .= str_repeat(chr($pad), $pad);
    return $string;
}
function strippadding($string)
{
    $slast = ord(substr($string, -1));
    $slastc = chr($slast);
    $pcheck = substr($string, -$slast);
    if(preg_match("/$slastc{".$slast."}/", $string)){
        $string = substr($string, 0, strlen($string)-$slast);
        return $string;
    } else {
        return false;
    }
}
function encrypt($string = "")
{
    global $KEY,$IV;
    $key = base64_decode($KEY);
    $iv = base64_decode($IV);
    return base64_encode(mcrypt_encrypt(MCRYPT_RIJNDAEL_256, $key,  addpadding($string), MCRYPT_MODE_CBC, $iv));
}
function decrypt($string = "")
{
    global $KEY,$IV;
    $key = base64_decode($KEY);
    $iv = base64_decode($IV);
    $string = base64_decode($string);
    return strippadding(mcrypt_decrypt(MCRYPT_RIJNDAEL_256, $key, $string, MCRYPT_MODE_CBC, $iv));
}