Redirect form data in encrypted form to another domain

I found a solution of my problem and sharing with everyone. This solution works in 4 steps as follow.

Step 1: For encryption and decryption, I am using following functions in my functions.php file.

function Encryptstr($password, $data)
{

    $salt = substr(md5(mt_rand(), true), 8);

    $key = md5($password . $salt, true);
    $iv  = md5($key . $password . $salt, true);

    $ct = mcrypt_encrypt(MCRYPT_RIJNDAEL_128, $key, $data, MCRYPT_MODE_CBC, $iv);

    return base64_encode('Salted__' . $salt . $ct);
}
function Decryptstr($password, $data)
{

    $data = base64_decode($data);
    $salt = substr($data, 8, 8);
    $ct   = substr($data, 16);

    $key = md5($password . $salt, true);
    $iv  = md5($key . $password . $salt, true);

    $pt = mcrypt_decrypt(MCRYPT_RIJNDAEL_128, $key, $ct, MCRYPT_MODE_CBC, $iv);

    return $pt;
}

I was told that encryption function can't be performed on action path of form directly So I am using another way for it. I am redirecting form to a page and on that page I am encrypting my form field.

Step 2:
First build a simple form like this and in action of form I have given path of page in which I will perform encryption

<form action="http://localhost:85/xyz/" method="POST">  //In action I am giving path to the page in which I will perform encryption     
    <input type="text" name="fname" placeholder="First Name">
    <input type="submit" value="Login">
</form>

Step 3: After form redirect to this page, I store data of my form field in a variable and encrypt it as follow

$name = $_POST['fname']; //fname is the name of the form control (Text Box)
// Performing encryption on it like this
$encrypt = Encryptstr('myPass123', $name); // Here "myPass123" is the key that will be use to encrypt and decrypt and "Encryptstr" Is function that I have put in functions.php as shown above.

After encrypt form data and storing it in a variable ($encrypt) I make another form whith hidden fields But in this form I am using GET method instead of POST.

<form action="http://localhost:85/abc/" method="GET">
    First name:<br>
    <input type="hidden" name="fname" value="<?php echo $encrypt; ?>">
    <input type="submit" value="Login">
</form>

In the value field of form's hidden field I used $encrypt varible in which I have stored the encrypted form of data earlier. I put it in value option so that we don't need to enter value again. And after clicking on Submit button form will send data to my mentioned page (Mentioned in action of form).

So this data will transmit via url something like this

http://localhost:85/abc/?fname=sdfhf3jh4jhdfjsdffsf

As you can see fname field is encrypted if I haven't put encryption then output will be like this

http://localhost:85/abc/?fname=Entered_value_by_user

Step 4: So in last step I just need to fetch data from url for that I used GET method like this. This is the page where encrypted data redirects

if(isset($_GET['fname']))    //Getting the value of fname field from url via GET method
{
    $entry = $_GET['fname'];  // Storing value in a variable
    //Decripting value using Decryptstr function where 'myPass123' is the key that we used to encrypt and same key needed to decrypt
    echo 'Result: '.Decryptstr('myPass123', $entry); 
}

Reference: http://heiswayi.github.io/php-encryption-decryption-and-password-hashing.html

Note: This method works very well But I don't know what is the level of security this method provides. I had two option for encryption first using ECB and second using CBC. So I searched on google to find out which is more secure to use. So I found a good article that describes ECB vs CBC In detail. And after reading article I found that cbc is more secure. Thats why I am using CBC.