Encrypt and Decrypt word using openssl_encrypt and openssl_decrypt

First You need to create 2 keys ( secret_key and secret_iv )  

PHP Code:

// Encryption Method
function encrypt($string) {
    $output = false;
     $encrypt_method = "AES-256-CBC";
	
    $secret_key = 'regYUDkbbdsc78yyBJB7J';
    $secret_iv = 'UIBbsvvjJHWUkubBubIVU';
  
    // hash
    $key = hash('sha256', $secret_key);
    
    $iv = substr(hash('sha256', $secret_iv), 0, 16);
   
        $output = openssl_encrypt($string, $encrypt_method, $key, 0, $iv);
        $output = base64_encode($output);
    
    return $output;
}

// Decryption Method
function decrypt($string) {
    $output = false;

    $encrypt_method = "AES-256-CBC";
    $secret_key = 'regYUDkbbdsc78yyBJB7J';
    $secret_iv = 'UIBbsvvjJHWUkubBubIVU';

    // hash
    $key = hash('sha256', $secret_key);

    // iv - encrypt method AES-256-CBC expects 16 bytes - else you will get a warning
    $iv = substr(hash('sha256', $secret_iv), 0, 16);
    
        $output = openssl_decrypt(base64_decode($string), $encrypt_method, $key, 0, $iv);
    
    return $output;
}
$msg = '';
if(isset($_POST['btn_encrypt'])){
$str = $_POST['str'];
$result = encrypt($str);
$msg = $result;
}
else if(isset($_POST['btn_decrypt'])){
$str = $_POST['str'];
$result = decrypt($str);
$msg = $result;
}

CSS Code:

        .wraper{
			width:80%;
			margin:auto;
			text-align:center
		}
		.input-field{
		    width: 40%;
			height: 35px;
			display: block;
			text-align:center;
			margin: auto;
		}
		.btn-group{
			    margin-top: 20px;
		}
		.btn-group input{
			border: none;
			color: #fff;
			padding: 8px 25px;
			font-weight: bold;
		}
		.success{
			background:#5CB85C
		}
		.danger{
			background:#D9534F
		}

HTML Code:

<div class="wraper">
	<div class="form-group">
	<h2>Custom Encryption and Decryption of the input word</h2>
	<form action="" method="post">
		<input type="text" name="str" value="<?php echo @$_POST['str']; ?>" class="input-field" placeholder="Enter your encrypted string to decrypt / word to encrypt..">
		<div class="btn-group">
		<input type="submit" class="success" name="btn_encrypt" value="Encrypt">
		<input type="submit" class="danger" name="btn_decrypt" value="Decrypt">
		</div>
		</form>
		<?php echo $msg; ?>
	</div>
</div>