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Don Alexander Eckford's Encryption/Decryption Demo

GOTO Decrypt
To understand more about this Encryption method (AES-256-CBC) see: Review this article.
"AES would take billions of years to break using current computing technology. Hackers would be foolish to even attempt this [brute-force] type of attack." -- taken from above article
CODE FOLLOWS

<?php
    include('includes/header.php');

    // code
    error_reporting(E_ALL);    // set error reporting to all
    $self = basename($_SERVER['SCRIPT_NAME']);

    $string = isset($_POST['string']) ? $_POST['string'] : "Now is the time.";

    $action = 'encrypt';
    $encrypted = encrypt_decrypt($action, $string);

    ?>

    <h1> Don Alexander Eckford's Encryption/Decryption Demo</h1>

    <form action="<?php echo($self); ?>" method="POST">

        <fieldset>
            <legend>String to be Encrypted</legend>
            <label>
    <textarea rows="10" cols="120" type="text" name="string" value="<?php echo($string); ?>">
    <?php echo($string); ?>
    </textarea>
            </label>
            <br>
        </fieldset>

        <br> <br>

        <fieldset>
            <legend>Encrypted String</legend>
            <label>
    <textarea rows="10" cols="120" type="text" name="encrypted" value="">
    <?php echo($encrypted); ?>
    </textarea>
            </label>
            <br>
        </fieldset>

        <p>
            <input type="submit" name="submit" value="Encrypt">
        </p>

    </form>

    <a href="decrypt.php">GOTO Decrypt</a>

    <p>
        To understand more about this Encryption method (AES-256-CBC) see:
        <a href="https://www.n-able.com/blog/aes-256-encryption-algorithm"> Review this article. </a>
    </p>

    <p>
        <div class="blue">
            "AES would take billions of years to break using current computing technology.
            Hackers would be foolish to even attempt this [brute-force] type of attack." -- taken from above article
        </div>

    </p>

    <?php

    // ======== functions ============

    function encrypt_decrypt($action, $string)
    {

        $output = false;
        $encrypt_method = "AES-256-CBC";

        // the following two values should be changed for your personal use.

        $secret_key = 'Epur si muove';
        $secret_iv = 'non sum qualis eram';

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

        // encrypt method AES-256-CBC expects 16 bytes.
        $iv = substr(hash('sha256', $secret_iv), 0, 16);

        if ($action == 'encrypt')
        {
            $output = base64_encode(openssl_encrypt($string, $encrypt_method, $key, 0, $iv));
        }
        else
        {
            if ($action == 'decrypt')
            {
                $output = openssl_decrypt(base64_decode($string), $encrypt_method, $key, 0, $iv);
            }
        }
        return $output;
    }

    include('includes/footer.php');
?>
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