PHP: error when encrypting and decrypting with openSSL

Question

I've been trying to make two PHP pages, one to encrypt and one to decrypt.

The code for the encrypting page:

<form action="encrypt.php" method="post">
<input type="text" name="data">
<input type="submit">
</form>

<?php
    if($_SERVER["REQUEST_METHOD"] == "POST")
    {
        $config = array(
                "digest_alg" => "sha512",
                "private_key_bits" => 4096,
                "private_key_type" => OPENSSL_KEYTYPE_RSA,
                );
        $keys = openssl_pkey_new($config);
        openssl_pkey_export($keys, $privKey);    
        $pubKey = openssl_pkey_get_details($keys);
        $pubKey = $pubKey["key"];

        require "openssl.php";
        openssl_public_encrypt($_POST["data"],$encrypted, $pubKey);
        echo $encrypted;
        echo "<br><br>";
        echo $privKey;
    }

    ?>

And this is the code for decrypting:

<form action="decrypt.php" method="post">
Encrypted Text: <textarea name="encrypted" rows="10" cols="100"></textarea><br><br>
Key: <textarea name="key" rows="10" cols="100"></textarea><br>
<input type="submit">
</form>

<?php
    if($_SERVER["REQUEST_METHOD"] == "POST")
    {
        openssl_private_decrypt($_POST["encrypted"],$decrypted,$_POST["key"]);
        echo $decrypted;
    }
?>

It seems to encrypt the data just fine, but when I try to decrypt using the other page, a get an error:

openssl_private_decrypt() [function.openssl-private-decrypt]: key parameter is not a valid private key

I copied and pasted the private key directly from the output of the encrypting file. Why am I getting an error?

Answer 1

It seems to encrypt the data just fine,

First thing to debug: Can you immediately decrypt your encrypted message on the encryption page and get the same plaintext message?

openssl_private_decrypt() [function.openssl-private-decrypt]: key parameter is not a valid private key

Your code contains:

 openssl_private_decrypt($_POST["encrypted"],$decrypted,$_POST["key"]); 

Try this instead:

$private = openssl_pkey_get_private($_POST['key']);
openssl_private_decrypt($_POST["encrypted"], $decrypted, $private);

---

A word about security : OpenSSL's default settings for RSA encryption are not secure .

For best results, in any real world applications that need public-key cryptography, consider switching to libsodium and just using the crypto_box_seal API instead.