Encrypt Files Using Pgp in PHP

Encrypt files using PGP in PHP?

Question 1: About PGP

• PGP (Pretty Good Privacy) is a product and trademark of Symantec Corporation (they bought it some years ago).
• OpenPGP is the standard used by PGP.
• GnuPG (Gnu Privacy Guard) is a free and open source implementation of PGP.

So what you want to do is encrypt to an OpenPGP key. Which implementation of OpenPGP your client uses to decrypt the data is not important for you. With PHP, commonly GnuPG is used and there are interfaces built-in.

Question 2: Using GnuPG in PHP

Use the GnuPG interface, which is an extension that can be installed for PHP.

At first, import the key, where $keydata is the ASCII armored public key:

<?php
$gpg = new gnupg();
$info = $gpg -> import($keydata);
print_r($info);
?>

Then use this key to encrypt the data, this time using the client's key's fingerprint:

<?php
  $gpg = new gnupg();
  $gpg -> addencryptkey("8660281B6051D071D94B5B230549F9DC851566DC");
  $enc = $gpg -> encrypt("just a test");
  echo $enc;
?>

If you want to encrypt files, read and pass them to encrypt(). Be sure to use at least long key IDs (eg. DEADBEEFDEADBEEF), better fingerprints (as in the example) when referencing keys; and never use short key IDs (DEADBEEF), as those are vulnerable to collision attacks.

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The is a more comprehensive example for doing both added by a user in the PHP manual.

How do I encrypt a file with gnupg and php?

Refering to the PHP-manpages (https://www.php.net/manual/en/function.gnupg-setarmor.php) the default output is a text file with base64 encoded data:

-----BEGIN PGP MESSAGE-----
Version: GnuPG v2.0.22 (GNU/Linux)
hQMOAx1dL4VEMtgUEAv/cOuJDBZ8FIYk7kqsh2vOvW2WRUvOUi54xm1LPGxLPiMS
...

Using the gnupg-setarmor function you can set the output to a binary output:

gnupg_setarmor($res,0);

Here is the complete code:

<?php
// init
$res = gnupg_init();
// # add this line
gnupg_setarmor($res,0); // deactivate default armored output
gnupg_addencryptkey($res,"8660281B6051D071D94B5B230549F9DC851566DC");
$enc = gnupg_encrypt($res, "just a test");
echo $enc;
?>

PGP Encryption - PHP openssl

OpenSSL does not support OpenPGP, formats and protocols are different. Together with PHP, the most reasonable way to go is interfacing GnuPG using PHP's GnuPG module, I provided an example in the question Encrypt files using PGP in PHP?. Accessing GnuPG directly might be possible if you can execute arbitrary applications from PHP, but this will very likely be restricted (and is considerably more dangerous regarding exploitability).

If you're asked to send OpenPGP encrypted messages but have no access to GnuPG and this module, find another hosting company providing GnuPG, ask your current provider to do so or setup your own web server.

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