Encrypt files using PGP in PHP?

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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.

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

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