(PECL gnupg >= 0.1)
gnupg_sign — Signs a given text
$identifier
   , string $plaintext
   )
   Signs the given plaintext with the keys, which were
   set with gnupg_addsignkey before and
   returns the signed text or the signature, depending on what was set with
   gnupg_setsignmode.
  
identifier
     The gnupg identifier, from a call to gnupg_init() or gnupg.
plaintext
     The plain text being signed.
   On success, this function returns the signed text or the signature.
   On failure, this function returns FALSE.
  
Example #1 Procedural gnupg_sign() example
<?php
$res = gnupg_init();
gnupg_addsignkey($res,"8660281B6051D071D94B5B230549F9DC851566DC","test");
$signed = gnupg_sign($res, "just a test");
echo $signed;
?>
Example #2 OO gnupg_sign() example
<?php
$gpg = new gnupg();
$gpg -> setsignkey("8660281B6051D071D94B5B230549F9DC851566DC","test");
$signed = $gpg -> sign("just a test");
echo $signed;
?>