Encrypting from web form to file: permissions error

[Parker Morse]

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I'm working on encrypting the output of a form on our website to a 
file, with the idea of then downloading the files from the web server 
and decrypting locally. I'm using PHP, like so (edited and line-wrapped 
for email):

shell_exec("echo $for_encryption | /usr/bin/gpg -e --no-secmem-warning 
- -ao \
  /path/to/file.asc -r \"Keyname\"");

I have successfully taken form output and encrypted it to an email 
message with a different form of this command. However, the line above 
now generates this error in the server error log:

gpg: fatal: /root/.gnupg: can't create directory: Permission denied
secmem usage: 0/0 bytes in 0/0 blocks of pool 0/16384

...and the output of the shell_exec() above is nothing.

Now, PHP is running as "nobody", so I'm not surprised that it can't 
create a directory in /root/. But why does it feel that it needs to? 
Isn't ~/.gnupg enough? How can I fix this?

If this is a PHP problem, not a GPG problem, please let me know.

Thanks in advance,

pjm
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