" - File name as a string (one-octet length, followed by file name),
if the encrypted data should be saved as a file."
but no mention of what if it shouldn't be saved as a file. 0 length,
perhaps?
That's what I'd do.
Then:
" - A four-octet number that indicates the modification date of the
file, or the creation time of the packet, or a zero that
indicates the present time."
I would _guess_ that it means modification date of the file if there's
a filename, the creation time if there isn't. I have no idea what zero
is supposed to mean. Nothing, would be the obvious interpretation -
"the present time" is nonsensical.
I think that the major problem is that OpenPGP gets used for a lot of
things, and this is giving latitude, which always means lack of
clarity. This dates back at least as far as RFC 1991, which says:
... Field (d) [labeled previously as "a time field"]
should be the time at which
the file was last modified, or the time at which the data packet was
created, or 0.
Which is even less helpful, as it doesn't tell us about the zero
option. Unfortunately, this is not only ambiguous, but insufficient.
Let's presume that I've decrypted a packet. If I'm storing that in a
file, it seems to me that I should take that time field and make it be
the creation and modification date of the file, or now if it's zero. If
I'm putting it in a text widget (for example), then obviously I don't
do anything as the time doesn't really apply.
If I am creating a literal packet, I have several options. One is that
I take the modification time of the file, assuming it's available.
Personally, I think if you're transferring files around, you should
preserve the creation time and the modification time, but I'm fussy
that way.
The next option that I have is to put the current time in there. The
reason I might do that is if I think I'm leaking data by doing it, or
-- whatever. If I don't want to put the modification time of the data
in the packet, I can put "now" in there.
The last option is that if I don't want to use *my* now, but the
*recipient's* now, I can put a zero in there.
It's completely up to me to decide for whatever arcane reasons I have
which of those is the right thing to do.
I added to the end of the paragraph there: "It is up to the creator of
the packet which of these they use." Does that help?
Jon