pcp/man/pcp.pod

=head1 DESCRIPTION

B<Pretty Curved Privacy> (pcp1) is a commandline utility which can
be used to encrypt files. B<pcp1> uses eliptc curve cryptography
for encryption (CURVE25519 by Dan J. Bernstein). While CURVE25519
is no worldwide accepted standard it hasn't been compromised by
the NSA - which might be better, depending on your point of view.

B<Caution>: since CURVE25519 is no accepted standard, B<pcp1> has
to be considered as experimental software. In fact, I wrote it just
to learn about the curve and see how it works.

Beside some differences it works like B<GNUPG>. So, if you already
know how to use gpg, you'll feel almost home.

=head1 QUICKSTART

Lets say, Alicia and Bobby want to exchange encrypted messages.
Here's what the've got to do.

First, both have create a secret key:

 Alicia                             Bobby
 pcp1 -k                            pcp1 -k

After entering their name, email address and a passphrase to protect
the key, it will be stored in their B<vault file> (by default ~/.pcpvault).

Now, both of them have to export the public key, which has to be
imported by the other one. With B<pcp> you can export the public
part of your primary key, but the better solution is to export
a derived public key especially for the recipient:

 Alicia                             Bobby
 pcp1 -p -r Bobby -O alicia.pub     pcp1 -p -r Alicia -O bobby.pub

They've to exchange the public key somehow (which is not my
problem at the moment, use ssh, encrypted mail, whatever). Once exchanged,
they have to import it:

 Alicia                             Bobby
 pcp1 -K -I bobby.pub               pcp1 -K -I alicia.pub

They will see a response as this when done:

 key 0x29A323A2C295D391 added to .pcpvault.

Now, Alicia finally writes the secret message, encrypts it and
sends it to Bobby, who in turn decrypts it:

 Alicia                             Bobby
 echo "Love you, honey" > letter
 pcp1 -e -r Bobby -I letter -O letter.asc
 cat letter.asc | mail bobby@foo.bar

                                    pcp1 -d -I letter.asc | less

And that's it.

Please note the big difference to B<GPG> though: both Alicia
AND Bobby have to enter the passphrase for their secret key!
That's the way CURVE25519 works: you encrypt a message using
your secret key and the recipients public key and the recipient
does the opposite, he uses his secret key and your public key
to actually decrypt the message.

Oh - and if you're wondering why I named them Alicia and Bobby:
I was just sick of Alice and Bob. We're running NSA-free, so we're
using other sample names as well.

=head1 FILES AND PIPES

Pcp behaves like any other unix tool. If not otherwise specified
it will read input from standard input (STDIN) and print output
to standard output (STDOUT). For instance:

 pcp1 -e -O output

will read the text to be encrypted from standard input, because B<-I>
has not been specified. It works the same with B<-O>:

 pcp1 -e -I myfile

In this case the encrypted result will be written to standard output.

Therefore it is possible to use pcp within pipes. Another more
realistic example:

 ssh remote cat file | pcp1 -ez | mailx -s 'as requested' bob@somewhere

here we encrypt a file symmetrically without downloading it from a
remote ssh server and sending the encrypted result via email to
someone.

The behavior is the same with any other functionality where files are involved
like importing or exporting keys. However, there's one exception:
If the option B<-X> (B<--password-file>) has been used and is set
to B<->, then this will take precedence over any other possible use
of standard input. So if you want to encrypt something and don't 
specify an input file you cannot use B<-X ->, and vice versa. IF
you use B<-X -> the passphrase will be read from standard input, which
then can't be used further for input files elsewhere. Pcp will exit
with an error in such a case.