Pretty Curved Privacy (pcp1) is a commandline utility which can be used to encrypt files. 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.

Caution: since CURVE25519 is no accepted standard, 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 GNUPG. So, if you already know how to use gpg, you'll feel almost home.

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 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 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 [email protected]

                                   pcp1 -d -I letter.asc | less

And that's it.

Please note the big difference to 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.

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 -I has not been specified. It works the same with -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 -X (--password-file) has been used and is set to -, 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 -X -, and vice versa. IF you use -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.

There are currently no packages available, so pcp has to be compiled from source. Follow these steps:

First, you will need libsodium:

git clone git://github.com/jedisct1/libsodium.git
cd libsodium
./autogen.sh
./configure && make check
sudo make install
sudo ldconfig
cd ..

If you want to have JSON support, you'll need to install the Jansson library (optional):

git clone git://github.com/akheron/jansson.git
cd jansson
autoreconf -i
./configure && make
sudo make install
cd ..

In order to use the python binding, you need to install the cffi python package.

Next, build pcp:

git clone git://github.com/tlinden/pcp.git
cd pcp
./configure
sudo make install
cd ..

Optionally, you might run the unit tests:

make test

To learn how to use pcp, read the manpage:

man pcp1

Copyright (c) 2013-2015 by T.v.Dein <tom AT vondein DOT org>

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T.v.Dein <tom AT vondein DOT org>

Licensed under the GNU GENERAL PUBLIC LICENSE version 3.

The homepage of Pretty Curved Privacy can be found on http://www.daemon.de/PrettyCurvedPrivacy. The source is on Github: https://github.com/TLINDEN/pcp