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=head1 NAME
Pretty Curved Privacy - File encryption using eliptic curve cryptography.
=head1 SYNOPSIS
Usage: pcp1 [options]
General Options:
-V --vault <vaultfile> Specify an alternate vault file.
The deault vault is ~/.pcpvault.
-O --outfile <file> Output file. If not specified, stdout
will be used.
-I --infile <file> Input file. If not specified, stdin
will be used.
-i --keyid <id> Specify a key id to import/export.
-r --recipient <string> Specify a recpipient, used for public
key export and encryption.
-t --text Print textual representation of some
item. Specify -V to get info about a
vault, -i to get info about a key id
installed in the vault or -I in which
case it determines itself what kind of
file it is.
-h --help Print this help message.
-v --version Print program version.
-D --debug Enable debug output.
Keymanagement Options:
-k --keygen Generate a CURVE25519 secret key. If
the generated key is the first one in
your vault, it will become the primary
secret key. If an output file (-O) has
been specified, don't store the generated
key to the vault but export it to the
file instead. You will be asked for
an owner, mail and a passphrase. If you
leave the passphrase empty, the key will
be stored unencrypted.
-l --listkeys List all keys currently stored in your
vault. Only the key id's and some info
about the keys will be printed, not the
actual keys.
-R --remove-key Remove a key from the vault. Requires
option -i <keyid>.
-s --export-secret Export a secret key. If your vault only
contains one secret key, this one will
be exported. If a key id have been
specified (-i), this one will be used.
If there are more than one secret keys
in the vault and no key id has been
given, export the primary secret key.
Use -O to export to a file.
-p --export-public Export a public key. If no key id have
been specified, the public part of your
primary secret key will be exported.
Use -O to export to a file.
-S --import-secret Import a secret key. Use -I to import
from a file.
-P --import-public Import a public key. Use -I to import
from a file.
-y --export-yaml Export all keys stored in your vault
as YAML formatted text. Use -O to put
the export into a file.
Encryption Options:
-e --encrypt Encrypt a message. Read from stdin or
specified via -I. If a keyid (-i) has been
given, use that public key for encryption.
If a recipient (-r) has been given, use
a derived public key. If none of -i or
-r has been given, use the primary
secret key and the public part of it
for encrytion (self-encryption mode).
-d --decrypt Decrypt a message. Read from stdin or
specified via -I. Output to stdout or
written to the file specified via -O.
The primary secret key will be used for
decryption, if there is no primary and
just one secret key in the vault, this
one will be used. Otherwise you'll have
to specify the keyid (-i) of the key.
Signature Options:
-g --sign Create a signature of file specified with
-I (or from stdin) using your primary
secret key. If -r has been given, a derived
secret key will be used for signing.
-c --check-signature <file> Verify a signature in file <file> against
the file specified with -I (or stdin).
The public key required for this must
exist in your vault file.
Encoding Options:
-z --z85-encode Encode something to Z85 encoding. Use
-I and -O respectively, otherwise it
stdin/stdout.
-Z --z85-decode Decode something from Z85 encoding. Use
-I and -O respectively, otherwise it
stdin/stdout
=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 -P -I bobby.pub pcp1 -P -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 -i 0x29A323A2C295D391 -I letter -O letter.z85
cat letter.z85 | mail bobby@foo.bar
pcp1 -d -I letter.z85 | 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.
# -*-perl-*-
=head1 PCP1 KEYS
B<pcp1> keys are stored in a binary file, called B<the vault>.
It's by default located in B<~/.pcpvault> but you can of course
specify another location using the B<-V> option.
There are two kinds of keys: secret and public keys. In reality
a secret key always includes its public key. Both types of keys
can be exported to files and transfered to other people who can
then import them. You should usually only do this with public keys
though.
There is a primary secret key which will always used for operations
when no keyid has been specified. However, you may have as many
secret keys in your vault as you like.
Each key can be identified using its B<keyid> which looks like this:
0xD49119E85266509F
A public key exported from a secret key will have the same keyid
as the secret key. When using for encryption, the keyid will be
added to the message so that the receiver knows who was the
sender of the message (B<This might change in the future. As of
this writing I'm not sure if this was a good idea>).
If you just want to know details about a key or the vault, use the
B<-t> option.
=head2 Derived Public Keys
In the real world you would not use your primary key to encrypt
messages, because this would require to send the public key part
to your recipient in one way or another. The much better and more
secure way is to use a B<Derived Public Key>:
Such a key will be dynamically generated from a hash of your
primary secret key and the recipient (an email address, name or key id).
The public part of this dynamic key will be exported and sent to
the recipient. A public key generated this way will only be usable
by the recipient (and yourself) and each recipient will have a different
public key from you (and vice versa).
=head1 ENCRYPTION
There are 3 modi for encryption available in pcp1:
=over
=item B<Standard public key encryption>
In this mode, which is the default, a public key as specified
with B<-i> and the primary secret key will be used for encryption.
The public key in question maybe a derived public key, which
is transparent for the sender however.
If you don't use derived keys, you will have to transfer
the public key part of your primary keypair to the recipient,
which is considered insecure if the transfer channel itself
uses untrusted transports or if the transferred public key
ends up on a public system (a shared server, a workstation
at your employer or the like). You should avoid this encryption
mode in such cases and use derived keys instead.
Example command:
pcp1 -e -i 0x2BD734B15CE2722D -I message.txt -O cipher.z85
Here we didn't specify a recipient. Therefore the public
key given with -i will be used directly.
=item B<Derived public key encryption>
Derived keys will be generated dynamically at runtime
(see B<Derived Public Keys> above). Therefore an exported
derived public key is unique for the sender AND recipient.
This mode can be considered the most secure. If such a key
gets lost (or into the wrong hands), only this specific
communication channel will be compromised.
Example command:
pcp1 -e -r bobby@local -I message.txt -O cipher.z85
We specified a recipient. pcp1 searches the vault for a
matching public key and generates a derived keypair for
encryption. You need to have a public key installed from
the recipient anyway, it won't work without one. You may
also specify a key id (-i) as well to make sure, the right
key will be used for derivation.
=item B<Self encryption mode>
Pretty Curved Privacy doesn't provide symetric file encryption.
However there are cases when you need to encrypt a file just
for yourself. In such a case the file will be encrypted using
the public key part of your primary secret key and the secret
key itself (thanks to the wonders of ECC this works like a charm).
The file can be decrypted using the primary key pair.
While this works, the security of it totally depends on the
strength of your password, especially if the primary secret
used for this kind of encryption is stored in a vault on the
same system.
Example command:
pcp1 -e -I message.txt -O cipher.z85
As you can see we didn't specify -i or -r and therefore pcp1
tries to use the primary keypair for encryption.
=back
=head1 VULNERABILITIES
Currently there are a couple of problems which are not
addressed. These are usually protocol problems, which are
not caused by pcp1.
=over
=item B<No secure native key exchange for store-and-forward systems>
Pretty Curved Privacy is a store-and-forward system, it works
on files and can't use any cool key exchange protocols therefore.
For example there would be B<CurveCP> which guarantees a
secure key exchange. But CurveCP cannot be used offline.
Users have to find other means to exchange keys. That's a pity
since with Curve25519 you can't just publish your public key
to some key server because in order to encrypt a message, both
the recipient AND the sender need to have the public key of
each other. It would be possible to publish public keys,
and attach the senders public key to the encrypted message, but
I'm not sure if such an aproach would be secure enough.
=item B<Curve25519 not widely adopted>
At the time of this writing the ECC algorithm Curve25519
is only rarely used, in most cases by experimental software
(such as Pretty Curved Privacy). As far as I know there haven't
been done the kind of exessive crypto analysis as with other
ECC algorithms.
While I, as the author of pcp1 totally trust D.J.Bernstein, this
may not be the case for you.
In short, I'd suggest not to use it on critical systems yet.
=back
=head1 INTERNALS
=head2 VAULT FORMAT
The vault file contains all public and secret keys. It's a portable
binary file.
The file starts with a header:
+-------------------------------------------+
| Field Size Description |
+-------------------------------------------+
| File ID | 1 | Vault Identifier 0xC4 |
+-------------------------------------------+
| Version | 4 | Big endian, version |
+-------------------------------------------+
| Checksum | 32 | SHA256 Checksum |
+-------------------------------------------+
The checksum is a checksum of all keys.
The header is followed by the keys. Each key is preceded by a
key header which looks like this:
+--------------------------------------------+
| Field Size Description |
+--------------------------------------------+
| Type | 1 | Key type (S,P,M) |
+--------------------------------------------+
| Size | 4 | Big endian, keysize |
+--------------------------------------------+
| Version | 4 | Big endian, keyversion |
+--------------------------------------------+
| Checksum | 32 | SHA256 Key Checksum |
+--------------------------------------------+
Type can be one of:
PCP_KEY_TYPE_MAINSECRET 0x01
PCP_KEY_TYPE_SECRET 0x02
PCP_KEY_TYPE_PUBLIC 0x03
The key header is followed by the actual key, see below.
=head2 SECRET KEY FORMAT
A secret key is a binary structure with the following format:
+---------------------------------------------------------+
| Field Size Description |
+-------------+--------+----------------------------------+
| Public | 32 | Curve25519 Public Key Part |
+-------------|--------|----------------------------------+
| Secret | 32 | Curve25519 Secret Key Unencrypted|
+-------------|--------|----------------------------------+
| ED25519 Pub | 32 | ED25519 Public Key Part |
+-------------|--------|----------------------------------+
| ED25519 Sec | 64 | ED25519 Secret Key Unencrypted |
+-------------|--------|----------------------------------+
| Nonce | 24 | Nonce for secret key encryption |
+-------------|--------|----------------------------------+
| Encrypted | 48 | Encrypted Curve25519 Secret Key |
+-------------|--------|----------------------------------+
| Owner | 255 | String, Name of Owner |
+-------------|--------|----------------------------------+
| Mail | 255 | String, Email Address |
+-------------|--------|----------------------------------+
| ID | 17 | String, Key ID |
+-------------|--------|----------------------------------+
| Ctime | 4 | Creation time, sec since epoch |
+-------------|--------|----------------------------------+
| Version | 4 | Key version |
+-------------|--------|----------------------------------+
| Serial | 4 | Serial Number |
+-------------|--------|----------------------------------+
| Type | 1 | Key Type |
+-------------+--------+----------------------------------+
Some notes:
The secret key fields will be filled with random data if the
key is encrypted. The first byte of it will be set to 0 in that
case.
The key id is a computed JEN Hash of the secret and public
key concatenated, put into hex, as a string.
The key version is a static value, currently 0x2. If the key
format changes in the future, this version number will be
increased to distinguish old from new keys.
Exported keys will be encoded in Z85 encoding. When such an
exported key is imported, only the actual Z85 encoded data
will be used. Header lines and lines starting with whitespace
will be ignored. They are only there for convenience.
Key generation works like this:
=over
=item *
Generate a random seed (32 bytes).
=item *
Generate a ED25519 keypair from that seed.
=item *
Take the first 32 bytes of the generated ED25519 secret
and generate a SHA512 hash from it.
=item *
Clamp bytes 0 and 31 which turns it into a Curve25519 secret.
=item *
Do scalar multiplication from that secret to retrieve
the matching public key.
=back
Take a look at the function B<pcp_keypairs()> for details.
=head2 ENCRYPTED OUTPUT FORMAT
Encrypted output will always be Z85 encoded and has the following
format:
+---------------------------------------------------------+
| Field Size Description |
+-------------+--------+----------------------------------+
| Hash | 32 | Hash of the sender key id |
+-------------|--------|----------------------------------+
| Encrypted | ~ | The actual encrypted data |
+-------------|--------|----------------------------------+
=head2 SIGNATURE FORMAT
Signatures will always be Z85 encoded and have the following
format:
+---------------------------------------------------------+
| Field Size Description |
+-------------+--------+----------------------------------+
| Key ID | 17 | Signers key id
+-------------|--------|----------------------------------+
| Ctime | 4 | Creation time, sec since epoch |
+-------------|--------|----------------------------------+
| Version | 4 | Signature version |
+-------------|--------|----------------------------------+
| Signature | 96 | ED25519 signature of SHA256 Hash |
+-------------|--------|----------------------------------+
The actual signature is not a signature over the whole content
of an input file but of a SHA256 hash of the content.
=head2 Z85 ENCODING
B<pcp1> uses Z85 to encode exported keys and encrypted messages.
Therefore it includes a Z85 utility mode:
B<pcp1> can be used to encode and decode strings to Z85 encoding.
The option B<-z> encodes B<to> Z85, the option B<-Z> does the opposite
and decodes B<from> Z85.
If no input file have been specified using B<-I>, B<pcp1> expects the
input to come from B<STDIN>, otherwise it reads the contents
of B<file>.
Encoded or decoded output will be written to B<STDOUT> unless an
output file has been specified using the option B<-O>.
=head3 Z85 EXAMPLES
To encode a given file to Z85 and write the output to another:
pcp1 -z myfile.bin > myfile.z85
To decode the file created above and restore the original:
pcp1 -Z -d myfile.z85 > myfile.bin
To encode something from stdin to Z85:
ps axuw | pcp1 -z > pslist.z85
To decode the above and print to stdout:
pcp1 -Z -d pslist.z85
=head3 Z85 BACKGROUND
The Z85 encoding format is described here: B<http://rfc.zeromq.org/spec:32>.
It's part of ZeroMQ (B<http://zeromq.org>). Z85 is based on ASCII85 with
a couple of modifications (portability, readability etc).
To fulfil the requirements of the ZeroMQ Z85 functions, B<pcp1>
does some additional preparations of raw input before actually doing the
encoding, since the input for zmq_z85_encode() must be divisible by 4:
Expand the input so that the resulting size is divisible by 4.
Fill the added bytes with zeroes.
Prepend the input with a one byte value which holds the number of zeroes
added in the previous step.
Example:
Raw input:
hello\0
Here, the input size is 6, which is insufficient, therefore it has to be expanded
to be 8. After the process the input looks like this:
1hello\0\0
So, we padded the input with 1 zero (makes 7 bytes) and preprended it with the
value 1 (the number of zeros added): makes 8 bytes total.
After decoding Z85 input the process will be reversed.
B<Trying to use another tool to decode an Z85 encoded string produced
by z85, might not work therefore, unless the tool takes the padding scheme
outlined above into account>.
=head1 COPYRIGHT
Copyright (c) 2013 by T.Linden <tom AT cpan DOT org>
=head1 ADDITIONAL COPYRIGHTS
=over
=item B<ZeroMQ Z85 encoding routine>
Copyright (c) 2007-2013 iMatix Corporation
Copyright (c) 2009-2011 250bpm s.r.o.
Copyright (c) 2010-2011 Miru Limited
Copyright (c) 2011 VMware, Inc.
Copyright (c) 2012 Spotify AB
=item B<Tarsnap readpass helpers>
Copyright 2009 Colin Percival
=item B<jen_hash() hash algorithm>
Bob Jenkins, Public Domain.
=item B<UTHASH hashing macros>
Copyright (c) 2003-2013, Troy D. Hanson
=item B<Random art image from OpenSSH keygen>
Copyright (c) 2000, 2001 Markus Friedl. All rights reserved.
Comitted by Alexander von Gernler in rev 1.7.
=back
Every incorporated source code is opensource and licensed
under the B<GPL> as well.
=head1 AUTHORS
I<T.Linden <tom AT cpan DOT org>>
=head1 LICENSE
Licensed under the GNU GENERAL PUBLIC LICENSE version 3.
=head1 HOME
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
=cut
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