Pretty Curved Privacy - File encryption using eliptic curve cryptography.
Usage: pcp1 [ --help | --version ]
[ --keygen | --listkeys | --remove-key | --edit-key ]
[ --export-public | --export-secret | --import ]
[ --encrypt | --decrypt ]
[ --sign | --check-signature ]
[ arguments ]
General Options:
-h --help Print this help message.
--version Print program version.
-D --debug Enable debug output.
-v --verbose Enable verbose output.
-V --vault <vaultfile> Specify an alternate vault file.
-O --outfile <file> Output file. STDOUT if unspecified.
-I --infile <file> Input file. STDIN if unspecified.
-X --password-file <file> Read passphrase from <file>.
-i --keyid <id> Specify a key id for various operations.
-r --recipient <string> Specify a recpipient, multiple allowed.
-t --text Print textual representation of ojects.
Keymanagement Options:
-k --keygen Generate new key pair.
-l --listkeys List all keys stored in your vault.
-R --remove-key Remove a key from the vault.
-s --export-secret Export a secret key.
-p --export-public Export a public key.
-K --import Import a secret or public key.
-F --export-format <fmt> Specify exportformat, either 'pbp' or 'pcp'.
'pcp' is the default if unspecified.
-j --json Enable JSON output (with -t, -p, -s and -K).
Encryption Options:
-e --encrypt Asym-Encrypt a message. If none of -i or -r
has been given, encrypt the message symetrically.
-A --anonymous Use anonymous sender key pair.
-M --add-myself Add you primary pub key to list of recipients.
-m --encrypt-sym Symetrically encrypt a message.
-d --decrypt Decrypt a message.
Signature Options:
-g --sign Create a signature of a file.
-c --check-signature Verify a signature of a file.
-f --sigfile <file> Write or check a detached signature file.
Encoding Options:
-z --z85-encode Armor with Z85 encoding.
-Z --z85-decode Decode Z85 encodeded input.
-a --armor --textmode same as -z
Misc Options:
-C --checksum [<key>] calculate a Blake2 checksum of one or more files.
Arguments:
Extra arguments after options are treated as filenames or
recipients, depending on operation mode.
=head1 OPTIONS
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.
-X --password-file <file> Read passphrase from <file>. If <file>
is -, read from stdin. This takes
precedence over other uses of stdin
elsewhere, see below for more details.
-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.
--version Print program version.
-D --debug Enable debug output.
-v --verbose Enable verbose 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.
-L --listkeys-verbose Display a more verbose key listing
-l -v including signature fingerprint, key
fingerprint, checksum and the like.
-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
--export been specified, the public part of your
primary secret key will be exported.
Use -O to export to a file.
-K --import Import a key. pcp determines automatically
--import-key the key type and encodingg. Use -I to import
from a file.
-F --format Export the key in a particular format.
Currently supported: pcp and pbp.
-j --json enable JSON output. Can be used with info
output (-t) and key export (-p and -s).
and import (-K).
Encryption Options:
-e --encrypt Asym-Encrypt a message. Read from stdin or
specified via -I. Output will be written
to stdout or the file given with -O.
If a keyid (-i) has been
given, use that public key for encryption.
If one or more recipient (-r) has been given,
encrypt the message for all recipients
asymetrically, given there are matching
public keys installed in the vault for them.
If none of -i or -r has been given, encrypt
the message symetrically. This is the same
as -m (self-encryption mode).
Add -z to ascii armor the output using Z85.
-A --anonymous Use anonymous sender key pair instead of
your own primary key pair. In this mode the
recipient doesn't need to have your public
key.
-m --encrypt-sym Sym-Encrypt a message. Specify -I and/or
-O for input/output file. You will be asked
for a passphrase. No key material will
be used. Same as -e without -r and -i.
-M --add-myself Add yourself to list of recipients in asymmetric
encryption mode, so that you can decrypt it as
well.
-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.
You need to have the public key of the
sender installed in your vault.
If the input is self-encrypted (symetrically)
a passphrase will be requested.
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.
-f --sigfile <file> Write a detached signature file, which doesn't
contain the original content. Output will be
z85 encoded always. To verify, you need to
specify the original file to be verified
against using -I as well (plus -f <sigfile>).
Encoding Options:
-z --z85-encode Encode (armor) something to Z85 encoding.
-a --armor If used with encryption or singing operation
--textmode encode its output. Otherwise encode a plain
file. Use -I and -O respectively, otherwise it
uses stdin/stdout.
-Z --z85-decode Decode (dearmor) something from Z85 encoding.
Use -I and -O respectively, otherwise it
uses stdin/stdout
Misc Options:
-C --checksum [<key>] Calculate a Blake2b checksum of one or more files.
If <key> is provided, an authenticated hash will
be calculated, otherwise a normal hash. If you don't
want to generate an authenticated hash, specify
-- after -C.
Use -I to specify one file or put multiple file
names after -C like "pcp1 -C -- file1 file2 file3".
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 -kAfter 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.pubThey'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.pubThey 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 | lessAnd 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 outputwill read the text to be encrypted from standard input, because -I has not been specified. It works the same with -O:
pcp1 -e -I myfileIn 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@somewherehere 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.
pcp1 keys are stored in a binary file, called the vault. It's by default located in ~/.pcpvault but you can of course specify another location using the -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 keyid which looks like this:
0xD49119E85266509FA public key exported from a secret key will have the same keyid as the secret key.
If you just want to know details about a key or the vault, use the -t option.
There are 3 modes of encryption available in pcp1:
In this mode, which is the default, a public key as specified with -i or -r and your primary secret key will be used for encryption.
Example command:
pcp1 -e -i 0x2BD734B15CE2722D -I message.txt -O message.ascHere we didn't specify a recipient. Therefore the public key given with -i will be used directly.
Another example:
pcp1 -e -r Bobby -r McCoy -I message.txt -O message.ascAs you can see, it is also possible to encrypt a message for multiple recipients.
In anonymous mode a random generated keypair will be used on the sender side. This way the recipient doesn't have to have your public key.
Example command:
pcp1 -r -r Bobby -A -I message.txt -O message.ascThe public key part of the generated key pair will be included in the output, which potentiall lessens security. Use with care and avoid this mode when possible.
You can also encrypt a file symetrically. No public key material will be used in this mode.
While this works, the security of it totally depends on the strength of the passphrase used for encryption.
Example command:
pcp1 -e -I message.txt -O cipher.z85As you can see we didn't specify any recipients (-i or -r) and therefore pcp1 operates in self mode encryption. It will ask you for a passphrase, from which an encryption key will be derived using scrypt().
PCP doesn't validate the security of the passphrase.
Self mode can be explicitly enforced with -m.
There are 3 modes for digital signatures available on pcp1:
In this mode, which is the default, an ED25519 signature will be calculated from a BLAKE2 hash of the input file content. Both the original file content plus the signature will be written to the output file.
Example:
pcp1 -g -I message.txt -O message.asc -gYou will be asked for the passphrase to access your primary secret key. The output file will be a binary file.
While this mode does the very same calculations, the output slightly differs. The output file will be marked as a signature file, the signature itself will be appended with its own headers and Z85 encoded.
Example:
pcp1 -g -I message.txt -O message.asc -g -zYou will be asked for the passphrase to access your primary secret key. The output file will be a text file.
In some cases you will need to have the signature separated from the original input file, e.g. to sign download files. You can generate detached signatures for such purposes. Still, the signature will be calculated the same way as in standard signatures but put out into a separate file. A detached signature file will always be Z85 encoded.
Example:
pcp1 -g -I message.txt -O -g --sigfile message.sigVerification by recipient:
pcp -c -f message.sig -I message.txtBeside pure encryption and signatures pcp1 also supports signed encryption. In this mode an input file will be encrypted and a signature of the encrypted content and encrypted recipients with your primary secret key will be appended.
The signature is encrypted as well.
Example:
pcp1 -e -g -r Bobby -I README.txt -O README.ascPlease note the additional -g parameter. The recipient can decrypt and verify the so created data like this:
pcp1 -d -I README.asc -o README.txtIf decryption works, the output file will be written. If signature verification fails you will be informed, but the decrypted output will be left untouched. It is up to you how to react on an invalid signature.
You can save typing if you supply additional arguments to pcp after commandline options. Such arguments are treated as filenames or recipients, depending what options you already specified.
Here is a list of commandlines and their possible alternatives:
ORIGINAL ALTERNATIVE DESCRIPTION
pcp -e -I message -r Bob pcp -e -r Bob message use 'message' as inputfile.
pcp -e -I message Bob use 'Bob' as recipient,
multiple recipients supported.
pcp -d -I crypted pcp -d crypted use 'crypted' as inputfile.
pcp -g -I message pcp -g message use 'message' as inputfile.
pcp -g -I msg -O sig pcp -g -I msg sig use 'sig' as outputfile.
pcp -p -O key.pcp pcp -p key.pcp use 'key.pcp' as outputfile.
pcp -p -O key.pcp -r Bob pcp -p -O key.pcp Bob use 'Bob' as recipient.
pcp -s -O key.pcp pcp -s key.pcp use 'key.pcp' as outputfile.
pcp -s -O key.pcp -r Bob pcp -s -O key.pcp Bob use 'Bob' as recipient.
pcp -K -I alice.pcp pcp -K alice.pcp use 'alice.pcp' as keyfile.pcp respects the following environment variables:
Use an alternative vaultfile. The default is ~/.pcpvault and can be overridden with the -V commandline option. If PCP_VAULT is set, this one will be used instead.
Enable debugging output, where supported. Same as -D.
Pcp may return one of several error codes if it encounters problems.
Default vault file where all keys are stored.
Currently there are a couple of problems which are unsolved or in the process to be solved.
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 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. Pcp implements this scheme though (refer to the option -A).
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.
As with every crypto software, pcp has to undergo a couple rounds of peer review (analysis) in order to be considered secure, trustable and stable. No any such review has been undertaken on pcp yet.
Pcp is a mere fun project aimed at teaching myself better C coding and crypto. In fact I don't even trust the software myself and I don't use it for anything remotely serious.
In short: don NOT use this software for production purposes!
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 0x03The key header is followed by the actual key, see below.
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:
Generate a random seed (32 bytes).
Generate a ED25519 sigining keypair from that seed.
Generate a random seed (32 bytes).
Generate a Curve25519 encryption keypair from that seed.
So, while both secrets are stored in the same PCP key, they are otherwise unrelated. If one of them leaks, the other cannot be recalculated from it.
Take a look at the function pcp_keypairs() for details.
Exported public and secret keys will be written in a portable way. Pcp uses RFC4880 export format for public keys with some slight modifications:
Key material is native to libsodium/pcp and not specified in the rfc for curve25519/ed25519. Therefore pcp encodes key material doing it like this: mp|sp|cp
where
mp = master keysigning public key (ed25519), 32 bytes
sp = signing public key (ed25519), 32 bytes
cp = encryption public key (curve25519), 32 bytesThe various cipher (algorithm) id's are unspecified for libsodium/pcp native ciphers. Therefore they are proprietary to pcp, starting at 33 (22 is the last officially assigned one). Once those cipher numbers become official, they will be used instead.
Pcp uses 64 bit integers for timestamps everywhere (ctime, expire, etc), to be year 2038 safe. Note, that this is a violation of the RFC spec. However, said RFC have to be modified to fit 2038 (and beyond) anyways. This applies for the keyfile ctime as well for the key sig sub fields containing time values.
The exported public key packet contains a signature. Pcp is filling out all required fields. A signature has a variable number of sig sub packets. Pcp uses only these types:
2 = Signature Creation Time (8 byte)
3 = Signature Expiration Time (8 byte)
9 = Key Expiration Time (8 bytes)
20 = Notation Data (4 byte flags, N bytes name+value)
27 = Key Flags (1 byte, use 0x02, 0x08 and 0x80Pcp uses 3 notation fields:
The actual signature field consists of the blake2 hash of (mp|sp|cp|keysig) followed by the nacl signature. However, pcp does not put an extra 16 byte value of the hash, since the nacl signature already contains the full hash. So, an implementation could simply pull the fist 16 bytes of said hash to get the same result if desired.
The mp keypair will be used for signing. The recipient can verify the signature, since mp is included.
While pcp puts expiration dates for the key and the signature into the export as the rfc demands, it mostly ignores them (yet). Key expiring is not implemented in PCP yet.
We use big-endian always.
Unlike RC4880 public key exports, pcp uses Z85 encoding if armoring have been requested by the user. Armored output has a header and a footer line, however they are ignored by the parser and are therefore optional. Newlines, if present, are optional as well.
http://tools.ietf.org/html/rfc4880#section-5.2.3
The key sig blob will be saved in the Vault unaltered during import, so pcp is able to verify the signature at will anytime. When exporting a foreign public key, pcp just puts out that key sig blob to the export untouched.
Currently PCP only supports self-signed public key exports.
Pcp only supports one key signature per key. However, it would be easily possible to support foreign keysigs as well in the future.
So, a full pubkey export looks like this
version
ctime
cipher
3 x raw keys \
sigheader > calculate hash from this
sigsubs (header+data) /
hash
signatureSecret keys are exported in a proprietary format.
The exported binary blob is symmetrically encrypted using the NACL function crypto_secret(). The passphrase will be used to derive an encryption key using the STAR function scrypt().
The binary data before encryption consists of:
ED25519 master signing secret
Curve25519 encryption secret
ED25519 signing secret
ED25519 master signing public
Curve25519 encryption public
ED25519 signing public
Optional notations, currently supported are the 'owner' and 'mail' attributes.
If an attribute is empty, the len field is zero.
-# len(VAL) (2 byte uint)
-# VAL (string without trailing zero)
8 byte creation time (epoch)
4 byte key version
4 byte serial numberThe encrypted cipher will be prepended with the random nonce used to encrypt the data and looks after encryption as such:
Nonce | CipherThe encryption protocol used by PCP uses mostly standard libsodium facilities with the exception that PCP uses counter mode (CTR-Mode) for stream encryption.
Detailed description:Symetric encryption works the very same without the recipient stuff.
Formal format description, asymetric encrypted files:
+-----------------------------------------------------------+
| Field Size Description |
+-------------+--------+------------------------------------+
| Type | 1 | Filetype, 5=ASYM, 23=SYM, 6=ANON |
+-------------|--------|------------------------------------+
| Anon PUB * | 32 | anon pubkey, only used with type 6 |
+-------------|--------|------------------------------------+
| Len R * | 4 | Number of recipients (*) |
+-------------|--------|------------------------------------+
| Recipients *| R*72 | C(recipient)|C(recipient)... (*) |
+-------------|--------|------------------------------------+
| Encrypted | ~ | The actual encrypted data |
+-------------|--------|------------------------------------+*) not included when doing symetric encryption.
Recipient field format:
+---------------------------------------------------------+
| Field Size Description |
+-------------+--------+----------------------------------+
| Nonce | 24 | Random Nonce, one per R |
+-------------|--------|----------------------------------+
| Cipher | 48 | S encrypted with PK or R |
+-------------|--------|----------------------------------+R is generated using crypto_box() with the senders secret key, the recipients public key and a random nonce.
Pseudocode:
R = foreach P: N | crypto_box(S, N, P, SK)
L = len(R)
T = 5
write (T | L | R)
foreach I: write (N | crypto_secret_box(I, N, S))where P is the public key of a recipient, SK is the senders secret key, R is the recipient list, L is the number of recipients, T is the filetype header, I is a block of input with a size of 32k, N is a nonce (new per block) and S the symmetric key.
If using anonymous encryption, the sender generates a ephemeral key pair, uses the secret part of it to generate R. The public part will be included with the output (right after the file type. In this mode a recipient is not required to have the public key of the sender.
The encrypted output maybe Z85 encoded. In this case the Z85 encoding will be done blockwise with blocks of 16k bytes. The decoded content inside will be as described above.
There are different signature formats. Standard binary NACL signatures have the following format:
+---------------------------------------------------------+
| Field Size Description |
+-------------+--------+----------------------------------+
| Content | ~ | Original file content |
+-------------|--------|----------------------------------+
| \nnacl- | 6 | Offset separator |
+-------------|--------|----------------------------------+
| Hash | 64 | BLAKE2 hash of the content |
+-------------|--------|----------------------------------+
| Signature | 64 | ED25519 signature of BLAKE2 Hash |
+-------------|--------|----------------------------------+The actual signature is not a signature over the whole content of an input file but of a BLAKE2 hash of the content.
Pseudo code:
H = crypto_generichash(C)
C | O | H | crypto_sign(H, S)where C is the message (content), H is the blake2 hash, O is the offset separator and S is the secret signing key of the sender.
Armored signatures have the following format:
----- BEGIN ED25519 SIGNED MESSAGE -----
Hash: Blake2
MESSAGE
----- BEGIN ED25519 SIGNATURE -----
Version: PCP v0.2.0
195j%-^/G[cVo4dSk7hU@D>NT-1rBJ]VbJ678H4I!%@-)bzi>zOba5$KSgz7b@R]A0!kL$m
MTQ-1DW(e1mma(<jH=QGA(VudgAMXaKF5AGo65Zx7-5fuMZt&:6IL:n2N{KMto*KQ$:J+]d
dp1{3}Ju*M&+Vk7=:a=J0}B
------ END ED25519 SIGNATURE ------The Z85 encoded signature at the end contains the same signature contents as the binary signature outlined above (hash+sig).
Signed encrypted files are in binary form only. The first part is the standard encrypted file as described in ENCRYPTED OUTPUT FORMAT followed by the binary encrypted signature described in SIGNATURE FORMAT without the offset separator.
However, not only the hash of the file content will be signed but the recipient list described in ENCRYPTED OUTPUT FORMAT as well. A valid recipient is therefore not able to re-encrypt the decrypted message, append the original signature and send it to other recipients. The signature would not match since the recipient list differs and so recipients know that the signature is forged.
Formal file description of sign+encrypt format:
+---------------------------------------------------------+
| Field Size Description |
+-------------+--------+----------------------------------+
| Type | 1 | Filetype, 5=ASYM, 23=SYM |
+-------------|--------|----------------------------------+
| Len R | 4 | Number of recipients (*) |
+-------------|--------|----------------------------------+
| Recipients | R*72 | C(recipient)|C(recipient)... (*) |
+-------------|--------|----------------------------------+
| Encrypted | ~ | The actual encrypted data |
+-------------|--------|----------------------------------+
| Signature | ~ | Encrypted signature(*) |
+-------------|--------|----------------------------------+As usual the encrypted signature consists of a nonce and the actual cipher, which is computed symmetrically (see above) from the following clear signature.
Before encryption the signature format is:
+---------------------------------------------------------+
| Field Size Description |
+-------------+--------+----------------------------------+
| Hash | 64 | BLAKE2 hash of content+R (*) |
+-------------|--------|----------------------------------+
| Signature | 64 | ED25519 signature of BLAKE2 Hash |
+-------------|--------|----------------------------------+where R is: C(recipient)|C(recipient)... (see ENCRYPTED OUTPUT FORMAT).
Pseudocode:
N | crypto_secret_box( crypto_sign( crypto_generichash( M + R, SK ) ), N, S)where N is the nonce, M the message, R the recipient list, SK is the senders secret signing key and S the symmetric key.
pcp1 uses Z85 to encode binary data (if requested with -z) such as encrypted data, exported keys or armored signatures.
Encoded data is always enclosed by a header and a footer and may have any number of comments. Example:
----- PCP ENCRYPTED FILE -----
Version: PCP 0.2.1
246ge]+yn={<I&&Z%(pm[09lc5[dx4TZALi/6cjVe)Kx5S}7>}]Xi3*N3Xx34Y^0rz:r.5j
v#6Sh/m3XKwy?VlA+h8ks]9:kVj{D[fd7]NA]T-(ne+xo!W5X5-gIUWqM
----- END PCP ENCRYPTED FILE -----However, the parser tries to be as tolerant as possible. It also accepts Z85 encoded data without headers or without newlines, empty lines or lines containing a space are ignored as well as comments. Empty comments are not allowed.
PCP uses a custom padding scheme. Z85 input data size must be a multiple of 4. To fulfill this requirement, PCP padds the input with zeros as neccessary. To tell the decoder if padding took place and how much zeros have been added, PCP adds another 4 bytes after each Z85 encoded block, from the last one which contains the number of zeros used for padding, even if the input hasn't been padded.
The Z85 encoding format is described here: http://rfc.zeromq.org/spec:32. It's part of ZeroMQ (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, 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. Therefore we pad the input with zeroes and remove them after decoding.
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.
Z85 encoding and decoding can be used separately as well to work with files. Examples:
Encode some file to Z85 encoding:
pcp1 -z -I file -O file.z85
Reverse the process:
pcp1 -Z -I file.z85 -O file
PCP tries to be fully compatible with PBP (https://github.com/stef/pbp). Encrypted files and signatures - at least their binary versions - should be exchangable. However, this is a work in progress and might not work under all circumstances. Also there's currently no shared key format between pbp and pcp. However, it is possible to export and import pbp keys from/to pcp.
If pcp have been compiled with --with-json (which requires the libjansson library), then it supports JSON objects as input and output with the following functions:
JSON support can be used either with the commandline tool pcp1 or programmatically using the C, C++ or Python API.
In order to use JSON all you've got to do is to switch a context flag:
PCPCTX *ptx = ptx_new();
ptx->json = 1;That all to it. Now any function normally used for key import and export works with JSON, just fill the Buffer object with a JSON string for imports or fetch the Buffer content of an export function as a string.
In order to use JSON on the commandline, add -j. This can be used in conjunction with the following options:
Public key export.
Secret key export.
Public and secret key import.
Text view mode (aka inspect mode).
The -z and -Z options are ignored in JSON mode.
The JSON object for a public key looks like this:
{
"id": "6BF2980419E0986A",
"owner": "tom",
"mail": "tom@local",
"ctime": 1436170865,
"expire": 1467706865,
"version": 6,
"serial": 1509801135,
"type": "public",
"cipher": "CURVE25519-ED25519-POLY1305-SALSA20",
"cryptpub": "0fdf0f7269f901b7f0fba989a1fddbf576c7cc148a2e5987fdeea3523978fe01",
"sigpub": "6980b76e17170194626b49cbab1ab35369a0635f52fe1a7cf39cc5421fb5c0c2",
"masterpub": "947a49f29e9cb0e92b61e2a1dea95f8ec81a24baed78e85c1b52cc3714f5e45e",
"signature": "947a49f29e9cb0e92b61e2a1dea95f8ec81a24baed78e85c1b52cc3714f5e45[..]"
}Actually the field signature contains the whole encoded public key.
Fields containing byte arrays are hex encoded.
Numbers are represented as literal integers.
The JSON object for a public key looks like this:
{
"id": "6BF2980419E0986A",
"owner": "tom",
"mail": "tom@local",
"ctime": 1436170865,
"expire": 1467706865,
"version": 6,
"serial": 1509801135,
"type": "secret",
"cipher": "CURVE25519-ED25519-POLY1305-SALSA20",
"cryptpub": "0fdf0f7269f901b7f0fba989a1fddbf576c7cc148a2e5987fdeea3523978fe01",
"sigpub": "6980b76e17170194626b49cbab1ab35369a0635f52fe1a7cf39cc5421fb5c0c2",
"masterpub": "947a49f29e9cb0e92b61e2a1dea95f8ec81a24baed78e85c1b52cc3714f5e45e",
"secrets": "ad5ce150f3cd7bffa299d4db5bf3d26ae56c3808ccba7[..]",
"nonce": "858ef9870fc8f39903cfb281d697ca29a935d2ae929fa4ea"
}As you can see that's pretty identical to a public key json object beside the secrets and nonce fields. The secrets field contains the encrypted secret key material. Pcp does not support exporting a secret key unencrypted.
The nonce is required for a later import and shall not be changed or decoupled from secrets. This may change in the future.
The JSON object for the vault looks like this:
{
"keyvaultfile": "/home/tom/.pcpvault",
"version": 2,
"checksum": "27b583dc2dacf5ccc874b7be3a39748d107c6b9e9f9d473f1c716a94561ef793",
"secretkeys": 1,
"publickey": 3,
"keys": []
}The field keys is an array containing one or more of the already described key objects.
Currently pcp does not support JSON program output, that is, success or error messages on STDERR are not encoded as json. This may change in the future.
Copyright (c) 2013-2015 by T.v.Dein <tom AT vondein DOT org>
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 Copyright 2009 Colin Percival Bob Jenkins, Public Domain. Copyright (c) 2003-2013, Troy D. Hanson Copyright (c) 2000, 2001 Markus Friedl. All rights reserved.
Comitted by Alexander von Gernler in rev 1.7.Every incorporated source code is opensource and licensed under the GPL as well.
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