codecrypt/man/ccr.1

.TH CCR 1 2015-11-07 "ccr" "Codecrypt"
.SH NAME
.B ccr
\- The post-quantum cryptography encryption and signing tool
.SH SYNOPSIS
.B ccr
.RI [OPTION]...

.SH DESCRIPTION

\fBccr\fR (short of Codecrypt) is a general purpose encryption/decryption
signing/verification tool that uses only quantum-computer resistant algorithms.

.SS
General options:

.TP
\fB\-h\fR, \fB\-\-help\fR
Show a simple help with option listing.

.TP
\fB\-V\fR, \fB\-\-version\fR
Display only version information.

.TP
\fB\-T\fR, \fB\-\-test\fR
This option exists as a convenience for hackers - in this case, \fBccr\fR
initializes itself, calls a test() function from source file src/main.cpp (that
is meant to be filled by testing stuff beforehand) and terminates. In
distribution packages, it will probably do nothing.

.TP
\fB\-R\fR, \fB\-\-in\fR <\fIfile\fR>
Redirect standard input to be read from \fIfile\fR instead from stdin. You can
still specify "-" to force reading from stdin.

.TP
\fB\-o\fR, \fB\-\-out\fR <\fIfile\fR> Redirect standard output to be written to
\fIfile\fR. You can specify "-" to force writing to stdout.

.TP
\fB\-a\fR, \fB\-\-armor\fR
Where expecting input or output of data in codecrypt communication format, use
ascii-armoring.

Codecrypt otherwise usually generates raw binary data, that are very hard to
pass through e-mail or similar text communication channels.

.TP
\fB\-y\fR, \fB\-\-yes\fR
Assume the user knows what he is doing, and answer "yes" to all questions.

.SS
Actions:

.TP
\fB\-s\fR, \fB\-\-sign\fR
Produce a signed message from input.

.TP
\fB\-v\fR, \fB\-\-verify\fR
Take a signed message from input, verify whether the signature is valid, and
output message content if the verification succeeded.

.TP
\fB\-e\fR, \fB\-\-encrypt\fR
Produce an encrypted message from input.

.TP
\fB\-d\fR, \fB\-\-decrypt\fR
Decrypt the message from input.

.P
Note that the actions for signature/encryption and decryption/verification can
be easily combined into one command, simply by specifying both options usually
as "-se" or "-dv".

.SS
Action options:

.TP
\fB\-r\fR, \fB\-\-recipient\fR <\fIkeyspec\fR>
Specify that the message for encryption should be encrypted so that only the
owner of a private key paired with public key specified by \fIkeyspec\fR can
decrypt it.

.TP
\fB\-u\fR, \fB\-\-user\fR <\fIkeyspec\fR>
Specify a private key to use for signing the message.

.TP
\fB\-C\fR, \fB\-\-cleartext\fR
When working with signatures, produce/expect a cleartext signature. The basic
property of cleartext signature is that the message it contains is easily
readable by users, therefore it is a very popular method to e.g. sign e-mails.

.TP
\fB\-b\fR, \fB\-\-detach\-sign\fR <\fIfile\fR>
On signing, produce a detached signature and save it to \fIfile\fR. When
verifying, read the detached signature from \fIfile\fR. Note that files that is
being signed or verified must be put into program's input (potentially using
"-R" option.

.TP
\fB\-S\fR, \fB\-\-symmetric\fR <\fIfile\fR>
Use symmetric cryptography.

When doing "sign" or "verify" operation, do not sign asymmetrically, but
instead generate \fIfile\fR with cryptographic hashes that can later be used to
verify if the contents of input was changed.

When doing "generate", "encrypt" or "decrypt" operation, do not encrypt
asymmetrically, but instead generate or use a file with a key for specified
symmetric cipher. Use "-g help" to see available symmetric primitives. For
symmetric encryption to work, at least one stream cipher (marked with C) and at
least one hash function (marked with H, used to protect agains malleability)
separated by comma need to be selected. Additionally, user can specify
"longblock" or "shortblock" keyword to manipulate size of internal encryption
block structure (longer blocks consume more RAM, but the ciphertext doesn't
grow very much); or the "longkey" flag which creates larger symmetric key to
provide more key material to the ciphers (which can help to protect against
low-quality random numbers, but is generally unneccesary and even considered to
be a bad practice). It is also possible to combine more stream ciphers and hash
functions.

Purpose of the \fB\-\-symmetric\fR option is that symmetric cryptography is a
lot faster than asymmetric, and symmetric primitives usually work also on very
large files and data streams, as they don't need to be fully copied into
allocated memory for this purpose. Thus, if working with a large file, process
it symmetrically first, then process the resulting small \fIfile\fR
asym,etrically and send it along with the large file.

.SS
Key management:

In Codecrypt, each public key has a KeyID, which is basically a hash of its
representation that is used to identify the key globally. Each public key is
stored along with a key name, which is a convenience tool for users who can
store arbitrary information about e.g. what is the key meant for or who it
belongs to. Public keys also have an algorithm identifier to specify how to
work with them, and sometimes also attached a private key to form a secret
"keypair".

Keys can be specified using several methods:

Using KeyID -- the key specification consists of @ and several first characters
to identify a prefix of KeyID of a single key.

Using a name -- key specification consists of string and matches any key, that
has a name that contains that string.

.TP
\fB\-g\fR, \fB\-\-gen\-key\fR <\fIalgorithm\fR>
Generate a keypair for usage with specified algorithm. Use "-g help" to get
list of all algorithms available. Listing also contains flags "S" and "E",
meaning that algorithm can be used for signatures or encryption, or "H" and "C"
for usage with symmetric hashes and ciphers. In asymmetric case (where the
algorithm names are long) the supplied algorithm name does not need to be a
full name, but must match only one available algorithm.

.TP
\fB\-N\fR, \fB\-\-name\fR <\fIkeyname\fR>
Specify that affected keys (those being imported, generated, exported or
renamed) should be newly renamed to \fIkeyname\fR.

.TP
\fB\-F\fR, \fB\-\-filter\fR <\fIkeyspec\fR>
When listing, importing or exporting keys, only process keys that match
\fIkeyspec\fR.

.TP
\fB\-k\fR, \fB\-\-list\fR
List available public keys.

.TP
\fB\-K\fR, \fB\-\-list\-secret\fR
List available private keys (in keypairs).

.TP
\fB\-i\fR, \fB\-\-import\fR
Import public keys.

.TP
\fB\-I\fR, \fB\-\-import\-secret\fR
Import private keypairs.

.TP
\fB\-n\fR, \fB\-\-no\-action\fR
On import, do not really import the keys, but only print what keys and names
will be imported. This is useful for preventing accepting unwanted private or
public keys.

.TP
\fB\-f\fR, \fB\-\-fingerprint\fR
When printing keys, format full KeyIDs. Note that full KeyIDs can be used in
similar way as fingerprints known from other cryptosystems.

.TP
\fB\-p\fR, \fB\-\-export\fR
Export public keys in keyring format.

.TP
\fB\-P\fR, \fB\-\-export\-secret\fR
Export private keys. (Do this carefully!)

.TP
\fB\-x\fR, \fB\-\-delete\fR <\fIkeyspec\fR>
Remove matching keys from public keyring.

.TP
\fB\-X\fR, \fB\-\-delete\-secret\fR <\fIkeyspec\fR>
Remove matching keys from private keypairs.

.TP
\fB\-m\fR, \fB\-\-rename\fR <\fIkeyspec\fR>
Rename matching public keys. Use "-N" to specify a new name.

.TP
\fB\-M\fR, \fB\-\-rename\-secret\fR <\fIkeyspec\fR>
Rename matching private keys.

.SH FILES

Codecrypt stores user data in a directory specified by environment variable
CCR_DIR, which defaults to "$HOME/.ccr". It contains the files "pubkeys" and
"secrets" which are sencode keyring representations of user's public and
private keyring.

Backups of user data (i.e. for each file the last state that was loaded
successfully) are, on each change, written to files "pubkeys~" and "secrets~".

When Codecrypt is running, it locks the .ccr directory using a lockfile "lock"
and applying flock(2) to it.

.SH RETURN VALUE

\fBccr\fR returns 0 if there was no error and all cryptography went fine, or 1
on errors. If the error was that a missing public or private key was needed to
complete the operation, 2 is returned. If signature verification fails (e.g.
the signature is bad or likely forged), the program returns 3.

.SH ALGORITHMS

Program offers several "algorithms" that can be used for signatures and
encryption. Use "ccr -g help" to get a list of supported algorithms.

FMTSeq-named schemes are the Merkle-tree signature algorithms. The name
FMTSEQxxx-HASH1-HASH2 means, that the scheme provides attack complexity ("bit
security") around 2^xxx, HASH1 is used as a message digest algorithm, and HASH2
is used for construction of Merkle tree.

McEliece-based encryption schemes are formed from McEliece trapdoor running on
quasi-dyadic Goppa codes (the MCEQD- algorithms) and on quasi-cyclis
medium-density parity-check (QCMDPC- ones) with Fujisaki-Okamoto encryption
padding for CCA2. Algorithm name MCEQDxxxFO-HASH-CIPHER means that the trapdoor
is designed to provide attack complexity around 2^xxx, and HASH and CIPHER are
the hash and symmetric cipher functions that are used in Fujisaki-Okamoto
padding scheme.

As of November 2015, users are advised to deploy the 2^128-secure variants of the
algorithms -- running 2^128 operations would require around 10^22 years of CPU
time (of a pretty fast CPU), which is considered more than sufficient for any
reasonable setup and using stronger algorithms seems just completely
unnecessary.

Note that using stronger algorithm variants does not come with any serious
performance drawback and protects the user from non-fatal attacks that decrease
the security of the scheme only by a small amount -- compare getting an attack
speedup of 2^20 on a scheme with 2^80 bit security (which is fatal) with
getting the same speedup on a scheme with 2^128 security (where the resulting
2^108 is still strong).

For comparison, 2^128 security level is very roughly equivalent to that of
classical RSA with 3072bit modulus (which is, accordingly to the best results
available in June 2013 for general public, reported to provide roughly 2^112
attack complexity).

For another comparison, a very good idea about the insane amount of energy that
is actually needed for brute-forcing 2^256 operations can be obtained from
wikipedia, which estimates the size of whole observable universe (!) to around
2^270 atoms.

All algorithms are believed to be resistant to quantum-computer-specific
attacks, except for the generic case of Grover search which (in a very
idealized case and very roughly) halves the bit security (although the attack
remains exponential).  Users who are aware of large quantum computers being
built are advised to use 2^192 or 2^256 bit security keys.

.SH WARNINGS AND CAVEATS

.SS General advice

Codecrypt does not do much to prevent damage from mistakes of the user. Be
especially careful when managing your keyring, be aware that some operations
can rename or delete more keys at once. Used cryptography is relatively new,
therefore be sure to verify current state of cryptanalysis before you put your
data at risk.

.SS Current state of cryptanalysis

In a fashion similar to aforementioned `new cryptography', the original
algebraic variant of quasi-dyadic McEliece that is still in codecrypt (MCEQD*
algorithms, kept for compatibility purposes) has been broken by an algebraic
attack. Security is greatly reduced. Use the QC-MDPC variant which dodges
similar attacks.

.SS Large files

Codecrypt is not very good for working directly with large files. Because of
the message format and code clarity, whole input files and messages are usually
loaded into memory before getting signed/encrypted. Fixing the problem requires
some deep structural changes in Codecrypt that would break most of the achieved
internal simplicity, therefore the fix is probably not going to happen. You can
easily workaround the whole problem using symmetric ciphers (for encryption of
large files) or hashfiles (for signatures of large files). See the
\fB\-\-symmetric\fR option.

.SS FMTSeq signatures

FMTSeq signatures are constructed from one-time signature scheme, for this
reason the private key changes after each signature, basically by increasing
some counter. IF THE PRIVATE KEY IS USED MORE THAN ONCE TO SIGN WITH THE SAME
COUNTER AND THE SIGNATURES GET PUBLISHED, SECURITY OF THE SCHEME IS SEVERELY
DAMAGED. Never use the same key on two places at once. If you backup the
private keys, be sure to backup it everytime after a signature is made.

If something goes wrong and you really need to use the key that has been, for
example, recovered from a backup, you can still "skip" the counter by producing
and \fBdiscarding\fR some dummy signatures (ccr -s </dev/null >/dev/null). If
you plan to do that for some real purpose, for your own safety be sure to
understand inner workings of FMTSeq, especially how the Diffie-Lamport
signature scheme degrades after publishing more than one signature.

FMTSeq can only produce a limited amount of signatures (but still a pretty
large number). When the remaining signature count starts to get low, Codecrypt
will print warning messages. In that case, users are advised to generate and
certify new keys.

.SS Working with keys

Try to always use the "-n" option before you actually import keys -- blind
import of keys can bring serious inconsistencies into your key naming scheme.

In a distant universe after much computation, KeyIDs can collide. If you find
someone who has a colliding KeyID, kiss him and generate another key.

.SH FAQ

Q: I can't read/verify messages from versions 1.3.1 and older!

A: KeyID algorithm changed after that version. If you want, you can manually
rewrite the message sencode envelopes to contain new recipient/signer KeyIDs
and new message identificators, things should work perfectly after that.

Q: Some signatures from version 1.5 and older fail to verify!

A: There was a slight mistake in padding of messages shorter than signature
hash function size (64 bytes in the 256-bit-secure signature types) with no
security implications. It was decided not to provide backward compatibility for
this minor use-case. If you really need to verify such signatures, edit the
msg_pad function in src/algos_sig.h so that the `load_key()' function os called
on empty vector instead of `out'.

Q: I want to sign/encrypt a large file but it took all my RAM and takes ages!

A: Use \fB--symmetric\fR option. See the `CAVEATS' section for more details.

Q: How much `broken' is the original quasi-dyadic McEliece?

A: The private key of proposed dyadic variant by Misoczki and Barreto can be
derived from the public key with standard computer equipment.

.SH EXAMPLE
Following commands roughly demonstrate command line usage of \fBccr\fR:
.nf
.sp
ccr -g help
ccr -g sig --name "John Doe"    # your signature key
ccr -g enc --name "John Doe"    # your encryption key

ccr -K  #watch the generated keys
ccr -k

ccr -p -a -o my_pubkeys.asc -F Doe  # export your pubkeys for friends

#see what people sent us
ccr -ina < friends_pubkeys.asc

#import Frank's key and rename it
ccr -ia -R friends_pubkeys.asc --name "Friendly Frank"

#send a nice message to Frank (you can also specify him by @12345 keyid)
ccr -se -r Frank < Document.doc > Message_to_frank.ccr

#receive a reply
ccr -dv -o Decrypted_verified_reply.doc <Reply_from_frank.ccr

#rename other's keys
ccr -m Frank -N "Unfriendly Frank"

#and delete pukeys of everyone who's Unfriendly
ccr -x Unfri

#create hashfile from a large file
ccr -sS hashfile.ccr < big_data.iso

#verify the hashfile
ccr -vS hashfile.ccr < the_same_big_data.iso

#create (ascii-armored) symmetric key and encrypt a large file
ccr -g sha256,chacha20 -aS symkey.asc
ccr -eaS symkey.asc -R big_data.iso -o big_data_encrypted.iso

#decrypt a large file
ccr -daS symkey.asc <big_data_encrypted.iso >big_data.iso
.fi

.SH DISCLAIMER

Used cryptography is relatively new. For this reason, codecrypt eats data. Use
it with caution.

.SH AUTHORS

Codecrypt was written by Mirek Kratochvil in 2013 and 2014.