Post-quantum cryptography tool
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README.md

Codecrypt

The post-quantum cryptography tool.

About

This is a GnuPG-like unix program for encryption and signing that uses only quantum-computer-resistant algorithms:

  • McEliece cryptosystem (compact QC-MDPC variant) for encryption
  • Hash-based Merkle tree algorithm (FMTSeq variant) for digital signatures

Codecrypt is free software. The code is licensed under terms of LGPL3 in a good hope that it will make combinations with other tools easier.

Why this?

Go read http://pqcrypto.org/

Distro packages

Language wrappers:

Documentation

There is a complete, UNIXy manual page supplied with the package. You can view it online here: http://e-x-a.org/codecrypt/ccr.1.html

Used cryptography overview

To achieve the stated goal, codecrypt uses a lot of (traditional, but “quantum-secure”) cryptographic primitives. Choices of primitives were based on easy auditability of design, simplicity and provided security.

The git repo of codecrypt contains doc/papers with an unsorted heap of academic papers and slides about relevant topics.

Stream ciphers used:

  • ChaCha20, the recommended choice from djb
  • XSynd stream cipher as an interesting and nontraditional candidate also based on assumptions from coding theory; used NUMS (it requires lot of NUMS) are explained in doc/nums directory in the repo.
  • Arcfour for initial simplicity of implementation. After recent statistical attacks I cannot recommend using any RC4 variant anymore, but provided padding and the “offline-only” usage of codecrypt keeps the usage mostly secure.

CRHFs used:

  • Cubehash variants were selected for implementation ease, really clean design, quite good speed and flexibility of parameter choices. This is also the only hash possibility when Crypto++ library is not linked to codecrypt. KeyIDs are CUBE256 hashes of corresponding serialized public keys.
  • ripemd128 for small hashes
  • tiger192 is used as an alternative for Cubehash for 192bit hashes
  • There’s always a variant with SHA-256, SHA-384 or SHA-512.

Signature algorithms:

  • FMTSeq with many possibilities and combinations of aforementioned CRHFs
  • SPHINCS256 support is scheduled for next release

Encryption algorithms:

  • MDPC McEliece on quasi-cyclic matrices. The implementation uses some tricks to speedup the (pretty slow) cyclic matrix multiplication (most notably libfftm3 in this version). For padding using the Fujisaki-Okamoto scheme, the cipher requires a stream cipher and a CRHF, used ciphers and CRHFs are specified in the algorithm name -- e.g. MCEQCMDPC128FO-CUBE256-CHACHA20 means that the parameters are tuned to provide 128bit security, uses CUBE256 hash, and ChaCha20 stream cipher.
  • Quasi-dyadic McEliece was included in codecrypt as an original algorithm, but is now broken and prints a warning message on any usage.

Caveats:

Cryptography is not intended for “online” use, because some algorithms (especially the MDPC decoding) are (slightly) vulnerable to timing attacks.

Quick How-To

Everything is meant to work mostly like GnuPG, but with some good simplicity margin. Let’s play with random data!

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

#(now you should exchange the pubkeys with friends)

#see what people sent us, possibly check the fingerprints
ccr -inaf < 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

#password-protect all your private keys
ccr -L

#protect a symmetric key using another symmetric key
ccr -L -S symkey1 -w symkey2

#password-protect symkey2 with a custom cipher
ccr -L -S symkey2 -w @xsynd,cube512

Option reference

For completeness I add listing of all options here (also available from ccr --help)

Usage: ./ccr [options]

Common options:
 -h, --help     display this help
 -V, --version  display version information
 -T, --test     perform (probably nonexistent) testing/debugging stuff

Global options:
 -R, --in      set input file, default is stdin
 -o, --out     set output file, default is stdout
 -E, --err     the same for stderr
 -a, --armor   use ascii-armored I/O
 -y, --yes     assume that answer is `yes' everytime

Actions:
 -s, --sign     sign a message
 -v, --verify   verify a signed message
 -e, --encrypt  encrypt a message
 -d, --decrypt  decrypt an encrypted message

Action options:
 -r, --recipient    encrypt for given user
 -u, --user         use specified secret key
 -C, --clearsign    work with cleartext signatures
 -b, --detach-sign  specify file with detached signature
 -S, --symmetric    enable symmetric mode of operation where encryption
            is done using symmetric cipher and signatures are
            hashes, and specify a filename of symmetric key or hashes

Key management:
 -g, --gen-key        generate keys for specified algorithm
 -g help              list available cryptographic algorithms
 -k, --list           list the contents of keyring
 -K, --list-secret
 -i, --import         import keys
 -I, --import-secret
 -p, --export         export keys
 -P, --export-secret
 -x, --delete         delete matching keys
 -X, --delete-secret
 -m, --rename         rename matching keys
 -M, --rename-secret
 -L, --lock           lock secrets
 -U, --unlock         unlock secrets

Key management options:
 -F, --filter       only work with keys with matching names
 -f, --fingerprint  format full key IDs nicely for human eyes
 -N, --name         specify a new name for renaming or importing
 -n, --no-action    on import, only show what would be imported
 -w, --with-lock    specify the symmetric key for (un)locking the secrets
 -w @SPEC           ask for password and expand it to a symmetric key
                    of type SPEC for (un)locking the secret

Disclaimer

Codecrypt eats data. Use it with caution. Read the F manual.

Author is a self-taught cryptographer.