HNCSL provides programs for client-server TCP communication that utilizes
the HNC cipher algorithm.
Please see our research paper "Secure, Fast, and Loss-Tolerant Communication
with Hill Cipher and Network Coding" (doc/HNC.pdf or
https://www.researchgate.net/publication/374776143_Secure_Fast_and_Loss-Tolerant_Communication_with_Hill_Cipher_and_Network_Coding),
for the details of HNC.

The programs in this repository are different from those used in the paper;
the original HNC algorithm processes data in Galois Field (GF), but those in
this repository use modular arithmetic.
This is because we found potential patent infringement (probably only in the USA)
in our GF arithmetic library, gf-nishida-16, and therefore had no choice but to
replace all calculation associated to GF with modular arithmetic and rewrite
the entire encryption and decryption code.

At the same time, we also modified the encryption and decryption algorithms
to achieve more secure communication and fit the modular arithmetic style,
which resulted in higher encryption and decryption speeds than our GF version.
The encryption and decryption speeds of HNC-16bit-4 are now 5.6 times faster on
Ryzen 7 5800X and 2.7 times faster on Apple M1 than OpenSSL's AES-256.

Note HNC is basically a block cipher with a block size of 32 x HNC_RANK 
(= usually 4) bytes (= 128bytes for HNC_RANK = 4), and therefore it requires
padding with up to 2 * HNC_RANK - 1 (7bytes for HNC_RANK = 4) bytes.
However, the functions HNCEncryptNoPad() and HNCDecryptNoPad provide no-padding
encryption and decryption, respectively.
Although they are not completely secure, because the "if (rem_size) {...}" part
in Mod16EncSIMD256xRRemNoPad() and Mod16DecSIMD256xRRemNoPad() may not achieve
a sufficient level of security, we think them helpful for simple coding.   

Note that encrypted data on an Intel CPU are diffrerent from those on an ARM
CPU due to the difference in endianness.
This can be easily resolved, but we leave it untouched for now.
The supported platforms are Linux, FreeBSD (maybe *BSD) and MacOS.
We have not tested with Windows.


To build the programs, just type:

  % ./build.sh

If this is your first build, then the script tries to generate PEM keys and
prompts you to enter some information for it, which are used for OpenSSL.

To run the programs, you have to start a server program first, then start
a client program on a different terminal.
For example, if you test HNC-16bit-4 algorithm:

  Start HNC-16bit-4 server program
  % cd hnc-16bit-4/server && ./run.sh

  Then on a different terminal, start HNC-16bit-4 client program
  % cd hnc-16bit-4/client && ./run.sh

Once all the data are transmitted from the client to server, the throughput
will be displayed on the client side as follows:

  Time: 13.001000
  Throughput: 48.073225 Gbps
 
Programs that use OpenSSL and no cipher are also included for comparison
and can be run in the same way.

To benchmark all the algorithms, do

  % cd benchmark && ./benchmark.sh

benchmark.sh automatically starts the server and client programs of each
algorithm and benchmarks all methods (no-crypt, hnc-32bit-4, hnc-16bit-4,
hnc-16bit-6 openssl).