encless.go

/*
GoVPN -- simple secure free software virtual private network daemon
Copyright (C) 2014-2016 Sergey Matveev <stargrave@stargrave.org>

This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program.  If not, see <http://www.gnu.org/licenses/>.
*/

package enc

import (
	"io"
	"crypto/rand"
	"github.com/1AD8BE38F271/vpncore/enc/cnw"
	"github.com/1AD8BE38F271/vpncore/enc/aont"
)

var (
	Rand io.Reader = rand.Reader
)

const (
	EnclessEnlargeSize = aont.AontHashSize + aont.AontKeySize *cnw.EnlargeFactor
)

// Zero each byte.
func SliceZero(data []byte) {
	for i := 0; i < len(data); i++ {
		data[i] = 0
	}
}

// Confidentiality preserving (but encryptionless) encoding.
//
// It uses Chaffing-and-Winnowing technology (it is neither
// encryption nor steganography) over All-Or-Nothing-Transformed data.
// nonce is 64-bit nonce. Output data will be EnclessEnlargeSize larger.
// It also consumes 64-bits of entropy.
func EnclessEncode(authKey *[32]byte, nonce, in []byte) ([]byte, error) {
	r := new([aont.AontKeySize]byte)
	var err error
	if _, err = io.ReadFull(Rand, r[:]); err != nil {
		return nil, err
	}
	aonted, err := aont.AontEncode(r, in)
	if err != nil {
		return nil, err
	}
	out := append(
		cnw.Chaff(authKey, nonce, aonted[:aont.AontKeySize]),
		aonted[aont.AontKeySize:]...,
	)
	SliceZero(aonted[:aont.AontKeySize])
	return out, nil
}

// Decode EnclessEncode-ed data.
func EnclessDecode(authKey *[32]byte, nonce, in []byte) ([]byte, error) {
	var err error
	winnowed, err := cnw.Winnow(
		authKey, nonce, in[:aont.AontKeySize *cnw.EnlargeFactor],
	)
	if err != nil {
		return nil, err
	}
	out, err := aont.AontDecode(append(
		winnowed, in[aont.AontKeySize *cnw.EnlargeFactor:]...,
	))
	SliceZero(winnowed)
	if err != nil {
		return nil, err
	}
	return out, nil
}