xs/herradurakex.go

133 lines
3.2 KiB
Go

/* Herradura - a Key exchange scheme in the style of Diffie-Hellman Key Exchange.
Copyright (C) 2017 Omar Alejandro Herrera Reyna
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 <https://www.gnu.org/licenses/>.
golang implementation by Russ Magee (rmagee_at_gmail.com) */
package herradurakex
import (
"fmt"
"math/big"
"math/rand"
"time"
)
// This type holds the session state for a key exchange
type HerraduraKEx struct {
intSz, pubSz int
randctx *rand.Rand
a *big.Int
b *big.Int
d, PeerD *big.Int
fa *big.Int
}
// Returns a new HerraduraKEx struct
func New(i int, p int) (h *HerraduraKEx) {
h = new(HerraduraKEx)
h.intSz = i
h.pubSz = p
h.seed()
h.a = h.rand()
h.b = h.rand()
h.d = h.fscxRevolve(h.a, h.b, h.pubSz)
return h
}
func (h *HerraduraKEx) seed() {
r := rand.New(rand.NewSource(time.Now().UnixNano()))
h.randctx = r
}
func (h *HerraduraKEx) rand() (v *big.Int) {
v = big.NewInt(0)
v.Rand(h.randctx, h.getMax())
return v
}
// Return max value for an n-bit big.Int
func (h *HerraduraKEx) getMax() (v *big.Int) {
v = big.NewInt(0)
var max big.Int
for i := 0; i < h.intSz; i++ {
max.SetBit(v, i, 1)
}
v = &max
return v
}
func (h *HerraduraKEx) bitX(x *big.Int, pos int) (ret int64) {
if pos < 0 {
pos = h.intSz - pos
}
if pos == 0 {
ret = int64(x.Bit(1) ^ x.Bit(0) ^ x.Bit(h.intSz-1))
} else if pos == h.intSz-1 {
ret = int64(x.Bit(0) ^ x.Bit(pos) ^ x.Bit(pos-1))
} else {
ret = int64(x.Bit((pos+1)%h.intSz) ^ x.Bit(pos) ^ x.Bit(pos-1))
}
return ret
}
func (h *HerraduraKEx) bit(up, down *big.Int, posU, posD int) (ret *big.Int) {
return big.NewInt(h.bitX(up, posU) ^ h.bitX(down, posD))
}
func (h *HerraduraKEx) fscx(up, down *big.Int) (result *big.Int) {
result = big.NewInt(0)
for count := 0; count < h.intSz; count++ {
result.Lsh(result, 1)
result.Add(result, h.bit(up, down, count, count))
}
return result
}
// This is the iteration function using the result of the previous iteration as the first
// parameter and the second parameter of the first iteration
func (h *HerraduraKEx) fscxRevolve(x, y *big.Int, passes int) (result *big.Int) {
result = big.NewInt(0)
result = x
for count := 0; count < passes; count++ {
result = h.fscx(result, y)
}
return result
}
func (h *HerraduraKEx) D() *big.Int {
return h.d
}
func (h *HerraduraKEx) FA() {
h.fa = h.fscxRevolve(h.PeerD, h.b, h.intSz-h.pubSz)
h.fa.Xor(h.fa, h.a)
}
func (h *HerraduraKEx) String() string {
return fmt.Sprintf("s:%d p:%d\na:%s\nb:%s\nd:->%s\n<-PeerD:%s\nfa:%s",
h.intSz, h.pubSz,
h.a.Text(16), h.b.Text(16),
h.d.Text(16),
h.PeerD.Text(16),
h.fa.Text(16))
}