xs/herradurakex.go

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// Package herradurakex - socket lib conforming to
// golang.org/pkg/net Conn interface, with
// experimental key exchange algorithm by
// Omar Alejandro Herrera Reyna
// (https://github.com/Caume/HerraduraKEx)
//
// See README.md for full license info.
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package herradurakex
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/* This is the core KEx algorithm. For client/server net support code,
See hkexnet.go for a golang/pkg/net for the compatible Conn interface
using this to transparently negotiate keys and secure a network channel. */
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import (
"fmt"
"math/big"
"math/rand"
"time"
)
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// HerraduraKEx holds the session state for a key exchange.
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type HerraduraKEx struct {
intSz, pubSz int
randctx *rand.Rand
a *big.Int
b *big.Int
d, PeerD *big.Int
fa *big.Int
}
// New returns a HerraduraKEx struct.
//
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// i - internal (private) random nonce
// p - public (exchanged) random nonce (typically 1/4 bitsize of i)
//
// If i or p are passed as zero, they will default to 256 and 64,
// respectively.
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func New(i int, p int) (h *HerraduraKEx) {
h = new(HerraduraKEx)
if i == 0 {
i = 256
}
if p == 0 {
p = 64
}
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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
}
// getMax returns the max value for an n-bit big.Int
func (h *HerraduraKEx) getMax() (n *big.Int) {
n = big.NewInt(0)
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var max big.Int
for i := 0; i < h.intSz; i++ {
max.SetBit(n, i, 1)
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}
n = &max
return n
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}
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
}
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// This is the iteration function using the result of the previous iteration
// as the first parameter and the second parameter of the first iteration.
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func (h *HerraduraKEx) fscxRevolve(x, y *big.Int, passes int) (result *big.Int) {
result = x
for count := 0; count < passes; count++ {
result = h.fscx(result, y)
}
return result
}
// D returns the D (FSCX Revolved) value, input to generate FA
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// (the value for peer KEx)
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func (h *HerraduraKEx) D() *big.Int {
return h.d
}
// FA returns the FA value, which must be sent to peer for KEx.
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func (h *HerraduraKEx) FA() {
h.fa = h.fscxRevolve(h.PeerD, h.b, h.intSz-h.pubSz)
h.fa.Xor(h.fa, h.a)
}
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// Output HerraduraKEx type value as a string. Implements Stringer interface.
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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))
}