Just copy double_ratchet.go to compare changes

simple_double_ratchet.go

+package main
+
+import (
+	"bytes"
+	"fmt"
+
+	"golang.org/x/crypto/sha3"
+
+	"github.com/twstrike/ed448"
+)
+
+const (
+	Q = iota
+	P1
+	P2
+	D
+)
+
+type Msg struct {
+	mtype    int
+	sender   string
+	rid, mid int
+	dh       pubkey
+
+	encKey key // this is here only to check if we can decrypt
+}
+
+func (m Msg) decryptWith(k key) {
+	if !bytes.Equal(k, m.encKey) {
+		panic("failed to decrypt message.")
+	}
+}
+
+var c = ed448.NewCurve()
+var NULLSEC = seckey{}
+var NULLPUB = pubkey{}
+
+type seckey [144]byte
+type pubkey [56]byte
+type key []byte
+
+type Entity struct {
+	name                 string
+	our_dh_pub, their_dh pubkey
+	our_dh_priv          seckey
+	R                    []key
+	Ca, Cb               []key
+	rid, j, k            int
+}
+
+func (e *Entity) sendData() Msg {
+	var cj key
+	if e.j == 0 {
+		fmt.Println()
+		fmt.Printf("%s \tRatcheting...\n", e.name)
+		e.our_dh_priv, e.our_dh_pub, _ = c.GenerateKeys()
+		e.rid += 1
+		secret := c.ComputeSecret(e.our_dh_priv, e.their_dh)
+		e.derive(secret[:])
+	}
+
+	cj = e.retriveChainkey(e.rid, e.j)
+	toSend := Msg{D, e.name, e.rid, e.j, e.our_dh_pub, cj}
+	e.j += 1
+
+	fmt.Printf("%s \tsending: %v\n", e.name, toSend)
+	fmt.Printf("%s \tour key: %x\n", e.name, cj)
+	return toSend
+}
+
+func (e *Entity) receive(m Msg) {
+	fmt.Println()
+	fmt.Printf("%s \treceive: %v\n", e.name, m)
+	switch m.mtype {
+	case D:
+		e.receiveData(m)
+		break
+	case Q:
+		break
+	case P1:
+		e.receiveP1(m)
+		break
+	case P2:
+		e.receiveP2(m)
+		break
+	}
+}
+
+func (e *Entity) receiveP1(m Msg) {
+	e.their_dh = m.dh
+	e.rid = e.rid + 1
+	if bytes.Compare(e.our_dh_priv[:], NULLSEC[:]) == 1 {
+		secret := c.ComputeSecret(e.our_dh_priv, e.their_dh)
+		e.derive(secret[:])
+	}
+}
+
+func (e *Entity) receiveP2(m Msg) {
+	e.their_dh = m.dh
+	e.rid = e.rid + 1
+
+	secret := c.ComputeSecret(e.our_dh_priv, e.their_dh)
+	e.derive(secret[:])
+}
+
+func (e *Entity) receiveData(m Msg) {
+	ck := make([]byte, 64)
+	if m.rid == e.rid+1 {
+		fmt.Printf("%s \tFollow Ratcheting...\n", e.name)
+		e.rid = m.rid
+		e.their_dh = m.dh
+		secret := c.ComputeSecret(e.our_dh_priv, e.their_dh)
+		e.derive(secret[:])
+		e.j = 0 // need to ratchet next time when send
+	} else if e.k > m.mid {
+		//panic("we received a message delayed out of order")
+	}
+
+	e.k = m.mid
+	ck = e.retriveChainkey(m.rid, m.mid)
+	fmt.Printf("%s \ttheir key: %x\n", e.name, ck)
+
+	m.decryptWith(ck)
+}
+
+func (e *Entity) wasAliceAt(rid int) bool {
+	return rid%2 == 1
+}
+
+func (e *Entity) retriveChainkey(rid, mid int) key {
+	var ck key
+	buf := make([]byte, 64)
+
+	if e.wasAliceAt(rid) {
+		ck = e.Ca[rid]
+	} else {
+		ck = e.Cb[rid]
+	}
+	copy(buf, ck)
+	for i := mid; i > 0; i-- {
+		sha3.ShakeSum256(buf, buf)
+	}
+	return buf
+}
+
+func (e *Entity) derive(secret []byte) {
+	r := make([]byte, 64)
+	ca := make([]byte, 64)
+	cb := make([]byte, 64)
+	if len(e.R) > 0 {
+		secret = append(secret, e.R[e.rid-1]...)
+	}
+	sha3.ShakeSum256(r, append(secret, 0))
+	sha3.ShakeSum256(ca, append(secret, 1))
+	sha3.ShakeSum256(cb, append(secret, 2))
+
+	e.R = append(e.R, r)
+	e.Ca = append(e.Ca, ca)
+	e.Cb = append(e.Cb, cb)
+}
+
+func (e *Entity) query() Msg {
+	toSend := Msg{mtype: Q, sender: e.name}
+	fmt.Printf("%s \tsending: %v\n", e.name, toSend)
+	return toSend
+}
+
+func (e *Entity) sendP1() Msg {
+	e.our_dh_priv, e.our_dh_pub, _ = c.GenerateKeys()
+
+	e.j = 1
+	e.rid = e.rid + 1
+	if bytes.Compare(e.their_dh[:], NULLPUB[:]) == 1 {
+		secret := c.ComputeSecret(e.our_dh_priv, e.their_dh)
+		e.derive(secret[:])
+	}
+
+	toSend := Msg{P1, e.name, -1, -1, e.our_dh_pub, nil}
+	fmt.Printf("%s \tsending: %v\n", e.name, toSend)
+	return toSend
+}
+
+func (e *Entity) sendP2() Msg {
+	e.j = 0
+	e.rid = e.rid + 1
+	e.our_dh_priv, e.our_dh_pub, _ = c.GenerateKeys()
+	secret := c.ComputeSecret(e.our_dh_priv, e.their_dh)
+	e.derive(secret[:])
+
+	toSend := Msg{P2, e.name, -1, -1, e.our_dh_pub, nil}
+	fmt.Printf("%s \tsending: %v\n", e.name, toSend)
+	return toSend
+}
+
+func main() {
+	a, b := initialize()
+	b.receive(a.query())
+	a.receive(b.sendP1())
+	b.receive(a.sendP2())
+
+	fmt.Println("=========================")
+	fmt.Println("Testing sync data message")
+	fmt.Println("=========================")
+
+	a.receive(b.sendData()) // b sends first, so no new ratchet happens.
+	a.receive(b.sendData()) // b again: this is another follow up msg.
+	b.receive(a.sendData()) // a sends, a new ratchet happens and bob follows.
+	b.receive(a.sendData()) // a again: this is a follow up.
+
+	fmt.Println("=========================")
+	fmt.Println("Testing async data message")
+	fmt.Println("=========================")
+
+	m1 := a.sendData() // a sends again: another follow up message.
+	m2 := b.sendData() // b sends now, a new ratcher happens for bob.
+	m3 := a.sendData() // a sends again: another follow up message.
+
+	b.receive(m1) // b receives follow up message from a previous ratchet.
+	b.receive(m3) // b receives follow up message from a previous ratchet.
+	a.receive(m2) // a receives a message from a new ratchet. She follows the ratchet.
+
+	fmt.Println("=========================")
+	fmt.Println("Testing new sync DAKE")
+	fmt.Println("=========================")
+
+	b.receive(a.query())
+	a.receive(b.sendP1())
+	b.receive(a.sendP2())
+
+	b.receive(a.sendData()) // a sends, a new ratchet starts and bob follows
+	b.receive(a.sendData()) // a sends a follow up
+	a.receive(b.sendData()) // b sends, a new ratchet starts and alice follows
+	a.receive(b.sendData()) // b sends a follow up
+
+	fmt.Println("=========================")
+	fmt.Println("Testing async DAKE message")
+	fmt.Println("=========================")
+
+	b.receive(a.query())
+	p1 := b.sendP1()
+	b0 := b.sendData() // bob sends a data message during a new DAKE, is this a follow up msg?
+	b1 := b.sendData() // bob sends a data message during a new DAKE - surely a follow up msg.
+
+	b.receive(a.sendData()) // a sends a new message before she receives p1, but after bob sends p1.
+	// this will be a new ratchet, and thats a problem because bob will also ratchet when sending p1.
+
+	a.receive(p1)      // a receives p1
+	p2 := a.sendP2()   // ... and immediately replies with a p2
+	a0 := a.sendData() // ... and send a new data msg
+
+	b.receive(p2) // bob receives a p2
+	b.receive(a0) // and the a0
+
+	a.receive(b0) // a receives b0 (I want to see how it works if she receives this BEFORE sending a0)
+	a.receive(b1) // a receives b1
+}
+
+func initialize() (alice, bob Entity) {
+	alice.name = "Alice"
+	alice.rid = -2
+	bob.name = "Bob"
+	bob.rid = -2
+
+	return alice, bob
+}