forked from coyim/otr3
/
key_management.go
235 lines (191 loc) · 5.52 KB
/
key_management.go
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package otr3
import (
"crypto/aes"
"crypto/sha1"
"crypto/sha256"
"fmt"
"hash"
"math/big"
)
type dhKeyPair struct {
pub *big.Int
priv *big.Int
}
type akeKeys struct {
c [aes.BlockSize]byte
m1, m2 [sha256.Size]byte
}
type macKey [sha1.Size]byte
type sessionKeys struct {
sendingAESKey, receivingAESKey [aes.BlockSize]byte
sendingMACKey, receivingMACKey macKey
}
type keyManagementContext struct {
ourKeyID, theirKeyID uint32
ourCurrentDHKeys, ourPreviousDHKeys dhKeyPair
theirCurrentDHPubKey, theirPreviousDHPubKey *big.Int
ourCounter uint64
macKeyHistory macKeyHistory
oldMACKeys []macKey
}
type macKeyUsage struct {
ourKeyID, theirKeyID uint32
receivingKey macKey
}
type macKeyHistory struct {
items []macKeyUsage
}
func (h *macKeyHistory) deleteKeysAt(del ...int) {
for j := len(del) - 1; j >= 0; j-- {
l := len(h.items)
h.items[del[j]], h.items = h.items[l-1], h.items[:l-1]
}
}
func (h *macKeyHistory) addKeys(ourKeyID uint32, theirKeyID uint32, sendingMACKey macKey, receivingMACKey macKey) {
macKeys := macKeyUsage{
ourKeyID: ourKeyID,
theirKeyID: theirKeyID,
receivingKey: receivingMACKey,
}
h.items = append(h.items, macKeys)
}
func (h *macKeyHistory) forgetMACKeysForOurKey(ourKeyID uint32) []macKey {
var ret []macKey
var del []int
for i, k := range h.items {
if k.ourKeyID == ourKeyID {
ret = append(ret, k.receivingKey)
del = append(del, i)
}
}
h.deleteKeysAt(del...)
return ret
}
func (h *macKeyHistory) forgetMACKeysForTheirKey(theirKeyID uint32) []macKey {
var ret []macKey
var del []int
for i, k := range h.items {
if k.theirKeyID == theirKeyID {
ret = append(ret, k.receivingKey)
del = append(del, i)
}
}
h.deleteKeysAt(del...)
return ret
}
func (c *keyManagementContext) revealMACKeys() []macKey {
ret := c.oldMACKeys
c.oldMACKeys = []macKey{}
return ret
}
func (c *keyManagementContext) generateNewDHKeyPair(newPrivKey *big.Int) {
c.ourPreviousDHKeys = c.ourCurrentDHKeys
c.ourCurrentDHKeys = dhKeyPair{
priv: newPrivKey,
pub: modExp(g1, newPrivKey),
}
c.ourKeyID++
}
func (c *keyManagementContext) revealMACKeysForOurPreviousKeyID() {
keys := c.macKeyHistory.forgetMACKeysForOurKey(c.ourKeyID - 1)
c.oldMACKeys = append(c.oldMACKeys, keys...)
}
func (c *keyManagementContext) rotateOurKeys(recipientKeyID uint32, newPrivKey *big.Int) {
if recipientKeyID == c.ourKeyID {
c.revealMACKeysForOurPreviousKeyID()
c.generateNewDHKeyPair(newPrivKey)
}
}
func (c *keyManagementContext) revealMACKeysForTheirPreviousKeyID() {
keys := c.macKeyHistory.forgetMACKeysForTheirKey(c.theirKeyID - 1)
c.oldMACKeys = append(c.oldMACKeys, keys...)
}
func (c *keyManagementContext) rotateTheirKey(senderKeyID uint32, pubDHKey *big.Int) {
if senderKeyID == c.theirKeyID {
c.revealMACKeysForTheirPreviousKeyID()
c.theirPreviousDHPubKey = c.theirCurrentDHPubKey
c.theirCurrentDHPubKey = pubDHKey
c.theirKeyID++
}
}
func (c *keyManagementContext) calculateDHSessionKeys(ourKeyID, theirKeyID uint32) (sessionKeys, error) {
var ret sessionKeys
var sendbyte, recvbyte byte
ourPrivKey, ourPubKey, err := c.pickOurKeys(ourKeyID)
if err != nil {
return ret, err
}
theirPubKey, err := c.pickTheirKey(theirKeyID)
if err != nil {
return ret, err
}
if gt(ourPubKey, theirPubKey) {
//we are high end
sendbyte, recvbyte = 0x01, 0x02
} else {
//we are low end
sendbyte, recvbyte = 0x02, 0x01
}
s := new(big.Int).Exp(theirPubKey, ourPrivKey, p)
secbytes := appendMPI(nil, s)
sha := sha1.New()
copy(ret.sendingAESKey[:], h(sendbyte, secbytes, sha))
copy(ret.receivingAESKey[:], h(recvbyte, secbytes, sha))
ret.sendingMACKey = sha1.Sum(ret.sendingAESKey[:])
ret.receivingMACKey = sha1.Sum(ret.receivingAESKey[:])
c.macKeyHistory.addKeys(ourKeyID, theirKeyID, ret.sendingMACKey, ret.receivingMACKey)
return ret, nil
}
func (c *keyManagementContext) pickOurKeys(ourKeyID uint32) (privKey, pubKey *big.Int, err error) {
if c.ourKeyID == 0 {
privKey, pubKey = c.ourCurrentDHKeys.priv, c.ourCurrentDHKeys.pub
} else {
switch ourKeyID {
case c.ourKeyID:
privKey, pubKey = c.ourCurrentDHKeys.priv, c.ourCurrentDHKeys.pub
case c.ourKeyID - 1:
privKey, pubKey = c.ourPreviousDHKeys.priv, c.ourPreviousDHKeys.pub
default:
err = fmt.Errorf("otr: unexpected ourKeyID %d", ourKeyID)
}
}
return privKey, pubKey, err
}
func (c *keyManagementContext) pickTheirKey(theirKeyID uint32) (pubKey *big.Int, err error) {
switch theirKeyID {
case c.theirKeyID:
pubKey = c.theirCurrentDHPubKey
case c.theirKeyID - 1:
if c.theirPreviousDHPubKey == nil {
err = fmt.Errorf("otr: unexpected theirKeyID %d", theirKeyID-1)
} else {
pubKey = c.theirPreviousDHPubKey
}
default:
err = fmt.Errorf("otr: unexpected theirKeyID %d", theirKeyID)
}
return pubKey, err
}
func calculateAKEKeys(s *big.Int) (ssid [8]byte, revealSigKeys, signatureKeys akeKeys) {
secbytes := appendMPI(nil, s)
sha := sha256.New()
keys := h(0x01, secbytes, sha)
copy(ssid[:], h(0x00, secbytes, sha)[:8])
copy(revealSigKeys.c[:], keys[:16])
copy(signatureKeys.c[:], keys[16:])
copy(revealSigKeys.m1[:], h(0x02, secbytes, sha))
copy(revealSigKeys.m2[:], h(0x03, secbytes, sha))
copy(signatureKeys.m1[:], h(0x04, secbytes, sha))
copy(signatureKeys.m2[:], h(0x05, secbytes, sha))
return
}
// h1() and h2() are the same
func h(b byte, secbytes []byte, h hash.Hash) []byte {
h.Reset()
h.Write([]byte{b})
h.Write(secbytes[:])
return h.Sum(nil)
}
//calculateSessionKeysWhenAKEIsCompleted (receiveRevealSig and recevieSig)
//rotateDhKeys
//rotateYKeys