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package otr3
import (
"bytes"
"crypto/aes"
"crypto/sha1"
"crypto/sha256"
"encoding/binary"
"fmt"
"hash"
"math/big"
"strconv"
)
var otrv3FragmentationPrefix = []byte("?OTR|")
const (
otrv3HeaderLen = 11
minValidInstanceTag = uint32(0x100)
)
type otrV3 struct{}
func (v otrV3) parameterLength() int {
return 192
}
func (v otrV3) isGroupElement(n *big.Int) bool {
return isGroupElement(n)
}
func (v otrV3) isFragmented(data []byte) bool {
return bytes.HasPrefix(data, otrv3FragmentationPrefix) || otrV2{}.isFragmented(data)
}
func parseItag(s []byte) (uint32, error) {
v, err := strconv.ParseInt(string(s), 16, 0)
if err != nil {
return 0, err
}
return uint32(v), nil
}
func (v otrV3) parseFragmentPrefix(c *Conversation, data []byte) (rest []byte, ignore bool, ok bool) {
if len(data) < 23 {
return data, false, false
}
header := data[:23]
headerPart := bytes.Split(header, fragmentSeparator)[0]
itagParts := bytes.Split(headerPart, fragmentItagsSeparator)
if len(itagParts) < 3 {
return data, false, false
}
senderInstanceTag, err1 := parseItag(itagParts[1])
if err1 != nil {
return data, false, false
}
receiverInstanceTag, err2 := parseItag(itagParts[2])
if err2 != nil {
return data, false, false
}
if err := v.verifyInstanceTags(c, senderInstanceTag, receiverInstanceTag); err != nil {
switch err {
case errInvalidOTRMessage:
return data, false, false
case errReceivedMessageForOtherInstance:
return data, true, true
}
}
return data[23:], false, true
}
func (v otrV3) fragmentPrefix(n, total int, itags uint32, itagr uint32) []byte {
return []byte(fmt.Sprintf("%s%08x|%08x,%05d,%05d,", string(otrv3FragmentationPrefix), itags, itagr, n+1, total))
}
func (v otrV3) protocolVersion() uint16 {
return 3
}
func (v otrV3) whitespaceTag() []byte {
return convertToWhitespace("3")
}
func (v otrV3) messageHeader(c *Conversation, msgType byte) ([]byte, error) {
if err := c.generateInstanceTag(); err != nil {
return nil, err
}
out := appendShort(nil, v.protocolVersion())
out = append(out, msgType)
out = appendWord(out, c.ourInstanceTag)
out = appendWord(out, c.theirInstanceTag)
return out, nil
}
func (c *Conversation) generateInstanceTag() error {
if c.ourInstanceTag != 0 {
return nil
}
var ret uint32
var dst [4]byte
for ret < minValidInstanceTag {
if err := c.randomInto(dst[:]); err != nil {
return err
}
ret = binary.BigEndian.Uint32(dst[:])
}
c.ourInstanceTag = ret
return nil
}
func malformedMessage(c *Conversation) {
c.messageEvent(MessageEventReceivedMessageMalformed)
c.generatePotentialErrorMessage(ErrorCodeMessageMalformed)
}
func (v otrV3) verifyInstanceTags(c *Conversation, their, our uint32) error {
if c.theirInstanceTag == 0 {
c.theirInstanceTag = their
}
if our > 0 && our < minValidInstanceTag {
malformedMessage(c)
return errInvalidOTRMessage
}
if their < minValidInstanceTag {
malformedMessage(c)
return errInvalidOTRMessage
}
if (our != 0 && c.ourInstanceTag != our) ||
(c.theirInstanceTag != their) {
c.messageEvent(MessageEventReceivedMessageForOtherInstance)
return errReceivedMessageForOtherInstance
}
return nil
}
func (v otrV3) parseMessageHeader(c *Conversation, msg []byte) ([]byte, []byte, error) {
if len(msg) < otrv3HeaderLen {
malformedMessage(c)
return nil, nil, errInvalidOTRMessage
}
header := msg[:otrv3HeaderLen]
msg, senderInstanceTag, _ := extractWord(msg[messageHeaderPrefix:])
msg, receiverInstanceTag, _ := extractWord(msg)
if err := v.verifyInstanceTags(c, senderInstanceTag, receiverInstanceTag); err != nil {
return nil, nil, err
}
return header, msg, nil
}
func (v otrV3) hashInstance() hash.Hash {
return sha1.New()
}
func (v otrV3) hash(val []byte) []byte {
ret := sha1.Sum(val)
return ret[:]
}
func (v otrV3) hashLength() int {
return sha1.Size
}
func (v otrV3) hash2Instance() hash.Hash {
return sha256.New()
}
func (v otrV3) hash2(val []byte) []byte {
ret := sha256.Sum256(val)
return ret[:]
}
func (v otrV3) hash2Length() int {
return sha256.Size
}
func (v otrV3) truncateLength() int {
return 20
}
func (v otrV3) keyLength() int {
return aes.BlockSize
}
|
