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|
package otr3
import (
"bytes"
"errors"
"hash"
"math/big"
)
type otrVersion interface {
protocolVersion() uint16
parameterLength() int
isGroupElement(n *big.Int) bool
isFragmented(data []byte) bool
parseFragmentPrefix(c *Conversation, data []byte) (rest []byte, ignore bool, ok bool)
fragmentPrefix(n, total int, itags uint32, itagr uint32) []byte
whitespaceTag() []byte
messageHeader(c *Conversation, msgType byte) ([]byte, error)
parseMessageHeader(c *Conversation, msg []byte) ([]byte, []byte, error)
hash([]byte) []byte
hashInstance() hash.Hash
hashLength() int
hash2([]byte) []byte
hash2Instance() hash.Hash
hash2Length() int
truncateLength() int
keyLength() int
}
func newOtrVersion(v uint16, p policies) (version otrVersion, err error) {
toCheck := policy(0)
switch v {
case 2:
version = otrV2{}
toCheck = allowV2
case 3:
version = otrV3{}
toCheck = allowV3
default:
return nil, errUnsupportedOTRVersion
}
if !p.has(toCheck) {
return nil, errInvalidVersion
}
return
}
func versionFromFragment(fragment []byte) uint16 {
var messageVersion uint16
switch {
case bytes.HasPrefix(fragment, otrv3FragmentationPrefix):
messageVersion = 3
case bytes.HasPrefix(fragment, otrv2FragmentationPrefix):
messageVersion = 2
}
return messageVersion
}
func (c *Conversation) checkVersion(message []byte) (err error) {
_, messageVersion, ok := extractShort(message)
if !ok {
return errInvalidOTRMessage
}
versions := 1 << messageVersion
if err := c.commitToVersionFrom(versions); err != nil {
return err
}
if c.version.protocolVersion() != messageVersion {
return errWrongProtocolVersion
}
return nil
}
// Based on the policy, commit to a version given a set of versions offered by the other peer unless the conversation has already committed to a version.
func (c *Conversation) commitToVersionFrom(versions int) error {
if c.version != nil {
return nil
}
var version otrVersion
switch {
case c.Policies.has(allowV3) && versions&(1<<3) > 0:
version = otrV3{}
case c.Policies.has(allowV2) && versions&(1<<2) > 0:
version = otrV2{}
default:
return errUnsupportedOTRVersion
}
c.version = version
return c.setKeyMatchingVersion()
}
func (c *Conversation) setKeyMatchingVersion() error {
for _, k := range c.ourKeys {
if k.IsAvailableForVersion(c.version.protocolVersion()) {
c.ourCurrentKey = k
return nil
}
}
return errors.New("no possible key for current version")
}
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