248 lines
9.4 KiB
Go
248 lines
9.4 KiB
Go
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// Copyright (c) 2021 Tulir Asokan
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//
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// This Source Code Form is subject to the terms of the Mozilla Public
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// License, v. 2.0. If a copy of the MPL was not distributed with this
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// file, You can obtain one at http://mozilla.org/MPL/2.0/.
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package crypto
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import (
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"encoding/json"
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"errors"
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"fmt"
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"time"
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"maunium.net/go/mautrix/event"
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"maunium.net/go/mautrix/id"
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)
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var (
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UnsupportedAlgorithm = errors.New("unsupported event encryption algorithm")
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NotEncryptedForMe = errors.New("olm event doesn't contain ciphertext for this device")
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UnsupportedOlmMessageType = errors.New("unsupported olm message type")
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DecryptionFailedWithMatchingSession = errors.New("decryption failed with matching session")
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DecryptionFailedForNormalMessage = errors.New("decryption failed for normal message")
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SenderMismatch = errors.New("mismatched sender in olm payload")
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RecipientMismatch = errors.New("mismatched recipient in olm payload")
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RecipientKeyMismatch = errors.New("mismatched recipient key in olm payload")
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)
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// DecryptedOlmEvent represents an event that was decrypted from an event encrypted with the m.olm.v1.curve25519-aes-sha2 algorithm.
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type DecryptedOlmEvent struct {
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Source *event.Event `json:"-"`
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SenderKey id.SenderKey `json:"-"`
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Sender id.UserID `json:"sender"`
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SenderDevice id.DeviceID `json:"sender_device"`
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Keys OlmEventKeys `json:"keys"`
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Recipient id.UserID `json:"recipient"`
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RecipientKeys OlmEventKeys `json:"recipient_keys"`
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Type event.Type `json:"type"`
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Content event.Content `json:"content"`
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}
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func (mach *OlmMachine) decryptOlmEvent(evt *event.Event, traceID string) (*DecryptedOlmEvent, error) {
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content, ok := evt.Content.Parsed.(*event.EncryptedEventContent)
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if !ok {
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return nil, IncorrectEncryptedContentType
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} else if content.Algorithm != id.AlgorithmOlmV1 {
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return nil, UnsupportedAlgorithm
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}
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ownContent, ok := content.OlmCiphertext[mach.account.IdentityKey()]
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if !ok {
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return nil, NotEncryptedForMe
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}
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decrypted, err := mach.decryptAndParseOlmCiphertext(evt.Sender, content.SenderKey, ownContent.Type, ownContent.Body, traceID)
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if err != nil {
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return nil, err
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}
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decrypted.Source = evt
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return decrypted, nil
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}
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type OlmEventKeys struct {
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Ed25519 id.Ed25519 `json:"ed25519"`
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}
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func (mach *OlmMachine) decryptAndParseOlmCiphertext(sender id.UserID, senderKey id.SenderKey, olmType id.OlmMsgType, ciphertext string, traceID string) (*DecryptedOlmEvent, error) {
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if olmType != id.OlmMsgTypePreKey && olmType != id.OlmMsgTypeMsg {
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return nil, UnsupportedOlmMessageType
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}
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endTimeTrace := mach.timeTrace("decrypting olm ciphertext", traceID, 5*time.Second)
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plaintext, err := mach.tryDecryptOlmCiphertext(sender, senderKey, olmType, ciphertext, traceID)
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endTimeTrace()
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if err != nil {
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return nil, err
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}
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defer mach.timeTrace("parsing decrypted olm event", traceID, time.Second)()
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var olmEvt DecryptedOlmEvent
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err = json.Unmarshal(plaintext, &olmEvt)
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if err != nil {
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return nil, fmt.Errorf("failed to parse olm payload: %w", err)
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}
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if sender != olmEvt.Sender {
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return nil, SenderMismatch
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} else if mach.Client.UserID != olmEvt.Recipient {
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return nil, RecipientMismatch
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} else if mach.account.SigningKey() != olmEvt.RecipientKeys.Ed25519 {
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return nil, RecipientKeyMismatch
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}
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err = olmEvt.Content.ParseRaw(olmEvt.Type)
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if err != nil && !event.IsUnsupportedContentType(err) {
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return nil, fmt.Errorf("failed to parse content of olm payload event: %w", err)
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}
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olmEvt.SenderKey = senderKey
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return &olmEvt, nil
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}
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func (mach *OlmMachine) tryDecryptOlmCiphertext(sender id.UserID, senderKey id.SenderKey, olmType id.OlmMsgType, ciphertext string, traceID string) ([]byte, error) {
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endTimeTrace := mach.timeTrace("waiting for olm lock", traceID, 5*time.Second)
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mach.olmLock.Lock()
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endTimeTrace()
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defer mach.olmLock.Unlock()
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plaintext, err := mach.tryDecryptOlmCiphertextWithExistingSession(senderKey, olmType, ciphertext, traceID)
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if err != nil {
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if err == DecryptionFailedWithMatchingSession {
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mach.Log.Warn("Found matching session yet decryption failed for sender %s with key %s", sender, senderKey)
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go mach.unwedgeDevice(sender, senderKey)
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}
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return nil, fmt.Errorf("failed to decrypt olm event: %w", err)
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}
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if plaintext != nil {
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// Decryption successful
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return plaintext, nil
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}
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// Decryption failed with every known session or no known sessions, let's try to create a new session.
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//
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// New sessions can only be created if it's a prekey message, we can't decrypt the message
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// if it isn't one at this point in time anymore, so return early.
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if olmType != id.OlmMsgTypePreKey {
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go mach.unwedgeDevice(sender, senderKey)
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return nil, DecryptionFailedForNormalMessage
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}
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mach.Log.Trace("Trying to create inbound session for %s/%s", sender, senderKey)
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endTimeTrace = mach.timeTrace("creating inbound olm session", traceID, time.Second)
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session, err := mach.createInboundSession(senderKey, ciphertext)
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endTimeTrace()
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if err != nil {
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go mach.unwedgeDevice(sender, senderKey)
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return nil, fmt.Errorf("failed to create new session from prekey message: %w", err)
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}
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mach.Log.Debug("Created inbound olm session %s for %s/%s: %s", session.ID(), sender, senderKey, session.Describe())
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endTimeTrace = mach.timeTrace(fmt.Sprintf("decrypting prekey olm message with %s/%s", senderKey, session.ID()), traceID, time.Second)
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plaintext, err = session.Decrypt(ciphertext, olmType)
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endTimeTrace()
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if err != nil {
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go mach.unwedgeDevice(sender, senderKey)
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return nil, fmt.Errorf("failed to decrypt olm event with session created from prekey message: %w", err)
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}
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endTimeTrace = mach.timeTrace(fmt.Sprintf("updating new session %s/%s in database", senderKey, session.ID()), traceID, time.Second)
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err = mach.CryptoStore.UpdateSession(senderKey, session)
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endTimeTrace()
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if err != nil {
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mach.Log.Warn("Failed to update new olm session in crypto store after decrypting: %v", err)
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}
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return plaintext, nil
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}
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func (mach *OlmMachine) tryDecryptOlmCiphertextWithExistingSession(senderKey id.SenderKey, olmType id.OlmMsgType, ciphertext string, traceID string) ([]byte, error) {
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endTimeTrace := mach.timeTrace(fmt.Sprintf("getting sessions with %s", senderKey), traceID, time.Second)
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sessions, err := mach.CryptoStore.GetSessions(senderKey)
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endTimeTrace()
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if err != nil {
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return nil, fmt.Errorf("failed to get session for %s: %w", senderKey, err)
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}
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for _, session := range sessions {
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if olmType == id.OlmMsgTypePreKey {
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endTimeTrace = mach.timeTrace(fmt.Sprintf("checking if prekey olm message matches session %s/%s", senderKey, session.ID()), traceID, time.Second)
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matches, err := session.Internal.MatchesInboundSession(ciphertext)
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endTimeTrace()
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if err != nil {
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return nil, fmt.Errorf("failed to check if ciphertext matches inbound session: %w", err)
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} else if !matches {
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continue
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}
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}
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mach.Log.Trace("Trying to decrypt olm message from %s with session %s: %s", senderKey, session.ID(), session.Describe())
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endTimeTrace = mach.timeTrace(fmt.Sprintf("decrypting olm message with %s/%s", senderKey, session.ID()), traceID, time.Second)
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plaintext, err := session.Decrypt(ciphertext, olmType)
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endTimeTrace()
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if err != nil {
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if olmType == id.OlmMsgTypePreKey {
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return nil, DecryptionFailedWithMatchingSession
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}
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} else {
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endTimeTrace = mach.timeTrace(fmt.Sprintf("updating session %s/%s in database", senderKey, session.ID()), traceID, time.Second)
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err = mach.CryptoStore.UpdateSession(senderKey, session)
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endTimeTrace()
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if err != nil {
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mach.Log.Warn("Failed to update olm session in crypto store after decrypting: %v", err)
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}
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mach.Log.Trace("Decrypted olm message from %s with session %s", senderKey, session.ID())
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return plaintext, nil
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}
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}
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return nil, nil
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}
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func (mach *OlmMachine) createInboundSession(senderKey id.SenderKey, ciphertext string) (*OlmSession, error) {
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session, err := mach.account.NewInboundSessionFrom(senderKey, ciphertext)
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if err != nil {
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return nil, err
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}
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mach.saveAccount()
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err = mach.CryptoStore.AddSession(senderKey, session)
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if err != nil {
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mach.Log.Error("Failed to store created inbound session: %v", err)
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}
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return session, nil
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}
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const MinUnwedgeInterval = 1 * time.Hour
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func (mach *OlmMachine) unwedgeDevice(sender id.UserID, senderKey id.SenderKey) {
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mach.recentlyUnwedgedLock.Lock()
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prevUnwedge, ok := mach.recentlyUnwedged[senderKey]
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delta := time.Now().Sub(prevUnwedge)
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if ok && delta < MinUnwedgeInterval {
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mach.Log.Debug("Not creating new Olm session with %s/%s, previous recreation was %s ago", sender, senderKey, delta)
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mach.recentlyUnwedgedLock.Unlock()
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return
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}
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mach.recentlyUnwedged[senderKey] = time.Now()
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mach.recentlyUnwedgedLock.Unlock()
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deviceIdentity, err := mach.GetOrFetchDeviceByKey(sender, senderKey)
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if err != nil {
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mach.Log.Error("Failed to find device info by identity key: %v", err)
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return
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} else if deviceIdentity == nil {
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mach.Log.Warn("Didn't find identity of %s/%s, can't unwedge session", sender, senderKey)
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return
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}
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mach.Log.Debug("Creating new Olm session with %s/%s (key: %s)", sender, deviceIdentity.DeviceID, senderKey)
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mach.devicesToUnwedgeLock.Lock()
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mach.devicesToUnwedge[senderKey] = true
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mach.devicesToUnwedgeLock.Unlock()
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err = mach.SendEncryptedToDevice(deviceIdentity, event.ToDeviceDummy, event.Content{})
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if err != nil {
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mach.Log.Error("Failed to send dummy event to unwedge session with %s/%s: %v", sender, senderKey, err)
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}
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}
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