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verificationhelper/sas: don't trust keys until both MAC events are sent
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Browse source 
Signed-off-by: Sumner Evans <sumner.evans@automattic.com>
This commit is contained in:
Sumner Evans 2025-02-20 14:13:42 -07:00
commit 4c58b82813
No known key found for this signature in database
1 changed files with 44 additions and 29 deletions
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115
crypto/verificationhelper/sas.go
View file

@ -111,6 +111,7 @@ func (vh *VerificationHelper) ConfirmSAS(ctx context.Context, txnID id.Verificat
keys := map[id.KeyID]jsonbytes.UnpaddedBytes{}
log.Info().Msg("Signing keys")
var masterKey string
// My device key
myDevice := vh.mach.OwnIdentity()
@ -123,8 +124,9 @@ func (vh *VerificationHelper) ConfirmSAS(ctx context.Context, txnID id.Verificat
// Master signing key
crossSigningKeys := vh.mach.GetOwnCrossSigningPublicKeys(ctx)
if crossSigningKeys != nil {
crossSigningKeyID := id.NewKeyID(id.KeyAlgorithmEd25519, crossSigningKeys.MasterKey.String())
keys[crossSigningKeyID], err = vh.verificationMACHKDF(txn, vh.client.UserID, vh.client.DeviceID, txn.TheirUserID, txn.TheirDeviceID, crossSigningKeyID.String(), crossSigningKeys.MasterKey.String())
masterKey = crossSigningKeys.MasterKey.String()
crossSigningKeyID := id.NewKeyID(id.KeyAlgorithmEd25519, masterKey)
keys[crossSigningKeyID], err = vh.verificationMACHKDF(txn, vh.client.UserID, vh.client.DeviceID, txn.TheirUserID, txn.TheirDeviceID, crossSigningKeyID.String(), masterKey)
if err != nil {
return err
}
@ -148,10 +150,16 @@ func (vh *VerificationHelper) ConfirmSAS(ctx context.Context, txnID id.Verificat
if err != nil {
return err
}
log.Info().Msg("Sent our MAC event")
txn.SentOurMAC = true
if txn.ReceivedTheirMAC {
txn.VerificationState = VerificationStateSASMACExchanged
if err := vh.trustKeysAfterMACCheck(ctx, txn, masterKey); err != nil {
return fmt.Errorf("failed to trust keys: %w", err)
}
err := vh.sendVerificationEvent(ctx, txn, event.InRoomVerificationDone, &event.VerificationDoneEventContent{})
if err != nil {
return err
@ -731,57 +739,15 @@ func (vh *VerificationHelper) onVerificationMAC(ctx context.Context, txn Verific
}
log.Info().Msg("All MACs verified")
// Trust their device
theirDevice.Trust = id.TrustStateVerified
err = vh.mach.CryptoStore.PutDevice(ctx, txn.TheirUserID, theirDevice)
if err != nil {
vh.cancelVerificationTxn(ctx, txn, event.VerificationCancelCodeUser, "failed to update device trust state after verifying: %w", err)
return
}
if txn.TheirUserID == vh.client.UserID {
// Self-signing situation.
//
// If we have the cross-signing keys, then we need to sign their device
// using the self-signing key. Otherwise, they have the master private
// key, so we need to trust the master public key.
if vh.mach.CrossSigningKeys != nil {
err = vh.mach.SignOwnDevice(ctx, theirDevice)
if err != nil {
vh.cancelVerificationTxn(ctx, txn, event.VerificationCancelCodeUser, "failed to sign our own new device: %w", err)
return
}
} else {
err = vh.mach.SignOwnMasterKey(ctx)
if err != nil {
vh.cancelVerificationTxn(ctx, txn, event.VerificationCancelCodeUser, "failed to sign our own master key: %w", err)
return
}
}
} else if masterKey != "" {
// Cross-signing situation.
//
// The master key was included in the list of keys to verify, so verify
// that it matches what we expect and sign their master key using the
// user-signing key.
theirSigningKeys, err := vh.mach.GetCrossSigningPublicKeys(ctx, txn.TheirUserID)
if err != nil {
vh.cancelVerificationTxn(ctx, txn, event.VerificationCancelCodeKeyMismatch, "couldn't get %s's cross-signing keys: %w", txn.TheirUserID, err)
return
} else if theirSigningKeys.MasterKey.String() != masterKey {
vh.cancelVerificationTxn(ctx, txn, event.VerificationCancelCodeKeyMismatch, "master keys do not match")
return
}
if err := vh.mach.SignUser(ctx, txn.TheirUserID, theirSigningKeys.MasterKey); err != nil {
vh.cancelVerificationTxn(ctx, txn, event.VerificationCancelCodeInternalError, "failed to sign their master key: %w", err)
return
}
}
txn.ReceivedTheirMAC = true
if txn.SentOurMAC {
txn.VerificationState = VerificationStateSASMACExchanged
if err := vh.trustKeysAfterMACCheck(ctx, txn, masterKey); err != nil {
vh.cancelVerificationTxn(ctx, txn, event.VerificationCancelCodeUser, "failed to trust keys: %w", err)
return
}
err := vh.sendVerificationEvent(ctx, txn, event.InRoomVerificationDone, &event.VerificationDoneEventContent{})
if err != nil {
vh.cancelVerificationTxn(ctx, txn, event.VerificationCancelCodeUser, "failed to send verification done event: %w", err)
@ -794,3 +760,52 @@ func (vh *VerificationHelper) onVerificationMAC(ctx context.Context, txn Verific
log.Err(err).Msg("failed to save verification transaction")
}
}
func (vh *VerificationHelper) trustKeysAfterMACCheck(ctx context.Context, txn VerificationTransaction, masterKey string) error {
theirDevice, err := vh.mach.GetOrFetchDevice(ctx, txn.TheirUserID, txn.TheirDeviceID)
if err != nil {
return fmt.Errorf("failed to fetch their device: %w", err)
}
// Trust their device
theirDevice.Trust = id.TrustStateVerified
err = vh.mach.CryptoStore.PutDevice(ctx, txn.TheirUserID, theirDevice)
if err != nil {
return fmt.Errorf("failed to update device trust state after verifying: %w", err)
}
if txn.TheirUserID == vh.client.UserID {
// Self-signing situation.
//
// If we have the cross-signing keys, then we need to sign their device
// using the self-signing key. Otherwise, they have the master private
// key, so we need to trust the master public key.
if vh.mach.CrossSigningKeys != nil {
err = vh.mach.SignOwnDevice(ctx, theirDevice)
if err != nil {
return fmt.Errorf("failed to sign our own new device: %w", err)
}
} else {
err = vh.mach.SignOwnMasterKey(ctx)
if err != nil {
return fmt.Errorf("failed to sign our own master key: %w", err)
}
}
} else if masterKey != "" {
// Cross-signing situation.
//
// The master key was included in the list of keys to verify, so verify
// that it matches what we expect and sign their master key using the
// user-signing key.
theirSigningKeys, err := vh.mach.GetCrossSigningPublicKeys(ctx, txn.TheirUserID)
if err != nil {
return fmt.Errorf("couldn't get %s's cross-signing keys: %w", txn.TheirUserID, err)
} else if theirSigningKeys.MasterKey.String() != masterKey {
return fmt.Errorf("master keys do not match")
}
if err := vh.mach.SignUser(ctx, txn.TheirUserID, theirSigningKeys.MasterKey); err != nil {
return fmt.Errorf("failed to sign %s's master key: %w", txn.TheirUserID, err)
}
}
return nil
}