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failure.go
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failure.go
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package htlcswitch
import (
"bytes"
"fmt"
"io"
"github.com/btcsuite/btcd/btcec"
"github.com/lightningnetwork/lightning-onion"
"github.com/lightningnetwork/lnd/lnwire"
)
// ForwardingError wraps an lnwire.FailureMessage in a struct that also
// includes the source of the error.
type ForwardingError struct {
// ErrorSource is the public key of the node that sent the error. With
// this information, the dispatcher of a payment can modify their set
// of candidate routes in response to the type of error extracted.
ErrorSource *btcec.PublicKey
// ExtraMsg is an additional error message that callers can provide in
// order to provide context specific error details.
ExtraMsg string
lnwire.FailureMessage
}
// Error implements the built-in error interface. We use this method to allow
// the switch or any callers to insert additional context to the error message
// returned.
func (f *ForwardingError) Error() string {
if f.ExtraMsg == "" {
return f.FailureMessage.Error()
}
return fmt.Sprintf("%v: %v", f.FailureMessage.Error(), f.ExtraMsg)
}
// ErrorDecrypter is an interface that is used to decrypt the onion encrypted
// failure reason an extra out a well formed error.
type ErrorDecrypter interface {
// DecryptError peels off each layer of onion encryption from the first
// hop, to the source of the error. A fully populated
// lnwire.FailureMessage is returned along with the source of the
// error.
DecryptError(lnwire.OpaqueReason) (*ForwardingError, error)
}
// EncrypterType establishes an enum used in serialization to indicate how to
// decode a concrete instance of the ErrorEncrypter interface.
type EncrypterType byte
const (
// EncrypterTypeNone signals that no error encyrpter is present, this
// can happen if the htlc is originates in the switch.
EncrypterTypeNone EncrypterType = 0
// EncrypterTypeSphinx is used to identify a sphinx onion error
// encrypter instance.
EncrypterTypeSphinx = 1
// EncrypterTypeMock is used to identify a mock obfuscator instance.
EncrypterTypeMock = 2
)
// UnknownEncrypterType is an error message used to signal that an unexpected
// EncrypterType was encountered during decoding.
type UnknownEncrypterType EncrypterType
// Error returns a formatted error indicating the invalid EncrypterType.
func (e UnknownEncrypterType) Error() string {
return fmt.Sprintf("unknown error encrypter type: %d", e)
}
// ErrorEncrypterExtracter defines a function signature that extracts an
// ErrorEncrypter from an sphinx OnionPacket.
type ErrorEncrypterExtracter func(*btcec.PublicKey) (ErrorEncrypter,
lnwire.FailCode)
// ErrorEncrypter is an interface that is used to encrypt HTLC related errors
// at the source of the error, and also at each intermediate hop all the way
// back to the source of the payment.
type ErrorEncrypter interface {
// EncryptFirstHop transforms a concrete failure message into an
// encrypted opaque failure reason. This method will be used at the
// source that the error occurs. It differs from IntermediateEncrypt
// slightly, in that it computes a proper MAC over the error.
EncryptFirstHop(lnwire.FailureMessage) (lnwire.OpaqueReason, error)
// IntermediateEncrypt wraps an already encrypted opaque reason error
// in an additional layer of onion encryption. This process repeats
// until the error arrives at the source of the payment.
IntermediateEncrypt(lnwire.OpaqueReason) lnwire.OpaqueReason
// Type returns an enum indicating the underlying concrete instance
// backing this interface.
Type() EncrypterType
// Encode serializes the encrypter's ephemeral public key to the given
// io.Writer.
Encode(io.Writer) error
// Decode deserializes the encrypter' ephemeral public key from the
// given io.Reader.
Decode(io.Reader) error
// Reextract rederives the encrypter using the extracter, performing an
// ECDH with the sphinx router's key and the ephemeral public key.
//
// NOTE: This should be called shortly after Decode to properly
// reinitialize the error encrypter.
Reextract(ErrorEncrypterExtracter) error
}
// SphinxErrorEncrypter is a concrete implementation of both the ErrorEncrypter
// interface backed by an implementation of the Sphinx packet format. As a
// result, all errors handled are themselves wrapped in layers of onion
// encryption and must be treated as such accordingly.
type SphinxErrorEncrypter struct {
*sphinx.OnionErrorEncrypter
EphemeralKey *btcec.PublicKey
}
// NewSphinxErrorEncrypter initializes a blank sphinx error encrypter, that
// should be used to deserialize an encoded SphinxErrorEncrypter. Since the
// actual encrypter is not stored in plaintext while at rest, reconstructing the
// error encrypter requires:
// 1) Decode: to deserialize the ephemeral public key.
// 2) Reextract: to "unlock" the actual error encrypter using an active
// OnionProcessor.
func NewSphinxErrorEncrypter() *SphinxErrorEncrypter {
return &SphinxErrorEncrypter{
OnionErrorEncrypter: nil,
EphemeralKey: &btcec.PublicKey{},
}
}
// EncryptFirstHop transforms a concrete failure message into an encrypted
// opaque failure reason. This method will be used at the source that the error
// occurs. It differs from BackwardObfuscate slightly, in that it computes a
// proper MAC over the error.
//
// NOTE: Part of the ErrorEncrypter interface.
func (s *SphinxErrorEncrypter) EncryptFirstHop(failure lnwire.FailureMessage) (lnwire.OpaqueReason, error) {
var b bytes.Buffer
if err := lnwire.EncodeFailure(&b, failure, 0); err != nil {
return nil, err
}
// We pass a true as the first parameter to indicate that a MAC should
// be added.
return s.EncryptError(true, b.Bytes()), nil
}
// IntermediateEncrypt wraps an already encrypted opaque reason error in an
// additional layer of onion encryption. This process repeats until the error
// arrives at the source of the payment. We re-encrypt the message on the
// backwards path to ensure that the error is indistinguishable from any other
// error seen.
//
// NOTE: Part of the ErrorEncrypter interface.
func (s *SphinxErrorEncrypter) IntermediateEncrypt(reason lnwire.OpaqueReason) lnwire.OpaqueReason {
return s.EncryptError(false, reason)
}
// Type returns the identifier for a sphinx error encrypter.
func (s *SphinxErrorEncrypter) Type() EncrypterType {
return EncrypterTypeSphinx
}
// Encode serializes the error encrypter' ephemeral public key to the provided
// io.Writer.
func (s *SphinxErrorEncrypter) Encode(w io.Writer) error {
ephemeral := s.EphemeralKey.SerializeCompressed()
_, err := w.Write(ephemeral)
return err
}
// Decode reconstructs the error encrypter's ephemeral public key from the
// provided io.Reader.
func (s *SphinxErrorEncrypter) Decode(r io.Reader) error {
var ephemeral [33]byte
if _, err := io.ReadFull(r, ephemeral[:]); err != nil {
return err
}
var err error
s.EphemeralKey, err = btcec.ParsePubKey(ephemeral[:], btcec.S256())
if err != nil {
return err
}
return nil
}
// Reextract rederives the error encrypter from the currently held EphemeralKey.
// This intended to be used shortly after Decode, to fully initialize a
// SphinxErrorEncrypter.
func (s *SphinxErrorEncrypter) Reextract(
extract ErrorEncrypterExtracter) error {
obfuscator, failcode := extract(s.EphemeralKey)
if failcode != lnwire.CodeNone {
// This should never happen, since we already validated that
// this obfuscator can be extracted when it was received in the
// link.
return fmt.Errorf("unable to reconstruct onion "+
"obfuscator, got failcode: %d", failcode)
}
sphinxEncrypter, ok := obfuscator.(*SphinxErrorEncrypter)
if !ok {
return fmt.Errorf("incorrect onion error extracter")
}
// Copy the freshly extracted encrypter.
s.OnionErrorEncrypter = sphinxEncrypter.OnionErrorEncrypter
return nil
}
// A compile time check to ensure SphinxErrorEncrypter implements the
// ErrorEncrypter interface.
var _ ErrorEncrypter = (*SphinxErrorEncrypter)(nil)
// SphinxErrorDecrypter wraps the sphinx data SphinxErrorDecrypter and maps the
// returned errors to concrete lnwire.FailureMessage instances.
type SphinxErrorDecrypter struct {
*sphinx.OnionErrorDecrypter
}
// DecryptError peels off each layer of onion encryption from the first hop, to
// the source of the error. A fully populated lnwire.FailureMessage is returned
// along with the source of the error.
//
// NOTE: Part of the ErrorDecrypter interface.
func (s *SphinxErrorDecrypter) DecryptError(reason lnwire.OpaqueReason) (*ForwardingError, error) {
source, failureData, err := s.OnionErrorDecrypter.DecryptError(reason)
if err != nil {
return nil, err
}
r := bytes.NewReader(failureData)
failureMsg, err := lnwire.DecodeFailure(r, 0)
if err != nil {
return nil, err
}
return &ForwardingError{
ErrorSource: source,
FailureMessage: failureMsg,
}, nil
}
// A compile time check to ensure ErrorDecrypter implements the Deobfuscator
// interface.
var _ ErrorDecrypter = (*SphinxErrorDecrypter)(nil)