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Fix Sphinx privacy leak #1247

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merged 3 commits into from
Jan 15, 2020
Merged

Fix Sphinx privacy leak #1247

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da8ca77
Final recipient should not collect a fee
t-bast Dec 10, 2019
2e18b18
Fix Sphinx small privacy leak
t-bast Dec 10, 2019
e9f74f2
fixup! Fix Sphinx small privacy leak See https://github.com/lightning…
t-bast Jan 15, 2020
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19 changes: 11 additions & 8 deletions eclair-core/src/main/scala/fr/acinq/eclair/crypto/Sphinx.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -210,19 +210,20 @@ object Sphinx extends Logging {
* @param associatedData associated data.
* @param ephemeralPublicKey ephemeral key shared with the target node.
* @param sharedSecret shared secret with this hop.
* @param packet current packet (None if the packet hasn't been initialized).
* @param packet current packet or random bytes if the packet hasn't been initialized.
* @param onionPayloadFiller optional onion payload filler, needed only when you're constructing the last packet.
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* @return the next packet.
*/
def wrap(payload: ByteVector, associatedData: ByteVector32, ephemeralPublicKey: PublicKey, sharedSecret: ByteVector32, packet: Option[wire.OnionRoutingPacket], onionPayloadFiller: ByteVector = ByteVector.empty): wire.OnionRoutingPacket = {
def wrap(payload: ByteVector, associatedData: ByteVector32, ephemeralPublicKey: PublicKey, sharedSecret: ByteVector32, packet: Either[ByteVector, wire.OnionRoutingPacket], onionPayloadFiller: ByteVector = ByteVector.empty): wire.OnionRoutingPacket = {
require(payload.length <= PayloadLength - MacLength, s"packet payload cannot exceed ${PayloadLength - MacLength} bytes")

val (currentMac, currentPayload): (ByteVector32, ByteVector) = packet match {
// Packet construction starts with an empty mac and payload.
case None => (ByteVector32.Zeroes, ByteVector.fill(PayloadLength)(0))
case Some(p) => (p.hmac, p.payload)
// Packet construction starts with an empty mac and random payload.
case Left(startingBytes) =>
require(startingBytes.length == PayloadLength, "invalid initial random bytes length")
(ByteVector32.Zeroes, startingBytes)
case Right(p) => (p.hmac, p.payload)
}

val nextOnionPayload = {
val onionPayload1 = payload ++ currentMac ++ currentPayload.dropRight(payload.length + MacLength)
val onionPayload2 = onionPayload1 xor generateStream(generateKey("rho", sharedSecret), PayloadLength)
Expand All @@ -248,12 +249,14 @@ object Sphinx extends Logging {
val (ephemeralPublicKeys, sharedsecrets) = computeEphemeralPublicKeysAndSharedSecrets(sessionKey, publicKeys)
val filler = generateFiller("rho", sharedsecrets.dropRight(1), payloads.dropRight(1))

val lastPacket = wrap(payloads.last, associatedData, ephemeralPublicKeys.last, sharedsecrets.last, None, filler)
// We deterministically-derive the initial payload bytes: see https://github.com/lightningnetwork/lightning-rfc/pull/697
val startingBytes = generateStream(generateKey("pad", sessionKey.value), PayloadLength)
val lastPacket = wrap(payloads.last, associatedData, ephemeralPublicKeys.last, sharedsecrets.last, Left(startingBytes), filler)

@tailrec
def loop(hopPayloads: Seq[ByteVector], ephKeys: Seq[PublicKey], sharedSecrets: Seq[ByteVector32], packet: wire.OnionRoutingPacket): wire.OnionRoutingPacket = {
if (hopPayloads.isEmpty) packet else {
val nextPacket = wrap(hopPayloads.last, associatedData, ephKeys.last, sharedSecrets.last, Some(packet))
val nextPacket = wrap(hopPayloads.last, associatedData, ephKeys.last, sharedSecrets.last, Right(packet))
loop(hopPayloads.dropRight(1), ephKeys.dropRight(1), sharedSecrets.dropRight(1), nextPacket)
}
}
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4 changes: 2 additions & 2 deletions eclair-core/src/main/scala/fr/acinq/eclair/payment/PaymentPacket.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -102,7 +102,7 @@ object IncomingPacket {
}

private def validateFinal(add: UpdateAddHtlc, payload: Onion.FinalPayload): Either[FailureMessage, IncomingPacket] = {
if (add.amountMsat < payload.amount) {
if (add.amountMsat != payload.amount) {
Left(FinalIncorrectHtlcAmount(add.amountMsat))
} else if (add.cltvExpiry != payload.expiry) {
Left(FinalIncorrectCltvExpiry(add.cltvExpiry))
Expand All @@ -112,7 +112,7 @@ object IncomingPacket {
}

private def validateFinal(add: UpdateAddHtlc, outerPayload: Onion.FinalPayload, innerPayload: Onion.FinalPayload): Either[FailureMessage, IncomingPacket] = {
if (add.amountMsat < outerPayload.amount) {
if (add.amountMsat != outerPayload.amount) {
Left(FinalIncorrectHtlcAmount(add.amountMsat))
} else if (add.cltvExpiry != outerPayload.expiry) {
Left(FinalIncorrectCltvExpiry(add.cltvExpiry))
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