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Use current timestamp in invoice preimage #256

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Use current timestamp in invoice preimage #256

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14 changes: 14 additions & 0 deletions src/commonMain/kotlin/fr/acinq/lightning/payment/PaymentRequest.kt
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Original file line number Diff line number Diff line change
Expand Up @@ -5,6 +5,7 @@ import fr.acinq.bitcoin.Script.tail
import fr.acinq.bitcoin.io.ByteArrayInput
import fr.acinq.bitcoin.io.ByteArrayOutput
import fr.acinq.lightning.*
import fr.acinq.lightning.Lightning.randomBytes
import fr.acinq.lightning.Lightning.randomBytes32
import fr.acinq.lightning.serialization.ByteVector32KSerializer
import fr.acinq.lightning.serialization.ByteVectorKSerializer
Expand Down Expand Up @@ -157,6 +158,19 @@ data class PaymentRequest(
return Features(activated = features.activated.filter { (f, _) -> bolt11Features.contains(f) })
}

/**
* To avoid collision on payment preimages, we use a mix of randomness and timestamping.
* The end of the preimage contains a timestamp and the rest (at least 192 bits) comes from our RNG.
* This ensures that even if the randomness fails, it's unlikely that preimages will be reused.
*/
fun generatePreimage(): ByteVector32 {
val timestamp = ByteArrayOutput()
LightningCodecs.writeTU64(currentTimestampMillis(), timestamp)
val timestampBytes = timestamp.toByteArray()
val random = randomBytes(32 - timestampBytes.size)
return ByteVector32(random + timestampBytes)
}

fun create(
chainHash: ByteVector32,
amount: MilliSatoshi?,
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14 changes: 14 additions & 0 deletions src/commonTest/kotlin/fr/acinq/lightning/payment/PaymentRequestTestsCommon.kt
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Original file line number Diff line number Diff line change
@@ -1,9 +1,11 @@
package fr.acinq.lightning.payment

import fr.acinq.bitcoin.*
import fr.acinq.bitcoin.io.ByteArrayInput
import fr.acinq.lightning.*
import fr.acinq.lightning.tests.utils.LightningTestSuite
import fr.acinq.lightning.utils.*
import fr.acinq.lightning.wire.LightningCodecs
import fr.acinq.secp256k1.Hex
import kotlin.test.*

Expand Down Expand Up @@ -317,6 +319,18 @@ class PaymentRequestTestsCommon : LightningTestSuite() {
assertEquals(ref, check)
}

@Test
fun `insert current timestamp in payment preimage generation`() {
val now = currentTimestampMillis()
val pr1 = PaymentRequest.generatePreimage()
val preimageTimestamp = LightningCodecs.tu64(ByteArrayInput(pr1.takeRight(6).toByteArray()))
assertTrue(now <= preimageTimestamp)
assertTrue(preimageTimestamp <= now + 5000)

val pr2 = PaymentRequest.generatePreimage()
assertNotEquals(pr1, pr2)
}

@Test
fun `reject invalid invoices`() {
val refs = listOf(
Expand Down