From 281a96ee9806f200020f4716d17e5d4c7880f213 Mon Sep 17 00:00:00 2001
From: Gus Narea <gnarea@users.noreply.github.com>
Date: Tue, 11 Jun 2024 15:49:24 +0100
Subject: [PATCH] fix: Tolerate clock drift when creating VeraId signatures
 (#275)

---
 .../utils/veraid/VeraidSignatureProcessor.kt  |  8 +++--
 .../veraid/VeraidSignatureProcessorTest.kt    | 33 ++++++++++++++++++-
 2 files changed, 37 insertions(+), 4 deletions(-)

diff --git a/app/src/main/java/tech/relaycorp/letro/utils/veraid/VeraidSignatureProcessor.kt b/app/src/main/java/tech/relaycorp/letro/utils/veraid/VeraidSignatureProcessor.kt
index 6ce4261b..c2bce39c 100644
--- a/app/src/main/java/tech/relaycorp/letro/utils/veraid/VeraidSignatureProcessor.kt
+++ b/app/src/main/java/tech/relaycorp/letro/utils/veraid/VeraidSignatureProcessor.kt
@@ -8,6 +8,7 @@ import tech.relaycorp.veraid.pki.MemberIdBundle
 import java.security.PrivateKey
 import java.time.ZonedDateTime
 import kotlin.time.Duration.Companion.days
+import kotlin.time.Duration.Companion.minutes
 import kotlin.time.toJavaDuration
 
 typealias BundleGenerator = (
@@ -26,6 +27,7 @@ class VeraidSignatureProcessor(
     private val bundleGenerator: BundleGenerator = SignatureBundle.Companion::generate,
     private val bundleDeserialiser: BundleDeserialiser = SignatureBundle.Companion::deserialise,
 ) {
+    private val bundleClockDriftTolerance = 5.minutes.toJavaDuration()
     private val bundleTtl = 90.days.toJavaDuration()
 
     @Throws(VeraidSignatureException::class)
@@ -34,15 +36,15 @@ class VeraidSignatureProcessor(
         memberIdBundle: MemberIdBundle,
         memberPrivateKey: PrivateKey,
     ): ByteArray {
-        val creationDate = ZonedDateTime.now()
+        val now = ZonedDateTime.now()
         val signatureBundle = try {
             bundleGenerator(
                 plaintext,
                 LetroOids.LETRO_VERAID_OID,
                 memberIdBundle,
                 memberPrivateKey,
-                creationDate.plus(bundleTtl),
-                creationDate,
+                now.plus(bundleTtl),
+                now.minus(bundleClockDriftTolerance),
                 true,
             )
         } catch (exc: SignatureException) {
diff --git a/app/src/test/java/tech/relaycorp/letro/utils/veraid/VeraidSignatureProcessorTest.kt b/app/src/test/java/tech/relaycorp/letro/utils/veraid/VeraidSignatureProcessorTest.kt
index ebf1ca73..0077f7a6 100644
--- a/app/src/test/java/tech/relaycorp/letro/utils/veraid/VeraidSignatureProcessorTest.kt
+++ b/app/src/test/java/tech/relaycorp/letro/utils/veraid/VeraidSignatureProcessorTest.kt
@@ -22,11 +22,13 @@ import tech.relaycorp.veraid.SignatureException
 import tech.relaycorp.veraid.pki.MemberIdBundle
 import java.time.ZonedDateTime
 import kotlin.time.Duration.Companion.days
+import kotlin.time.Duration.Companion.minutes
 import kotlin.time.toJavaDuration
 
 class VeraidSignatureProcessorTest {
     private val stubPlaintext = "plaintext".toByteArray()
 
+    val clockDriftTolerance = 5.minutes.toJavaDuration()
     val ninetyDays = 90.days.toJavaDuration()
 
     @Nested
@@ -96,6 +98,35 @@ class VeraidSignatureProcessorTest {
             }
         }
 
+        @Test
+        fun `Signature creation date should be within a few minutes in the past`() {
+            val generator = mockSignatureBundleGenerator(Result.success(stubSignatureBundle))
+            val processor = VeraidSignatureProcessor(generator)
+            val timeBefore = ZonedDateTime.now()
+
+            processor.produce(
+                stubPlaintext,
+                mockMemberIdBundle,
+                VERAID_MEMBER_KEY_PAIR.private,
+            )
+
+            val timeAfter = ZonedDateTime.now()
+            verify {
+                generator(
+                    any(),
+                    any(),
+                    any(),
+                    any(),
+                    any(),
+                    match {
+                        timeBefore.minus(clockDriftTolerance) <= it &&
+                            it <= timeAfter.minus(clockDriftTolerance)
+                    },
+                    any(),
+                )
+            }
+        }
+
         @Test
         fun `Signature should expire in 90 days`() {
             val generator = mockSignatureBundleGenerator(Result.success(stubSignatureBundle))
@@ -118,7 +149,7 @@ class VeraidSignatureProcessorTest {
                     match {
                         timeBefore.plus(ninetyDays) <= it && it <= timeAfter.plus(ninetyDays)
                     },
-                    match { timeBefore <= it && it <= timeAfter },
+                    any(),
                     any(),
                 )
             }