Add constant-time equals for ByteString

okio/api/okio.api

@@ -310,6 +310,9 @@ public class okio/ByteString : java/io/Serializable, java/lang/Comparable {
 	public final fun endsWith (Lokio/ByteString;)Z
 	public final fun endsWith ([B)Z
 	public fun equals (Ljava/lang/Object;)Z
+	public final fun equals (Lokio/ByteString;)Z
+	public final fun equals (Lokio/ByteString;Z)Z
+	public static synthetic fun equals$default (Lokio/ByteString;Lokio/ByteString;ZILjava/lang/Object;)Z
 	public final fun getByte (I)B
 	public fun hashCode ()I
 	public fun hex ()Ljava/lang/String;

okio/src/appleMain/kotlin/okio/ByteString.kt

@@ -168,6 +168,8 @@ internal actual constructor(
 
   actual override fun equals(other: Any?) = commonEquals(other)
 
+  actual fun equals(other: ByteString, constantTime: Boolean) = commonEquals(other, constantTime)
+
   actual override fun hashCode() = commonHashCode()
 
   actual override fun compareTo(other: ByteString) = commonCompareTo(other)

okio/src/commonMain/kotlin/okio/ByteString.kt

@@ -170,6 +170,9 @@ internal constructor(data: ByteArray) : Comparable<ByteString> {
 
   override fun equals(other: Any?): Boolean
 
+  @JvmOverloads
+  fun equals(other: ByteString, constantTime: Boolean = false): Boolean
+
   override fun hashCode(): Int
 
   override fun compareTo(other: ByteString): Int

okio/src/commonMain/kotlin/okio/internal/ByteString.kt

@@ -229,11 +229,23 @@ internal inline fun ByteString.commonLastIndexOf(other: ByteArray, fromIndex: In
 internal inline fun ByteString.commonEquals(other: Any?): Boolean {
   return when {
     other === this -> true
-    other is ByteString -> other.size == data.size && other.rangeEquals(0, data, 0, data.size)
+    other is ByteString -> equals(other, constantTime = false)
     else -> false
   }
 }
 
+@Suppress("NOTHING_TO_INLINE")
+internal inline fun ByteString.commonEquals(other: ByteString, constantTime: Boolean): Boolean {
+  if (other.size != data.size) return false
+  if (!constantTime) return other.rangeEquals(0, data, 0, data.size)
+
+  var result = true
+  for (i in data.indices) {
+    result = result and ((data[i].toInt() xor other.data[i].toInt()) == 0)
+  }
+  return result
+}
+
 @Suppress("NOTHING_TO_INLINE")
 internal inline fun ByteString.commonHashCode(): Int {
   val result = hashCode

okio/src/commonTest/kotlin/okio/ByteStringTest.kt

@@ -17,6 +17,9 @@
 package okio
 
 import app.cash.burst.Burst
+import assertk.assertThat
+import assertk.assertions.isLessThanOrEqualTo
+import kotlin.math.absoluteValue
 import kotlin.random.Random
 import kotlin.test.Test
 import kotlin.test.assertEquals
@@ -26,6 +29,7 @@ import kotlin.test.assertNotEquals
 import kotlin.test.assertSame
 import kotlin.test.assertTrue
 import kotlin.test.fail
+import kotlin.time.measureTime
 import okio.ByteString.Companion.decodeBase64
 import okio.ByteString.Companion.decodeHex
 import okio.ByteString.Companion.encodeUtf8
@@ -201,6 +205,40 @@ class ByteStringTest(
     assertEquals(ByteString.of(), factory.decodeHex(""))
   }
 
+  @Test fun equalsConstantTimeTest() {
+    val bytes = Random(1234).nextBytes(1024 * 1024)
+    val subject = bytes.toByteString()
+    val subjectSame = bytes.toByteString()
+
+    // This instance is the same as the subject except with the first byte changed.
+    bytes[0] = (bytes[0] + 1).toByte()
+    val subjectDifferent = bytes.toByteString()
+
+    val iterations = 1000
+    var result = true
+
+    val equalsTime = measureTime {
+      repeat(iterations) {
+        result = result and subject.equals(subjectSame, constantTime = true)
+      }
+    }
+    val notEqualsTime = measureTime {
+      repeat(iterations) {
+        result = result and subject.equals(subjectDifferent, constantTime = true)
+      }
+    }
+    assertFalse(result)
+
+    // If the equals method was short-circuiting then the difference percentage will be huge >99%.
+    // We'll just check if it's under 50% to account for variance, especially on CI machines.
+    val equalsMean = equalsTime.inWholeNanoseconds
+    val notEqualsMean = notEqualsTime.inWholeNanoseconds
+    val maxMean = maxOf(equalsMean, notEqualsMean)
+    val difference = (equalsMean - notEqualsMean).absoluteValue
+    val differencePercentage = 100 * difference / maxMean
+    assertThat(differencePercentage).isLessThanOrEqualTo(50)
+  }
+
   private val bronzeHorseman = "На берегу пустынных волн"
 
   @Test fun utf8() {

okio/src/jvmMain/kotlin/okio/ByteString.kt

@@ -187,6 +187,9 @@ internal actual constructor(
 
   actual override fun equals(other: Any?) = commonEquals(other)
 
+  @JvmOverloads
+  actual fun equals(other: ByteString, constantTime: Boolean) = commonEquals(other, constantTime)
+
   actual override fun hashCode() = commonHashCode()
 
   actual override fun compareTo(other: ByteString) = commonCompareTo(other)

okio/src/nonAppleMain/kotlin/okio/ByteString.kt

@@ -162,6 +162,8 @@ internal actual constructor(
 
   actual override fun equals(other: Any?) = commonEquals(other)
 
+  actual fun equals(other: ByteString, constantTime: Boolean) = commonEquals(other, constantTime)
+
   actual override fun hashCode() = commonHashCode()
 
   actual override fun compareTo(other: ByteString) = commonCompareTo(other)