Refactor getting serial numbers into its own method.

src/main/kotlin/Verifier.kt

@@ -225,11 +225,7 @@ open class Verifier(
     log: VerifyRequestLog? = null,
   ): VerificationResult {
     log?.logInputChain(certPath.certificatesWithAnchor.map { it.getEncoded().toByteString() })
-    log?.logCertSerialNumbers(
-      certPath.certificatesWithAnchor.subList(1, certPath.certificatesWithAnchor.size).map {
-        it.serialNumber.toString(16)
-      }
-    )
+    log?.logCertSerialNumbers(certPath.serialNumbers())
     val certPathValidator = CertPathValidator.getInstance("KeyAttestation")
     val certPathParameters =
       PKIXParameters(trustAnchorsSource()).apply {

src/main/kotlin/provider/KeyAttestationCertPath.kt

@@ -63,6 +63,15 @@ class KeyAttestationCertPath(certs: List<X509Certificate>) : CertPath("X.509") {
 
   override fun getCertificates(): List<X509Certificate> = certificatesWithAnchor.dropLast(1)
 
+  /**
+   * Returns the serial numbers of the certificates in the certificate chain.
+   *
+   * The format is unpadded hex strings.
+   *
+   * @return the serial numbers of the certificates in the certificate chain.
+   */
+  fun serialNumbers() = certificatesWithAnchor.map { it.serialNumber.toString(16) }
+
   fun provisioningMethod() =
     when {
       isFactoryProvisioned() -> ProvisioningMethod.FACTORY_PROVISIONED

src/test/kotlin/provider/KeyAttestationCertPathTest.kt

@@ -94,6 +94,13 @@ class KeyAttestationCertPathTest {
       .isEqualTo(CertLists.validFactoryProvisioned.first())
   }
 
+  @Test
+  fun getSerialNumbers_returnsExpectedSerialNumbers() {
+    assertThat(KeyAttestationCertPath(CertLists.validFactoryProvisioned).serialNumbers())
+      .containsExactly("1", "cafbad", "1234567890", "ca11cafe")
+      .inOrder()
+  }
+
   @Test
   fun provisioningMethod_returnsExpectedType(@TestParameter testCase: ProvisioningMethodTestCase) {
     val certPath = readCertPath("${testCase.path}.pem")