diff --git a/README.md b/README.md
index 1fdaa12..328804a 100644
--- a/README.md
+++ b/README.md
@@ -155,20 +155,27 @@ publicKey=example_key
 
 * **publicKey** - this is the public key used to verify the cookie
 
-### Generating Keys
+### Rotating Keys
 
-**Guardian Devs**: See the [Emergency Panda key-rotation Guide](https://docs.google.com/document/d/1haVnQ9D8zNYUU-fOfkudPC1WpPGrlelLygd8V7xb3eQ/edit?usp=sharing).
+**Guardian Devs**: See the [Panda key-rotation Guide](https://docs.google.com/document/d/1haVnQ9D8zNYUU-fOfkudPC1WpPGrlelLygd8V7xb3eQ/edit?usp=sharing)
+for Guardian-specific details of where config details are stored, etc.
 
-You can generate an rsa key pair as follows:
+To avoid disruption to users, rotating keys requires 3 distinct settings updates, with pauses between each one. First
+obtain a copy of the current settings file (eg `current-from-s3.settings`), then use the sbt console to run
+the `CryptoConfForRotation` Scala script on that `.settings` file to generate a new RSA 4096 keypair and the new
+required config files for each step:
 
-    openssl genrsa -out private_key.pem 4096
-    openssl rsa -pubout -in private_key.pem -out public_key.pem
-
-There is a helper script in the root of this project that uses the commands above and outputs a new keypair in the format used by the panda settings file:
+```
+pan-domain-auth-verification / Test / runMain com.gu.pandomainauth.CryptoConfForRotation current-from-s3.settings
+```
 
-    ./generateKeyPair.sh
+3 new partial `.settings` files will be created, providing _just_ the updated crypto settings - you'll need to
+edit them into the existing `current-from-s3.settings` & `current-from-s3.settings.public` files before uploading
+those updates:
 
-Note: you only need to pass the key ie the blob of base64 between the start and end markers in the pem file.
+* 1.rotation-upcoming.settings - give this 2 minutes of settling time 
+* 2.rotation-in-progress.settings - give this at least 1 hour of settling time
+* 3.rotation-complete.settings
 
 ## Integrating with your Scala app
 
diff --git a/build.sbt b/build.sbt
index 1ac5c09..129d9c4 100644
--- a/build.sbt
+++ b/build.sbt
@@ -22,7 +22,7 @@ val commonSettings =
       "-deprecation",
       // upgrade warnings to errors except deprecations
       "-Wconf:cat=deprecation:ws,any:e",
-      "-release:8"
+      "-release:11"
     ),
     licenses := Seq(License.Apache2),
   )
diff --git a/generateKeyPair.sh b/generateKeyPair.sh
deleted file mode 100755
index 1f1c892..0000000
--- a/generateKeyPair.sh
+++ /dev/null
@@ -1,21 +0,0 @@
-#!/bin/bash
-set -e
-
-PRIVATE_KEY_FILE=$(mktemp /tmp/private-key.XXXXXX)
-PUBLIC_KEY_FILE=$(mktemp /tmp/public-key.XXXXXX)
-
-function on_exit() {
-	rm -f ${PRIVATE_KEY_FILE}
-	rm -f ${PUBLIC_KEY_FILE}
-}
-
-trap on_exit EXIT
-
-openssl genrsa -out ${PRIVATE_KEY_FILE} 4096
-openssl rsa -pubout -in ${PRIVATE_KEY_FILE} -out ${PUBLIC_KEY_FILE}
-
-TRIMMED_PRIVATE_KEY=`cat ${PRIVATE_KEY_FILE} | sed -e '1d' -e '$d' | tr -d '\n'`
-TRIMMED_PUBLIC_KEY=`cat ${PUBLIC_KEY_FILE} | sed -e '1d' -e '$d' | tr -d '\n'`
-
-echo privateKey=${TRIMMED_PRIVATE_KEY}
-echo publicKey=${TRIMMED_PUBLIC_KEY}
diff --git a/pan-domain-auth-core/src/main/scala/com/gu/pandomainauth/PanDomainAuthSettingsRefresher.scala b/pan-domain-auth-core/src/main/scala/com/gu/pandomainauth/PanDomainAuthSettingsRefresher.scala
index 13d8608..fe28101 100644
--- a/pan-domain-auth-core/src/main/scala/com/gu/pandomainauth/PanDomainAuthSettingsRefresher.scala
+++ b/pan-domain-auth-core/src/main/scala/com/gu/pandomainauth/PanDomainAuthSettingsRefresher.scala
@@ -35,9 +35,10 @@ class PanDomainAuthSettingsRefresher(
   private val settingsRefresher = new Settings.Refresher[PanDomainAuthSettings](
     new Settings.Loader(s3BucketLoader, settingsFileKey),
     PanDomainAuthSettings.apply,
+    _.signingAndVerification,
     scheduler
   )
-  settingsRefresher.start(1)
+  settingsRefresher.start()
 
   def settings: PanDomainAuthSettings = settingsRefresher.get()
 }
diff --git a/pan-domain-auth-core/src/main/scala/com/gu/pandomainauth/model/PanDomainAuthSettings.scala b/pan-domain-auth-core/src/main/scala/com/gu/pandomainauth/model/PanDomainAuthSettings.scala
index 478576b..a771315 100644
--- a/pan-domain-auth-core/src/main/scala/com/gu/pandomainauth/model/PanDomainAuthSettings.scala
+++ b/pan-domain-auth-core/src/main/scala/com/gu/pandomainauth/model/PanDomainAuthSettings.scala
@@ -1,10 +1,11 @@
 package com.gu.pandomainauth.model
 
-import com.gu.pandomainauth.SettingsFailure.SettingsResult
-import com.gu.pandomainauth.service.{CryptoConf, KeyPair}
+import com.gu.pandomainauth.Settings.SettingsResult
+import com.gu.pandomainauth.service.CryptoConf
+import com.gu.pandomainauth.service.CryptoConf.SigningAndVerification
 
 case class PanDomainAuthSettings(
-  signingKeyPair: KeyPair,
+  signingAndVerification: SigningAndVerification,
   cookieSettings: CookieSettings,
   oAuthSettings: OAuthSettings,
   google2FAGroupSettings: Option[Google2FAGroupSettings]
@@ -51,9 +52,9 @@ object PanDomainAuthSettings{
     ) yield Google2FAGroupSettings(serviceAccountId, serviceAccountCert, adminUser, group)
 
     for {
-      activeKeyPair <- CryptoConf.SettingsReader(settingMap).activeKeyPair
+      cryptoConf <- CryptoConf.SettingsReader(settingMap).signingAndVerificationConf
     } yield PanDomainAuthSettings(
-      activeKeyPair,
+      cryptoConf,
       cookieSettings,
       oAuthSettings,
       google2faSettings
diff --git a/pan-domain-auth-example/app/VerifyExample.scala b/pan-domain-auth-example/app/VerifyExample.scala
index 2c2a470..05253da 100644
--- a/pan-domain-auth-example/app/VerifyExample.scala
+++ b/pan-domain-auth-example/app/VerifyExample.scala
@@ -3,6 +3,7 @@ import com.amazonaws.regions.Regions
 import com.amazonaws.services.s3.AmazonS3ClientBuilder
 import com.gu.pandomainauth.S3BucketLoader.forAwsSdkV1
 import com.gu.pandomainauth.model.{Authenticated, AuthenticatedUser, GracePeriod}
+import com.gu.pandomainauth.service.CryptoConf
 import com.gu.pandomainauth.{PanDomain, PublicSettings, Settings}
 
 object VerifyExample {
@@ -21,7 +22,7 @@ object VerifyExample {
   // Call the start method when your application starts up to ensure the settings are kept up to date
   publicSettings.start()
 
-  val publicKey = publicSettings.publicKey
+  val verification: CryptoConf.Verification = publicSettings.verification
 
   // The name of this particular application
   val system = "test"
@@ -42,7 +43,7 @@ object VerifyExample {
   val cacheValidation = false
 
   // To verify, call the authStatus method with the encoded cookie data
-  val status = PanDomain.authStatus("<<cookie data>>>", publicKey, validateUser, apiGracePeriod, system, cacheValidation, forceExpiry = false)
+  val status = PanDomain.authStatus("<<cookie data>>>", verification, validateUser, apiGracePeriod, system, cacheValidation, forceExpiry = false)
 
   status match {
     case Authenticated(_) | GracePeriod(_) =>
diff --git a/pan-domain-auth-play/src/main/scala/com/gu/pandomainauth/action/Actions.scala b/pan-domain-auth-play/src/main/scala/com/gu/pandomainauth/action/Actions.scala
index 718ec56..0aa96f5 100644
--- a/pan-domain-auth-play/src/main/scala/com/gu/pandomainauth/action/Actions.scala
+++ b/pan-domain-auth-play/src/main/scala/com/gu/pandomainauth/action/Actions.scala
@@ -8,9 +8,8 @@ import play.api.libs.ws.WSClient
 import play.api.mvc.Results._
 import play.api.mvc._
 
+import java.net.{URLDecoder, URLEncoder}
 import scala.concurrent.{ExecutionContext, Future}
-import java.net.URLEncoder
-import java.net.URLDecoder
 
 class UserRequest[A](val user: User, request: Request[A]) extends WrappedRequest[A](request)
 
@@ -198,7 +197,7 @@ trait AuthActions {
   }
 
   def readAuthenticatedUser(request: RequestHeader): Option[AuthenticatedUser] = readCookie(request) flatMap { cookie =>
-    CookieUtils.parseCookieData(cookie.cookie.value, settings.signingKeyPair.publicKey).toOption
+    CookieUtils.parseCookieData(cookie.cookie.value, settings.signingAndVerification).toOption
   }
 
   def readCookie(request: RequestHeader): Option[PandomainCookie] = {
@@ -208,14 +207,13 @@ trait AuthActions {
     }
   }
 
-  def generateCookie(authedUser: AuthenticatedUser): Cookie =
-    Cookie(
-      name = settings.cookieSettings.cookieName,
-      value = CookieUtils.generateCookieData(authedUser, settings.signingKeyPair.privateKey),
-      domain = Some(domain),
-      secure = true,
-      httpOnly = true
-    )
+  def generateCookie(authedUser: AuthenticatedUser): Cookie = Cookie(
+    name = settings.cookieSettings.cookieName,
+    value = CookieUtils.generateCookieData(authedUser, settings.signingAndVerification),
+    domain = Some(domain),
+    secure = true,
+    httpOnly = true
+  )
 
   def includeSystemInCookie(authedUser: AuthenticatedUser)(result: Result): Result = {
     val updatedAuth    = authedUser.copy(authenticatedIn = authedUser.authenticatedIn + system)
@@ -237,7 +235,7 @@ trait AuthActions {
     */
   def extractAuth(request: RequestHeader): AuthenticationStatus = {
     readCookie(request).map { cookie =>
-      PanDomain.authStatus(cookie.cookie.value, settings.signingKeyPair.publicKey, validateUser, apiGracePeriod, system, cacheValidation, cookie.forceExpiry)
+      PanDomain.authStatus(cookie.cookie.value, settings.signingAndVerification, validateUser, apiGracePeriod, system, cacheValidation, cookie.forceExpiry)
     } getOrElse NotAuthenticated
   }
 
diff --git a/pan-domain-auth-verification/src/main/scala/com/gu/pandomainauth/PanDomain.scala b/pan-domain-auth-verification/src/main/scala/com/gu/pandomainauth/PanDomain.scala
index 7dd8ba1..68ca4a0 100644
--- a/pan-domain-auth-verification/src/main/scala/com/gu/pandomainauth/PanDomain.scala
+++ b/pan-domain-auth-verification/src/main/scala/com/gu/pandomainauth/PanDomain.scala
@@ -2,17 +2,16 @@ package com.gu.pandomainauth
 
 import com.gu.pandomainauth.model._
 import com.gu.pandomainauth.service.CookieUtils
-
-import java.security.PublicKey
+import com.gu.pandomainauth.service.CryptoConf.Verification
 
 
 object PanDomain {
   /**
    * Check the authentication status of the provided credentials by examining the signed cookie data.
    */
-  def authStatus(cookieData: String, publicKey: PublicKey, validateUser: AuthenticatedUser => Boolean,
+  def authStatus(cookieData: String, verification: Verification, validateUser: AuthenticatedUser => Boolean,
                  apiGracePeriod: Long, system: String, cacheValidation: Boolean, forceExpiry: Boolean): AuthenticationStatus = {
-    CookieUtils.parseCookieData(cookieData, publicKey).fold(InvalidCookie, { authedUser =>
+    CookieUtils.parseCookieData(cookieData, verification).fold(InvalidCookie, { authedUser =>
       checkStatus(authedUser, validateUser, apiGracePeriod, system, cacheValidation, forceExpiry)
     })
   }
diff --git a/pan-domain-auth-verification/src/main/scala/com/gu/pandomainauth/PublicSettings.scala b/pan-domain-auth-verification/src/main/scala/com/gu/pandomainauth/PublicSettings.scala
index cdc80ed..e569a7a 100644
--- a/pan-domain-auth-verification/src/main/scala/com/gu/pandomainauth/PublicSettings.scala
+++ b/pan-domain-auth-verification/src/main/scala/com/gu/pandomainauth/PublicSettings.scala
@@ -1,14 +1,15 @@
 package com.gu.pandomainauth
 
 import com.amazonaws.services.s3.AmazonS3
-import com.gu.pandomainauth.Settings.Loader
-import com.gu.pandomainauth.SettingsFailure.SettingsResult
+import com.gu.pandomainauth.Settings.{Loader, SettingsResult}
 import com.gu.pandomainauth.service.CryptoConf
+import com.gu.pandomainauth.service.CryptoConf.Verification
 
 import java.security.PublicKey
+import java.time.Duration
+import java.time.Duration.ofMinutes
 import java.util.concurrent.Executors.newScheduledThreadPool
 import java.util.concurrent.{Executors, ScheduledExecutorService}
-import scala.concurrent.duration._
 
 /**
  * Class that contains the static public settings and includes mechanism for fetching the public key. Once you have an
@@ -21,15 +22,19 @@ class PublicSettings(loader: Settings.Loader, scheduler: ScheduledExecutorServic
     new Settings.Loader(S3BucketLoader.forAwsSdkV1(s3Client, bucketName), settingsFileKey), scheduler
   )
 
-  private val settingsRefresher = new Settings.Refresher[PublicKey](
+  private val settingsRefresher = new Settings.Refresher[Verification](
     loader,
-    CryptoConf.SettingsReader(_).activePublicKey,
+    CryptoConf.SettingsReader(_).verificationConf,
+    identity,
     scheduler
   )
 
-  def start(interval: FiniteDuration = 60.seconds): Unit = settingsRefresher.start(interval.toMinutes.toInt)
+  def start(interval: Duration = ofMinutes(1)): Unit = settingsRefresher.start(interval)
 
-  def publicKey: PublicKey = settingsRefresher.get()
+  def verification: Verification = settingsRefresher.get()
+
+  @deprecated("Use `verification` instead, to allow smooth transition to new public keys")
+  def publicKey: PublicKey = verification.activePublicKey
 }
 
 /**
@@ -40,11 +45,6 @@ object PublicSettings {
 
   def apply(loader: Settings.Loader): PublicSettings = new PublicSettings(loader, newScheduledThreadPool(1))
 
-  /**
-   * Fetches the public key from the public S3 bucket
-   *
-   * @param domain the domain to fetch the public key for
-   */
-  def getPublicKey(loader: Loader): SettingsResult[PublicKey] =
-    loader.loadAndParseSettingsMap().flatMap(CryptoConf.SettingsReader(_).activePublicKey)
+  def getVerification(loader: Loader): SettingsResult[Verification] =
+    loader.loadAndParseSettingsMap().flatMap(CryptoConf.SettingsReader(_).verificationConf)
 }
diff --git a/pan-domain-auth-verification/src/main/scala/com/gu/pandomainauth/Settings.scala b/pan-domain-auth-verification/src/main/scala/com/gu/pandomainauth/Settings.scala
index bfc0bbc..2bec6d8 100644
--- a/pan-domain-auth-verification/src/main/scala/com/gu/pandomainauth/Settings.scala
+++ b/pan-domain-auth-verification/src/main/scala/com/gu/pandomainauth/Settings.scala
@@ -1,12 +1,15 @@
 package com.gu.pandomainauth
 
 import com.amazonaws.util.IOUtils
-import com.gu.pandomainauth.SettingsFailure.SettingsResult
+import com.gu.pandomainauth.service.CryptoConf
+import com.gu.pandomainauth.service.CryptoConf.Verification
 import org.slf4j.{Logger, LoggerFactory}
 
 import java.io.ByteArrayInputStream
+import java.time.Duration
+import java.time.Duration.ofMinutes
 import java.util.Properties
-import java.util.concurrent.TimeUnit.MINUTES
+import java.util.concurrent.TimeUnit.MILLISECONDS
 import java.util.concurrent.atomic.AtomicReference
 import java.util.concurrent.{Executors, ScheduledExecutorService}
 import scala.jdk.CollectionConverters._
@@ -48,11 +51,15 @@ case object InvalidBase64 extends SettingsFailure {
   override val description: String = "Settings file value for cryptographic key is not valid base64"
 }
 
-object SettingsFailure {
+object Settings {
   type SettingsResult[A] = Either[SettingsFailure, A]
-}
 
-object Settings {
+  implicit class RichSettingsResultSeq[A](result: Seq[SettingsResult[A]]) {
+    def sequence: SettingsResult[Seq[A]] = result.foldLeft[SettingsResult[List[A]]](Right(Nil)) { // Easier with Cats!
+      (acc, e) => for (keys <- acc; key <- e) yield key :: keys
+    }
+  }
+
   /**
    * @param settingsFileKey the name of the file that contains the private settings for the given domain
    */
@@ -77,6 +84,7 @@ object Settings {
   class Refresher[A](
     loader: Settings.Loader,
     settingsParser: Map[String, String] => SettingsResult[A],
+    verificationIn: A => Verification,
     scheduler: ScheduledExecutorService = Executors.newScheduledThreadPool(1)
   ) {
     // This is deliberately designed to throw an exception during construction if we cannot immediately read the settings
@@ -86,7 +94,10 @@ object Settings {
 
     private val logger = LoggerFactory.getLogger(getClass)
 
-    def start(interval: Int): Unit = scheduler.scheduleAtFixedRate(() => refresh(), 0, interval, MINUTES)
+    def start(interval: Duration = ofMinutes(1)): Unit = {
+      logger.info(s"Starting refresh schedule with an interval of $interval")
+      scheduler.scheduleAtFixedRate(() => refresh(), 0, interval.toMillis, MILLISECONDS)
+    }
 
     def loadAndParseSettings(): SettingsResult[A] =
       loader.loadAndParseSettingsMap().flatMap(settingsParser)
@@ -94,7 +105,10 @@ object Settings {
     private def refresh(): Unit = loadAndParseSettings() match {
       case Right(newSettings) =>
         val oldSettings = store.getAndSet(newSettings)
-        if (oldSettings != newSettings) logger.info("Updated pan-domain settings")
+        for (change <- CryptoConf.Change.compare(verificationIn(oldSettings), verificationIn(newSettings))) {
+          val message = s"Panda settings changed: ${change.summary}"
+          if (change.isBreakingChange) logger.warn(message) else logger.info(message)
+        }
       case Left(err) =>
         logger.error("Failed to update pan-domain settings for $domain")
         err.logError(logger)
diff --git a/pan-domain-auth-verification/src/main/scala/com/gu/pandomainauth/service/CookieUtils.scala b/pan-domain-auth-verification/src/main/scala/com/gu/pandomainauth/service/CookieUtils.scala
index 34941e4..b190e30 100644
--- a/pan-domain-auth-verification/src/main/scala/com/gu/pandomainauth/service/CookieUtils.scala
+++ b/pan-domain-auth-verification/src/main/scala/com/gu/pandomainauth/service/CookieUtils.scala
@@ -2,8 +2,8 @@ package com.gu.pandomainauth.service
 
 import com.gu.pandomainauth.model.{AuthenticatedUser, User}
 import com.gu.pandomainauth.service.CookieUtils.CookieIntegrityFailure.{MalformedCookieText, MissingOrMalformedUserData, SignatureNotValid}
+import com.gu.pandomainauth.service.CryptoConf.{Signing, Verification}
 
-import java.security.{PrivateKey, PublicKey}
 import scala.util.Try
 
 object CookieUtils {
@@ -50,12 +50,12 @@ object CookieUtils {
     )
   }
 
-  def generateCookieData(authUser: AuthenticatedUser, prvKey: PrivateKey): String =
-    CookiePayload.generateForPayloadText(serializeAuthenticatedUser(authUser), prvKey).asCookieText
+  def generateCookieData(authUser: AuthenticatedUser, signing: Signing): String =
+    CookiePayload.generateForPayloadText(serializeAuthenticatedUser(authUser), signing.activePrivateKey).asCookieText
 
-  def parseCookieData(cookieString: String, publicKey: PublicKey): CookieResult[AuthenticatedUser] = for {
+  def parseCookieData(cookieString: String, verification: Verification): CookieResult[AuthenticatedUser] = for {
     cookiePayload <- CookiePayload.parse(cookieString).toRight(MalformedCookieText)
-    cookiePayloadText <- cookiePayload.payloadTextVerifiedSignedWith(publicKey).toRight(SignatureNotValid)
+    cookiePayloadText <- verification.decode(cookiePayload.payloadTextVerifiedSignedWith).toRight(SignatureNotValid)
     authUser <- deserializeAuthenticatedUser(cookiePayloadText).toRight(MissingOrMalformedUserData)
   } yield authUser
 }
diff --git a/pan-domain-auth-verification/src/main/scala/com/gu/pandomainauth/service/Crypto.scala b/pan-domain-auth-verification/src/main/scala/com/gu/pandomainauth/service/Crypto.scala
index b21059d..07d83b6 100644
--- a/pan-domain-auth-verification/src/main/scala/com/gu/pandomainauth/service/Crypto.scala
+++ b/pan-domain-auth-verification/src/main/scala/com/gu/pandomainauth/service/Crypto.scala
@@ -14,14 +14,13 @@ object Crypto {
    *
    * Note: you only need to pass the key ie the blob of base64 between the start and end markers in the pem file.
    */
-
   Security.addProvider(new BouncyCastleProvider())
 
-  val signatureAlgorithm: String = "SHA256withRSA"
   val keyFactory = KeyFactory.getInstance("RSA")
+  private def signatureInstance() = Signature.getInstance("SHA256withRSA", "BC")
 
   def signData(data: Array[Byte], prvKey: PrivateKey): Array[Byte] = {
-    val rsa = Signature.getInstance(signatureAlgorithm, "BC")
+    val rsa = signatureInstance()
     rsa.initSign(prvKey)
 
     rsa.update(data)
@@ -29,7 +28,7 @@ object Crypto {
   }
 
   def verifySignature(data: Array[Byte], signature: Array[Byte], pubKey: PublicKey) : Boolean = {
-    val rsa = Signature.getInstance(signatureAlgorithm, "BC")
+    val rsa = signatureInstance()
     rsa.initVerify(pubKey)
 
     rsa.update(data)
diff --git a/pan-domain-auth-verification/src/main/scala/com/gu/pandomainauth/service/CryptoConf.scala b/pan-domain-auth-verification/src/main/scala/com/gu/pandomainauth/service/CryptoConf.scala
index 5a74130..7e2c3e2 100644
--- a/pan-domain-auth-verification/src/main/scala/com/gu/pandomainauth/service/CryptoConf.scala
+++ b/pan-domain-auth-verification/src/main/scala/com/gu/pandomainauth/service/CryptoConf.scala
@@ -1,6 +1,6 @@
 package com.gu.pandomainauth.service
 
-import com.gu.pandomainauth.SettingsFailure.SettingsResult
+import com.gu.pandomainauth.Settings._
 import com.gu.pandomainauth.service.Crypto.keyFactory
 import com.gu.pandomainauth.service.CryptoConf.SettingsReader.{privateKeyFor, publicKeyFor}
 import com.gu.pandomainauth.{InvalidBase64, MissingSetting, PublicKeyFormatFailure}
@@ -9,17 +9,53 @@ import org.apache.commons.codec.binary.Base64.{decodeBase64, isBase64}
 import java.security.spec.{InvalidKeySpecException, KeySpec, PKCS8EncodedKeySpec, X509EncodedKeySpec}
 import java.security.{KeyFactory, PrivateKey, PublicKey}
 import scala.util.Try
+import scala.collection.compat._
+import immutable.LazyList
 
 object CryptoConf {
+  trait Signing {
+    val activePrivateKey: PrivateKey
+  }
+
+  trait Verification {
+    val activePublicKey: PublicKey
+    val alsoAccepted: Seq[PublicKey]
+
+    lazy val acceptedPublicKeys: LazyList[PublicKey] = LazyList(activePublicKey) ++ alsoAccepted
+
+    private[CryptoConf] def acceptsActiveKeyFrom(other: Verification): Boolean = acceptedPublicKeys.contains(other.activePublicKey)
+
+    def decode[A](f: PublicKey => Option[A]): Option[A] = acceptedPublicKeys.flatMap(f(_)).headOption
+  }
+
+  case class SigningAndVerification(activeKeyPair: KeyPair, alsoAccepted: Seq[PublicKey]) extends Signing with Verification {
+    val activePublicKey: PublicKey = activeKeyPair.publicKey
+    val activePrivateKey: PrivateKey = activeKeyPair.privateKey
+  }
+
+  case class OnlyVerification(activePublicKey: PublicKey, alsoAccepted: Seq[PublicKey] = Seq.empty) extends Verification
+
   case class SettingsReader(settingMap: Map[String,String]) {
     def setting(key: String): SettingsResult[String] = settingMap.get(key).toRight(MissingSetting(key))
 
+    def signingAndVerificationConf: SettingsResult[SigningAndVerification] = makeConfWith(activeKeyPair)(SigningAndVerification)
+    def verificationConf: SettingsResult[Verification] = makeConfWith(activePublicKey)(OnlyVerification)
+
     val activePublicKey: SettingsResult[PublicKey] = setting("publicKey").flatMap(publicKeyFor)
 
-    def activeKeyPair: SettingsResult[KeyPair] = for {
+    private val alsoAcceptedPublicKeys: SettingsResult[Seq[PublicKey]] = settingMap.collect {
+      case (k, v) if k.startsWith("alsoAccept.") && k.endsWith(".publicKey") => publicKeyFor(v)
+    }.toSeq.sequence
+
+    private def activeKeyPair: SettingsResult[KeyPair] = for {
       publicKey <- activePublicKey
       privateKey <- setting("privateKey").flatMap(privateKeyFor)
     } yield KeyPair(publicKey, privateKey)
+
+    private def makeConfWith[A, T](activePartResult: SettingsResult[A])(createConf: (A, Seq[PublicKey]) => T): SettingsResult[T] = for {
+      activePart <- activePartResult
+      alsoAccepted <- alsoAcceptedPublicKeys
+    } yield createConf(activePart, alsoAccepted)
   }
 
   object SettingsReader {
@@ -42,4 +78,41 @@ object CryptoConf {
     def privateKeyFor(base64Key: String): SettingsResult[PrivateKey] =
       keyFor(base64Key, new PKCS8EncodedKeySpec(_), _.generatePrivate)
   }
+
+  object Change {
+    def compare(oldConf: Verification, newConf: Verification): Option[CryptoConf.Change] =
+      Option.when(newConf != oldConf)(Change(
+        activeKey = Option.when(newConf.activePublicKey != oldConf.activePublicKey)(ActiveKey(
+          toleratingOldKey = newConf.acceptsActiveKeyFrom(oldConf),
+          newKeyAlreadyAccepted = oldConf.acceptsActiveKeyFrom(newConf)
+        )),
+        SeqDiff.compare(oldConf.alsoAccepted, newConf.alsoAccepted)
+      ))
+
+    /**
+     * CryptoConf.Change.ActiveKey details the consequences of a change to the active key,
+     * allowing us to know if the change could disrupt existing user sessions.
+     */
+    case class ActiveKey(toleratingOldKey: Boolean, newKeyAlreadyAccepted: Boolean) {
+      val isBreakingChange: Boolean = !(toleratingOldKey && newKeyAlreadyAccepted)
+      val summary: String = s"Active key changed: ${if (isBreakingChange) s"BREAKING - old-tolerated=$toleratingOldKey new-already-accepted=$newKeyAlreadyAccepted" else "non-breaking"}"
+    }
+  }
+
+  /**
+   * CryptoConf.Change denotes that there's been a change to the crypto settings. If the active key
+   * has changed, we'll have a CryptoConf.Change.ActiveKey detailing if the update is safe.
+   */
+  case class Change(activeKey: Option[Change.ActiveKey], acceptedKeys: SeqDiff[PublicKey]) {
+    val isBreakingChange: Boolean = activeKey.exists(_.isBreakingChange)
+    val summary: String = (activeKey.map(_.summary).toSeq :+ s"acceptedKeys: ${acceptedKeys.summary}").mkString(" ")
+  }
+
+  case class SeqDiff[T](added: Seq[T], removed: Seq[T]) {
+    val summary: String = s"added ${added.size}, removed ${removed.size}"
+  }
+  object SeqDiff {
+    def compare[T](oldItems: Seq[T], newItems: Seq[T]): SeqDiff[T] =
+      SeqDiff(added = newItems.diff(oldItems), removed = oldItems.diff(newItems))
+  }
 }
\ No newline at end of file
diff --git a/pan-domain-auth-verification/src/main/scala/com/gu/pandomainauth/service/KeyPair.scala b/pan-domain-auth-verification/src/main/scala/com/gu/pandomainauth/service/KeyPair.scala
index b2d6dc9..02df87a 100644
--- a/pan-domain-auth-verification/src/main/scala/com/gu/pandomainauth/service/KeyPair.scala
+++ b/pan-domain-auth-verification/src/main/scala/com/gu/pandomainauth/service/KeyPair.scala
@@ -3,7 +3,7 @@ package com.gu.pandomainauth.service
 import java.security.{PrivateKey, PublicKey}
 
 /**
- * This class mainly exists because java.security.KeyPair does not implement a useful `.equals()`` method,
+ * This class mainly exists because java.security.KeyPair does not implement a useful `.equals()` method,
  * and we're going to want to be able to check whether two key-pairs are equal.
  */
 case class KeyPair(publicKey: PublicKey, privateKey: PrivateKey)
diff --git a/pan-domain-auth-verification/src/test/resources/crypto-conf-rotation-example/0.legacy.settings b/pan-domain-auth-verification/src/test/resources/crypto-conf-rotation-example/0.legacy.settings
new file mode 100644
index 0000000..257ab52
--- /dev/null
+++ b/pan-domain-auth-verification/src/test/resources/crypto-conf-rotation-example/0.legacy.settings
@@ -0,0 +1,2 @@
+privateKey=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
+publicKey=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
diff --git a/pan-domain-auth-verification/src/test/resources/crypto-conf-rotation-example/1.rotation-upcoming.settings b/pan-domain-auth-verification/src/test/resources/crypto-conf-rotation-example/1.rotation-upcoming.settings
new file mode 100644
index 0000000..fed22eb
--- /dev/null
+++ b/pan-domain-auth-verification/src/test/resources/crypto-conf-rotation-example/1.rotation-upcoming.settings
@@ -0,0 +1,7 @@
+# 1.rotation-upcoming.settings - Generated at 2024-09-11T16:10:11Z
+
+privateKey=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
+
+publicKey=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
+
+alsoAccept.0.publicKey=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
diff --git a/pan-domain-auth-verification/src/test/resources/crypto-conf-rotation-example/2.rotation-in-progress.settings b/pan-domain-auth-verification/src/test/resources/crypto-conf-rotation-example/2.rotation-in-progress.settings
new file mode 100644
index 0000000..fced507
--- /dev/null
+++ b/pan-domain-auth-verification/src/test/resources/crypto-conf-rotation-example/2.rotation-in-progress.settings
@@ -0,0 +1,7 @@
+# 2.rotation-in-progress.settings - Generated at 2024-09-11T16:10:11Z
+
+privateKey=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
+
+publicKey=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
+
+alsoAccept.0.publicKey=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
diff --git a/pan-domain-auth-verification/src/test/resources/crypto-conf-rotation-example/3.rotation-complete.settings b/pan-domain-auth-verification/src/test/resources/crypto-conf-rotation-example/3.rotation-complete.settings
new file mode 100644
index 0000000..efc9e72
--- /dev/null
+++ b/pan-domain-auth-verification/src/test/resources/crypto-conf-rotation-example/3.rotation-complete.settings
@@ -0,0 +1,5 @@
+# 3.rotation-complete.settings - Generated at 2024-09-11T16:10:11Z
+
+privateKey=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
+
+publicKey=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
diff --git a/pan-domain-auth-verification/src/test/scala/com/gu/pandomainauth/CryptoConfForRotation.scala b/pan-domain-auth-verification/src/test/scala/com/gu/pandomainauth/CryptoConfForRotation.scala
new file mode 100644
index 0000000..8fbdd97
--- /dev/null
+++ b/pan-domain-auth-verification/src/test/scala/com/gu/pandomainauth/CryptoConfForRotation.scala
@@ -0,0 +1,84 @@
+package com.gu.pandomainauth
+
+import com.gu.pandomainauth.service.CryptoConf.SigningAndVerification
+import com.gu.pandomainauth.service.{CryptoConf, KeyPair}
+import org.scalatest.EitherValues
+
+import java.io.FileInputStream
+import java.nio.file.Files
+import java.security.{Key, KeyPairGenerator}
+import java.time.ZoneOffset.UTC
+import java.time.ZonedDateTime
+import java.time.format.DateTimeFormatter.ISO_LOCAL_DATE_TIME
+import java.time.temporal.ChronoUnit.SECONDS
+import java.util.Base64
+
+/**
+ * This class can be run from the sbt console with `pan-domain-auth-verification / Test / run`.
+ *
+ * You need to supply the _current_ Panda .settings file as the command line argument, eg:
+ *
+ * {{{
+ * pan-domain-auth-verification / Test / run pan-domain-auth-verification/src/test/resources/crypto-conf-rotation-example/0.legacy.
+ * settings
+ * }}}
+ */
+object CryptoConfForRotation extends App with EitherValues {
+
+  val base64Encoder = Base64.getEncoder
+
+  args.headOption.fold(
+    Console.err.println("\nYou must supply the path to the current Panda .settings file, downloaded from S3.\n")
+  )(generateForExistingConf)
+
+  def generateForExistingConf(pathForCurrentConf: String): Unit = {
+    val keyPairGenerator: KeyPairGenerator = {
+      val g = KeyPairGenerator.getInstance("RSA")
+      g.initialize(4096)
+      g
+    }
+
+    val newTargetKeyPair = {
+      val kp = keyPairGenerator.generateKeyPair
+      KeyPair(kp.getPublic, kp.getPrivate)
+    }
+
+    println(s"Loading current conf from $pathForCurrentConf")
+    val loader = new Settings.Loader(
+      _ => new FileInputStream(pathForCurrentConf),
+      ""
+    )
+    val originalConf = CryptoConf.SettingsReader(loader.loadAndParseSettingsMap().value).signingAndVerificationConf.value
+    val rotationInProgressConf = originalConf.copy(activeKeyPair = newTargetKeyPair, alsoAccepted = Seq(originalConf.activePublicKey))
+
+    val tempDirWithPrefix = Files.createTempDirectory("panda-rotation")
+    val timeStamp = s"Generated at ${ZonedDateTime.now(UTC).truncatedTo(SECONDS).format(ISO_LOCAL_DATE_TIME)}Z"
+    println(s"$timeStamp - files are in:\n\n$tempDirWithPrefix\n")
+    for {
+      ((description, conf), index) <- Seq(
+        "upcoming" -> originalConf.copy(alsoAccepted = Seq(newTargetKeyPair.publicKey)),
+        "in-progress" -> rotationInProgressConf,
+        "complete" -> rotationInProgressConf.copy(alsoAccepted = Nil)
+      ).zipWithIndex
+    } {
+      val filename = s"${1 + index}.rotation-$description.settings"
+      println(filename)
+      Files.writeString(tempDirWithPrefix.resolve(filename), s"# $filename - $timeStamp\n\n${textFor(conf)}")
+    }
+  }
+
+  def textFor(conf: SigningAndVerification): String = {
+    def base64For(key: Key): String = base64Encoder.encodeToString(key.getEncoded)
+
+    val keyValues = Seq(
+      "privateKey" -> base64For(conf.activePrivateKey),
+      "publicKey" -> base64For(conf.activePublicKey)
+    ) ++ conf.alsoAccepted.zipWithIndex.map {
+      case (key, index) => s"alsoAccept.$index.publicKey" -> base64For(key)
+    }
+    assert(CryptoConf.SettingsReader(keyValues.toMap).signingAndVerificationConf.value == conf)
+    keyValues.map {
+      case (key, value) =>  s"$key=$value\n"
+    }.mkString("\n")
+  }
+}
diff --git a/pan-domain-auth-verification/src/test/scala/com/gu/pandomainauth/CryptoConfTest.scala b/pan-domain-auth-verification/src/test/scala/com/gu/pandomainauth/CryptoConfTest.scala
index b708f05..7498b40 100644
--- a/pan-domain-auth-verification/src/test/scala/com/gu/pandomainauth/CryptoConfTest.scala
+++ b/pan-domain-auth-verification/src/test/scala/com/gu/pandomainauth/CryptoConfTest.scala
@@ -1,13 +1,42 @@
 package com.gu.pandomainauth
 
-import com.gu.pandomainauth.service.CryptoConf.SettingsReader
+import com.gu.pandomainauth.service.CryptoConf.{SettingsReader, SigningAndVerification}
 import com.gu.pandomainauth.service.TestKeys.testPublicKey
 import org.scalatest.EitherValues
 import org.scalatest.freespec.AnyFreeSpec
 import org.scalatest.matchers.should.Matchers
 
+import java.nio.charset.StandardCharsets.UTF_8
+
 
 class CryptoConfTest extends AnyFreeSpec with Matchers with EitherValues {
+  "loading crypto configuration" - {
+    "follow a safe set of transition steps" in {
+      val legacyConf = loadExample("0.legacy")
+      legacyConf.alsoAccepted shouldBe empty
+
+      val rotationUpcomingConf = loadExample("1.rotation-upcoming")
+      rotationUpcomingConf.activeKeyPair should === (legacyConf.activeKeyPair)
+      rotationUpcomingConf.alsoAccepted should not be empty
+      val expectedAcceptedPublicKeys = rotationUpcomingConf.activeKeyPair.publicKey +: rotationUpcomingConf.alsoAccepted
+      rotationUpcomingConf.acceptedPublicKeys should === (expectedAcceptedPublicKeys)
+
+      val rotationInProgressConf = loadExample("2.rotation-in-progress")
+      rotationInProgressConf.activeKeyPair should !== (legacyConf.activeKeyPair)
+      rotationInProgressConf.alsoAccepted shouldBe Seq(legacyConf.activeKeyPair.publicKey)
+
+      val rotationCompleteConf = loadExample("3.rotation-complete")
+      rotationCompleteConf.activeKeyPair should === (rotationInProgressConf.activeKeyPair)
+      rotationCompleteConf.alsoAccepted shouldBe empty
+    }
+  }
+
+  private def loadExample(name: String): SigningAndVerification = {
+    val settingsText =
+      new String(getClass.getResourceAsStream(s"/crypto-conf-rotation-example/$name.settings").readAllBytes(), UTF_8)
+    SettingsReader(Settings.extractSettings(settingsText).value).signingAndVerificationConf.value
+  }
+
   "CryptoConf.SettingsReader" - {
     "returns an error if the key looks invalid" in {
       SettingsReader.publicKeyFor("not a valid key").left.value shouldEqual PublicKeyFormatFailure
@@ -31,4 +60,5 @@ class CryptoConfTest extends AnyFreeSpec with Matchers with EitherValues {
       SettingsReader(Map("another key" -> "bar")).activePublicKey.left.value should be(MissingSetting("publicKey"))
     }
   }
+
 }
diff --git a/pan-domain-auth-verification/src/test/scala/com/gu/pandomainauth/PanDomainTest.scala b/pan-domain-auth-verification/src/test/scala/com/gu/pandomainauth/PanDomainTest.scala
index 21c0058..88b180b 100644
--- a/pan-domain-auth-verification/src/test/scala/com/gu/pandomainauth/PanDomainTest.scala
+++ b/pan-domain-auth-verification/src/test/scala/com/gu/pandomainauth/PanDomainTest.scala
@@ -1,13 +1,14 @@
 package com.gu.pandomainauth
 
-import java.util.Date
-
 import com.gu.pandomainauth.model._
 import com.gu.pandomainauth.service.CookieUtils
-import org.scalatest.freespec.AnyFreeSpec
+import com.gu.pandomainauth.service.CryptoConf.OnlyVerification
 import org.scalatest.Inside
+import org.scalatest.freespec.AnyFreeSpec
 import org.scalatest.matchers.should.Matchers
 
+import java.util.Date
+
 class PanDomainTest extends AnyFreeSpec with Matchers with Inside {
   import com.gu.pandomainauth.service.TestKeys._
 
@@ -19,23 +20,21 @@ class PanDomainTest extends AnyFreeSpec with Matchers with Inside {
     system: String = "testsuite",
     cacheValidation: Boolean = false,
     forceExpiry: Boolean = false,
-  ) = {
-    PanDomain.authStatus(cookieData, testPublicKey.key, validateUser, apiGracePeriod, system, cacheValidation, forceExpiry)
-  }
+  ) = PanDomain.authStatus(cookieData, OnlyVerification(testPublicKey.key), validateUser, apiGracePeriod, system, cacheValidation, forceExpiry)
 
   "authStatus" - {
     val authUser = AuthenticatedUser(User("test", "user", "test.user@example.com", None), "testsuite", Set("testsuite"), new Date().getTime + 86400, multiFactor = true)
-    val validCookieData = CookieUtils.generateCookieData(authUser, testPrivateKey.key)
+    val validCookieData = CookieUtils.generateCookieData(authUser, signingWith(testPrivateKey.key))
 
     "returns `Authenticated` for valid cookie data that passes the validation check" in {
       def validateUser(au: AuthenticatedUser): Boolean = au.multiFactor && au.user.emailDomain == "example.com"
-      val cookieData = CookieUtils.generateCookieData(authUser, testPrivateKey.key)
+      val cookieData = CookieUtils.generateCookieData(authUser, signingWith(testPrivateKey.key))
 
       authStatus(cookieData, validateUser) shouldBe a [Authenticated]
     }
 
     "gives back the provided auth user if successful" in {
-      val cookieData = CookieUtils.generateCookieData(authUser, testPrivateKey.key)
+      val cookieData = CookieUtils.generateCookieData(authUser, signingWith(testPrivateKey.key))
 
       authStatus(cookieData) should equal(Authenticated(authUser))
     }
@@ -45,40 +44,40 @@ class PanDomainTest extends AnyFreeSpec with Matchers with Inside {
     }
 
     "returns `InvalidCookie` if the cookie fails its signature check" in {
-      val incorrectCookieData = CookieUtils.generateCookieData(authUser, testINCORRECTPrivateKey.key)
+      val incorrectCookieData = CookieUtils.generateCookieData(authUser, signingWith(testINCORRECTPrivateKey.key))
 
       authStatus(incorrectCookieData) shouldBe a [InvalidCookie]
     }
 
     "returns `Expired` if the time is after the cookie's expiry" in {
       val expiredAuthUser = authUser.copy(expires = new Date().getTime - 86400)
-      val cookieData = CookieUtils.generateCookieData(expiredAuthUser, testPrivateKey.key)
+      val cookieData = CookieUtils.generateCookieData(expiredAuthUser, signingWith(testPrivateKey.key))
 
       authStatus(cookieData) shouldBe a [Expired]
     }
 
     "returns `Expired` if the cookie has expired and is outside the grace period" in {
       val expiredAuthUser = authUser.copy(expires = new Date().getTime - 86400)
-      val cookieData = CookieUtils.generateCookieData(expiredAuthUser, testPrivateKey.key)
+      val cookieData = CookieUtils.generateCookieData(expiredAuthUser, signingWith(testPrivateKey.key))
 
       authStatus(cookieData) shouldBe a [Expired]
     }
 
     "returns `Expired` if cookie has not expired, but forceExpiry is set" in {
-      val validCookieData = CookieUtils.generateCookieData(authUser, testPrivateKey.key)
+      val validCookieData = CookieUtils.generateCookieData(authUser, signingWith(testPrivateKey.key))
       authStatus(validCookieData, forceExpiry = true) shouldBe a [Expired]
     }
 
     "returns `GracePeriod` if the cookie has expired but is within the grace period" in {
       val expiredAuthUser = authUser.copy(expires = new Date().getTime - 3000)
-      val cookieData = CookieUtils.generateCookieData(expiredAuthUser, testPrivateKey.key)
+      val cookieData = CookieUtils.generateCookieData(expiredAuthUser, signingWith(testPrivateKey.key))
 
       authStatus(cookieData, apiGracePeriod = 3600) shouldBe a [GracePeriod]
     }
 
     "returns `NotAuthorized` if the cookie does not pass the verification check" in {
       def validateUser(au: AuthenticatedUser): Boolean = au.multiFactor && au.user.emailDomain == "example.com"
-      val cookieData = CookieUtils.generateCookieData(authUser, testPrivateKey.key)
+      val cookieData = CookieUtils.generateCookieData(authUser, signingWith(testPrivateKey.key))
 
       authStatus(cookieData, _ => false) shouldBe a [NotAuthorized]
     }
diff --git a/pan-domain-auth-verification/src/test/scala/com/gu/pandomainauth/service/CookieUtilsTest.scala b/pan-domain-auth-verification/src/test/scala/com/gu/pandomainauth/service/CookieUtilsTest.scala
index 346da2e..10d8da2 100644
--- a/pan-domain-auth-verification/src/test/scala/com/gu/pandomainauth/service/CookieUtilsTest.scala
+++ b/pan-domain-auth-verification/src/test/scala/com/gu/pandomainauth/service/CookieUtilsTest.scala
@@ -3,10 +3,12 @@ package com.gu.pandomainauth.service
 import com.gu.pandomainauth.model.{AuthenticatedUser, User}
 import com.gu.pandomainauth.service.CookieUtils.CookieIntegrityFailure.{MalformedCookieText, SignatureNotValid}
 import com.gu.pandomainauth.service.CookieUtils.{deserializeAuthenticatedUser, parseCookieData, serializeAuthenticatedUser}
+import com.gu.pandomainauth.service.CryptoConf.{OnlyVerification, Signing}
 import org.scalatest.freespec.AnyFreeSpec
 import org.scalatest.matchers.should.Matchers
 import org.scalatest.{EitherValues, OptionValues}
 
+import java.security.PrivateKey
 import java.util.Date
 
 
@@ -17,28 +19,30 @@ class CookieUtilsTest extends AnyFreeSpec with Matchers with EitherValues with O
 
   "generateCookieData" - {
     "generates a base64-encoded 'data.signature' cookie value" in {
-      CookieUtils.generateCookieData(authUser, testPrivateKey.key) should fullyMatch regex "[\\w+/]+=*\\.[\\w+/]+=*".r
+      CookieUtils.generateCookieData(authUser, signingWith(testPrivateKey.key)) should fullyMatch regex "[\\w+/]+=*\\.[\\w+/]+=*".r
     }
   }
 
   "parseCookieData" - {
+    val cryptoConf = OnlyVerification(testPublicKey.key)
+
     "can extract an authenticatedUser from real cookie data" in {
-      val cookieData = CookieUtils.generateCookieData(authUser, testPrivateKey.key)
+      val cookieData = CookieUtils.generateCookieData(authUser, signingWith(testPrivateKey.key))
 
-      parseCookieData(cookieData, testPublicKey.key).value should equal(authUser)
+      parseCookieData(cookieData, cryptoConf).value should equal(authUser)
     }
 
     "fails to extract invalid data with a SignatureNotValid" in {
-      parseCookieData("data.invalidSignature", testPublicKey.key).left.value shouldBe SignatureNotValid
+      parseCookieData("data.invalidSignature", cryptoConf).left.value shouldBe SignatureNotValid
     }
 
     "fails to extract incorrectly signed data with a CookieSignatureInvalidException" in {
-      val cookieData = CookieUtils.generateCookieData(authUser, testINCORRECTPrivateKey.key)
-      parseCookieData(cookieData, testPublicKey.key).left.value should equal(SignatureNotValid)
+      val cookieData = CookieUtils.generateCookieData(authUser, signingWith(testINCORRECTPrivateKey.key))
+      parseCookieData(cookieData, cryptoConf).left.value should equal(SignatureNotValid)
     }
 
     "fails to extract completely incorrect cookie data with a CookieParseException" in {
-      parseCookieData("Completely incorrect cookie data", testPublicKey.key).left.value shouldBe MalformedCookieText
+      parseCookieData("Completely incorrect cookie data", cryptoConf).left.value shouldBe MalformedCookieText
     }
   }
 
diff --git a/pan-domain-auth-verification/src/test/scala/com/gu/pandomainauth/service/TestKeys.scala b/pan-domain-auth-verification/src/test/scala/com/gu/pandomainauth/service/TestKeys.scala
index ac31866..5d23656 100644
--- a/pan-domain-auth-verification/src/test/scala/com/gu/pandomainauth/service/TestKeys.scala
+++ b/pan-domain-auth-verification/src/test/scala/com/gu/pandomainauth/service/TestKeys.scala
@@ -1,9 +1,10 @@
 package com.gu.pandomainauth.service
 
-import com.gu.pandomainauth.SettingsFailure.SettingsResult
+import com.gu.pandomainauth.Settings.SettingsResult
 import com.gu.pandomainauth.service.CryptoConf.SettingsReader.{privateKeyFor, publicKeyFor}
+import com.gu.pandomainauth.service.CryptoConf.Signing
 
-import java.security.Key
+import java.security.{Key, PrivateKey}
 
 object TestKeys {
 
@@ -11,6 +12,10 @@ object TestKeys {
   def example[K <: Key](f: String => SettingsResult[K])(base64Encoded: String): Example[K] =
     Example(f(base64Encoded).toOption.get, base64Encoded)
 
+  def signingWith(privateKey: PrivateKey): Signing = new Signing {
+    override val activePrivateKey: PrivateKey = privateKey
+  }
+
   /**
    * A test public/private key-pair
    */
diff --git a/project/Dependencies.scala b/project/Dependencies.scala
index 85565c5..d009b64 100644
--- a/project/Dependencies.scala
+++ b/project/Dependencies.scala
@@ -49,5 +49,5 @@ object Dependencies {
 
   // provide compatibility between scala 2.12 and 2.13
   // see https://github.com/scala/scala-collection-compat/issues/208
-  val scalaCollectionCompatDependencies = Seq("org.scala-lang.modules" %% "scala-collection-compat" % "2.1.6")
+  val scalaCollectionCompatDependencies = Seq("org.scala-lang.modules" %% "scala-collection-compat" % "2.12.0")
 }