Recommend duration of challenge validity

index.bs

@@ -1736,17 +1736,9 @@ When this method is invoked, the user agent MUST execute the following algorithm
     |lifetimeTimer| to this adjusted value. If <code>|pkOptions|.{{PublicKeyCredentialCreationOptions/timeout}}</code> is not
     present, then set |lifetimeTimer| to a [=client=]-specific default.
 
-        Recommended ranges and defaults for <code>|pkOptions|.{{PublicKeyCredentialCreationOptions/timeout}}</code> are as follows.
-          If <code>|pkOptions|.{{PublicKeyCredentialCreationOptions/authenticatorSelection}}.{{AuthenticatorSelectionCriteria/userVerification}}</code>
-            <dl class="switch">
-                :   is set to {{UserVerificationRequirement/discouraged}}
-                ::  Recommended range: 30000 milliseconds to 180000 milliseconds.
-                ::  Recommended default value: 120000 milliseconds (2 minutes).
-
-                :   is set to {{UserVerificationRequirement/required}} or {{UserVerificationRequirement/preferred}}
-                ::  Recommended range: 30000 milliseconds to 600000 milliseconds.
-                ::  Recommended default value: 300000 milliseconds (5 minutes).
-            </dl>
+        See the [=recommended ranges and defaults for a WebAuthn ceremony timeout=]
+        for guidance on deciding a reasonable range and default for <code>|pkOptions|.{{PublicKeyCredentialCreationOptions/timeout}}</code>,
+        depending on the value of <code>|pkOptions|.{{PublicKeyCredentialCreationOptions/authenticatorSelection}}.{{AuthenticatorSelectionCriteria/userVerification}}</code>.
 
         Note: The user agent should take cognitive guidelines into considerations regarding timeout for users with special needs.
 
@@ -2232,17 +2224,9 @@ When this method is invoked, the user agent MUST execute the following algorithm
         Set a timer |lifetimeTimer| to this adjusted value. If <code>|pkOptions|.{{PublicKeyCredentialRequestOptions/timeout}}</code>
         is not present, then set |lifetimeTimer| to a [=client=]-specific default.
 
-            Recommended ranges and defaults for <code>|pkOptions|.{{PublicKeyCredentialRequestOptions/timeout}}</code> are as follows.
-              If <code>|pkOptions|.{{PublicKeyCredentialRequestOptions/userVerification}}</code>
-                <dl class="switch">
-                    :   is set to {{UserVerificationRequirement/discouraged}}
-                    ::  Recommended range: 30000 milliseconds to 180000 milliseconds.
-                    ::  Recommended default value: 120000 milliseconds (2 minutes).
-
-                    :   is set to {{UserVerificationRequirement/required}} or {{UserVerificationRequirement/preferred}}
-                    ::  Recommended range: 30000 milliseconds to 600000 milliseconds.
-                    ::  Recommended default value: 300000 milliseconds (5 minutes).
-                </dl>
+            See the [=recommended ranges and defaults for a WebAuthn ceremony timeout=]
+            for guidance on deciding a reasonable range and default for <code>|pkOptions|.{{PublicKeyCredentialRequestOptions/timeout}}</code>,
+            depending on the value of <code>|pkOptions|.{{PublicKeyCredentialRequestOptions/userVerification}}</code>.
 
             Note: The user agent should take cognitive guidelines into considerations regarding timeout for users with special needs.
 
@@ -8068,6 +8052,9 @@ upon a client's behavior, e.g., the [=[RP]=] SHOULD store the challenge temporar
 until the operation is complete. Tolerating a mismatch will compromise the security
 of the protocol.
 
+Challenges SHOULD be valid for a duration similar to the
+upper limit of the [=recommended ranges and defaults for a WebAuthn ceremony timeout=].
+
 In order to prevent replay attacks, the challenges MUST contain enough entropy to make guessing them infeasible. Challenges SHOULD
 therefore be at least 16 bytes long.
 
@@ -8501,8 +8488,25 @@ as discussed in [[#sctn-username-enumeration]].
 
 [=[RPS]=], at [=registration=] time, SHOULD provide affordances for users to complete future [=authorization gestures=] correctly. This could involve naming the authenticator, choosing a picture to associate with the device, or entering freeform text instructions (e.g., as a reminder-to-self).
 
+
+## Recommended Ranges for Ceremony Timeouts ## {#sctn-timeout-recommended-ranges}
+
 [=Ceremonies=] relying on timing, e.g., a [=registration ceremony=] (see {{PublicKeyCredentialCreationOptions/timeout}}) or an [=authentication ceremony=] (see {{PublicKeyCredentialRequestOptions/timeout}}), ought to follow [[!WCAG21]]'s [Guideline 2.2 Enough Time](https://www.w3.org/TR/WCAG21/#enough-time). If a [=client platform=] determines that a [=[RP]=]-supplied timeout does not appropriately adhere to the latter [[!WCAG21]] guidelines, then the [=client platform=] MAY adjust the timeout accordingly.
 
+The <dfn>recommended ranges and defaults for a WebAuthn ceremony timeout</dfn> are as follows:
+
+If the [=[RP]=]'s [=user verification=] preference for the ceremony is
+
+  <dl class="switch">
+      :   {{UserVerificationRequirement/discouraged}}:
+      ::  Recommended range: 30000 milliseconds to 180000 milliseconds.
+      ::  Recommended default value: 120000 milliseconds (2 minutes).
+
+      :   {{UserVerificationRequirement/required}}, {{UserVerificationRequirement/preferred}}, or unspecified:
+      ::  Recommended range: 30000 milliseconds to 600000 milliseconds.
+      ::  Recommended default value: 300000 milliseconds (5 minutes).
+  </dl>
+
 
 # Acknowledgements # {#sctn-acknowledgements}
 We thank the following people for their reviews of, and contributions to, this specification: