Previously, receiving an unexpected message type in response to a key listing or a signing request could cause a panic due to a failed type assertion. This change adds a default case to the type switch in order to detect and explicitly handle unknown or invalid message types, returning a descriptive error instead of crashing. Fixes golang/go#75178 Change-Id: Icbc3432adc79fe3c56b1ff23c6724d7a6f710f3a Reviewed-on: https://go-review.googlesource.com/c/crypto/+/700295 Reviewed-by: Roland Shoemaker <roland@golang.org> LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com> Reviewed-by: Michael Pratt <mpratt@google.com> Reviewed-by: Jakub Ciolek <jakub@ciolek.dev>