35f4c7f created the issue

Trying to use KMS with custom keys in Cyberduck (and also Mountain Duck).
Noted that the keys listed in the encryption drop down for the Info box on a bucket only list keys in us-east-1 - even when the bucket is in a different region.

Looking at debug output, I see the connection to kms.us-east-1.amazonaws.com although the bucket is in eu-west-1

This should be updated to use the KMS regional endpoints for the associated buckets region - http://docs.aws.amazon.com/general/latest/gr/rande.html#kms_region