audited using ineffassign tool from
github.com/gordonklaus/ineffassign
go generate does not generate any changes
Change-Id: Iabbec9ec1aae39081289d503d79fd7b4caadf17b
GitHub-Last-Rev: acd17cce41
GitHub-Pull-Request: golang/crypto#70
Reviewed-on: https://go-review.googlesource.com/c/155942
Reviewed-by: Filippo Valsorda <filippo@golang.org>