Red Hat, Inc. This document specifies additions to RFC 8017. Specifically, it provides guidance to implementers of the standard to protect against side-channel attacks. It also recommends against the RSAES-PKCS-v1_5 encryption scheme, and provides an alternative depadding algorithm that protects against side-channel attacks raising from users of vulnerable APIs. The purpose of this specification is to increase security of RSA implementations. The document is a product of the Crypto Forum Research Group (CFRG).