RSA-PSS - EVP_PKEY RSA-PSS algorithm support
The RSA-PSS EVP_PKEY implementation is a restricted version of the RSA
  algorithm which only supports signing, verification and key generation using
  PSS padding modes with optional parameter restrictions.
It has associated private key and public key formats.
This algorithm shares several control operations with the
    RSA algorithm but with some restrictions described below.
Signing and verification is similar to the RSA algorithm except the
  padding mode is always PSS. If the key in use has parameter restrictions then
  the corresponding signature parameters are set to the restrictions: for
  example, if the key can only be used with digest SHA256, MGF1 SHA256 and
  minimum salt length 32 then the digest, MGF1 digest and salt length will be
  set to SHA256, SHA256 and 32 respectively.
By default no parameter restrictions are placed on the generated key.
The public key format is documented in RFC4055.
The PKCS#8 private key format used for RSA-PSS keys is similar to
    the RSA format except it uses the id-RSASSA-PSS OID and the
    parameters field, if present, restricts the key parameters in the same way
    as the public key.
EVP_PKEY_CTX_set_rsa_pss_keygen_md(3),
  EVP_PKEY_CTX_set_rsa_pss_keygen_mgf1_md(3),
  EVP_PKEY_CTX_set_rsa_pss_keygen_saltlen(3), EVP_PKEY_CTX_new(3),
  EVP_PKEY_CTX_ctrl_str(3), EVP_PKEY_derive(3)
Copyright 2017-2018 The OpenSSL Project Authors. All Rights Reserved.
Licensed under the Apache License 2.0 (the "License").
    You may not use this file except in compliance with the License. You can
    obtain a copy in the file LICENSE in the source distribution or at
    <https://www.openssl.org/source/license.html>.