RFC2985: PKCS #9: Selected Object Classes and Attribute Types
Introduction
辅助其他PKCS系列的class、attribute定义
例如PKCS#7的消息签名、PKCS#10的证书请求、PKCS#12的个人信息交换、PKCS#15的token及encrypted private key等。
针对pkcsEntity、naturePerson定义objectClass。
以PKCS#7为例， Attribute types defined in this document that are useful in PKCS #7 digitally signed messages are content type, message digest, signing time, sequence number, random nonce and countersignature.
