+CMS stands for Cryptographic Message Syntax. It is defined in the
+[RFC 5652](http://tools.ietf.org/html/rfc5652).
+CMS defines several types of documents. There is **SignedData**,
+which can be read by anyone, but is protected from authorized changes
+by digital signature of its author. There is **EnvelopedData** protected
+from unauthorized reading by cipher and allowed to be read only by
+owners of certain private keys, and there is **EncryptedData**, which
+are protected by symmetric cipher keys.
+
+