+**StackOfX509** implements collection of certificates, neccessary for
+some operations with CMS and certificate verification.
+
+CMS documents
+-------------
+
+There is basic constructor function **CMS()**, which parses PEM or der
+representation of cryptographic message and generates appropriate
+object. There are **SignedData**, **EnvelopedData** and
+**EncryptedData** clases. Each class has static method **create**
+allowing to create this subtype of message from raw data and appropriate
+keys and certificates.
+
+**SignedData** has **verify()** method. **EnvelopedData** and
+**EncryptedData** - **decrypt** method.
+
+Unfortunatly, **SignedAndEnvelopedData** seems to be unsupported in
+libcrypto as of version 1.0.1 of OpenSSL.
+
+PBKDF2
+------
+
+Provices interface to password based keyderivation function
+Interface slightly differs from the **hashlib.pbkdf2_hmac** function,
+which have appeared in Python 2.7.8 but functionality is just same,
+although OpenSSL implementation might be faster.
+
+
+
+