mono/mcs/class/System.Core/System.Security.Cryptography/README.CNG

CNG stands for "Cryptography API: Next Generation"

CNG is the replacement for CryptoAPI under Windows Vista (and later) and
just like CryptoAPI it is a Windows-specific, native (unmanaged) library.

In MS implementation the *Cng classes are simply managed wrappers around
the native CNG libraries. This is similar to older *CryptoServiceProvider
classes that provided managed wrappers around CryptoAPI.

In Mono implementation the *Cng classes are, mostly[1], wrappers around 
existing managed classes provided in older version of the framework. 
This is essentially similar to what Mono already does for the 
*CryptoServiceProvider classes (i.e. provide managed implementation).

Of couse this won't affect people using the base algorithm classes to
create the default instance of their algorithm. 

E.g.
	SHA256 hash = SHA256.Create ();
has been working for years and will continue to do so.


New CNG crypto classes		Wrapper around
----------------------		--------------
ECDsaCng			none [1]
ECDiffieHellmanCng		none [1]
MD5Cng				MD5CryptoServiceProvider [mscorlib]
SHA1Cng				SHA1Managed [mscorlib]
SHA256Cng			SHA256Managed [mscorlib]
SHA384Cng			SHA384Managed [mscorlib]
SHA512Cng			SHA512Managed [mscorlib]


[1] Two specific cases, namely ECDH and ECDSA, are new algorithms that
were not available before CNG and for which Mono does not, at the 
present time, have managed alternatives.

The *actual* behavior of both class is to throw a PlatformException
just like running the same code would do under Windows XP (or earlier).
Once we have managed implementations for both algorithms we'll behave
like Vista.