Bouncy Castle 是一种用于 Java 平台的开放源码的轻量级密码术包。它支持大量的密码术算法，并提供 JCE 1.2.1 的实现.现在有了C#的版本。下面是网站上的介绍
This port features tools for X.509 Certificate generation, Certificate request generation, generation and reading of PKCS12 files, password based encryption, a full port of the ASN.1 library, including the OCSP, CMS classes and the full X.509 set. In addition the code has been cleaned up to remove classes that were deprecated in the Java version and the new BigInteger class and SHA224 have been added as well. There are also some tool classes for extracting/constructing public and private keys from their ASN.1 equivalents.
网站：http://www.bouncycastle.org/csharp/
http://www-128.ibm.com/developerworks/cn/java/j-midpds/index.html