Free Encryption Libraries

Network Security Services (NSS)
If you want add support for SSL, S/MIME, or other Internet security standards to your application, you can use Network Security Services (NSS) to implement all your security features. NSS provides a complete open-source implementation of the crypto libraries used by Netscape, Sun, and other companies in a variety of products.

Crypto++ Library 5.6.2
Crypto++ Library is a free C++ class library of cryptographic schemes.

cryptlib is a powerful security toolkit which allows even inexperienced crypto programmers to easily add encryption and authentication services to their software.

OpenSSL Project
The OpenSSL Project is a collaborative effort to develop a robust, commercial-grade, full-featured, and Open Source toolkit implementing the Secure Sockets Layer (SSL v2/v3) and Transport Layer Security (TLS v1) protocols

LockBox is a cross-platform toolkit for data encryption. It contains routines & components for use with Borland Delphi, C++Builder, & Kylix