You can use Google for you domain for free, you just don't get unlimited users.
"The armed services have long barred members of the military from sharing information that could jeopardize their missions or safety, whether electronically or by other means.
The new policy is different because it creates a blanket ban on several sites used by military personnel to exchange messages, pictures, video and audio with family and friends.
Members of the military can still access the sites on their own computers and networks, but Defense Department computers and networks are the only ones available to many soldiers and sailors in Iraq and Afghanistan.
The assignment has students write a "Public Key Cryptosystem" described here:Legal notice. It is a violation of US law to export your solution for this assignment to foreign governments or embargoed destinations (Cuba, Iran, Iraq, Libya, North Korea, Serbia, Sudan, Syria, and Taliban-controlled areas of Afghanistan as of January 2000). It is also illegal to import your solution into several countries, including France, Iran, Iraq, and Russia.
""The RSA (Rivest-Shamir-Adleman) cryptosystem is widely used for secure communication in browsers, bank ATM machines, credit card machines, mobile phones, smart cards, and the Windows operating system. It works by manipulating integers. To thwart eavesdroppers, the RSA cryptosystem must manipulate huge integers (hundreds of digits). The built-in C type int is only capable of dealing with 16 or 32 bit integers, providing little or no security. You will design, implement, and analyze an extended precision arithmetic data type that is capable of manipulating much larger integers. You will use this data type to write a client program that encrypts and decrypts messages using RSA."
... though his invention worked superbly -- his theory was a crock of sewage from beginning to end. -- Vernor Vinge, "The Peace War"