That is simply completely incorrect. All major databases support this. Oracle, Sybase, and Informix for sure. Hell, I was doing that with Sybase DBAPI 10 years ago.
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."