In this system, the only way
to decrypt such a coded message is to use Mary??™s private key. Joe cannot even decrypt the message using the
public key he used to encrypt the message!
Because of the mathematical relationship between the public and private keys, it is theoretically possible
to deduce the private key value from the public key. However, the problem of guessing the private key becomes
much greater as the size of the key becomes larger. Large keys, such as 128-bit keys, are thought to provide
good security. It should take something like 1000 years using a powerful computer to directly break (as contrasted
with a lucky guess) such a public key encryption code.
In the last quarter of the 20th century, the US government prohibited the export of encryption technology
in an effort to prevent the spread of public key encryption systems that offered strong security. The reason for
this was that the government had an interest in monitoring certain communications for reasons of national security
and the prosecution of criminals. After the technology spread outside the US anyway, some people felt the
government??™s actions seemed to punish or hold back US companies, while the rest of the world went ahead
using strong encryption anyway.
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