Cryptography Reference
In-Depth Information
In classical cryptology the participants trust each
other but not outsiders; typical examples include dip-
lomatic communications and military commands. In
business and personal transactions, though, the situation
is almost the opposite, as the participants may have vari-
ous motives for cheating. For example, the cheater may
wish to impersonate some other participant, to eavesdrop
on communications between other participants, or to
intercept and modify information being communicated
between other users. The cheater may be an insider who
wishes to disavow communications he actually originated
or to claim to have received messages from other partici-
pants who did not send them. He may wish to enlarge his
license to gain access to information to which he is not
supposed to have access or to alter the license of others.
He may wish simply to subvert the system to deny services
to others or to cause other users to reject as fraudulent
information that is in fact legitimate. Therefore, modern
cryptology must also prevent every form of cheating or,
failing that, detect cheating in information-based systems
where the means for cheating depends only on tampering
with electronic information.
At the beginning of the 1990s most people would have
been hard-pressed to say where cryptology had an impact
on their day-to-day lives. Today, people who have pur-
chased merchandise over the Internet are familiar with
warnings that they are about to exchange information
over a secure link. When a warning appears from time to
time alerting consumers that a merchant's authentication
has either expired or is not working, they are aware that
this is a warning to proceed at their own risk in providing
personal information, such as credit card numbers. Only
a few are aware, however, that behind this exchange of
authentications is a 128-bit cryptography key that has been
