Cryptography Reference
In-Depth Information
to test it. The 128-bit key offers “strong encryption” that
protects Internet transactions against almost any threat;
nevertheless, some Web browsers used on personal com-
puters will support an even stronger 256-bit encryption
key, which offers a level of protection required by many
governments for top-secret documents.
Cryptology, indeed, has long been a part of modern daily
life. In particular, electronic banking and various finan-
cial, medical, and legal databases depend on cryptology
for security. One example is the personal identity number
(PIN), a coded identification that must be entered into an
automated teller machine (ATM) along with a bankcard to
corroborate that the card is being used by an authorized
bearer. The PIN may be stored in an encrypted form (as a
cipher) either in the bank's computers or on the card itself.
The transformation used in this type of cryptography is
called one-way; i.e., it is easy to compute a cipher given
the bank's key and the customer's PIN, but it is compu-
tationally infeasible to compute the plaintext PIN from
the cipher even when the key is known. This protects the
cardholder from being impersonated by someone who has
access to the bank's computer files. Similarly, communica-
tions between the ATM and the bank's central computer
are encrypted to prevent a would-be thief from tapping
into the phone lines and recording the signals sent to the
ATM to authorize the dispensing of cash in response to
a legitimate user request and then later feeding the same
signals to the ATM repeatedly to deceive it into dispens-
ing money illegitimately from the customer's account.
A novel application that involves all aspects of
cryptography is the “smart” credit card, which has a
microprocessor built into the card itself. The user must
corroborate his identity to the card each time a transac-
tion is made in much the same way that a PIN is used
