Cryptography Reference
In-Depth Information
digital computers and networking, the last three decades have experienced
a tremendous growth in the application of cryptography in diverse domains.
The topics [80,170] provide interesting historical facts about cryptography.
1.2 Primary Goals of Cryptography
The objective of modern cryptography is mainly four-fold [119, Chapter
1]. Below, we initiate the reader into each of these goals through examples.
1. Confidentiality or Privacy: Suppose, one makes an online payment
through credit card. Then the credit card information should be read
only by the intended merchant, and not by any eavesdropper. Confiden-
tiality means keeping the content hidden from all but those authorized
to have it. Not only transmitted messages, but stored data may also
need to be protected against unauthorized access (e.g. by hackers).
2. Integrity: Suppose, A gives his laptop to B for a day and asks B not to
alter contents of folder F. IfB adds or deletes or modifies anything inside
F, A should be able to detect it. Integrity means detecting unauthorized
alteration of data.
3. Authentication: Suppose two police o
cers are entering into a communi-
cation via telephone. Before sending any important message, they must
identify each other. Authentication simply means verifying identity.
Usually, two broad classes of authentication are considered. Validating
the identity of a person, a machine or an object, is called entity au-
thentication or identification. Corroborating the source of information
is called data origin authentication or message authentication.
4. Non-repudiation: Suppose A sells a property to B and both sign an
agreement. It may happen that A later claims that the signature on
the agreement is not his. A method involving a “trusted” third party
(TTP) may be needed to resolve such a dispute. Non-repudiation means
preventing an entity from denying previous commitments or actions.
Cryptography provides many other services that became quite relevant in
recent times. Some of these are related to the four principal goals listed above.
Let us discuss a few important ones.
• Digital Signature: Suppose A signs a check in favor of B. When B sub-
mits the check to the bank, the bank authority matches A's signature on
the check with that in their records before withdrawing the money from
A's account. Similarly, a digital signature [141] scheme is a method of
signing a message stored in electronic form. Such a signature should be
