#Engineering

2.  It is the study of information hiding and
verification. It includes the protocols,
algorithms and strategies to securely and
consistently prevent or delay unauthorized
access to sensitive information and enable
verifiability of every component in a
communication.
 It is derived from the Greek words: kryptós,
"hidden", and gráphein, "to write" - or "hidden
writing".

3.  People who study and develop cryptography are called
cryptographers. The study of how to circumvent the use of
cryptography for unintended recipients is called cryptanalysis.
 There are five primary functions of cryptography today:
 Privacy/confidentiality: Ensuring that no one can read the message
except the intended receiver.
 Authentication: The process of proving one's identity.
 Integrity: Assuring the receiver that the received message has not
been altered in any way from the original.
 Non-repudiation: A mechanism to prove that the sender really sent
this message.
 Key exchange: The method by which crypto keys are shared
between sender and receiver.

4.  The first known evidence of the use of
cryptography (in some form) was found in an
inscription carved around 1900 BC, in the main
chamber of the tomb of the nobleman
Khnumhotep II, in Egypt. The scribe used some
unusual hieroglyphic symbols here and there in
place of more ordinary ones. The purpose was
not to hide the message but perhaps to change
its form in a way which would make it appear
dignified.

5.  Time Stamping:-
 Time stamping is a technique that can certify that a
certain electronic document or communication
existed or was delivered at a certain time. Time
stamping uses an encryption model called a blind
signature scheme. Blind signature schemes allow
the sender to get a message receipted by another
party without revealing any information about the
message to the other party.

6.  Electronic Money:-
 Encryption is used in electronic money schemes
to protect conventional transaction data like
account numbers and transaction amounts,
digital signatures can replace handwritten
signatures or a credit-card authorizations, and
public-key encryption can provide confidentiality.
There are several systems that cover this range of
applications, from transactions mimicking
conventional paper transactions with values of
several dollars and up, to various micropayment
schemes that batch extremely low cost
transactions into amounts that will bear the
overhead of encryption and clearing the bank.

7.  Cryptography's chief advantage is as a security tool. Any
system connected to the Internet is bound to eventually
be attacked by hackers, and it can be extremely difficult
to create a system that is impregnable to outsiders.
However, the mathematical formulas involved in
encryption are complex enough that even if a hacker
manages to steal an encrypted file, he may never be able
to break through the code and access the contents.
Strong encryption can be a last line of defense against
outsiders, and can protect data even when it is being
transferred through a connection that is not secure.

8.  The public and private keys associated with public key
cryptography also offer some unique advantages to their
users. If a user encrypts data with his private key, anyone
can decrypt it with his public key, verifying that he and
only he could have sent the transmission. A public key
can also encode data that only that specific user can
decode, creating secure one-way communications on the
Internet.

9.  Cryptography does not guard against the vulnerabilities
and threats that emerge from the poor design of systems.
 It is always vulnerable to brute force attack.
 Cryptography comes at cost in terms of time and money.
 It depends on the secret key if you forget the keys you
cannot recover data.