- Cryptography is the practice that involves study
and application of the techniques for making communication secure with the
adversaries or the third parties.

**To be more general, it involves construction and the analyzation of the protocols for overcoming the impact of the adversaries and other aspects concerning the information security such as the following:**

Ø Data
confidentiality

Ø Data
integrity

Ø Authentication

Ø Non –
repudiation

- The modern cryptography in contrast to the traditional
cryptography intersects the computer science, mathematical and the engineering
disciplines.

*There are various applications of cryptography as in the following:*
Ø ATM cards

Ø Computer
passwords

Ø Electronic
commerce

- The traditional cryptography was synonymous with
the process of encryption which involves converting the information which is in
readable state to such a state in which it appears like utter nonsense.

- The one
who generated the encrypted message also shared the technique for decoding the
message only with the desired recipients, thus the unwanted people are precluded
from doing so.

- Cryptography is in use since the World War I and the methods
that were used then now have become so complex and eventually its application
increased.

- Modern cryptography’s foundation is based up on the computer science
and the mathematical theory.

- The designing of the cryptographic algorithms is
done around the computational hardness assumptions.

- In practice, this makes
these algorithms quite hard to break by any third party.

- However, theoretically
it is possible to break in to such a system but for doing so any known
practical means are in-feasible.

- That is why, all these schemes are considered to
be computationally safe and secure.

__For the following, the continuous adaptation of these methods is required:__
Ø Improvements
in the algorithms for the integer factorization.

Ø Faster
computing technology.

- Also, there are schemes that are information –
theoretically secure and even with unlimited computing power, these schemes
cannot be broken.

- One such scheme is one time pad.

- Also, the implementation of
these schemes is also quite difficult when compared to the schemes that are
computationally secure but are theoretically breakable.

**- Traditionally cryptography referred only to the encryption**which involves conversion of the ordinary info in to cipher text or unintelligible text.

- The reverse process of
this is decryption.

- The pair of algorithms that carry out these two processes
is called the cipher. - Each instance of the operation of the cipher is
controlled by a key which is kept secret between the communicants.

- The purpose
of this key lies in decryption of the cipher text.

- Earlier the encryption and
the decryption process were carried out directly by the ciphers without
involvement of any integrity or authentication checks.

**-**

**Before the advent of the modern cryptography, the traditional cryptography was known to be concerned only with the message confidentiality i.e., converting the message from comprehensible text in to incomprehensible text and vice versa.**

- The message was
thus unreadable for the eavesdroppers and the interceptors without key.

- For
ensuring the secrecy in the communications, the encryption process was used.

- But now the field expands far beyond the confidentiality issues.

- It now
consists of techniques for authentication and message integrity checking,
secure computation techniques, interactive proofs, digital signatures and so
on.

**- Earlier two types of classical ciphers were used namely substitution ciphers and the transposition ciphers.**

- The former type involved replacing the
letters by some other letters.

- The transposition ciphers involved rearrangement
of the letters.

- Some examples of early ciphers are caeser cipher, atbash cipher
etc.

- The early ciphers were assisted by some other physical aids and devices.

- Eventually more complex ciphers could be developed with the development of the
digital computers.

- Any kind of data that could be represented in binary
format could be encrypted.

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