Cryptography

Cryptography
By
Nastypradeep@gmail.com
Pradeep…

₰ The art of protecting information by transforming it
(encrypting it) into an unreadable format, called cipher text.
Only those who possess a secret key can decipher (or decrypt)
the message into plain text.

₰ Cryptanalysis is the study of how to crack encryption
algorithms or their implementations.


Why do we need Cryptography
Security often require that data be kept safe from
unauthorized access. This problem can be broken down into five
requirements that must be addressed:

※ Confidentiality: assuring that private data remains private.
※ Authentication: assuring the identity of all parties attempting
access.
※ Authorization: assuring that a certain party attempting to
perform a function has the permissions to do so.
※ Data Integrity: assuring that an object is not altered illegally.
※ Non-Repudiation: assuring against a party denying a data or a
communication that was initiated by them.

Basic Concept of Cryptography


Major Categories
Classic cryptography
Classic cryptography details cryptography styles used in the
olden age. It includes simple methods which was used superiorly during
war times etc. this was before the invention of computers.

modern cryptography
The development of digital computers and electronics after
WWII made possible much more complex ciphers. Furthermore,
computers allowed for the encryption of any kind of data representable
in any binary format, unlike classical ciphers which only encrypted
written language texts; this was new and significant. This was the
beginning of computer age.


Classic Cryptography

(Crypting techniques of olden age)

The main classical cipher types are

Transposition ciphers

Substitution ciphers


Transposition ciphers

Transposition ciphers are rearranging the
order of letters in a message .

• e.g.,
hello world' becomes 'ehlol owrdl' in a
trivially simple rearrangement scheme


Substitution ciphers
 Substitution ciphers, which systematically replace
letters or groups of letters with other letters or
groups.

e.g.,
‘Fly at once' becomes 'gmz bu podf' by replacing
each letter with the one following it in the Latin
alphabet.


The development of digital computers
and electronics after WWII made possible much
more complex ciphers. Furthermore, computers
allowed for the encryption of any kind of data
representable in any binary format, unlike classical
ciphers which only encrypted written language
texts; this was new and significant.

Computer use has thus supplanted linguistic
cryptography, both for cipher design and
cryptanalysis. Many computer ciphers can be
characterized by their operation
on binary bit sequences (sometimes in groups or
blocks), unlike classical and mechanical schemes,
which generally manipulate traditional characters
(i.e., letters and digits) directly.


The main Modern cipher types are

Symmetric-key cryptography

Public-key cryptography

Symmetric-key cryptography
₰ Symmetric-key cryptography refers to encryption methods in
which both the sender and receiver share the same key.

₰ Symmetric-key cryptosystems use the same key for
encryption and decryption of a message, though a message
or group of messages may have a different key than others.
A significant disadvantage of symmetric ciphers is the key
management necessary to use them securely.

Public-key cryptography
 Whitfield Diffie and Martin Hellman proposed the notion
of public-key (also, more generally, called asymmetric key)
cryptography in which two different but mathematically related
keys are used—a public key and a private key.

A public key system is so constructed that calculation of one key
(the 'private key') is computationally infeasible from the other
(the 'public key'), even though they are necessarily related.
Instead, both keys are generated secretly, as an interrelated pair.

Cryptanalysis


Cryptanalysis
Definition
Cryptanalysis is the study of methods
for obtaining the meaning of encrypted
information, without access to
the secret information that is normally required
to do so. Typically, this involves knowing how
the system works and finding a secret key. In
non-technical language, this is the practice
of codebreaking or cracking the code,

As the cryptography plays an important role
in today’s computer security. The cryptography
algorithms are highly confidential. And so We
cannot discuss the latest encrypting and
decrypting techniques used my mail servers, social
networks and etc..

Though we have several hackers and other
forces were seriously trying to encrypt and decrypt
the network servers.

Applications
 Used for security issues.
 Used by social networks to provide security
 Used to pass messages secretly
 Used during war times
 Even we can try to pass messages without other’s
knowledge about the message


Cryptography

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