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M PRADEEP KUMAR & P RAHUL

HT.NO 08AU1A0559 08AU1A0571

1ST B.TECH

CSE BRANCH

GNYANA SARASWATI COLLEGE OF ENG.&TECHNOLOGY

DHARMARAM(B)

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Information security means protecting information and information systems

from unauthorized access, use, disclosure, disruption, modification, or

destruction

Cryptography (from Greek "hidden, secret") is the practice and study of hiding

information

Information security is concerned with the confidentiality, integrity and

availability of data regardless of the form the data may take: electronic, print,

or other forms.Cryptography is used in applications present in technologically advanced

societies; examples include the security ofATM cards, computer passwords,

and electronic commerce, which all depend on cryptography.

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Information security uses cryptography to transform usable information

into a form that renders it unusable by anyone other than an authorized

user; this process is called encryption

Encrypted information can be transformed back into its original form byan authorized user, who possesses the cryptographic key, through the

process of decryption

Cryptography is used in information security to protect information from

unauthorized users while the information is in transit and storage

Cryptography provides information security with improved authentication

methods, message digests, digital signatures, and encrypted network

communications

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Modern Information Security

Computer Security

It mainly focuses on shared system, such as time-sharing system andnecessary to provide some tools to protect file and other information stored

on the computer

Network (Communication) SecurityIt mainly concerns distributed system, such as internet and its purpose is to

protect the information over the internet

It also focuses on measures to deter, prevent, detect and correct security

violations that involve the transmission of information.

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Confidentiality : Information is accessible only for reading

Authentication :Information is correctly identified, with an assurance

that identity is not false

Integrity :Only authorized parties are able to modify computersystem assets and transmitted information

Nonrepudiation :Both the sender and receiver of message are unable

to deny the transmission.

Access Control : Requires that access to information resources maybe

controlled by or for the target system..

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Source Destination

INTERRUPTION

Source Destination

INTERCEPTION

Source Destination

MODIFICATION

Source Destination

FABRICATION

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Passive Attacks

Passive threats

Interception

Release of message contents Traffic analysis

Active Attacks

Passive threats

Interruption

(availability)

Fabrication

(authenticity)

Modification

(integrity)

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Integrity

Confidentiality

Avaliability

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The art or science encompassing the principles and methods of

transforming an intelligible message into unintelligibleone, and then

retransforming that message back to original form.

Plaintext

Ciphertext

Cipher

Key

code

Encipher(encode)

Decipher(decode)

Cryptanalysis

Cryptology

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The development of digital computers

and electronics afterWWII made

possible much more complex ciphers

Many computer ciphers can be charact-

erized by their operation on binary bit

sequences,unlike classical and

mechanical schemes

The Enigma machine, used, in several

variants, by the German military

between the late 1920s and the end of

WorldWar II

Enigma machine

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Cryptography, then, not only protects data from theft or alteration, but

can also be used for user authentication. There are, in general, three

types of cryptographic schemes typically used to accomplish these goals

Secret key cryptography (or symmetric)

Public-key cryptography (or asymmetric)

Hash functions,

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In this form single key is used for both encryption and decryption

The sender uses the key to encrypt the plaintext and sends the

ciphertext to the receiver. The receiver applies the same key to decrypt

the message and recover the plaintext

Because a single key is used for both functions, secret key

cryptography is also called symmetric encryption

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Secret key cryptography schemes are generally categorized as being

either stream ciphers or block ciphers.

Stream ciphers operate on a single bit (byte or computer word) at a

time and implement some form of feedback mechanism so that the

key is constantly changing.

A block cipher is so-called because the scheme encrypts one block

of data at a time using the same key on each block.

In general, the same plaintext block will always encrypt to the sameciphertext when using the same key in a block cipher whereas the

same plaintext will encrypt to different ciphertext in a stream cipher.

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Hash functions, also called message digests and one-way encryption,

are algorithms that, in some sense, use no key

A fixed-length hash value is computed based upon the plaintext that

makes it impossible for either the contents or length of the plaintext to berecovered.

Hash algorithms are typically used to provide a digital fingerprint of a

file's contents and are also commonly employed by many operating

systems to encrypt passwords and then, provide a measure of the

integrity of a file

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Combines all functions to form a secure transmission comprising digital signature and

digital envelope

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Nearly all modern network operating systems employ passwords at

the very least to protect and authenticate users accessing computer

and network resources

But passwords are not typically kept on a host or server in plaintext,but are generally encrypted using some sort of hash scheme

As the passwords are not saved in plaintext on computer systems

precisely,they cannot be easily compromised.

An even stronger authentication method uses the password to modifya shared secret between the client and server, but never allows the

password in any form to go across the network.

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PGP can be used to sign or encrypt e-mail messages with the mere

click of the mouse

Depending upon the version ofPGP, the software uses SHA or MD5

for calculating the message hash; CAST, Triple-DES, or IDEA forencryption; and RSA or DSS/Diffie-Hellman for key exchange and

digital signatures.

PGP is available as a plug-in for many e-mail clients, such as Claris

Emailer, Microsoft Outlook and Qualcomm Eudora

Pretty Good Privacy (PGP) is one of today's most widely used

public key cryptography programs, developed by Philip Zimmermann

in the early 1990s

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In typical applications workstation are attached to LAN. The user

can reach other hosts, workstations and servers in the same LAN

that are interconnected via bridges and routers.

Transmissions from station to station is visible on the LAN to allstation. Data is transmitted in the form of packets which contain

source/destination Ids, and other information.

On this basis, an eavesdropper can monitor and capture traffic

packets. Eavesdropper needs not be a local LAN user; it could be

anyone to whom the LAN offers a dial-up capacity.

Eavesdropping may also occur in any of the communication links

which provide connectivity to the system

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Link Encryption

Each vulnerable communication link is equipped on both end with an

encryption devices

End-to-End EncryptionData is encrypted only at the source node and decrypted at the destination

node

Problem

Data consists of packets have a header portion and content portion. we canencrypt the header. So the data is secure and the traffic pattern is not

Solution

Use a combination of above two approaches.

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