Cryptography Network Security Computer Science Essay


Network security is a complicated topic, historically merely tackled by well-trained and experient experts. However, as more and more people become “ wired ” , an increasing figure of people need to understand the rudimentss of security in a networked universe. This papers was written with the basic computing machine user and information systems director in head, explicating the constructs needed to read through the ballyhoo in the market place and understand hazards and how to cover with them.

Some history of networking is included, every bit good as an debut to TCP/IP and internetworking. We go on to see hazard direction, web menaces, firewalls, and more special-purpose secure networking devices.

This is non intended to be a “ often asked inquiries ” mention, nor is it a “ hands-on ” papers depicting how to carry through specific functionality.

It is hoped that the reader will hold a wider position on security in general, and better understand how to cut down and pull off hazard personally, at place, and in the workplace.

Cryptography and Network Security

Does security supply some really basic protections that we are naif to believe that we do n’t necessitate? During this clip when the Internet provides indispensable communicating between 10s of 1000000s of people and is being progressively used as a tool for commercialism, security becomes a enormously of import issue to cover with.

There are many facets to security and many applications,

Ranging from secure commercialism and payments to private

Communicationss and protecting watchwords. One indispensable facet for

Secure communications is that of cryptanalysis.

Cryptanalysis is the scientific discipline of composing in secret codification and is an ancient art. The first documented usage of cryptanalysis in composing day of the months back to circa 1900 B.C. when an Egyptian Scribe used non-standard hieroglyphs in an lettering.

In informations and telecommunications, cryptanalysis is necessary when pass oning over any untrusted medium, which includes merely about any web, peculiarly the Internet.

Within the context of any application-to-application communicating, there are some specific security demands, including:

Authentication: The procedure of turn outing one ‘s individuality. ( The primary signifiers of host-to-host hallmark on the Internet today are name-based or address-based, both of which are notoriously weak. )

Privacy/confidentiality: Ensuring that no 1 can read the message except the intended receiving system.

Integrity: Guaranting the receiving system that the standard message has non been altered in any manner from the original.

Non-repudiation: A mechanism to turn out that the transmitter truly sent this message. Cryptography, so, non merely protects informations from larceny or change, but can besides be used for user hallmark.

The three types of cryptanalytic algorithms that will be discussed are ( Figure 1 ) :

Secret Key Cryptography ( SKC ) : Uses a individual key for both encoding and decoding

Public Key Cryptography ( PKC ) : Uses one key for encoding and another for decoding

Hash Functions: Uses a mathematical transmutation to irreversibly “ encrypt ” information

1. Secret Key Cryptography

With secret key cryptanalysis, a individual key is used for both encoding and decoding.

As shown in Figure the transmitter uses the key ( or some set of regulations ) to code the field text and sends the cypher text to the receiving system. The receiving system applies the same key ( or regulation set ) to decode the message and retrieve the field text. Because a individual key is used for both maps, secret key cryptanalysis is besides called symmetric encoding.

With this signifier of cryptanalysis, it is obvious that the key must be known to both the transmitter and the receiving system ; that, in fact, is the secret. The biggest trouble with this attack, of class, is the distribution of the key.

Secret key cryptanalysis strategies are by and large categorized as being either watercourse cyphers or block cyphers.

Stream cyphers operate on a individual spot ( byte or computing machine word ) at a clip and implement some signifier of feedback mechanism so that the key is invariably altering. A block cypher is so- called because the strategy encrypts one block of informations at a clip utilizing the same key on each block. In general, the same field text block will ever code to the same cypher text when utilizing the same key in a block cypher whereas the same plaintext will code to different cypher text in a watercourse cypher.

2. Public cardinal cryptanalysis

Modern PKC was foremost described publically by Stanford University professor Martin Hellman and graduate pupil Whitfield Diffie in 1976. Their paper described a two-key crypto system in which two parties could prosecute in a secure communicating over a non-secure communications channel without holding to portion a secret key.

Generic PKC employs two keys that are mathematically

related although cognition of one key does non let person to

easy find the other key. One key is used to code the

plaintext and the other key is used to decode the cypher text. The

of import point here is that it does non count which key is applied

foremost, but that both keys are required for the procedure to work ( Figure

1B ) . Because a brace of keys are required, this attack is besides called

asymmetric cryptanalysis

3. Hash Functions

Hash maps, besides called message digests and one-way encoding, are algorithms that, in some sense, use no key ( Figure 1C ) . Alternatively, 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 be recovered. Hash algorithms are typically used to supply a digital fingerprint of a file ‘s contents frequently used to guarantee that the file has non been altered by an interloper or virus. Hash maps are besides normally employed by many runing systems to code watchwords. Hash maps, so, aid continue the unity of a file.


Secure usage of cryptanalysis requires trust. While secret cardinal cryptanalysis can guarantee message confidentiality and hash codifications can guarantee unity, none of this works without trust. In SKC, PKC solved the secret distribution job. There are a figure of trust theoretical accounts employed by assorted cryptanalytic strategies.

The web of trust employed by Pretty Good Privacy ( PGP ) users, who hold their ain set of sure public keys.

Kerberos, a secret key distribution strategy utilizing a sure 3rd party.

Certificates, which allow a set of sure 3rd parties to authenticate each other and, by deduction, each other ‘s users.

Each of these trust theoretical accounts differs in complexness, general pertinence, range, and scalability.

Types of authorization

Establish individuality: Associate, or bind, a public key to an person, organisation, corporate place, or other entity.

Assign authorization: Establish what actions the holder may or may non take based upon this certification.

Secure confidential information ( e.g. , coding the session ‘s symmetric key for informations confidentiality ) .

— — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — —

Todaies latest used cryptanalytic techniques:

Hash algorithms that are in common usage today include:

Message Digest ( MD ) algorithms

Secure Hash Algorithm ( SHA )

Reasonably Good Privacy ( PGP )

Reasonably Good Privacy ( PGP ) is one of today ‘s most widely used public cardinal cryptanalysis plans. PGP can be used to subscribe or code e-mail messages with mere chink of the mouse.

Depending upon the version of PGP, the package uses SHA or MD5 for ciphering the message hash ; CAST, Triple-DES, or IDEA for encoding ; and RSA or DSS/Diffie-Hellman for cardinal exchange and digital signatures. And much more techniques used.

Time is the lone true trial of good cryptanalysis ; any cryptanalytic strategy that stays in usage twelvemonth after twelvemonth is most likely a good 1. The strength of cryptanalysis prevarications in the pick ( and direction ) of the keys ; longer keys will defy attack better than shorter keys

Encrypt and decrypt messages utilizing any of the classical permutation cyphers discussed, both by manus and with the aid of plans.

understand the constructs of linguistic communication redundancy and unicity distance.

Different types of menaces to web:

Application back doors – Some plans have particular characteristics that allow for distant entree. Others contain bugs that provide a back door, or concealed entree, that provides some degree of control of the plan.

SMTP session commandeering – SMTP is the most common method of Sending electronic mail over the Internet. By deriving entree to a list of e- mail Addresses, a individual can direct unasked debris electronic mail ( Spam ) to 1000s of users. This is done rather frequently by airting the electronic mail through the SMTP waiter of an unsuspicious host, doing the existent transmitter of the Spam hard to follow.

Operating system bugs – Like applications, some operating systems Have back doors. Others provide distant entree with deficient security controls or have bugs that an experient hacker can take advantage of.

Denial of service – You have likely heard this phrase used in intelligence studies on the onslaughts on major Web sites. This type of onslaught is about Impossible to counter. What happens is that the hacker sends a petition to the waiter to link to it. When the waiter responds with an recognition and attempts to set up a session, it can non happen the system that made the petition. By deluging a waiter with these unanswerable session petitions, a hacker causes the waiter to decelerate to a crawl or finally clang.

E-mail bombs – An e-mail bomb is normally a personal onslaught. Person sends you the same e-mail 100s or 1000s of times until your e-mail system can non accept any more messages.

Macros – To simplify complicated processs, many applications allow you to make a book of bids that the application can run. This book is known as a macro. Hackers have taken advantage of this to make their ain macros that, depending on the application, can destruct your informations or crash your computing machine.

Viruss – Probably the most well-known menace is computing machine viruses. A virus is a little plan that can copy itself to other computing machines. This manner it can distribute rapidly from one system to the following. Viruss range from harmless messages to wipe outing all of your informations.

Spam – Typically harmless but ever annoyance, Spam is the electronic equivalent of debris mail. Spam can be unsafe though. Quite frequently it contains links to Web sites. Be careful of snaping on these because you may by chance accept a cooky that provides a back door to your computing machine.

Redirect bombs – Hackers can utilize ICMP to alter ( redirect ) the Path information takes by directing it to a different router. This is one of the ways that a denial of service onslaught is set up.

Network security can be done by assorted methods.

1. Virtual Private Network:

A practical private web ( VPN ) is a manner to utilize a public telecommunication substructure, such as the Internet, to supply distant offices or single users with unafraid entree to their organisation ‘s web. A practical private web can be contrasted with an expensive system of owned or leased lines that can merely be used by one organisation. The end of a VPN is to supply the organisation with the same capablenesss, but at a much lower cost

Execution of web security by VPN.

Measure 1. – The distant user dials into their local ISP and logs into the ISPaa‚¬a„?s web every bit usual.

Measure 2. – When connectivity to the corporate web is desired, the user initiates a tunnel petition to the finish Security waiter on the corporate web. The security waiter authenticates the user and creates the other terminal of tunnel.

Figure: a ) A leased line private web B ) A practical private web

Measure 3. – The user so sends informations through the tunnel which encrypted by the VPN package before being sent over the ISP connexion.

Measure 4. – The finish Security waiter receives the encrypted informations and decrypts. The Security waiter so forwards the decrypted informations packages onto the corporate web. Any information sent back to the Remote user is besides encrypted before being sent over the Internet.


A firewall provides a strong barrier between your private web and the Internet. You can put firewalls to curtail the figure of unfastened ports, what type of packages are passed through and which protocols are allowed through. You should already hold a good firewall in topographic point before you implement a VPN, but a firewall can besides be used to end the VPN Sessionss.

Fig2: A fire wall dwelling of two package filters and an application gateway

3.IPSec –

Internet Protocol Security Protocol ( IPSec ) provides

enhanced security characteristics such as better encoding algorithms and more comprehensive hallmark. IPSec has two encoding manners: tunnel and conveyance. Tunnel encrypts the heading and the warhead of each package while conveyance merely encrypts the warhead. Merely systems that are IPSec compliant can take advantage of this Protocol. Besides, all devices must utilize a common key and the firewalls of each web must hold really similar security policies set up. IPSec can code informations between assorted devices, such as:

Router to router

Firewall to router

Personal computer to router

Personal computer to server

A package firewall can be installed on the computing machine in your place that has an Internet connexion. This computing machine is considered a gateway because it provides the lone point of entree between your place web and the Internet.

4. AAA Server – AAA ( hallmark, mandate and accounting )

waiters are used for more unafraid entree in a remote-access VPN environment. When a petition to set up a session comes in from a dial up client, the Request is placeholders to the AAA waiter. AAA so checks the followers:

Who you are ( hallmark )

What you are allowed to make ( mandate )

What you really do ( accounting )

The accounting information is particularly utile for tracking client. Use for security auditing, charge or coverage intents.


The New Lexicon Webster ‘s Encyclopedic Dictionary of the English Language. New York: Lexicon.

Cryptography And Network Security — William Stallings

R.T. Morris, 1985. A Failing in the 4.2BSD Unix TCP/IP Software. Calculating Science Technical Report No. 117, AT & A ; T Bell Laboratories, Murray Hill, New Jersey.


S.M. Bellovin. Security Problems in the TCP/IP Protocol Suite. Computer Communication Review, Vol. 19, No. 2, pp. 32-48, April 1989.

Y. Rekhter, R. Moskowitz, D. Karrenberg, G. de Groot, E. Lear, “ Address Allocation for Private Internets. ” RFC 1918.

J.P. Holbrook, J.K. Reynolds. “ Site Security Handbook. ” RFC 1244.

M. Curtin, “ Snake Oil Warning Signs: Encoding Software to Avoid. ” USENET & lt ; sci.crypt & gt ; Frequently Asked Questions File.