History Of Cryptography And Internet Security Computer Science Essay

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Internet security is the main part of computer study. The security which is straightly connected to the internet is known as "Internet security. The main purpose of internet security is to develop some regulations and evaluate against attacks over the internet. Different types of method are used to protect the transferring data.

I am going to explain about cryptography in this assignment. This piece of work has so many purposes in which I am defining fundamental cryptographic plan of action which has some conditions and idea behind it. I will explain the brief history of cryptography, types of cryptography, role of algorithm and some examples in this document.


The word cryptography is derived from the very old Greek word. It is completed by two components "kryptos" and "logos", kryptos means hidden and logos which means word. A very long time age it is used for army and diplomatic conversations. There are two separate technologies in the field of cryptology, one is "cryptography" and the second is "cryptanalysis". The seekers of cryptography are used the methods to ensure the safety and security of communications while the cryptanalyst tries to convert the original former's work by blocking his system. The development of cryptography has been similar by the development of cryptanalyst. Cryptanalyst is basically the "breaking" of codes and "cipher". Cryptography is very famous, important and one of the oldest fields of that study which is relating to the technology. We can find out at least 4,000 years previous records. Only 3 systems are use in remain hard enough to break to be of real value. One of them takes large space, another is very slow and the third one is serious weaknesses. (1)


The process in which we encrypt and decrypt the data is called "cryptography". We can store different amount of information or transmit it across the securable internet by using cryptography. Nobody can be read it except the deliberated recipient.

Cryptography is very useful now a day. It is needed for communication. Cryptography has one fundamental facet for secure communication.


The main purpose of cryptography is reversible or irreversible transformation. It is the mathematical manipulation of data for the purpose of writing in secret code. When we communicate over any untreated mediocre, which contain any type of network specially the internet. Some special type of securities are required when we communicate within the context, these securities are as follows:

'Authentication'. (The procedure which is proving the similarity.)

'Privacy/confidentiality' (We have to ensure that except the deliberated receiver nobody can read the message.)

'Integrity/unity' (to make sure that the receiver has received the same message from the original data.)

'Non-repudiation or non-refusal' (The process which proves that the sender has sent the message.) (2)


The process in which a 'plaintext' is transformed into 'cipher text' is called "encryption". A simple piece of data is called 'clear text' or 'plaintext'. It can be read and understood without and special measuring and translating. And the transformed piece of work is called 'cipher text'. The cipher text is not being readable. We can use the encrypted process in those places where we want to hide our data from anyone.

Clear text

Cipher text Encryption

Key 1


The reverse process of encryption is called "decryption". In encryption we use plaintext to create cipher text and in decryption we create cipher text from a plain text. One thing is common or same in both sides, the cipher text is same in the whole process.

Clear text

Cipher text Decryption

Key 2

Types of Cryptography:

There are three types of cryptography:

Symmetric Cryptography

Asymmetric Cryptography

Hash Cryptography

1: Symmetric Cryptography:

Any cryptography which is encrypted and decrypted by the using one single key is called "symmetric cryptography". This cryptography is one of the oldest and well-known techniques. This single secret is selected by the randomly, and this secret or private key is useable to change the data in specific manner. Both communicators have known about that secret key, they can change the whole process by using one single key.

Same key

Secret Key Secret Key



Cipher text

Data in Data out

Symmetric Encryption

Stream Cipher:

Symmetric or private key cryptography are mostly divided into "stream cipher" or "block cipher". In the block cipher the simple or plain text will be same, when it will encrypt to the same cipher text. The same key is used in the process. This process will be the reverse in the stream cipher. The plain test will be same but the cipher text will be different when it is encrypted form plain text.

Conventional Cryptography:

Private Key or symmetric cryptography is same like the "conventional cryptography". As I mentioned above, in both sides encryption and decryption only one key is used. The most convenient example of conventional cryptography is "The Data Encryption Standard" which is used in a wide range by Federal Government.

Same key

Secret Key Secret Key





Plain Text

Plain Text

Conventional Cryptography

Substitution cipher works same like as the conventional cryptography. We can say it is an exemplary sample of conventional cryptography. Substitution cipher is also transferred just a single byte of information. It is done by disturbing letters of the alphabet.

Conventional cryptography is beneficial one. It is very fast than other cryptography. It is useful for broadcasting of data protection which is very costly. (4)

2: Asymmetric Cryptography:

A process in which a set of two keys is used for encryption is known as 'asymmetric encryption'. The data is encrypted by the one key and the other key is used for decryption. One key is called public key, this key is very important because both parties know about it. If anyone wants to communicate with you, they can send you a message by using the public key. Second key is called private key, nobody knows about it except you so this key is kept in a secret. That person can decrypt the message who knows the secret key.

Different Key (Key pair)

Secret Key Public Key



Cipher Text

Data in Data out

Asymmetric Encryption

Any type of data is encrypted by the public key and the private key is used for decryption. Those messages which are encrypted by using the private key and the matching public key are used for the decryption. Only the matching public key can be decrypt that data.

Public Key:

Public key cryptography can also called single direction function. Modern public key cryptography (PKC) was first time invented by the professor Martin Hellman of Stanford University and graduate student Whitefield defined in 1976. They introduce two type of key in which two people can communicate by using one key. In public key cryptography, both parties have got the different type of information. Public key is very common to use in asymmetric cryptography. One thing is very interesting, it is that we can make one of the two keys widely available and give it to everybody. Those senders who want to send us a message which is encrypted; those senders use the public key to encrypt this message but we can only decrypt it with the secret key or private key. Just recipient knows about that key.

(Private Side) (Public Side)

Cipher Text

Plain Text



"Cipher Text"

"Plain Text"

Public Key

"Private Key"

"Cipher Text"

"Plain Text"



Cipher Text

Plain Text


The above diagram is showing the comparison between both private key and public key.

Public key cryptography is a fundamental technology which is used all over the world. Many of the applications are underneath the public key such as Transport Layer Security (TLS), PGP, and GPG.

Hash Functions:

The fourth type of cryptography is called hash functions. Any well defined function or mathematical procedure in which a large amount of data is converted into the variable sized small amount of data or datum. Hash function is also called single-track encryption and mostly known "message digest". A fingerprint of file's components and this type of fingerprint is called digital fingerprint, these functions are used in the hash function. In early stages, it is used to ensure that the files which are using, it can be changed by a trespasser or it can't be. A fixed length hash value is calculated depends upon the normal or simple text that makes it impossible for either the components of data or length of the plaintext to be recovered. Hash function is also use to encrypt the password of different types of operating systems. It gives a specific size of unimpaired condition of a data.

Sometime, it is very difficult to understand and some sources are sued that the two file cannot contain the identical hash value. It is mostly used to look special items in the large amount of data to very fast, for example searching some items in a database, finding similar records in a large file etc.

"Cipher Text"

"Plain Text" "Hash Function"

(Hash function (one way cryptography). There is no key used in this process. It is not being able to recuperate from the cipher text.) (3)


A set of special type of steps and a formula which can be used for solving the problems called algorithms. These set of rules must have clear starting and ending points. It can be expressed in any language. Algorithm usually used in the mathematics and computer science for solve the recurrent problems.

Cryptography and algorithm are relatively same. Both are used for same purpose and they have same procedure. There are two types of algorithms:

Symmetric key algorithm

Asymmetric key algorithm

Symmetric and asymmetric algorithms are same like the cryptographic system.

Symmetric algorithms:

Same key is used for encryption and decryption process in the symmetric algorithm. There is no requirement for initial securing replacement. Blowfish, serpent, IDEA, triple DES are some popular example of symmetric or private key algorithms.

'Asymmetric key algorithms':

Asymmetric key algorithms have two different types of key. It is same as the asymmetric cryptography. The decryption key is different from the encryption and it cannot be extracted from the encryption key. Asymmetric key algorithms are not fast and it is not use to encrypt a large amount of data. But symmetric key algorithms are very fast and secure than others.

Symmetric key algorithms are more famous and useful than asymmetric key algorithms.

Data Encrypted with Symmetric Key

Y decrypted the data

X is sending the data

Z is a hacker

Trust Models:

If we want to use secure cryptographic system then trust is very significant requirement for this. Secret key cryptography and hash codes are trustable, except these two, the remaining works are without trust.

Different types of cryptographic schemes have a different number of trust models.

Pretty Good Privacy (PGP) users used to increase the security of e-mail communications. The users of (PGP) hold their own a set of trusted public key. It is a web trust model. It is invented by the Philip Zimmermann in 1991.












One more trust model is known as Kerberos. In which a treated third party is used a private key allotment scheme.

Kerberos client

AS to contain TGS and


Key distribution center to obtaining the AS and


2..Kerberos client

TGS to obtain ASK and

Session key


Application Server

3 AS application send to

Server key to initiates connection.


Client Server running kerberobs and application client software.

Certificates, give permission to other parties which are trusted, to verify each other

All trusted models are different from each other in complexity, scope and ability to measure.

Uses of Cryptography:

The process of 'cryptography' can be used in different types of software. It is mostly used in ATM cards, computer password, and electronic commerce. Cryptography is used in all of them. (6)


Cryptography is very important part of the security. It is more securable product when it is used in the international electronic activities. This document has briefly delineated that how cryptography works. Cryptography is a most interesting field. A lot of work is done in secret. Data can be secure by using this technique. Cryptography algorithm is a very famous and good organized algorithm because it is trustable process. I hope that we have acquired a well understanding of the basics of the cryptography.