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'''Cryptography''' (from the Greek word “hidden, secret” and “I write”) [1]  is the practice and study of hiding information. Until recently, cryptography only referred to [[encryption]], which is the process of converting ordinary information into gibberish only known to the person who did the encryption while [[decryption]] is the opposite, meaning to move the gibberish into known language once again. Nowadays, cryptography has expanded onto a whole mass thanks to the evolution of technology and time. Cryptography is unique in that it branches towards [[mathematics]] and [[computer science]] while being closely affiliated with [[information theory]], [[computer security]] and [[engineering]]. In regards to its connections, cryptography was originally concerned with [[linguistic patterns]], which is making use of communications and manipulating them in whatever way possible. Since then, mathematics has been the chief focus with aspects of [[information theory]], [[computational complexity]], [[statistics]], and [[number theory]]. However, engineering also plays a part in determining other branches of cryptography in that it deals with active, intelligent and malevolent opposition while other engineering aspects only deal with neutral natural forces. Also, cryptography may relate to [[physics]] in that research is being done to see the similarities between cryptographic problems and [[quantum physics]] <sup>[[#1]]</sup> <sup>[[#2]]</sup> <sup>[[#3]]</sup> <sup>[[#8]]</sup>

== History ==
The first encryption case occurred in ancient [[Egypt]] as a series of disordered [[hieroglyphics]]. This method was very simple, using a method called [[simple substitution. The original message i.e. [[plaintext]], was encoded using a [[substitution cipher]] (a mode of encryption). Each letter in the text was basically replaced by another letter in the alphabet, resulting in the encoded message, or [[cipher text]].

As an example, the message, 

“Hello Johnny”

Could be encrypted as 

“Ifmmp Kmiooz”

One thing to keep in mind is that the letter encrypted has to be followed by the next letter in the alphabet so “e” has to follow up with “f,” so as to maintain some sort of order.

This cipher is known as [[Caesar Cipher]] as [[Caesar]] is reported to have used it when he commanded his generals.

Over time, however, people began to set up pre-determined word lengths as to make the substitution cipher harder to crack, so for example…

“Hello Johnny” 

Could now be encrypted as

“if mmpk miooz”

The main classical type is; however, [[transposition ciphers]], a process that just rearranges the letters so 

“hi John” becomes “ih ojnh”

Encryption attempts to ensure secrecy in communications, especially with spies, military leaders and diplomats. However, encryption does not necessarily protect the information from harm as it can reveal statistical information about the plaintext, which can be used to crack it. In the 9th century, [[Al-Kindi]] managed to discover [[frequency analysis]] – “An analysis of sound to determine the character of the sound by determining the amount of sounds at various frequencies that make up the overall sound spectrum. For example, higher frequency sound or pitch vs. low frequency.” [7] Eventually, all ciphers were rendered useless after this method and it was not until the invention of the [[Enigma]] machine by the [[Germans]] from [[1920s]] to [[WWII]] that cryptography resurfaced itself.  Recently, because of the invention of computers, cryptographs have been more difficult to crack and are several times harder to crack than before, making cryptanalysis – the cracking of cryptographs that much harder to do. As the tradition of increasingly powerful computers continue, brute force attacks – strength of greater processing capabilities of computers, on cryptography intensifies and is bordering a dangerous line of when will information be safe? <sup>[[#4]]</sup> <sup>[[#5]]</sup> <sup>[[#8]]</sup>

== Modern day study of cryptography == 

Cryptography and be divided into 5 different studies
* 

==== Symmetric-key cryptography ====

'''Symmetric-key Cryptography:''' This refers to the sender and receiver receiving the same key – which is the basis of control behind the algorithm for the cipher. The two main topics related to this type of crack are block ciphers – a cipher that inputs information, while using the block as a middleman and outputs the same information in an encrypted form and steam ciphers – which is an advanced form of block cipher in that it does the same thing but also does it faster and use lower capacity to perform it. With the added speed comes added risk however and steam cipher is the more risky one to use.

[[Image:Ofb encryption.png]]<sup>[[#9]]</sup>

==== Public-key cryptography ====

'''Public-Key Cryptography:''' This form of cryptography acts in a different way in which the key used to encrypt it is different from the key used to decrypt it. A public key, one known to the public is known while a private key, the secret key, is unknown. The public key may be used to encrypt it but only the public key can be used to decrypt it.

[[Image:Public-key cryptography image.png]] <sup>[[#10]]</sup>

==== Cryptanalysis ====

'''Cryptoanalysis:''' This is the study of obtaining the meaning of encrypted information, without access to the secret information on how to crack it. This is basically the major form of cracking the code, which involves finding the secret key

[[Image:FIALKA-rotors-in-machine.jpg|thumb]] <sup>[[#11]]</sup>

==== Cryptographic primitives ====

'''Cryptoanalysis:''' This is the study of obtaining the meaning of encrypted information, without access to the secret information on how to crack it. This is basically the major form of cracking the code, which involves finding the secret key

[[Image:Cryptographic Primitives image.gif]] <sup>[[#11]]</sup>

==== Cryptosystems ====

'''Cryptographic Primitives:''' This term is used to describe the process of transforming algorithms with basic cryptographic properties and their associates to other cryptographic problems. This is mainly used to build computer security systems and to counter the threats of cryptographic attacks.

[[Image:Cryptographic systems image.gif]] <sup>[[#12]]</sup>

== Advantages and disadvantages ==

Just like any other program, cryptographic has been able to provide good results and bad consequences.

Advantages:
* Added protection for uses such as [[ATM]] cards, [[internet]] [[passwords]] and buying stuff online
* Automated security programs for electronic systems
* As cryptographic ways improve, so do computers and so do consumer lives with it
* Puzzles like [[Sudoku]] and [[crosswords]]
* Constantly improving new ways and technologies to fight negative cryptography

Disadvantages:
* Widespread hackings
* [[Internet spam]]
* Malicious [[viruses]]
* [[Keyloggers]] and other programs that try to steal valuable information
* Bombs and other physical devices that threaten society
* Secret locations that may be encrypted since its secrecy is paramount to the success of terrorist attacks

<sup>[[#6]]</sup> <sup>[[#7]]</sup> <sup>[[#8]]</sup>

== Controversy ==

Just like any other topic, there has been a load of controversy surrounding cryptographic.

Matters like [[Prohibition]], [[Export Controls]], [[NSA]] involvement and [[Digital Rights Management]] has been involved.

All of these represent legal issues on whether cryptography is legal or not to use freely. Because of its look into privacy, it may even be referred to as a treasonous offense. 

<sup>[[#8]]</sup>

== Relationship to computer science ==

Computer science is the study of anything to do with computational devices and its uses. Cryptography may not have been related to computers in its early days but because of the tremendous dependence on computers nowadays, widespread programs have been created just to attack or defend a computer from hacks. Because of these very recent developments, computer science disciplines are widely associated with cryptography in ways that are beyond anything that was related to cryptography before. Because of the huge customer base with computers, almost anyone nowadays can be tracked through computers and so if computers are compromised, dangerous actions can happen and so, the relation of the two topics are very close.

== Relationship to CSC104H ==

Cryptography relates to some topics associated in CSC104H; in particular, programming, security and the internet. Because of cryptography’s wide usage in computers in the form of Trojans, keyloggers and spam, computers are in danger of becoming increasingly attacked and so all three forms play a part in the protection or degradation of the computer.

== See also ==
* [[Cryptography]]
* [[Topics in cryptography]]
* [[List of cryptographers]]
* [[Books on cryptography]]
* [[List of important publications in computer science#Cryptography]]
* [[List of open problems in computer science#Cryptography]]
* [[Cryptography Classification]]

== References ==
1)"Cryptology (definition)". Merriam-Webster's Collegiate Dictionary (11th edition). Merriam-Webster. Retrieved on 2008-12-03

2)Oded Goldreich, Foundations of Cryptography, Volume 1: Basic Tools, Cambridge University Press, 2001, {{ISBN|0-521-79172-3}} Retrieved on 2008-12-03

3)Friedrich Ludwig Bauer, Decrypted secrets [electronic resource] : methods and maxims of cryptology, Springer, 2007, Retrieved on 2008-12-03

4)Bill Unruh, Cryptography, University of British Columbia Physics, 1998, Retrieved 2008-12-03
http://axion.physics.ubc.ca/crypt.html  

5)Cryptography Introduction and guide, Cryptography World, 2004-2005, Retrieved 2008-12-03
http://www.cryptographyworld.com/ 

6)Cryptography, Trinity College Department of Computer Science, 2006-01-18, Retrieved 2008-12-03 http://starbase.trincoll.edu/~crypto/ 

7)Frequency Analysis (definition). Sound Seal. Retrieved 2008-12-03
www.soundseal.com/glossary.shtml

8)Cryptography, Wikipedia, 2008-11-18, Retrieved 2008-12-03
http://en.wikipedia.org/wiki/Cryptography#History_of_cryptography_and_cryptanalysis 

9)http://www.cs.bham.ac.uk/~mdr/teaching/modules/security/lectures/symmetric-docs/Ofb_encryption.png (Symmetric-key cryptography image)

10)http://upload.wikimedia.org/wikipedia/commons/thumb/f/f9/Public_key_encryption.svg/525px-Public_key_encryption.svg.png (Public-key cryptography image)

11)http://upload.wikimedia.org/wikipedia/en/0/05/FIALKA-rotors-in-machine.jpg (Cryptanalysis image)

12)http://www.codeproject.com/KB/vista-security/CryptographyNextGenDemo/cng1.gif (Cryptographic Primitives image)

13)http://jya.com/t851.gif (Cryptographic systems image)

== External links ==
* [http://netsecurity.about.com/cs/encryptionbooks/gr/aaprmalcrypto.htm Book Review: Malicious Cryptography]
* [http://www.ssh.com/support/cryptography/introduction/ Introduction to Cryptography]
* [http://research.microsoft.com/crypto/ Microsoft Cryptography]

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[[:Category:Number theory]]
[[:Category:Applied mathematics]]
[[:Category:Formal sciences]]
[[:Category:Cryptography]]
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[[:Category:Mathematical science occupations]]
[[:Category:Military communications]]
[[:Category:Security]]
[[:Category:Banking technology]]

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