Difference between revisions of "Encryption"

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{{Need_Expanding}}
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=TRC Video=
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<youtube>Fso4xTG2FMw</youtube>
  
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== Definitions ==
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https://www.youtube.com/watch?v=Fso4xTG2FMw
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=Definitions=
  
 
'''Plain text''' - The data in human readable form.
 
'''Plain text''' - The data in human readable form.
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'''Cipher text''' - The encrypted data which can only be understood if decrypted.
 
'''Cipher text''' - The encrypted data which can only be understood if decrypted.
  
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== Caesar Cipher ==
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=Encryption Methods=
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The creator was Julius Caesar.
 
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It is a substitution cipher which works by shifting letters by a number. The easiest way to look at a caesar cipher is to think of an inner and outer wheel, each wheel has the letters of the alphabet on its edge. When the letter A on both wheels are aligned the shift is 0 as in the image below:
 
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[[File:Caesar-shift-0.jpg]]
 
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The shift turns the inner wheel a specific number of spaces.  The image below shows a shift of 7:
 
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[[File:Caesar-shift-7.jpg]]
 
  
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===Issues with Caesar Cipher===
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[[Caesar / Substitution Cipher]]
  
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*There are only 25 possible keys, 26 makes the same output as the input so is just like a shift of 0. Any shift above 26, eg 45 will create an identical output as one of the shifts between 1 & 25.
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[[Vernam Cipher]]
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*This cipher only encrypts letters so the letter spacing pattern will be identical to the plain text. You can therefore select an encrypted block of text and know it has a meaning. With brute force you could discover the exact shift (ie one shift will make a recognisable word).
 
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*The key is constant throughout the text, so if you crack one word you crack the entire cipher text.
 
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*With sufficient cipher text you could count the frequency of every letter used. The most frequent is likely to be the character for 'e', you can then calculate the shift.
 

Latest revision as of 08:55, 23 August 2023

TRC Video

https://www.youtube.com/watch?v=Fso4xTG2FMw

Definitions

Plain text - The data in human readable form.

Cipher - An encryption method or algorithm.

Key - The data used to encrypt or decrypt the plain text.

Cipher text - The encrypted data which can only be understood if decrypted.

Encryption Methods

Caesar / Substitution Cipher

Vernam Cipher

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