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| − | {{Need_Expanding}}
| + | =TRC Video= |
| | + | <youtube>Fso4xTG2FMw</youtube> |
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| − | == Definitions == | + | https://www.youtube.com/watch?v=Fso4xTG2FMw |
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| | + | =Definitions= |
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| | '''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 == | + | =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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| − | *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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| − | *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.
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| − | ==Alternative Substitution Cipher==
| + | [[Caesar / Substitution Cipher]] |
| − | The caesar cipher is a very basic substitution cipher. A more secure method would be to generate a random alphabet (including a space) which could then be used with the standard alphabet to map from an existing character to the new character:
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| − | [[File:Subcipher.jpg]] | + | [[Vernam Cipher]] |
