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Unit 3 Topic 1 - Coggle Diagram
Unit 3 Topic 1
Encryption
Caesar Cipher
All characters in a plaintext message are shifted by a positive or negative integer of character set identifier numbers / codes
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Vernam Cipher
The “one-time pass” (encryption / decryption key) is generated using a purely random physical event, such as radioactive decay, atmospheric noise, or the bubbles in a lava lamp. This is because computer generated sequences are never truly random.
The key generated must be equal to or longer in length than the message that is being encrypted. The key is given to the recipient by hand and destroyed after it is used.
The encrypted / decrypted message is created by applying the XOR algorithm onto the key and message in their binary forms.
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Compression
Lossy
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Methods
Image
Colour / Bit Depth Reduction, often undetectable to the human eye
Audio
Limiting frequencies to 20 - 20,000 Hz (average human hearing range), so sample rate reduction
Lossless
Example Formats
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Methods
Run-Length Encoding
Looking for consecutive patterns of repeating data, and specifying the number of times that it repeats rather than storing each iteration separately.
In images: storing pixel data in two-sectioned packets, where the first section determines the colour of the pixel(s) and the second section determines how many times the pixel appears consecutively
In audio: storing sample data in two-sectioned packets, where the first section determines the sound of the sample, and the second section determines how many times the sample appears consecutively
Dictionary Encoding
Looking for regularly occurring pieces of data in a file, assigning the data values in a dictionary, and replacing the data with their dictionary addresses instead. (Mostly used for text files.)
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