Reducing the size of a file so that it can be stored using less memory or transmitted using less bandwidth.
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Lossy Compression
Compression by removal of non-essential data from a file, such as reducing the number of pixels in an image or removing sound outside the range of human hearing. Can result in large reduction of file size, but also reduce the quality of the file.
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Lossless Compression
Compression of a file with no data loss, allowing the file to be fully recreated from the compressed version with no quality reduction. For example, run-length encoding or dictionary coding.
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Run-Length Encoding
A method of lossless compression in which a repeated item of data (such as a character) is stored once, alongside the number of times it is repeated, instead of being stored multiple times consecutively.
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Dictionary Coding
A method of lossless compression in which a frequently used pattern of data is stored in a dictionary, and then represented in the main body of the file as a single symbol or token.
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Encryption
The alteration of a file for storage or transmission so that it cannot be read or understood by people who do not have the means to decode it.
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Symmetric Encryption
Encryption in which a file is decrypted using the same key as was used to encrypt it initially.
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Asymmetric Encryption
Encryption in which a file is encrypted using a public key, but decrypted using a private key available only to the intended recipient of the file.
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Caesar Cipher
An encryption method in which every character in a file is offset by a consistent factor (e.g 'abcd' offset by 3 to 'defg'). Spaces are also sometimes removed to mask word length.
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Verman Cipher (AKA 'One-Time Pad')
Considered the only truly unbreakable encryption. Each character in a file is offset by a different amount, dictated by a single-use key that is generated by a truly random natural phenomenon and transferred by hand to prevent it from being stolen.
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Hashing
A similar concept to encryption, but the conversion of the input data into a hashed form (using a hash function) is irreversible, making it impossible to retrieve the original data. Often used for the storage of PINs or passwords.
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Other cards in this set
Card 2
Front
Compression by removal of non-essential data from a file, such as reducing the number of pixels in an image or removing sound outside the range of human hearing. Can result in large reduction of file size, but also reduce the quality of the file.
Back
Lossy Compression
Card 3
Front
Compression of a file with no data loss, allowing the file to be fully recreated from the compressed version with no quality reduction. For example, run-length encoding or dictionary coding.
Back
Card 4
Front
A method of lossless compression in which a repeated item of data (such as a character) is stored once, alongside the number of times it is repeated, instead of being stored multiple times consecutively.
Back
Card 5
Front
A method of lossless compression in which a frequently used pattern of data is stored in a dictionary, and then represented in the main body of the file as a single symbol or token.
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