← Dashboard 1.3.1 Compression, encryption and hashing A-Level Computer Science
Learning Objectives Notes Flashcards Quiz Exam Questions

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Term: Define compression.

Definition:

is the of file size to allow for more efficient data transfer and storage.
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Term: Define lossy compression.

Definition:

is a method of file size by permanently removing some data from the file, which cannot be recovered.
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Term: Define lossless compression.

Definition:

is a method of file size without losing any original data, so the file can be perfectly restored.
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Term: Why is compression important in data transfer over the Internet?

Definition:

is because it file size which allows for faster transmission and less bandwidth consumption.
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Term: There are two main types of compression: _________ and _________.

Definition:

There are types of compression: lossy and lossless.
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Term: True or False? Lossless compression discards some data to reduce file size.

Definition:

False. keeps all original data and does not discard anything.
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Term: Lossy compression is suitable for _________ streaming, but not suitable for _________ storage.

Definition:

is suitable for media streaming, but not suitable for archival storage.
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Term: Which type of compression should be recommended when data integrity is essential, and why?

Definition:

Lossless should be because it maintains original without any loss, ensuring data integrity.
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Term: Define run length encoding (RLE).

Definition:

(RLE) is a data compression method that replaces consecutive identical elements with a single value and a count.
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Term: In run length encoding, a sequence like AAAABBBCCDAA is compressed to _________.

Definition:

In encoding, a sequence like AAAABBBCCDAA is compressed to 4A3B2C1D2A.
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Term: True or False? Run length encoding is most effective when data has long runs of repeated elements.

Definition:

. encoding works best when there are long sequences of repeated values, as it can significantly reduce the amount of data stored.
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Term: What does the run length encoded sequence 3C3M4C decompress to?

Definition:

The decompresses to CCCMMMCCCC.
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Term: Define dictionary coding.

Definition:

coding is a data that replaces recurring sequences with shorter, unique codes stored in a dictionary.
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Term: Dictionary coding is effective for both _________ and _________ data.

Definition:

is effective for both text and binary data.
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Term: What is the main advantage of using dictionary coding over run length encoding?

Definition:

is more and can compress a wider range of data types, as it replaces recurring sequences with unique codes, not just repeated elements.
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Term: Compress the sequence CCCCOLLLCCCCCMOCCCCC using run length encoding.

Definition:

The is 4C1O3L5C1M1O5C.
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Term: Define encryption.

Definition:

is the of readable data into an unreadable format to secure it from unauthorised access.
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Term: What is the primary aim of encryption?

Definition:

The of encryption is to secure data from unauthorised access.
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Term: Symmetric encryption uses the _________ key for both encryption and decryption.

Definition:

uses the same key for both encryption and decryption.
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Term: What is the main disadvantage of symmetric encryption?

Definition:

The of encryption is the challenge of securely sharing the key; if someone intercepts the key, they can decrypt all messages transmitted.
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Term: Asymmetric encryption uses a _________ key for encryption and a _________ key for decryption.

Definition:

uses a public key for encryption and a private key for decryption.
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Term: True or False? Asymmetric encryption is generally faster than symmetric encryption.

Definition:

False. is typically slower than encryption, and is usually used for smaller, more secure data transfers.
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Term: Give one example of when symmetric encryption is most suitable.

Definition:

is most for encrypting large files or databases, such as when backing up data within a secure system.
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Term: Why has modern encryption become a fundamental part of online communication?

Definition:

is essential for protecting private data during communication, defending against cyber-attacks and data breaches, and enabling secure transactions such as online banking and shopping.
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Term: Define hashing.

Definition:

is a method to any data into a string of characters, known as a hash value, using a hash function.
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Term: What is a hash value?

Definition:

A value is the output string produced by a hashing algorithm from any input data. called a hash digest.
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Term: A good hash function provides _________ to data changes, producing very different outputs even for small changes in input.

Definition:

A provides sensitivity to data changes, producing very different outputs even for small changes in input.
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Term: True or False? Hashing algorithms like SHA-256 always produce the same output for the same input.

Definition:

. is consistent; the same input will produce the same hash value with the same algorithm.
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Term: Define collision in the context of hash tables

Definition:

A is when two inputs produce the same value, compromising hash function security.
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Term: Explain the main difference between encryption and hashing.

Definition:

is , data to be decrypted, while hashing is a one-way process and cannot be reversed to the original data.
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Term: Hashing is commonly used for _________ storage to increase security and prevent exposure of raw text.

Definition:

is used for password to increase security and prevent exposure of raw text.
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Term: Why is hashing considered efficient for data retrieval in databases?

Definition:

is for retrieval because hash values have a fixed length, making comparisons faster and allowing uniform distribution across hash tables.
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