Flashcards What is compression used for?

Compression, encryption and hashing

Teach Computer Science
A-level

Flashcards

What is compression used for?

To reduce the size of the files and reduce the download time of an image, audio and video from the Internet.

What are the two types of compression?

Lossless compression and lossy compression.

What is lossless compression?

When the file is compressed, the quality of the image remains the same and the file can be reconstructed to its original form.

What is lossy compression?

When a file is compressed, the unnecessary bits of information are removed permanently.

What are the file formats for images?

What are the file formats for images?

PNG, JPEG and GIF

Which file format is used to store animated graphics?

GIF

What is an MPEG?

MPEG (Moving Pictures Experts Group) is a standard to encode audio-video files that uses lossy compression technique.

What is the file format for DVD movies?

MPEG

How is a video created?

How is a video created?

By playing a series of images at high speed.

What attributes of a video file are affected due to compression?

Compression reduces the resolution, dimensions and bit rate.

What are artefacts?

Compressing a video file may also lead to poor quality and random coloured blocks on the screen. These blocks are called artefacts.

List a few lossy video file formats.
MP4 and MOV

What are codecs?

What are codecs?

Codecs are programs that encode or decode an audio, image or video file.

What are compression codecs?

Codecs are programs that encode or decode an audio, image or video file. Compression codecs reduce the size of a file without affecting its quality.

What is run-length encoding?

Run-length encoding (RLE) is a compression algorithm that converts the consecutive similar values into a code.

True or False: Run-length encoding is a lossy compression technique.
False. Run-length encoding is a lossless compression technique.

What is MP3?

What is MP3?

A file format used for audio compression. This is a lossy compression technique.

Name an uncompressed audio file format.
WAV
Name a few uncompressed image file formats.
TIFF (.tif) and BMP (.bmp)
What data structure is used in Huffman coding?
Binary tree

True or False: In Huffman coding, the most frequently appearing letters are represented with fewer number of bits.

True or False: In Huffman coding, the most frequently appearing letters are represented with fewer number of bits.

True

Give an example of a substitution algorithm.
Caesar cipher
Give an example for an encryption algorithm that uses a one-type pad.
Vernam cypher
In Vernam cypher, what operation takes place between ASCII codes and one-time pad?
XOR operation

Why is Caesar cypher not secure enough for wireless networks?

Why is Caesar cypher not secure enough for wireless networks?

Because it can be easily cracked by unintended users.

What is a public key?

Keys that are available to all users and are used to encrypt messages.

What is a private key?

Keys that are only available to the intended recipient and are used to decrypt messages.

Where can a sender find public keys?
Senders can find public keys in a directory.

What is hashing function?

What is hashing function?

A hashing function maps input of arbitrary length to a fixed-length or smaller output.

What is a digital certificate?
An electronic document that confirms the ownership of public keys.
What is a digital signature?
An electronic signature that authenticates documents and websites.
What is hash total?
A mathematical value calculated by applying hash function to original messages.