Utilisateur
At a given time point in a sound, a measurement is taken
Sampling rate(no of bits) x sample resolution x length of the sound(seconds)
The process of reducing a file's size.
Lossy compression
Lossless compression
- Reduces file size
- Files are quicker to be transferred
Reduces file size by permanently removing data from the file.
JPEG
MP3
MPEG-1
MPEG-2
Reduces the size of the file however doesn't remove data from the file.
PNG
ZIP
GIF
- Store a lower number of colours
- Store a larger area of pixels as a single colour
Dictionary coding
Run-length encoding
Replaces recurring sequences with shorter unique codes
Useful: Large text documents with repeating data
Not Useful: text documents with no repeating data, takes up more space
Condenses identical data into single values with a count
In bitmap images. Where you have contiguous pixels of the same colour so you store the binary for one of the pixels and multiply it by the number of pixels with that colour
To make the original code impossible to crack without the key
Plain text - text that is reabdable by anyone
Cipher text - text that can only be read by someone with a decryption key
Where a single key is used to both encrypt and decrypt a message.
- Messages can be cracked by someone intercepting the key
- Messages can be crakced by someone duplicating the production of the key to get a copy
Where the key used to encrypt the message (public key) is different to the key needed to decrypt (private key) the message (key pair)
- The sender and recipient are sure no one else can read their message
- You're sure the message hasn't been modified
- You can be sure the message is authentic
The sender gives the recipient their public key. The recipient uses the public key to encrypt a message and send back to the sender. The sender then uses their private key to decrypt the message
Symmetric: On large files and databases
Asymmetric: Confidential data
Transforms a string into a fixed length value or a key that represents the input string
MDA
SHA-1
SHA-256
SHA-3
A data structure used to remove & insert key value pairs
Hashing is a one-way process, meaning you can't get the original value from the hashed value even if you have the hashing algorithm
In order to reduce the chance of a collision occurring
Where two different inputs produce the same hashed value
- Be calculated quickly
- Result in as little collisions as possible
- Use as little memory as possible
A process which searches for the next available empty space in a hash table and stores the item there.
Searching for an empty spot by checking the next slot sequentially
- It prevents certain items being stroed in their correct location
- Can cause clustering
Where many inputs have the same hashed value or similar hashed values causing large blocks of occupied slots, which increases search time (reduces efficiency)
2D hash tables, this can allow more than one item to be placed in the same index (chaining)
Overflow tables, a second table used to handle collisions when the first table is either full or items can't fit in their expected location