Unit 4 - Exchanging data Flashcards
What does reducing data requirements ensure?
- Data is sent quicker
- Less bandwidth is used as transfer limits apply
- Audio and video buffering occurs less
- Less storage is required
What are the two types of compression?
Lossless: patterns in the data are spotted and summarised in a shorter format without any information being removed
lossy: non-essential data is permanently removed
What is Run Length Encoding? (RLE)
Summarised consecutive patterns of the same data
What is dictionary compression?
Spots regularly occurring data and stores it separately in a dictionary
What is encryption?
A way of making sure that data can not be understood if you don’t possess the means to decrypt it
Plaintext of a message sent is encrypted using cipher algorithm and keyed into equivalent ciphertext. When sent back, the cyphertext is decrypted back to plaintext using the same or different key
What are the 2 types of encryption?
Caesar cypher: Letters of the alphabet are shifted by a consistent amount. Most basic and insecure
Vernam cypher: proven to be unbreakable.
The key must be:
a truly random sequence greater or equal in length than the
plaintext and only ever used once
Shared with the recipient by hand, independently of the
message and destroyed immediately after use
What is brute force attack?
Attempts to apply every possible key to decrypt cyphertext until one works
spaces are often removed to mask the word lengths
What is the one-time-pad?
A system where a randomly generated private key is used only once to encrypt a message, then decrypted by the receiver using a matching one-time pad and key
The one-time pad must be truly
random, generated from a physical
and unpredictable phenomenon
Algorithm security
Ciphers are based on computational security:
- The keys are determined using a computer algorithm
- A key derived from an algorthm can also be unpicked
- Given enough ciphertext, computer power and time,any key except the one time pad can be determined and the message cracked
What is symmetrical encryption?
Also known as private key encryption
- the same key is used to encrypt and decrypt data
- This means the key must also be transferred to the recipient
What security problems does this create?
The key can be intercepted as easily as the ciphertext message
- for this reason asymetrical encryption may be used instead
What is asymetrical encryption?
Uses two seperate but related keys
- One key known as the public key is made pubic so those who wish to send data can use this key to encrypt it
- The public key can not decyrpt the data
- A private key only known to you is used to decrypt the data
What is hashing and what is it used for?
- A hashing function provides a mapping between an arbitary lenght input and a usually fixed length or smaller output
- It one-way YOU CANNOT GO BACK TO THE ORIGINAL
- A useful way of storing encrypted PIN’s and passwords so they cannot be read by a hacker
What is the simplest kind of database?
A flat file containing information about a single entity
What is an entity?
A category of object, person, event or thing of interest about which data needs to be recorded
