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Flashcards by Malachy Moran-Tun, updated more than 1 year ago
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| Question | Answer |
| What is Compression and its 2 Types? | > An algorithm which helps to reduce the size of files > Useful to reduce space taken up in secondary storage, or to make sending the file quicker over a network > Two types: lossy and lossless |
| What is the Difference between Lossy and Lossless Compression? | > Lossy - removes unnecessary detail; some data is permanently lost, but enough remains so the file is still useful > Lossless - none of the original data is lost; an algorithm is used to perfectly restore the original file. This is useful for text or executable files, where all the data is necessary > Lossy reduces the file size more than lossless |
| What is Run-Length Encoding? | > Form of lossless compression that replaces repeating sequences with more efficient representations > Each repeating string is replaced by a code, which represents the section that repeats, and the amount of times it is to be repeated > For example, AAABBCCCC becomes 3A2B4C > This is useful in images, as adjacent pixels are likely to be the same colour |
| What is Dictionary (En)coding? | > Useful for text files > Each word is replaced by a binary number, which represents the word > A dictionary stores which number represents which word > Both the dictionary and the string of binary numbers are stored > Sometimes, pre-existing dictionaries may be used to encode the text |
| What are the Advantages of Dictionary (En)coding? | > Takes less bits to store a small binary number than a long word > No data is lost (i.e., lossless compression) > Pre-existing dictionaries can be used, meaning the algorithm can quickly encode the data |
| What is Encryption? | > Process of scrambling data so that is cannot be read by third parties > Done so by using a specific algorithm > Only the intended recipient should know how to decode the data |
| What is a Key in Encryption? | > A pair of very large prime numbers, usually 256 or 1,024 bits long, that the encryption algorithm depends upon to encrypt / decrypt data > It would take an impractical amount of time to guess the key |
| Why is Encryption Important in Wireless Communication? | > Wireless information can be intercepted by anyone, unlike wired communication, which requires a physical connection > Wireless protocols, such as WPA2, encrypt all traffic to prevent this |
| What is Symmetric Encryption? | > The same key is used to encrypt and decrypt data > This encryption is usually done via a cypher algorithm > Both the encrypted data and private key is transferred |
| What is the Problem with Symmetric Encryption? | > Anyone with the key can decrypt the data > The key could be intercepted to decrypt the data |
| What is Asymmetric Encryption? | > Uses two keys: a public key and a private key, related to each other through mathematical operations > The public key is given to the sender by the recipient > This public key is one-way, i.e., it can only encrypt and not decrypt the data > The private key can decrypt the data previously encrypted by the public key. This must never be shared. |
| What is Hashing? | > Process of taking an input, performing some algorithm / calculation on the input, and outputting a value of fixed size > The output is known as a hash > Hashing algorithms are non-invertible, meaning you cannot reverse a hash and get back to the original data |
| How can Hashing be used to Store Passwords? | > The password is put through a hashing function, and stored as the encrypted password > Password attempts are entered, but only the same password will output the same output of the hashing function > No one can know the password just by looking in the database where it is stored |
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