Compression, Encryption and Hashing Flashcards
How does dictionary based compression work?
Each unique word is recorded in a dictionary and assigned a number value. The file is then compressed by using that dictionary to replace the text with the relevant numbers. When the compressed file is sent the dictionary is sent with it.
How does symmetric encryption work?
The same key is used to decrypt and encrypt the data. This means the key has to be sent to the same place as the data, which makes it easy to intercept.
How does Asymmetric encryption work?
Everybody has two keys, a public key and a private key. A public key can be used to encrypt the data, but the private key must decrypt it, and vice versa. When data is being sent the sender encrypts the data with the recipient’s public key, so that they can then decrypt it with their private key.
How does a digital signature work?
By encrypting a message with your private key, the person you are sending it to knows that it must have come from you as the message can only by decrypted with your public key.
What is a digital certificate?
Issued by official certificate authorities and verifies the trustworthiness of a message sender of a website.
What is lossy compression?
Non-essential information is removed from the file, so that the file is still useable but much smaller in size. For example for reducing the color depth for the pixels in a JPEG.
What kind of files should lossy compression be used on?
Files that can still be used without the complete information, for example audio, video and image files.
What is lossless compression?
The original file size is reduced but all of the information is retained. This is done by recording patterns in the data.
What kind of files should lossless compression be used on?
Files where the file can only be used if all the information if retained, for example text files and executable files.
What is RLE?
Run Length Encoding. A method for compressing images. Records the colour value of a pixel and the number of times it repeats.
What is the original data before encryption known as?
plaintext
What is the data after it has been encrypted known as?
ciphertext
What is hashing?
Taking a string of data and encrypting it so that you can not get the original data back.
What is hashing used for? (3 things)
Storing passwords
Hash tables
Compare if two files are the same
