Algorithm: A clear step-by-step set of instructions (a way of solving a problem).

Program: The code used to implement an algorithm.

Data Compression:

Data Compression: Sending or storing data into a smaller amount of bits

Lossy Compression:

• Inexact approximations for compressed content

• Used in image, video, and sound files

  • e.g. JPEG, MPEG, and MP3 files

• Can take less time than lossless, but lower quality

Lossless Compression:

• All data is conserved

• Redundant data is removed during compression and added back during decompression

• Used for files where data integrity is most important

• Uses Run-Length Encoding and Dictionary Encoding

Run-Length Encoding:

• XXXY
  YXXY becomes 3X 2Y 2X 1Y

• Uses binary

Dictionary Encoding:

• Assigning a value to sections of text so that the values are shorter than the original text

Raster Image Files:

• Each individual pixel has its own value

• If images are enlarged, more pixels of the same quality are used which makes the quality decrease

• e.g. JPEG, PNG, GIF

• JPEG compression algorithm removes a certain amount of colours that can’t be seen by humans according to the QF (Quality Factor) number

Vector Image Files:

• Vectors note lines and curves

• If images are enlarged, so are the lines and curves which retain the image quality

• e.g. SVG, EPG, AI, PDF

Data Encryption

Symmetric Encryption:

• 1 private key is used for both encryption and decryption

• Used for backing up hard drives

• Can be fairly insecure as if the key is gained, messages are easily read - interceptable key

• Send messages fairly quickly

• Keys have to be exchanged prior to using this encryption

Asymmetric Encryption:

• 1 public key used for encryption

• 1 private key used for decryption

• The same person creates both keys

• Used for sending messages, emails and files

• Having 2 keys makes this very secure

• Can take longer to encrypt and send

• You can ensure that only the intended sender will get the message

Authentication:

• Real-life implementation of asymmetric encryption

• The message gets encrypted by the sender’s private key.

• The message then gets encrypted by the receiver’s private key.

• The encrypted message is received.

• The message gets decrypted by the receiver’s private key.

• The message gets decrypted by the sender’s public key.

• Messages are decrypted in the opposite order of keys as they are encrypted.

• You can verify if it is sent or received by the intended person

Hashing:

• Turns text or files into a hash

• A hash is a hexadecimal

• Hashes cannot be turned back into the original text / file

• Can be used to transfer large amounts of data to check if it is compromised

• Hashes are usually smaller than the original data (with the exception of some passwords)

Passwords:

• Can be stored via plain text or hash

• Plain text is incredibly insecure as if the data is hacked, there is no encryption

• For authentication, the entered hash is checked if it matches the stored hash

• Duplicate hashes for different logins are set as different hashes

Collisions

• Occur if 2 different values have the same hash output from the hash function