1.3.1 compression, encryption etc

• compression

  dictionary coding

  Benefits of dictionary coding

  -it takes less bits to store a 2 digit binary number than we can a 10 letter word(takes up less memory to store)

  the code is loseless(no data is lost)

  -the encoder may not always build its own dictionary. A pre-existing dictionary may be used to encode the text
• compression

  dictionary coding

  how does it work

  1)the coder scans through a body of text

  2)each word is replaced with a binary number of the word in a dictionary

  3)when it finds a word not in the dictionary, it will add it and give it a binary number

  4)the word in the actual text is replaced with the binary number
• compression

  dictionary coding

  what is it

  this is used to store text in a loseless format
• compression

  In Images

  -image compression algorithms often group these pixel together, and give them an average color

  what does Run Length Encoding(RLE) do

  this alogrithm can be run on the new images, this technique then becomes lossy
• compression

  lossless compression

  what does it cause file size to do

  to reduce moderately
• compression

  Run-Length-Encoding (RLE)

  what does this mean

  this is a form of lossless compression that replaces repeating sequences of 0's and 1's with more efficient representations
• compression

  type of compression

  what is lossless compression

  none of the original data is lost
• compression

  types of compression

  is data lost permanetly?

  some data is permanetly lost but enough remains so that file can be useful and there is barely any difference
• compression

  types of compression

  there are 2 name them

  lossless compression

  lossy compression
• compression

  types of compression

  what is lossy compression

  an algorithm is applied to remove unneccessary detail from the original file
• compression

  what is it

  compression helps to reduce the size of these(secondary storage) files so that we can store more data
• encryption

  Keys(shared secrets)

  what does this mean

  made up of a pair of large prime numbers example: 256 or 1024 bit long
• Encryption

  symmetric and asymmetric encryption

  Asymmetric encryption( or public key)

  what does it use

  used both public and private key
• Encryption

  symmetric and asymmetric encryption

  Asymmetric encryption( or public key)

  what does public key mean

  given to a person who you wish to send your encrypted data
• Encryption

  symmetric and asymmetric encryption

  public and private key

  both are related through what?

  mathematical operations

  note: the private key you set can not be figured out from the public key
• Encryption

  symmetric and asymmetric encryption

  Symmetric encryption( or private key)

  how does symmertric encryption work


  1)this cypher text and private key are then transferred to anohter location or person

  2)the key is then used to decrypt text back into plain text security

  3) using a single key to encrypt and decrypt text proposes a massive flaws in security, as anyone with the key can decrypt the cypher
• Encryption

  symmetric and asymmetric encryption

  Symmetric encryption( or private key)

  what does private key mean

  is used to convert plain text into cypher text
• Encryption

  symmetric and asymmetric encryption

  what can the private key do

  is used to decrypt the data and only you have this key
• Encryption

  symmetric and asymmetric encryption

  what can the public key do

  can encrypt and decrypt data
• Encryption

  what does this mean

  is the process of scrambling data according to a specific algorithm so that it cannot be read by third parties
• Hashing

  is secure but why?

  because cannot reverse to get back to original data
• Hashing

  the hash function has no what?

  no inverce
• Hashing

  the uses of Hashes

  -password

  -digital signture- the hash output value can be encrypted with a private key and sent to someone else and they use the matching public key to decrypt
• Hashing

  what does this mean

  is the process of taking an input, performing some form of calculation on the input that outputs a value of fixed size (output is known as hash)