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A2 1.3.1 - Compression, Encryption and Hashing

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run length encoding
a form of lossless compression where data is stored as a single data value and count instead of as the original run
dictionary encoding
a form of lossless compression where each element in the data stream is replaced by a reference to the lookup table (dictionary)
huffman coding
an optimised dictionary encoding method where the code to reference elements depends on the element's frequency
least frequently
In huffman coding, the ... occurring words are added to the binary tree first, building up to the most frequent
the transformation of data from one form to another to prevent unauthorised third parties being able to understand it
the original data or message
the encrypted data
the method or algorithm used to encrypt the plaintext
the secret information to lock or unlock the ciphertext
symmetric encryption
encryption that uses a single key where access to this key allows for both encryption and decryption
key exchange
required by symmetric encryption, thus creating security flaws as the key could easily be intercepted
asymmetric encryption
encryption that uses two separate keys to encrypt the data and one to decrypt it
public key
one of the keys used in asymmetric encryption that is made public by the recipient so that others can encrypt the data they send
private key
one of the keys used in asymmetric encryption that is only known by the recipient and can only be used to decrypt the data the recipient receives (encrypted by the public key)
digitally signed
an encrypted message can be ... to authenticate the user and thus prevent harm from malicious third parties
session key
this can be generated and exchanged between computers using asymmetric encryption, and then this key be used for the duration of communications by symmetric encryption
prime numbers
large ... are used to create the public and private keys (through multiplication), which is very difficult to factorise, meaning the keys are incredibly difficult to crack
when an algorithm is used to map data of an arbitrary size to a fixed size; it is one-way only (lossy)
password verification
hashing can be used for ... as any hackers cannot read them and the hash function can be applied to the user's input to verify it
corruption detection
hashing can also be used for rapid data access in a hash table and for error checking or ...
avalanche effect
the concept of hashing where the smallest change to the data will cause a distinct change in the hash, so that they appear uncorrelated
digital signature
the encrypted hash total of a message which is sent with it, so that the recipient can decrypt it, calculate the hash total and compare them to verify the sender
digital certificate
issued by official certificate authorities, which verifies the trustworthiness of a sender or website
when storing passwords, each entry should have a random ... generated, which is added to the password before it is hashed to prevent giving away information about the passwords