Define the following security terms.

a) digital signature
b) hash function
c) symmetric key encryption
d) digital certificate
e) Denial of Service attack
f) worm
g) message digest
h) collision
i) triple DES
j) session keys

a) A digital signature, the electronic equivalent of a written signature, authenticates the sender's identity. To create a
digital signature, the sender runs the original plaintext message through a hash function to get a hash value for the message
(also known as a message digest). The sender then uses a unique private-key to encrypt the message digest. This creates a
digital signature because the keys are unique and only the owner of that specific key could have encrypted the message.
b) A hash function is a mathematical formula. It could be as simple as adding up all the 1s and 0s in a message, though
it is usually more complex.
c) In symmetric-key encryption, the same key is used to both encrypt and decrypt a message.
d) A digital certificate is issued by a certificate authority. It includes information such as company name, public-key,
certificate number, expiration date, URL and the certificate authority's signature.
e) A Denial of Service attack occurs when a network's resources are taken up by an unauthorized individual, leaving
the network unavailable for legitimate users; typically the attack is performed by flooding servers with data packets. This
greatly increases the traffic on the network, overwhelming servers and making it impossible for legitimate users to down-
load information.
f) A worm is a computer program that attaches to or overwrites other programs. A worm can spread and infect files on
its own; worms do not need to be attached to another program to spread.
g) The message digest is the hash value of a message. It is derived by taking the message and running it through a hash
function to get a hash value.
h) Collision occurs when two messages have the same hash value or message digest.
i) Triple DES is an encryption algorithm based on DES (the Data Encryption Standard). Triple DES uses the DES
cipher three times to make encryption more secure than the standard DES cipher.
j) Session keys are symmetric keys used in one communication session between two parties. They are generated by a
key distribution center. New session keys are generated for each new communication session.