The internet - Internet security

Question 1

Explain what the key exchange problem is, in relation to a symmetric cipher

Answer 1

• How to pass the key (from the sender) to the receiver;
• Without it being intercepted / securely;

Question 2

Explain what it means for a cipher to be described as being computationally secure

Answer 2

The cipher cannot be cracked, by any known method in a polynomial amount of time

Question 3

what is a TCP/IP protocol

Answer 3

a stack set of protocols used in turn, to format a message so it can be sent over a network
- each layer provides a specific function within the transmission of the message

Question 4

layers of the TCP/IP

Answer 4

• application layer
• transport layer
• network layer
• link layer

Question 5

summarise the application layer

Answer 5

• at the top of the stack
• uses protocols relating to the application being used to transmit data over a network, usually the Internet
• eg SMTP,HTTP

Question 6

summarise the transport layer

Answer 6

• second layer
• uses the TCP to establish an end to end connection with the recipient computer
• splits data into packets, numbers them sequentially
• adds a port number
• performs error detection
• any missing packets are requested to be resent

Question 7

what does TCP/IP stand for

Answer 7

transmission control protocol/internet protocol

Question 8

summarise the network layer

Answer 8

• adds the IP addresses of the source and destination
• router uses IP addresses to forward the packets on to the destination
• the addition of an IP address to the port number forms a socket
• each router uses a routing table to instruct the next hop

Question 9

summarise the link layer

Answer 9

• last layer
• physical connection between network nodes
• adds the MAC addresses, identifying the NIC of the source and destination devices
• MAC addresses change with each hop

Question 10

how is data received after tcp/ip

Answer 10

• link layer removes mac address from each packet
• passes it to network layer
• network layer removes IP address from each packet, passes it to transport layer
• transport layer removes removes the port number from each packet, reassembles the packet in the correct order
• passes it to app layer
• app layer presents the image data for the user in a brpwser

Question 11

features of a mac address

Answer 11

uniquely identifies a physical device with an NIC (NETWORK INTERFACE CARD)
- may be the destination computer or a router
-packets move around the lower layers of the stack as they hop across routers, changing their mac address as they go

Question 12

well known ports

Answer 12

20 = file transfer protocol
80 and 8080 = HTTP
443 = HTTPS(encrypted HTTP)
25 = SMTP (simple mail transfer protocol)

Question 13

what is a port

Answer 13

a port determines which application must deal with a data packet as it enters your computer