- (Noise spike) is a noncontinuous noise and one of the most difficult errors to detect because it can occur randomly.  

- the noise is an analog burst of energy. If the impulse spike interferes with an analog signal, removing it without affecting the original signal can be difficult. 

- is an unwanted coupling between two (2) different signal paths.  

- This unwanted coupling can be electrical, as might occur between two (2) sets of twisted pair wire (as in a phone line), or it can be electromagnetic (as when unwanted signals are picked up by microwave antennas). 

- is the reflective feedback of a transmitted signal as the signal moves through a medium.  

-It is usually a signal bouncing back from the end of a cable and creating an echo. 

- is the result of small timing irregularities that become magnified during the transmission of digital signals 

as the signals are passed from one device to another.  

- when a digital signal is being transmitted, the rises and falls of the signal can start to shift or become blurry and, thus, produce "blank"

- is the continuous loss of a signal's strength as it travels through a medium.  

- It is not necessarily a form of error but can indirectly lead to an increase in errors affecting the transmitted signal. 

indicates that only one (1) bit of a given data unit (such as a byte, character, or packet) is changed from 1 to 0 or from 0 to 1

indicates that two (2) or more bits in the data unit have changed from 1 to 0 or from 0 to 1.  

- is more likely to occur than a single-bit error because the duration of the noise signal is normally longer than the duration of 1 bit, which means that when noise affects data, it affects a set of bits

- The central concept in detecting or correcting errors is redundancy. 

- To be able to detect or correct errors, we need to send some extra bits with our data. 

- These redundant bits are added by the sender and removed by the receiver. Their presence allows the receiver to detect or correct corrupted bits. 

- can be performed in the data link layer.   

- When a device creates a frame of data at the data link layer, it inserts some type of error _____ code.   

- When the frame arrives at the next device in the transmission sequence, the receiver extracts the error ________ code and applies it to the data frame.   

- Then, the data frame is reconstructed and sent to the next device in the transmission sequence. 

- The number of errors and the size of the message are important factors in dealing with error __________.  

- These mechanisms deal with error __________ by retransmission.  

- When an error occurs, the receiver will detect it and inform the source, and the source will have to retransmit the frame either on positive acknowledgment (ACK) or negative acknowledgment (NAK).  

• - A simple method of error detection is by adding redundant bits called parity bits to each character. 

- commonly used for ASCII characters where seven (7) bits are used for actual character encoding, and the eighth bit is for parity. 

• - blocks of data are organized as a two-dimensional array.  

  - This method increases the likelihood of detecting burst errors. 

  - each row of the array is a data block that is to be transmitted. 

  - A parity bit is appended to each column based on if even or odd parity is used. 

• is a sequence of numbers and letters used to check data for errors.  

  -This sum is then added to the end of the message, and the message is transmitted to the receiving end. 

  - Many higher-level protocols used on the Internet (such as TCP and IP) use a form of error detection in which the characters to be transmitted are "summed" together. 

• – This method treats the packet of data to be transmitted (the message) as a large polynomial, which adds 8 to 32 check bits to large data packets and yields an error-detection capability, approaching 100 percent. 

  - Review the XOR function and Binary Division. 

  - The remainder of the binary division is the CRC to be appended to the original message. 

- is used to deal with errors that occur when the stop-and-wait flow control protocol is used.

deals with errors that occur when the sliding window protocol is used. 

- Under this scheme, only the frame in error is retransmitted. The drawback is that the receiver must provide enough buffer to store the frames that were transmitted after the erroneous frame until the frame has been retransmitted.

- is the art of ensuring that data is kept private and accessed only by the intended recipient.  

• - It is accomplished through encryption. 

• - It is when we send a piece of information to be stored in a remote computer, or when we retrieve a piece of information from a remote computer, we need to conceal it during transmission. 

- is the art of ensuring that data is transmitted from source to destination without alteration. 

• - changes need to be done only by authorized entities and through authorized mechanisms 

• - is accomplished with the use of a digital signature, which is a way to know that an electronic document is legit and authentic 

- is the information created and stored by an organization that needs to be available to authorized entities 

• - Information needs to be constantly changed, which means it must be accessible to authorized entities 

- is the process of verifying that the user is exactly who he claims to be 

o Single-factor authentication - is usually done through the use of passwords or user IDS.  

o Two-factor authentication - is a two-step verification that provides an extra layer of security beyond user ID and password, usually with a software code generator or a hardware-based login key 

• - is an intrusion on network infrastructure 

• - An attack can be performed either from outside of the organization by an unauthorized entity or from within the company by an “insider” that already has some access to the network 

refers to unauthorized access to or interception of data

s/he can obtain some other types of information by monitoring online traffic

the attacker modifies the information to make it beneficial to herself 

it happens when the attacker impersonates somebody else 

attacker obtains a copy of a message sent by a user and later tries to replay it 

it is performed by one of the two parties in the communication: the sender or the receiver

may slow down or totally interrupt the service of a system

- is a process of capturing the data packets traveling in the network 

• - is used by IT professionals to analyze and monitor the traffic to find such things as unexpected suspicious traffic 

- is a process by which an intruder masquerades as a trusted user in order to gain unauthorized access to a secure environment 

- is an attack that involves placing a software agent between the client and server ends before or during a communication session 

is an attack that is aimed at preventing unauthorized users from accessing services on the network 

is a program that installs malicious software while under the guise of doing something else

- refers to the exploitation of a valid computer to gain unauthorized access to information or services in a computer system

- is an attack in which the attacker attempts to fraudulently acquire sensitive information by masquerading as a trustworthy entity in a communication session

is a process of creating IP packets with forged source IP address to impersonate a legitimate system. Often used in denial-of-service attacks 

is a process of sending fake ARP messages in the network 

• this type of spoofing is to associate the MAC address with the IP address of another legitimate host, causing traffic redirection to the attacker’s system. 

is an attack where the wrong data is inserted into the DNS server cache, causing the DNS server to divert the traffic by returning wrong IP addresses as the results for client queries 

"blank" attack is a variation on the man-in-the-middle attack

is a method of concealing information from a recognizable text into encrypted form 

it transforms readable text, called plaintext (or cleartext) 

is the process of recovering plaintext from its ciphertext 

A system that encrypts and decrypts information

is the unintelligible form of plaintext (or cleartext) 

The art of creating and using cryptosystems

the art of breaking encrypted messages (usually by intruders) 

The study of cryptography and cryptanalysis

Both encryption and decryption use a key, in which in the cryptographic sense, is a long string of characters that permits a cryptosystem to encrypt or decrypt information in a distinct way

The same key is used for encryption and decryption 

• Both the originator and the recipient of a message must know the key 

- A public-key cryptosystem uses one key (public-key) for encryption and another key (private-key) for decryption 

• The private key is a secret key that is available only to the owner, and the public key is published.