Encryption, Data & Communication

plaintext

the original message that anyone can be fully read and understood by anyone

ciphertext

the transformed plaintext which is only readable/understandable by those who possess the correct key

encryption

the process of turning a plaintext into a ciphertext, to make it unreadable to anyone except for those who possess the correct key

decryption

the process of turning a ciphertext into the original plaintext using the correct key, so that it can be understood again

logical operation associated with Vernam Cipher

XOR (the plaintext against the key, producing the ciphertext, which can be decoded via the same process)

ASCII

an encoding system using strings of 0s and 1s to represent characters, limited to 128 characters

Unicode

an encoding system using strings of 0s and 1s to represent characters, able to represent millions of characters

Reason for using encryption

To protect sensitive information & ensure data is secure

Negative of encryption

Protects criminals from detection

Error detection

being able to detect whether the data contains any errors

Error encryption

error detection with the ability to correct these errors

Odd/even parity check bit

Bit included to make the overall number of 1s odd/even

2D parity check

• parity check bit for each row

• THEN parity check bit for each column

Majority voting

each bit is sent a pre-decided number of times

Lossless compression

information is repackaged, but the file can be perfectly reconstructed

Lossy compression

information is repackaged, where some of it is lost or permanently deleted, so the file cannot be perfectly reconstructed

Serial transmission

only one communication channel used at a time

Parallel transmission & its disadvantages

multiple communication channels used at once

• skew - bits on different channels arrive at different times

• crosstalk - electrical interference between channels may corrupt bits

• expensive & hard to maintain

Bitrate

number of bits of information transmitted per unit time

= baud rate x number of bits each level of transmission represents

Baud rate

maximum times signal can change per unit time

Bandwidth

• the range of frequencies of signals that can be transmitted without a significant reduction in signal strength

• max frequency minus the min frequency signal that can be transmitted without a significant reduction in signal strength

• to accommodate a signal whose bitrate is W bits per second, the communication medium should have a bandwidth of at least 2W Hz

Propagation latency

time taken for a logic gate to transmit data

Transmission latency

time taken to pass through a particular communication medium

Processing latency

time taken to pass around a network, depending on how many devices it has to pass through.

Synchronous data transmission

the data transmitter and the data receiver will pulse in synchronization, so that the data arrives and is read at the correct intervals

Asynchronous transmission

the transmitter will send a start bit to ‘wake up’ a receiver of equal baud rate, so that their clocks pulse in synchronisation

Protocol

a set of rules governing how a particular task should be accomplished (looser than an algorithm)