FOUNDATIONS OF COMPUTER SCIENCE FINAL 220
QUESTIONS WITH VERIFIED ANSWERS 2025/2026
ordinary text - CORRECT ANSWER plaintext
"unreadable" encrypted text - CORRECT ANSWER ciphertext
plaintext to ciphertext - CORRECT ANSWER encryption
ciphertext to plaintext - CORRECT ANSWER decryption
an algorithm used to encrypt and decrypt text - CORRECT ANSWER cipher
a set of particular parameters that guide the cipher algorithm - CORRECT ANSWER
key
1. Substitution cipher
2. Transposition cipher - CORRECT ANSWER 2 big types of ciphers
replacing one character with another
not very secure b/c easy to break by figuring out "e" then "the" etc. - CORRECT
ANSWER Substitution cipher
type of substitution cipher used between Caesar and his generals
,done by shifting a certain number of positions up/down the alphabet
spaces can be omitted or represented by character(s)
punctuation could be included
easy to crack - CORRECT ANSWER Caesar cipher
rearranging the order of existing characters
easy to crack but not as easy as substitution ciphers - CORRECT ANSWER
Transposition cipher
encryption = characters laid out in grid and then moved into a string of letters by
following a particular route around the grid
decryption = string of letters written on grid via the reversal of the route and then
read - CORRECT ANSWER route cipher
the process of "breaking" an encryption
figuring out the plaintext without knowing the cipher or key - CORRECT ANSWER
cryptanalysis
they've tried/are trying (idk) to force citizens to hand over deciphering keys
they also want "back door" access to certain secure sites which poses a risk to the
information on those sites as they would then be easier to hack - CORRECT
ANSWER FBI issues
father of computers
worked for Britain's code-breaking center
,during WWII, he was a key player in breaking the German military's code (known
as Enigma) - CORRECT ANSWER Turing
(idk if this is aka RSA or if RSA is an example)
2 mathematically related public and private keys
most secure be extremely difficult to decrypt - CORRECT ANSWER public-key
cryptography
an asymmetric code created with a trapdoor function which makes it easy to
encrypt messages but difficult to decrypt them - CORRECT ANSWER RSA algorithm
definition
cod mod n = m - CORRECT ANSWER RSA private key
2+ numbers that share no factors other than 1 - CORRECT ANSWER coprime
Φ
created by Euler
Φ(n) would be all the numbers less than n which are also coprime (with n, I
think...idk if it means coprime with each other)
{ I wrote if n > 7, Φ = usually prime - 1, but if what I meant } - CORRECT ANSWER
totient
the quotient left over in a closed number system
, ex: time = on a closed system of 12 hour cycles, it's 10 AM and I want to know
what time it'll be in 4 hours 10 + 4 = 14 ==> 14/12 has a remainder of 2 so it'll be 2
o'clock; 14 mod 12 = 2 - CORRECT ANSWER modulo operation
usually begin with 192.168. - CORRECT ANSWER home network IP addresses
making it look like something came from some other device - CORRECT ANSWER
spoofing
didn't exist b/c it was only used by a small number of military branches and
educational institutions so why would they need encryption - CORRECT ANSWER
ARPAnet encryption
used in written messages in the US military during way as a way of sending
messages without encryption - CORRECT ANSWER Navajo
a collection of computing devices connected to share info + resources - CORRECT
ANSWER computer network
connected via radio waves to a wireless access point (which is at least one node in
the network which allows others to access one another wirelessly) - CORRECT
ANSWER wireless
any device in the network - CORRECT ANSWER node/host
speed; data transfer rate w/in network - CORRECT ANSWER bandwidth
QUESTIONS WITH VERIFIED ANSWERS 2025/2026
ordinary text - CORRECT ANSWER plaintext
"unreadable" encrypted text - CORRECT ANSWER ciphertext
plaintext to ciphertext - CORRECT ANSWER encryption
ciphertext to plaintext - CORRECT ANSWER decryption
an algorithm used to encrypt and decrypt text - CORRECT ANSWER cipher
a set of particular parameters that guide the cipher algorithm - CORRECT ANSWER
key
1. Substitution cipher
2. Transposition cipher - CORRECT ANSWER 2 big types of ciphers
replacing one character with another
not very secure b/c easy to break by figuring out "e" then "the" etc. - CORRECT
ANSWER Substitution cipher
type of substitution cipher used between Caesar and his generals
,done by shifting a certain number of positions up/down the alphabet
spaces can be omitted or represented by character(s)
punctuation could be included
easy to crack - CORRECT ANSWER Caesar cipher
rearranging the order of existing characters
easy to crack but not as easy as substitution ciphers - CORRECT ANSWER
Transposition cipher
encryption = characters laid out in grid and then moved into a string of letters by
following a particular route around the grid
decryption = string of letters written on grid via the reversal of the route and then
read - CORRECT ANSWER route cipher
the process of "breaking" an encryption
figuring out the plaintext without knowing the cipher or key - CORRECT ANSWER
cryptanalysis
they've tried/are trying (idk) to force citizens to hand over deciphering keys
they also want "back door" access to certain secure sites which poses a risk to the
information on those sites as they would then be easier to hack - CORRECT
ANSWER FBI issues
father of computers
worked for Britain's code-breaking center
,during WWII, he was a key player in breaking the German military's code (known
as Enigma) - CORRECT ANSWER Turing
(idk if this is aka RSA or if RSA is an example)
2 mathematically related public and private keys
most secure be extremely difficult to decrypt - CORRECT ANSWER public-key
cryptography
an asymmetric code created with a trapdoor function which makes it easy to
encrypt messages but difficult to decrypt them - CORRECT ANSWER RSA algorithm
definition
cod mod n = m - CORRECT ANSWER RSA private key
2+ numbers that share no factors other than 1 - CORRECT ANSWER coprime
Φ
created by Euler
Φ(n) would be all the numbers less than n which are also coprime (with n, I
think...idk if it means coprime with each other)
{ I wrote if n > 7, Φ = usually prime - 1, but if what I meant } - CORRECT ANSWER
totient
the quotient left over in a closed number system
, ex: time = on a closed system of 12 hour cycles, it's 10 AM and I want to know
what time it'll be in 4 hours 10 + 4 = 14 ==> 14/12 has a remainder of 2 so it'll be 2
o'clock; 14 mod 12 = 2 - CORRECT ANSWER modulo operation
usually begin with 192.168. - CORRECT ANSWER home network IP addresses
making it look like something came from some other device - CORRECT ANSWER
spoofing
didn't exist b/c it was only used by a small number of military branches and
educational institutions so why would they need encryption - CORRECT ANSWER
ARPAnet encryption
used in written messages in the US military during way as a way of sending
messages without encryption - CORRECT ANSWER Navajo
a collection of computing devices connected to share info + resources - CORRECT
ANSWER computer network
connected via radio waves to a wireless access point (which is at least one node in
the network which allows others to access one another wirelessly) - CORRECT
ANSWER wireless
any device in the network - CORRECT ANSWER node/host
speed; data transfer rate w/in network - CORRECT ANSWER bandwidth
