C839V5 (D334) WGU COURSE INTRO TO CRYPTOGRAPHY EXAM
QUESTIONS WITH CORRECT ANSWERS
Atbash Cipher - ANSWER-Invented by the Hebrew. Single substitution monoalphabetic cipher that
substitutes each letter with it's reverse (a and z, b and y, etc).
Caesar Cipher - ANSWER-Monoalphabetic cipher where letters are shifted one or more letters in either
direction.
ROT 13 - ANSWER-Monoalphabetic cipher that shifts characters 13 characters. Stands for Rotate 13. A
would become N, B would become O, etc.
Scytale Cipher - ANSWER-Was a staff with papyrus or letter wrapped around it so edges would line up.
There would be a stream of characters which would show you your message. When unwound it would
be a random string of characters. Would need an identical size staff on other end for other individuals to
decode message.
Multi-Alphabet Substitution Cipher - ANSWER-Doing something like +1, -2, +3 and shifting each
character a different amount to the left or right. For example, doing +1, -2, +3 with dog would results in
emj.
Cipher Disks - ANSWER-A disk you rotated to encrypt/decrypt. Created by Leon Alberti. Similar
technologies were used in the Enigma machine. Considered the forefather of modern encryption.
Vigenere Cipher - ANSWER-Invented by Giovan Battista Bellaso in middle 1553. Vigenere created a
stronger version of the cipher. Combining/Weaving Caesar cipher. Not cracked until late 1800s. It is a
cipher square with A to Z across all the columns and rows. You then use a keyword to encrypt the
message. For example, if the message is cat, and the keyword is horse, you would look up where c and h
intersect on the table (which is j), then where a and o intersect (o) and t and r (k). Cat would then be
encrypted as jok.
Playfair Cipher - ANSWER-Invented by Charles Wheatstone in mid 1800s. Lord Playfair pushed use of it.
Uses a 5x5 table and a key word. Rest of the alphabet is placed on table in alphabetic order, skipping
,letters used in the keyword. You break up the message into two character chunks and return a single
character value. If the letters appear on the same row of your table, replace them with the letters to the
right. If it is on the same column, replace them with the letters below.
ADFGVX Cipher - ANSWER-Invented by Colonel Fritz Nebel in 1918. It is a 6x6 grid with ADFGVX at the
top of each column and beginning of each row. The 26 letters and numbers 0-10 are placed randomly on
the table. You then replace each character of your message with two characters which are represented
by the column followed by the row each character is present in.
Enigma Machine - ANSWER-Invented between World Wars, used by Germans and Japanese. Data could
be transmitted both via radio or printed on paper. Designed so that when a key was pressed, the cipher
text for that plain text was different each time. Was a multi-alphabet cipher with 26 possible alphabets.
Kerckhoff's Principle - ANSWER-We can expose everything but the private key and the data can still be
secure.
Issue with Symmetric Encryption - ANSWER-There's only one key, and it's difficult to only have both
parties who need the key to have it. It typically needs to be sent via another medium than the message
or else it could be compromised by the attacker. Keys can also be sent via out of band (off the network
being used to send the message).
Binary Math - ANSWER-Base 2 system instead of base 10 system.
Binary AND - ANSWER-If both numbers have a one in the same place, then the resultant number is a
one. If not then it is a zero
1st number - 1100
2nd number - 0100
--------------------------
Result - 0100
Binary OR - ANSWER-Checks to see if there is a one in either or both numbers in the same place. If so,
the resultant number is one, if not, it is zero.
,1st number - 1100
2nd number - 0100
--------------------------
Result - 1100
Binary XOR (Exclusive OR) ⊕ - ANSWER-Checks to see if there is a one in either number in the same
place. If so, the resultant number is one, if not, it is zero.
1st number - 1100
2nd number - 0100
--------------------------
Result - 1000
XOR is reversible. If you XOR the result with the 2nd number, you will get the 1st number as a result. If
you XOR the result with the 1st number, you will get the 2nd number as a result.
Substitution - ANSWER-XORing the plain text with the key.
Transposition - ANSWER-Swapping blocks of text.
Confusion - ANSWER-Making the relationship between a key and the ciphertext as complex as possible.
Diffusion - ANSWER-Each binary digit (bit) of the ciphertext should depend on several parts of the key,
obscuring the connections between the two.
Avalanche - ANSWER-The concept that if one bit of data changes, the cipher text will all completely
change as well.
, Key Schedule - ANSWER-An algorithm for the key that calculates the subkeys for each round that the
encryption goes through.
Hybrid Encryption - ANSWER-Data is encrypted with a symmetric encryption algorithm, the symmetric
private key is sent to the other party with asymmetric encryption.
Symmetric Algorithms - ANSWER-Examples are DES, 3DES, DESX, AES, Blowfish, Serpent, Twofish,
Skipjack, IDEA
Whitening - ANSWER-A technique used to increase the security of block ciphers. It consists of steps that
combine the data with portions of the key (most commonly using a simple XOR) before the first round
and after the last round of encryption.
Block Cipher - ANSWER-Data fills up a block (typically 64 or 128 bits) and that block is encrypted as a
whole. Slower than stream ciphers. If a block was not full, you would need to pad the data to end up at
the block size.
Feistel Network - ANSWER-Chunk data into evenly sized blocks. The two chunks are typically called L0
and R0 (left 0 and right 0). As long as these are even, it is considered a traditional/normal Feistel Cipher.
An unbalanced Feistel Cipher is when the basket does not split evenly. Next is the round function, which
is applied to both halves and is used to go through the multiple rounds/iterations based on the
symmetric encryption algorithm. Output of each round function is XORed with the other half (L0 is
XORed with R0). R0 is then moved over to L0. R0 is moved over to the left and XORed.
DES - ANSWER-Symmetric algorithm. One of the most widely deployed algorithms in the world, even
though it is no longer recommended or considered secure. 64 bit key (56 bits + 8 bits party), 64 bit block
sizes.
3DES - ANSWER-Symmetric algorithm. Does DES 3 times, doing one of the following: 1st key encrypts,
2nd key decrypts, 3rd key encrypts, or one key encrypts/decrypts/encrypts, or 1st key encrypts, 2nd key
decrypts, and 1st key encrypts again.
DESX - ANSWER-Symmetric algorithm. 64 bit key is appended to data, XOR it, and then apply the DES
algorithm.
QUESTIONS WITH CORRECT ANSWERS
Atbash Cipher - ANSWER-Invented by the Hebrew. Single substitution monoalphabetic cipher that
substitutes each letter with it's reverse (a and z, b and y, etc).
Caesar Cipher - ANSWER-Monoalphabetic cipher where letters are shifted one or more letters in either
direction.
ROT 13 - ANSWER-Monoalphabetic cipher that shifts characters 13 characters. Stands for Rotate 13. A
would become N, B would become O, etc.
Scytale Cipher - ANSWER-Was a staff with papyrus or letter wrapped around it so edges would line up.
There would be a stream of characters which would show you your message. When unwound it would
be a random string of characters. Would need an identical size staff on other end for other individuals to
decode message.
Multi-Alphabet Substitution Cipher - ANSWER-Doing something like +1, -2, +3 and shifting each
character a different amount to the left or right. For example, doing +1, -2, +3 with dog would results in
emj.
Cipher Disks - ANSWER-A disk you rotated to encrypt/decrypt. Created by Leon Alberti. Similar
technologies were used in the Enigma machine. Considered the forefather of modern encryption.
Vigenere Cipher - ANSWER-Invented by Giovan Battista Bellaso in middle 1553. Vigenere created a
stronger version of the cipher. Combining/Weaving Caesar cipher. Not cracked until late 1800s. It is a
cipher square with A to Z across all the columns and rows. You then use a keyword to encrypt the
message. For example, if the message is cat, and the keyword is horse, you would look up where c and h
intersect on the table (which is j), then where a and o intersect (o) and t and r (k). Cat would then be
encrypted as jok.
Playfair Cipher - ANSWER-Invented by Charles Wheatstone in mid 1800s. Lord Playfair pushed use of it.
Uses a 5x5 table and a key word. Rest of the alphabet is placed on table in alphabetic order, skipping
,letters used in the keyword. You break up the message into two character chunks and return a single
character value. If the letters appear on the same row of your table, replace them with the letters to the
right. If it is on the same column, replace them with the letters below.
ADFGVX Cipher - ANSWER-Invented by Colonel Fritz Nebel in 1918. It is a 6x6 grid with ADFGVX at the
top of each column and beginning of each row. The 26 letters and numbers 0-10 are placed randomly on
the table. You then replace each character of your message with two characters which are represented
by the column followed by the row each character is present in.
Enigma Machine - ANSWER-Invented between World Wars, used by Germans and Japanese. Data could
be transmitted both via radio or printed on paper. Designed so that when a key was pressed, the cipher
text for that plain text was different each time. Was a multi-alphabet cipher with 26 possible alphabets.
Kerckhoff's Principle - ANSWER-We can expose everything but the private key and the data can still be
secure.
Issue with Symmetric Encryption - ANSWER-There's only one key, and it's difficult to only have both
parties who need the key to have it. It typically needs to be sent via another medium than the message
or else it could be compromised by the attacker. Keys can also be sent via out of band (off the network
being used to send the message).
Binary Math - ANSWER-Base 2 system instead of base 10 system.
Binary AND - ANSWER-If both numbers have a one in the same place, then the resultant number is a
one. If not then it is a zero
1st number - 1100
2nd number - 0100
--------------------------
Result - 0100
Binary OR - ANSWER-Checks to see if there is a one in either or both numbers in the same place. If so,
the resultant number is one, if not, it is zero.
,1st number - 1100
2nd number - 0100
--------------------------
Result - 1100
Binary XOR (Exclusive OR) ⊕ - ANSWER-Checks to see if there is a one in either number in the same
place. If so, the resultant number is one, if not, it is zero.
1st number - 1100
2nd number - 0100
--------------------------
Result - 1000
XOR is reversible. If you XOR the result with the 2nd number, you will get the 1st number as a result. If
you XOR the result with the 1st number, you will get the 2nd number as a result.
Substitution - ANSWER-XORing the plain text with the key.
Transposition - ANSWER-Swapping blocks of text.
Confusion - ANSWER-Making the relationship between a key and the ciphertext as complex as possible.
Diffusion - ANSWER-Each binary digit (bit) of the ciphertext should depend on several parts of the key,
obscuring the connections between the two.
Avalanche - ANSWER-The concept that if one bit of data changes, the cipher text will all completely
change as well.
, Key Schedule - ANSWER-An algorithm for the key that calculates the subkeys for each round that the
encryption goes through.
Hybrid Encryption - ANSWER-Data is encrypted with a symmetric encryption algorithm, the symmetric
private key is sent to the other party with asymmetric encryption.
Symmetric Algorithms - ANSWER-Examples are DES, 3DES, DESX, AES, Blowfish, Serpent, Twofish,
Skipjack, IDEA
Whitening - ANSWER-A technique used to increase the security of block ciphers. It consists of steps that
combine the data with portions of the key (most commonly using a simple XOR) before the first round
and after the last round of encryption.
Block Cipher - ANSWER-Data fills up a block (typically 64 or 128 bits) and that block is encrypted as a
whole. Slower than stream ciphers. If a block was not full, you would need to pad the data to end up at
the block size.
Feistel Network - ANSWER-Chunk data into evenly sized blocks. The two chunks are typically called L0
and R0 (left 0 and right 0). As long as these are even, it is considered a traditional/normal Feistel Cipher.
An unbalanced Feistel Cipher is when the basket does not split evenly. Next is the round function, which
is applied to both halves and is used to go through the multiple rounds/iterations based on the
symmetric encryption algorithm. Output of each round function is XORed with the other half (L0 is
XORed with R0). R0 is then moved over to L0. R0 is moved over to the left and XORed.
DES - ANSWER-Symmetric algorithm. One of the most widely deployed algorithms in the world, even
though it is no longer recommended or considered secure. 64 bit key (56 bits + 8 bits party), 64 bit block
sizes.
3DES - ANSWER-Symmetric algorithm. Does DES 3 times, doing one of the following: 1st key encrypts,
2nd key decrypts, 3rd key encrypts, or one key encrypts/decrypts/encrypts, or 1st key encrypts, 2nd key
decrypts, and 1st key encrypts again.
DESX - ANSWER-Symmetric algorithm. 64 bit key is appended to data, XOR it, and then apply the DES
algorithm.
