C839 Intro to Cyrpto with 100%
correct answers
Key Clustering - answer 2 different keys generate the same cipher
text
Pseudo-Random Number Generators (PRNGs) - answer repeats the
random numbers after a given time (periodic); fast, but
deterministic
True Random Number Generators (TRNGs) - answer generates a true
random number, and uses some form of random process; usually
used by crypto, lotteries, games etc.
symmetric encryption advantages - answer Less computationally
intensive • Produces a smaller file size • Allows for faster
transmissions
symmetric encryption disadvantages - answer Exchanging of the
shared secret key • Trust between parties sharing the key •
Management of keys: n(n − 1)/2 • No authentication or non-
repudiation
binary XOR - answer If they are the same, the result is "0" • If they
are different the result is "1"
binary AND - answer will always produce a 1 output if both of its
inputs are 1 and • will produce a 0 output if one or both of its inputs
are 0
binary OR - answer will always produce a 1 output if either of its
inputs are 1 and will produce a 0 output if both of its inputs are 0
, keys - answer tells the algorithm how to work; should be longer
than the msg
DES - answer 64 bit block; 56 bit key; 16 rounds; Feistel structure
3DES - answer 64 bit block; 168 bit key; 48 rounds
Electronic Code Book (ECB) - answer weakest DES mode; no IV or
error propagation; encrypts each group with the same key, leaving
each group independent of the others; ciphertext won't change for
the same plaintext used in diff blocks
cipher block chaining (CBC) - answer DES mode that depends on
cipher text from prior block to encrypt next block; contains IV and
error propagation
cipher feedback (CFB) - answer DES mode that is a stream, similar
to CBC; real-time encryption; self-synching
output feedback mode (OFB) - answer DES mode that's just like CFB,
but no error, propagation because the seed value is used before it
becomes ciphertext or the XOR is applied
counter mode (CTR) - answer DES mode that's much like OFB, but
instead of a seed, there's an incremental counter; each packet is
done independently (no chaining); often used to improve
performance
AES - answer 128 bit block; 128, 192, 256 bit key; 10, 12, 14 rounds;
Substitution-permutation structure
correct answers
Key Clustering - answer 2 different keys generate the same cipher
text
Pseudo-Random Number Generators (PRNGs) - answer repeats the
random numbers after a given time (periodic); fast, but
deterministic
True Random Number Generators (TRNGs) - answer generates a true
random number, and uses some form of random process; usually
used by crypto, lotteries, games etc.
symmetric encryption advantages - answer Less computationally
intensive • Produces a smaller file size • Allows for faster
transmissions
symmetric encryption disadvantages - answer Exchanging of the
shared secret key • Trust between parties sharing the key •
Management of keys: n(n − 1)/2 • No authentication or non-
repudiation
binary XOR - answer If they are the same, the result is "0" • If they
are different the result is "1"
binary AND - answer will always produce a 1 output if both of its
inputs are 1 and • will produce a 0 output if one or both of its inputs
are 0
binary OR - answer will always produce a 1 output if either of its
inputs are 1 and will produce a 0 output if both of its inputs are 0
, keys - answer tells the algorithm how to work; should be longer
than the msg
DES - answer 64 bit block; 56 bit key; 16 rounds; Feistel structure
3DES - answer 64 bit block; 168 bit key; 48 rounds
Electronic Code Book (ECB) - answer weakest DES mode; no IV or
error propagation; encrypts each group with the same key, leaving
each group independent of the others; ciphertext won't change for
the same plaintext used in diff blocks
cipher block chaining (CBC) - answer DES mode that depends on
cipher text from prior block to encrypt next block; contains IV and
error propagation
cipher feedback (CFB) - answer DES mode that is a stream, similar
to CBC; real-time encryption; self-synching
output feedback mode (OFB) - answer DES mode that's just like CFB,
but no error, propagation because the seed value is used before it
becomes ciphertext or the XOR is applied
counter mode (CTR) - answer DES mode that's much like OFB, but
instead of a seed, there's an incremental counter; each packet is
done independently (no chaining); often used to improve
performance
AES - answer 128 bit block; 128, 192, 256 bit key; 10, 12, 14 rounds;
Substitution-permutation structure
