Crypto Flashcards
If a particular cipher uses 128 bit keys, and can be brute-forced in 100 years, how many years would it take to brute-force that same cipher if the keys are increased to 130 bits?
400
Power = KeySpace / Time where KS = 2exp-bits
Which statement is false?
a. Generally, symmetric ciphers are much faster than asymmetric ciphers.
b. The two major cipher types are block ciphers and stream ciphers.
c. Cryptanalysis is the process of brute-forcing keys.
d. Chaining used in conjunction with a block cipher enhances the strength of the encryption.
c. Cryptanalysis is the process of brute-forcing keys.
Cryptanalysis is the unwrapping of the algorithms
In addition to intense public scrutiny/review, the dominant factor contributing to the security strength of most modern encryption ciphers is
a. key length
b. the secrecy of the underlying cipher algorithm
c. the use of parallelism to divide the key space
d. chaining to increase the time required to test each key
a. key length
If a given cipher algorithm uses 100 iterations of processing for a single block of plaintext and key, and each iteration i is dependent upon iteration i-1; then a single 800MHz CPU could check a theoretic-cal maximum of ______ keys per second. (assume no pipelining or other “tricks”)
8 million
800MHz (cycles/sec) and 100 keys/sec
=> 800x10exp6 cycles/sec / 100 keys/sec = 8x10exp6
Which of these represent hashes (or hash “functions”)?
a. Human birthdates
b. Modulo arithmetic
c. Truncate function
d. All the above are examples of hashes
d. All the above are examples of hashes
According to Moore’s Law, approximately how much “faster” will computers be 30 years from now?
a. about 1,000 times faster
b. about 32,000 times faster
c. about 1,000,000 times faster
d. about 64,000,000 times faster
c. about 1,000,000 times faster
Py = Pnow x 2exp(y/1.5) P30 = P0 x 2exp(30/1.5) = 1048576
The term “collision” when applied to hashing algorithms is best defined as
a. the size of the “fingerprint”.
b. two separate messages hashing to the same “fingerprint”.
c. a “fingerprint” that does not properly un-hash back to the original message.
d. a single message that hashes to two or more different “fingerprints”.
b. two separate messages hashing to the same “fingerprint”.
Proper management of public keys requires that they…
a. can be distributed without any protection
b. need to have their integrity protected in the form of a digital certificate
c. should be kept confidential
d. should be “signed” with the issuer’s public key
b. need to have their integrity protected in the form of a digital certificate
Digital certificates…
a. contain the owner’s private key and are signed with the CA’s private key.
b. contain the owner’s private key and are signed with the CA’s public key.
c. contain the owner’s public key and are signed with the CA’s public key.
d. contain the owner’s public key and are signed with the CA’s private key.
d. contain the owner’s public key and are signed with the CA’s private key.
Briefly describe the two reasons that we cannot generally (i.e., for all types of message exchanges) rely on the “readability” of decrypted plaintext to ensure it has decrypted correctly.
- _________________________
- _________________________
- Non Human Reader
2. Non Human Readable Text
What is the approximate bit-entropy of an 8 (decimal) digit PIN? [log2 = 0.3]
a. ~19
b. ~42
c. ~96
d. ~26
d. ~26
X = log(password space) / log2
=> X = 8 / 0.3
Check this!
If a cipher has keys of length L, mathematically express the average number of keys that would have to be checked when conducting a brute-force attack before the correct key is identified.
a. Lexp2 – L/2 b. 2expL/2 c. 2expL-1 d. (L-1)exp2
c. 2expL-1
2expL (total KeySpace) / 2 (to find halfway point)
=> 2expL-1
For any 2 of n users to be able to communicate securely, how many public keys would have to be distributed within this domain of n users? (Assume there is NO central public key server)
a. n b. n-1 c. n(n-1) d. n(n-1) / 2
c. n(n-1)
Which of these is the “best compliment” to a cipher developer?
a. We could not discover how your cipher works. b. Your cipher employs both substitution and transposition. c. The entropy of your cipher results in complete “avalanche” effect. d. The cheapest way to attack your cipher is to brute-force the key.
d. The cheapest way to attack your cipher is to brute-force the key.
Which best describes Kerckhoff’s Principle?
a. The entire defense is the sum total of the synergy of each individual security control. b. The implementation/design is open to public scrutiny and analysis. c. All crypto ciphers must include both substitutions and transpositions. d. Key entropy is maximized when all key combinations are “equally likely”.
b. The implementation/design is open to public scrutiny and analysis.
