Term
| what is the usage of linear feedback shift register in security? |
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Definition
| stream cipher and block cipher will need it |
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Term
| what is primitive polynomial? |
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Definition
| a function that will give m-sequence |
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Term
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Definition
| binary sequence with period N, k consecutive 0s or 1s preceded by 1 and followed by 1 is a run with length k |
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Term
| what is auto-correlation? |
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Definition
| cross-correlation with itself |
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Term
| how to compute auto-correlation? |
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Definition
| a exor a shifted right by T bits. if exored bit is 1 then assign -1, if exored bit is 0 then assign 1. Then add them together |
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Term
| what is auto-correlation useful at? |
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Definition
| figuring out sequence of a sequence |
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Term
| what is cross-correlation? |
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Definition
| measures similarities of two sequences |
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Term
| how to find period of sequence a and b from cross-correlation? |
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Definition
| the resulting function is periodic |
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Term
| in cross-correlation, what if two sequences have different length? |
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Definition
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Term
| Describe Golumb's three random properties for sequences |
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Definition
1. number of 1 is 1 more than number of 0
2. (1/2)^k should have run (of 0 and 1) with length k
3. auto-correlation when not same is always -1 |
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Term
| why is LFSR with m-sequence not good? |
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Definition
| hacker can get 2n consecutive sequence and regover LFSR algorithm |
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Term
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Definition
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Term
| give an example of how stop-and-go NL LFSR work |
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Definition
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Term
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Definition
| Uses pseudorandom generator to produce cipher text |
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Term
| is stream cipher symmetric key or public key crypto? |
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Definition
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Term
| describe one-time-pad principle and why it's important |
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Definition
| key is used once -> key is unbreakable |
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Term
| what are design principles of stream ciphers? |
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Definition
1. stream cipher algoirhm is public(i.e everybody show know it)
2. only secrete is pre-shared key
3. hacker can intercept communication so they have ciphertext
4. hackers can also create ciphertexts |
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Term
| what are two phases in stream cipher? |
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Definition
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Term
| what does v mean in bit wise operation? |
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Definition
|
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Term
| what does /\ mean in bit wise operation? |
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Definition
|
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Term
| what does + mean in bit wise operation? |
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Definition
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Term
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Definition
| takes in IV and key, generate a random stream |
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Term
| PSG usually use what to implement? |
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Definition
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Term
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Definition
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Term
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Definition
|
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Term
| how many times does KIA execute for each encryption session? |
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Definition
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Term
| usually what are used to implement PSG? |
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Definition
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Term
| why should low power be used for KIA and PSG? |
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Definition
| to protect side-channel attacks |
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Term
| describe how linear cryptanalysis works? |
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Definition
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Term
| describe how differential cryptanalysis works |
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Definition
| difference between itself and time shifted version, or difference between two keys or messages |
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Term
| describe how correlation attack works |
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Definition
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Term
| what's the requirement for time-space attack? |
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Definition
| for N bits, sqrt(s^N) should exceed computatiblity of current computors |
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Term
| What is the requirement for internal state of stream cipher |
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Definition
| If internal state has n-bits, sqrt(2^n) should resist exhausive attack |
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Term
| how to attack using birthday attack |
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Definition
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Term
| why should stream cipher algorithm be public? |
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Definition
| give hacker a lot of power, if still the hacker can't crack it, then it's good |
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Term
| A5/1 uses what LSFR model? |
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Definition
| stop-and-go LFSR model, 64 stages |
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Term
| how many cycles does A5/1 take to output? |
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Definition
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Term
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Definition
|
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Term
| how many cycles does Grain 2 take to output? |
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Definition
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Term
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Definition
| LSFR using vector, each holds 29 bits, 11 stages, linear span is 2^45 |
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Term
| how many cycles does WG-29 take to output? |
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Definition
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Term
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Definition
| output probability is unbalanced |
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Term
| How did hackers hacked A5/1? |
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Definition
| People reverse engineered |
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Term
| draw a block cipher diagram |
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Definition
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Term
| what are differences between steam cipher and block cipher? |
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Definition
stream is bit by bit, block is block by block. So performance wise block cipher might be faster generally.
Generally steam cipher needs LFSR to compute output stream bit by bit, block cipher needs some state to mix a block up(using thing such as a LUT) |
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Term
| how come requirements for stream cipher and block cipher are so different? |
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Definition
| nature is different, stream cipher depends on function while block cipher depends on number of different operations |
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Term
| what are two things block cipher require? |
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Definition
| 1. diffusion and confusion |
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Term
|
Definition
| if message is changed by 1 bit, then cipher should change totally |
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Term
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Definition
| if key is changed by 1 bit, then cipher should change totally |
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Term
| what is a substitution box? |
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Definition
| a small box that takes in m bits of data and transform it to m bits of data |
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Term
| how to improve security of block cipher which uses s-box in block cipher? |
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Definition
| perform algorithm in s-box many times(rounds) |
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Term
| what are two structures in block cipher? |
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Definition
1. Feistel structure(NLFSR) with input
2. substitute permutation network(a finite state machine) |
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Term
| what is done in each round of block cipher? |
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Definition
1. add keys
2. NL permutation S-box layer(diffusion)
3. linear permutation layer(confusion) |
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Term
| how is cipher text produced in DES? |
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Definition
| run 16 rounds, then internal state is cipher text |
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Term
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Definition
| since the key is 56 bits, using birthday attack can hack |
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Term
| how many rounds are there in AES? |
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Definition
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Term
| DES belongs to where in block cipher? |
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Definition
| Feistel structure(NLLFSR) |
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Term
| how many bits is message for DES? |
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Definition
|
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Term
| how many bits is key for DES? |
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Definition
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Term
| how many bits is message for AES? |
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Definition
|
|
Term
| how many bits is key for AES? |
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Definition
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Term
| are 8 bit cipher text in AES same? |
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Definition
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Term
| how is 128 bits represented in AES? |
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Definition
| each 8 bit is a vector, there are 16 vectors in a matrix |
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Term
| what's the usage of finite field? |
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Definition
finite field is a way to allow add and mult for binary numbers.
usually finite field is implemented in LUT, so computation of binary numbers are faster |
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Term
| Describes the steps in AES |
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Definition
1. inverse
2. affine transform
3. shift row transform
4. mix column transform |
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Term
| total of how many bits of keys are encrypted in AES? |
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Definition
| block length * (number of rounds + 1) |
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Term
| what are two types of encryption modes for block cipher? |
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Definition
1. block cipher mode
2. block cipher implemented as stream cipher |
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Term
| what are two types of block cipher mode? |
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Definition
1. electronic codebook mode
2. cipher block chaining mode |
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Term
|
Definition
1. Electronic code mode
2. CBC mode
3. Cipher Feedback Mode
4. Counter Mode |
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Term
| what are three requirements in Secure Hash Functions? |
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Definition
1. collision resistance
2. second pre-image resistance
2. pre-image resistance |
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Term
| what is second pre-image resistance and why it's important? |
|
Definition
find y st h(y) = h(x)
Because attacker, if able to find y st h(y) = h(x), can use y to pretend to be person who generated h(x). |
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Term
| what is pre-image resistance and why it's important? |
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Definition
given z, find x such that h(x) = z
Because attacker, if able to find y st h(y) = h(x), can use y to pretend to be person who generated h(x). |
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Term
| what's the different reason why second pre-image resistance and pre-image resistance exist? |
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Definition
1. pre-image: to impersonate Alice
2. second pre-image: to change Alice's data |
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Term
| how many bits are input to SHA1? |
|
Definition
|
|
Term
| how many bits are output to SHA1? |
|
Definition
|
|
Term
|
Definition
|
|
Term
| what are three ways MAC can be implemented? |
|
Definition
1. normal stream cipher mode
2. CBC mode
3. hash mode |
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Term
| What does it mean by KIA and PSG should be public but protected? |
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Definition
| it means design should be public, but they should resist attack |
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Term
| Symmetric key and public key, which one causes lower overhead to computation? |
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Definition
| symmetric key, recall AES in 128 bits is over 4000 bits in RSA. So as soon as symmetric key is computed, should switch to symmetric key |
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Term
| What are two advantages of stream cipher compared to block cipher? |
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Definition
1. one bit of error will result in output has one bit of error
2. stream cipher does not need to pad plain text, but block cipher need to |
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Term
| what are two disadvantages of stream cipher compared to block cipher? |
|
Definition
1. design principles of steam ciphers are hardly realized
2.if message is short, initialization if relatively long |
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