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Jul
22
comment MAC using a modified CBC mode of operation
What have you tried? What are your thoughts? What kinds of attacks have you considered? Have you tried to see if you could prove it secure? Have you looked at the special case where there are exactly 2 plaintext blocks? I don't think copy-pasting an exercise from an earlier course is a great fit for this site. We want to help clear up any confusions you might have, but as for doing an exercise problem for you -- well, maybe not so much. I don't think it benefits the world for us to be a site where people can paste exercises and have someone else produce a complete solution for them.
Jul
21
answered How to construct a next bit predictor from a distinguisher
Jul
20
comment Turning PRPs in PRGs with a counter
You might like to read about the PRP/PRF switching lemma, which helps show that CTR mode is a secure PRG "up to the birthday bound" (i.e., as long as you don't generate too many outputs).
Jul
18
revised Is it safe to seed a random number generator from system time?
Clean up the answer to be self-contained. We don't add "edit: never mind, everything above is wrong" on this site -- we have revision control, we don't need to keep around incorrect statements.
Jul
18
comment Modes of operation that allow padding oracle attacks
Can you define what you mean by padding oracle attacks? If you count switching the order of the blocks around in ECB mode to be a padding oracle attack, then you're using a non-standard meaning of the phrase (since in that case you're not even attacking the padding function nor using it as an oracle). Do you maybe simply mean chosen-ciphertext attacks on confidentiality?
Jul
16
comment Does having a known plaintext prefix weaken AES256?
What research have you done? This is already answered by several questions on this site, e.g., crypto.stackexchange.com/q/1512/351, crypto.stackexchange.com/q/3952/351. (If you'd searched, you should have found them immediately; and they already show up in the related questions list.) We expect you to do a significant amount of research before asking here, including searching on this site for other questions and answers that might shed light on your question. At worst, it will help you frame a better, more focused question; at best, it might answer your question for you.
Jul
14
awarded  Nice Answer
Jul
14
awarded  Nice Answer
Jul
10
comment CBC-MAC length extension attack with IV simulation
Please edit the question to make clearer what the problem is. We don't have the second part of 49th problem in Matasano's problem set memorized in our head. Right now, the question does not seem answerable to me. Also, I suggest you edit the question to tell us what research you've done, what attacks on CBC-MAC you are familiar with, and what you've tried.
Jul
10
comment Choosing primes in the Paillier cryptosystem
I can't understand what you are asking. What does "Give me a reference if proof for above equation complex otherwise provide a proof." mean? Also, what research have you done? Did you read the original research paper?
Jul
7
revised Password-based encrypted key storage?
fix typo caught by e-sushi
Jul
7
revised Password-based encrypted key storage?
added 34 characters in body
Jul
3
answered Password-based encrypted key storage?
Jul
2
comment Password-based encrypted key storage?
@otus, RFC 5959 only uses AES in ECB mode if the plaintext is exactly 128 bits long. That is not malleable (not in any useful way that would enable related-key attacks).
Jul
2
awarded  Curious
Jun
30
awarded  Revival
Jun
30
revised Associative standard cryptographic hash function
added 1251 characters in body
Jun
30
answered Associative standard cryptographic hash function
Jun
26
awarded  Custodian
Jun
26
reviewed Leave Closed RSA: Common modulus attack problem