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Jul
28
revised Rainbow table for DES with all-zero plaintext?
deleted 14 characters in body
Jul
28
comment Elliptic Curve Cryptography
What have you tried? Do you know the equation that defines the tangent line?
Jul
28
comment Known plaintext attack on ElGamal encryption
What are your thoughts? What have you tried? Sounds like an exercise. We're not here to do your exercise for you; this is not a site where you can paste your exercise and we'll solve it for you. Instead, we expect you to make a serious effort, to show us what you tried in the question, and to formulate a specific question about a specific aspect of the problem or your approach.
Jul
28
answered Rainbow table for DES with all-zero plaintext?
Jul
28
comment CSPRNG that cannot be used as random extractor
@owlstead, OK, I've edited the answer accordingly, and to try to make it match my understanding. Now the answer makes more sense to me. AES CTR_DRBG is different from AES CTR.
Jul
28
revised CSPRNG that cannot be used as random extractor
Fix typo to clarify what primitive was intended.
Jul
28
comment CSPRNG that cannot be used as random extractor
OK, so I think part of the problem here is that you don't yet have a clear definition of what you mean by CSPRNG: what it is intended to achieve, what its API is, what its security definition is. A PRG is one well-defined notion in cryptography (AES-CTR, RC4, etc. are examples of a PRG). A CSPRNG is another, different primitive (Yarrow, /dev/urandom, etc. are examples of this primitive; it typically must accept non-uniformly distributed inputs, provide robustness to state compromise extension attacks, etc.). See my comment underneath otus's answer for some elaboration.
Jul
28
comment CSPRNG that cannot be used as random extractor
Based upon the answers it has become clear that there is some confusion about what you mean by CSPRNG (e.g., the distinction between CSPRNG and PRG). I suggest you edit the question to give us your definition of what you mean by CSPRNG: do you mean something like Yarrow, /dev/urandom, etc? or something like AES-CTR, RC4, etc.?
Jul
28
revised CSPRNG that cannot be used as random extractor
added 763 characters in body
Jul
28
answered CSPRNG that cannot be used as random extractor
Jul
28
comment Whitening and randomness extraction
What definition of whitening would you like us to use? I have not heard the term "whitening" used in this particular context, so you'll probably need to define your terms (or provide some more context and more information about why you're asking and how you will use the answer) before I could answer this.
Jul
28
comment Can you help me understand this “Message Modification by Meet-in-the-Middle” related to Tiger Hash?
I'm afraid we probably can't explain this to you. We want to help, but there are limits to what kinds of help can be expected from this kind of site. It looks like you first need to gain more fundamental knowledge about cryptanalysis before you will be in a good position to understand that research paper. Mathematics is the language of cryptanalysis; asking us to explain it without mathematics is not reasonable. If you have a specific question about a specific aspect of that article, I suggest you edit the question accordingly; otherwise, this is simply too broad as it currently stands.
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