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Nov
13
revised Getting the encryption method and key from the encrypted data and the raw data
formatting, tag
Nov
13
revised Are these emerging threats against AES affecting your designs?
formatting, spelling
Nov
13
revised For public-key encryption, why does COA resistance imply CPA resistance?
tags + shorter title, see Chat (http://chat.stackexchange.com/transcript/message/2421197#2421197 and following) for discussion
Nov
13
comment For public-key encryption, why does COA resistance imply CPA resistance?
Does "ciphertext-only attack" mean that the attacker doesn't know the public key?
Nov
13
comment For public-key encryption, why does COA resistance imply CPA resistance?
Why does this help? (Please add a bit of clarification to your answer.)
Nov
12
comment What is pre-image resistance, and how can the lack thereof be exploited?
@Fixee: I would thought we want the existence (or our knowledge, to go with this paper) of an algorithm which for every $d$ (or at least a large proportion) outputs a fitting $m$, not a separate algorithm for each $d$ (which of course is trivial). I don't see a need for a key here. (Should we move this discussion to chat?)
Nov
12
comment What is pre-image resistance, and how can the lack thereof be exploited?
@Fixee: Thanks for the link, I'm reading right now. But this seems to talk mainly about collision resistance, and I think the same problem doesn't apply to preimage resistance (where we don't want preimages for any hash (which is always easy), but for a given one). (But I see that I interpreted your "family of hash functions" wrong.)
Nov
12
revised What is the relation between RSA & Fermat's little theorem?
formatting
Nov
12
revised What is the relation between RSA & Fermat's little theorem?
formatting using MathJax formulas
Nov
12
revised What is the relation between RSA & Fermat's little theorem?
formatting, spelling
Nov
12
comment What is pre-image resistance, and how can the lack thereof be exploited?
@Fixee: Thanks for this comment. I added a note according to this to my answer - can one say it this way, is it too sloppy, or even plainly wrong?
Nov
12
revised What is pre-image resistance, and how can the lack thereof be exploited?
add tag, spelling/formatting
Nov
12
comment What is pre-image resistance, and how can the lack thereof be exploited?
I think often a (first-)preimage attack is more devastating than a second-preimage attack, as (usually) preimage attacks are easily extended to second-preimage attacks, but not the other way around.
Nov
12
revised What is pre-image resistance, and how can the lack thereof be exploited?
add preimage example (from Henno's answer), add note about formal definition (thanks to Fixees comment)
Nov
12
comment Best way to reduce chance of hash collisions: Multiple hashes, or larger hash?
@Theodor: For a random collision, a simple look at the combined output size $n$ (in bits) is enough: You need about $2^{n/2}$ blocks to have a good chance. As $256 + 128 = 384$, the probabilities are quite the same. If you fear malicious collisions by attackers, avoid MD5 as its collision resistance is broken, and avoid concatenations of different hash functions, as in the answer by Thomas.
Nov
12
answered What is pre-image resistance, and how can the lack thereof be exploited?
Nov
10
comment Linear Cryptanalysis
Also, have a look at How do I apply differential cryptanalysis to a block cipher?.
Nov
10
comment Linear Cryptanalysis
Did you read the Wikipedia articles about Linear Cryptanalysis and Differential Cryptanalysis? Please note what you don't understand about them, and make your question more concrete.
Nov
10
awarded  Nice Answer
Nov
10
awarded  Enlightened