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May
19
reviewed Leave Open Building a combined encryption scheme from two encryption schemes that's secure if at least on of them is secure
May
19
comment What should I think about these unique certificate serial numbers
What is your specific question? "What should I think about X?" is not really something we can answer here. See our help center for more information about asking good questions.
May
19
reviewed Reviewed Is the hash function defined in this exercise collision-resistant?
May
19
answered Is the hash function defined in this exercise collision-resistant?
May
19
comment Is the hash function defined in this exercise collision-resistant?
This is true (and should certainly be counted as a correct answer), but it's probably not the answer the author of the exercise was looking for. (If it was, why bother with all the extra details about the internals of the hashing algorithm?)
May
19
comment Is the hash function defined in this exercise collision-resistant?
Generally, the point of homework exercises is to give you some practice in applying the methods you've learned, and to help you notice any gaps in your skillset. Thus, to get the full benefit from the exercises, you should first try to solve them as far as you can on your own, and only then turn to others for help. In particular, when asking for help with homework on Stack Exchange, it helps a lot if you mention how far you've got on your own (even if it's "I tried X and Y and Z, but none of them work because..."), and where specifically (you think) you're stuck.
May
19
revised Is the hash function defined in this exercise collision-resistant?
improve formatting, slightly less generic title, misc. copyedits
May
16
awarded  Enlightened
May
16
awarded  Nice Answer
May
16
awarded  cryptanalysis
May
15
reviewed Edit Does the plaintext have to be at least as long as the key in Polyalphabetic substituion cipher
May
15
revised Does the plaintext have to be at least as long as the key in Polyalphabetic substituion cipher
It would be shift cipher not a monoalphabetic substitution cipher
May
15
revised Does the plaintext have to be at least as long as the key in Polyalphabetic substituion cipher
added 685 characters in body
May
15
answered Does the plaintext have to be at least as long as the key in Polyalphabetic substituion cipher
May
13
comment Time Capsule cryptography?
@kasperd: Sure, but it's a one-time setup cost. You launch the reflector / retransmitter well in advance, so that you can use it later when it's far enough. I never said this was a practical solution right now (if ever). Although, if you only need a delay of a few seconds, there's a convenient reflector already on the Moon. And we do technically have an active retransmitter at about 17 light hours away, even if contacting it discreetly may be tricky. ;-)
May
12
comment Time Capsule cryptography?
@kasperd: An active retransmitter would cut that down to the square of the distance. And, of course, the scaling law only starts to apply at distances where the beam width exceeds the size of the receiver / reflector, so the bigger you can make the reflector, and the better you can collimate the beam, the further you can reach with the same energy.
May
10
revised What is the main difference between a key, an IV and a nonce?
fix title grammar, misc. copyedits, add terminology tag
May
10
comment how does an initialization vector work?
Related question: crypto.stackexchange.com/questions/3965/…
May
9
reviewed Approve How to break AES/CBC/PKCS5 when key and IV are reused?
May
9
revised Optimal bandwidth cost for Oblivious RAM
better title