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Oct
28
comment Client-server communication
My point was to add no risk and this sounds as good (and simple) as it can get!
Oct
28
comment Advantages of combined PRNGs
Agreed, but there could be something else broken with the OS PRNG (what could block my attempts to add entropy), so I'd prefer to combine it with my own (even if my own seeding was far from perfect; still better than 2**15).
Oct
27
comment Advantages of combined PRNGs
Concerning practical use: Imagine your OS PRNG works just like Debian OpenSSL 2006-2008. Wouldn't you recommend to add some own stuff in order to counter this?
Oct
27
comment Encrypt a file for random access but only after an initial read of the whole file
@otus Yes, that was the intention. Although I wrote "decrypted", my point was to require some "useful" work to be done at the beginning. I guess, with AONT I get authentication, so this hashing qualifies as useful work?
Oct
14
comment Bouncy Castle and Salsa 20
@owlstead I've looked already into the sources and it looks fine (for a non-cryptographer). It was the lack of checking of anything what made me to ask as passing any nonsense worked, too. I'll probably edit out the code as suggested and turn it into a regular question for here.
Oct
13
comment Bouncy Castle and Salsa 20
@Nova I know SO pretty well. I know, there are Java experts there, but I do know myself enough. But the documentation is lacking at best and the interface allows about every nonsense you can think of. BC has a mailing list, I'm giving it a try.
Oct
13
comment Bouncy Castle and Salsa 20
@Nova OK, BC forum sounds good. Java forum is non-sense, as most people there know close to nothing about crypto and the few who just do don't come along.
Oct
13
comment Bouncy Castle and Salsa 20
@ddddavidee How is it different from e.g. this one or this one? I just didn't ask explicitly about what key derivation algorithm should I use, etc., but the question is there. And assuming it's not appropriate here, where should it be? Buddhism? Pets? Just don't say SO or CR, as the kind of knowledge I need is not there.
Oct
13
comment Bouncy Castle and Salsa 20
Downvoter, feel free to add an answer. If the code is crap... well, then I'm right as I expected it.
Jan
16
comment Keyed-hash of a lot of small numbers
I'm definitely no expert here, but couldn't a stream cipher encrypted data be used instead of both (storing the data twice makes no sense to me)?
Nov
11
comment How can two (or more) parties share and agree upon a common random seed?
@nightcracker: I was thinking about generating large random numbers, as cutting them is trivial and they may be useful when the requirements change. And I was thinking about seeding Salsa20 where 256 bits fit perfectly (as the key).
Oct
18
comment Encryption of small messages
I was actually interested in a length preserving encyption, but I failed to state it, and your answer is interesting, too. Thanks.
Oct
18
comment Encryption of small messages
@Thomas Pornin: I didn't say that I wanted a length preserving encryption, but you understood it well. Thanks for the perfect answer.
Feb
14
comment How to best obtain bit sequences from throwing normal dice?
@Mok-Kong Shen: Yes, there's an efficiency drop for 3 rolls. You figures seem to be right.
Jan
17
comment LFSR for small numbers with large periods
@gl3829: No idea, what you're doing wrong, but fgrieu is obviously right. Try to pick the lower 1 bit. According to you you'll get a period of two, but it must be just like described in the second paragraph. Moreover, for any $m<n$ there's no number missing. I'd guess your LSFR is wrong.
Oct
28
comment How do ciphers change plaintext into numeric digits for computing?
@fgrieu: This is surely true (and I should have said it), but this goes far beyond "converting message into number" (which is probably what the OP wanted to know).
Oct
28
comment Is there an algorithm for factoring N, which is just as simple as this one, but faster?
@Thomas: Doesn't it? I'm basically saying that the choice of Ň gains nothing. So yes, there are better algorithms out there, and for number as small as the given one it's easy to implement.
Oct
28
comment Is there an algorithm for factoring N, which is just as simple as this one, but faster?
I'm no expert in cryptography and have spent only few minutes reading it, but it looks bad too. Unfortunately, whenever it looks like it needs no advanced math, it can't be right (unless it's one of the known algorithms). Note that something as simple as Pollard's rho can factor a number like the above in a few milliseconds.
Aug
31
comment Can you help me with this Random Number Generator function?
Can't any even-permutations-only generating cipher be made "perfect" by a trivial postprocessing conditionally switching two outputs (with a 50% probability based on the key)?
Aug
30
comment No SHA-1 collision? Yet SHA-1 is broken?
@Andrew Tomazos - Fathomling: Using the "birthday paradox", there's a brute force attack against any hash of length 160 bits (like SHA-1) taking $2^{80}$ operations. Anything faster is a break.