A digital currency system like Lucre (OpenTransaction) creates a coin by a mint blind signing the output of a hash function, which the payer then unblinds and pairs with the input to the has function.
In this way, the coins themselves cannot be used to identify the payer; however, the payee and ...
I need to divide some input (for example, the string helloworldhelloworld) in blocks of 512 bytes, to use it in a cryptography function.
But my function needs that the block contains exactly 512 bytes, i.e., if the input is smaller than 512 bytes (or, after breaking it in blocks, the last last b...
There is apparently a provably secure cipher that was proposed by Diffie but enhanced by another cryptographer that works like this:
Measure the length of the plain-text, n.
Multiply it by 128.
Generate this much real random data and split it out in to 128 byte arrays of equal length to the pla...
ok so the general idea for this first chat meeting / cast / thing is just to see how they go. I set the first topics as "meet the moderators", so I propose if we have other people here and listening in (hello!) we introduce ourselves and then we go from there into any questions anyone has.
we as in us moderators, although I'm more than happy for anyone else to chip in with introductions
Us moderators have colluded and found a time we can all make for the first chatcast event (see the link for the proposed idea).
The first chatcast thing will be on (Monday) the 28th of November at 19:00 UTC for one hour. Of course, the event can overrun if demand is there.
The topics will be:
...
current questions of the moment and things we might discuss post intro include handling book requests (we've covered that a little before) and I had an idea I wanted to moot too, if we have time.
ok maybe a lot before, but never mind
So I'll go first for introductions
I am ninefingers. That's not my name in real life, obviously and you can work out what my real life name is from the email on my profile. I am a maths undergrad at present with no "formal" crypto except for what I've gone hunting for myself. I study part time work full time as a software engineer; I'm currently working for a company that provides solutions to ISPs.
I am Thomas Pornin, this is my real name. I have a PhD in cryptography, and, since 2001, I work for a small company which edits software solutions for digital signatures (including PKI and time stamping).
Is there anybody other than us moderators reading that ?
My real name is "Paul Ebermann", I'm using the Esperanto version of my given name for Stack Exchange. Almost every "Paul Ebermann" you can find on Google is me, and for "Paŭlo Ebermann" quite completely. Like @Ninefingers, I have no official cryptography education ... I'm still a student of Mathematics, and will start to work as a software developer soon. I think I learned quite a lot about cryptography by reading this site since the private beta, and by following links to papers posted here.
I got to this site by chance ... committed to it just before it launched.
@Ninefingers I'm down to writing my diploma thesis, which is the last exam of undergraduate. But I'm a long-time student, and already did help instructing some first-semester students.
I got my new job by means of Stack Overflow Careers, by the way.
I am doing an EPQ at school, which is alike an essay at university, although I am struggling to find any books on the matter of cryptography.
It is a brief overview on how cryptography (public, private and hash based ciphers) has impacted the economy.
What would be the best source of articles o...
The question is, how do we start that ball rolling? I agree and have been concerned for some time that we're going a little slowly. So the question is - how do we attract more people to ask questions?
I was thinking we could work on "avid users" and "answer ratio" internally without requiring new users...
for example, we could look for users that are close to 200/2000/3000 and see if they deserve upvotes...
if a question has one really good, correct answer; maybe we could try and add other answers that are complimentary and provide background or a different take?
@PulpSpy There is no need to arbitrarily inflate the "avid users" statistics. What we want are users which actually are active, not just ones which look like that.
The metrics are not a criteria used to shut down the site, they are just some indicators.
And as far as I can judge, no one at SE thinks about shutting down our site even if we stay on this activity level we have now ... we are small, but our quality is better than most similar sites.
@PulpSpy For moving out of beta, the criteria is something like "has reached some traffic level growth that we (SE) think it is self-sustaining". I don't think we will be there for quite some time yet.
@Ninefingers Still, tag wikis should not look like a copy of Wikipedia ... they also should explain what the tag is used for in the context of our site. The last one is especially important for the tag wiki excerpts.
So I have a question to our quieter members @mikeazo, @SamuelNeves, @poncho - looking at your profiles you're all mostly "new" to stackexchange in that crypto is in all three cases your highest reputation site.
@PulpSpy Yes, our answer ratio is quite low, as many questions get one answer by Thomas, and it already says everything needed ... so nobody else cares to answer.
How are you finding it? When you see us diamonds moderating, does what we're saying make sense in terms of the comments we leave?
I'm trying to get a feel for how new users coming on board experience the site - I've been on SO for nearly two years, so I've lost the "new user" perspective entirely!
I'm not sure if anyone has noticed ... I'm occasionally going through old questions and looking for comments which should be incorporated into the questions/answers, doing the edits, and then delete the comments.
Is this a good thing to do, or does it unnecessarily bump old questions to the front page?
I personally find it interesting. As for the moderation, well, sometimes questions are closed (for being too broad) that I would leave open, but that's just my option. I don't have any complaints other than that
So, next question of mine then - I had an idea I stole slightly from a website called cybersecuritychallenge - it's a UK event being run at the moment - that we might ask our more experienced members to set reasonably challenging puzzles related to modern crypto problems, post them say here in chat and then have the rest of us try to work them out. Any thoughts/initial reactions to that? If we did it say at a challenge per month and let people work on them as and when... and hopefully ask qs!
2
I'm happy for "it's a rubbish idea" to be the answer; I just thought I'd put it out there. As a person I prefer practical things I can try as a way of learning, so I have a slight self interest factor too ;)
I could see solving the challenges as being enjoyable and could increase interest in the site... I'm not sure how to design a challenge that would be interesting and "modern"
I think it is worth pursuing at least to the "let's brainstorm some puzzles" stage
@Ninefingers Yeah that is more what I associate with puzzles... the complexity of modern crypto / protocols make it hard to come up with assessible yet difficult puzzles
@mikeazo yes - we have a chat room for that purpose already which is invite only and not visible to the public. Mods can invite any member who can chat to it, so, if anyone wants to participate in brainstorming, we have a room.
I also have to dash - supposed to be off out for food. Feel free to carry on though and I'll pick up anything else that is said when I get back. One question - do we want to do this again and what do we want for a topic? Book reviews??!!
As you know, we have a chat room! Where you are welcome to come and have a chat about... whatever you like.
I have previously suggested potentially having chatcast/organised meetings in there. To kick things off, I think we should name it. Why?
Cryptography
is pretty boring really. I mean, I'...
So I have a question to our quieter members @mikeazo, @SamuelNeves, @poncho - looking at your profiles you're all mostly "new" to stackexchange in that crypto is in all three cases your highest reputation site.
I'm trying to get a feel for how new users coming on board experience the site - I've been on SO for nearly two years, so I've lost the "new user" perspective entirely!
Well, with sci.crypt, there's no way to prevent cranks from incessantly writing about their "discoveries". Here, they don't (and if they tried, their contributions would be closed)
@ThomasPornin I'm using whatever is necessary for my article ... which mostly means ISO-8859-1 for german articles and UTF-8 for esperanto ones. There is MIME.
I don't think an adacrypt or David Scott's Bijective encryption stuff would survive here for very long. Plus the lack of threads make it very difficult to troll. I think, like Stackoverflow generally, it will survive cranks.
From an old exam question:
Consider this existential forgery attack on ElGamal. Choose $u$, and $v$ such that $gcd(v, p - 1) = 1$.
Compute $r := (y^v g^u mod$ $p)$
(recall that $y := (g^x$ $mod$ $p))$ and $s := (-r(v^{-1})$ $mod (p-1))$ s will be used as part of the forged signature
(a) Prov...
After about 8 months of SE experience (starting with Stack Overflow), what I'm most missing in Usenet (and other web forums) is the upvote button. Next is the ability to edit other people's posts for typos.
@CryptographyStackExchange As you all can see, we have an automatic feed of new questions here. So hanging out in this chat room is a good way to get notified of new questions to answer (or to edit).
Other than this, does anyone still have any questions, answers, remarks, ...? The allocated time is up, and if no one has anything to say, I'll officially close this event.
Chat-cast #1 is closed.
Actually, is chat-cast a good name for these meetings? We took this name from the same-named regular meetings in the moderator chat room, but I think nobody will object if we find a better name.
I also have to dash - supposed to be off out for food. Feel free to carry on though and I'll pick up anything else that is said when I get back. One question - do we want to do this again and what do we want for a topic? Book reviews??!!
http://en.wikipedia.org/wiki/Blom%27s_scheme
Another old exam question, I definitely missed the class on this one, because I've never heard of the Blom Scheme. Any other additional information on this would be greatly appreciated!
Question:
(a) First how can we show that in the Blom Scheme
...
All rounds of AES (and Rijndael) have a MixColumns step, save the last round which omits it. DES has a similar feature where the last round differs slightly. The rationale, if I recall correctly, was to "make the cipher appear similar in reverse as it does in the forward direction."
Why does t...
There is apparently a provably secure cipher that was proposed by Diffie but enhanced by another cryptographer that works like this:
Measure the length of the plain-text, n.
Multiply it by 128.
Generate this much real random data and split it out in to 128 byte arrays of equal length to the pla...
Us moderators have colluded and found a time we can all make for the first chatcast event (see the link for the proposed idea).
The first chatcast thing will be on (Monday) the 28th of November at 19:00 UTC for one hour. Of course, the event can overrun if demand is there.
The topics will be:
...
I am doing an EPQ at school, which is alike an essay at university, although I am struggling to find any books on the matter of cryptography.
It is a brief overview on how cryptography (public, private and hash based ciphers) has impacted the economy.
What would be the best source of articles o...
From an old exam question:
Consider this existential forgery attack on ElGamal. Choose $u$, and $v$ such that $gcd(v, p - 1) = 1$.
Compute $r := (y^v g^u mod$ $p)$
(recall that $y := (g^x$ $mod$ $p))$ and $s := (-r(v^{-1})$ $mod (p-1))$ s will be used as part of the forged signature
(a) Prov...
All rounds of AES (and Rijndael) have a MixColumns step, save the last round which omits it. DES has a similar feature where the last round differs slightly. The rationale, if I recall correctly, was to "make the cipher appear similar in reverse as it does in the forward direction."
Why does t...
