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4:28 AM
Q: Is there any serious discussion about using blinding intermediaries in digital currency scenarios?

Jeff BurdgesA 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 ...

7 hours later…
11:09 AM
Q: C++ 512 block size message encryption

melvinI 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...

6 hours later…
5:04 PM
Q: Diffie's cipher

Simon JohnsonThere 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...

2 hours later…
6:54 PM
I'm slightly early, but here.
I'm here, too :-)
So am I.
Excellent, ready to begin?
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
7:01 PM
Just as reference, here is the relevant meta post:
Q: Chatcast event #1 - meet the moderators

NinefingersUs 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.
So that's me - @PaŭloEbermann, @ThomasPornin?
My turn, then
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 ?
I am... also if this chat gets snipped into a transcript, others may later
I'm here (mostly)
7:10 PM
Ah see everyone's here :) @PaŭloEbermann your turn?
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.
@PaŭloEbermann In my mind I had you down as a lecturer (!!) - are you doing postgraduate or undergraduate maths?
@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.
@PaŭloEbermann Where do you work ?
I ask that because Careers seems to be quite US-oriented
@ThomasPornin For Zalando, in Berlin (Germany). Not yet, actually ... but starting on Thursday.
It was one of about four offers in Berlin.
7:18 PM
@ThomasPornin I actually found my job through careers also
but the jobs on there for the UK compared to the US are tiny
Someone else wanting to introduce themselves, or having questions?
Q: Good source of notable articles on cryptography

Will03ukI 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 bot clearly has a sense of humour...
I have a general question... how can we improve the site stats? For example, the stats here: area51.stackexchange.com/proposals/15811/cryptography
7:21 PM
@PulpSpy Generally speaking, by asking more good questions
Good questions will attract answers
answers attract readership
the whole thing is supposed to have its own positive feedback, so after a while it becomes self-sustaining
The cornerstone is having experts
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?
people who know their trade and are willing to post answers
experts are retributed by the intellectual satisfaction of having written a good answer, and this comes only from good questions
Good points
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 I think this is a good approach. Perhaps we should (on meta?) shortlist some questions we can add more detail to?
anyways, maybe this should be discussed on meta in more detail
I just was throwing it out there
7:27 PM
@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.
I have another suggestion - can we reach out to the IACR? Does anyone here have any links?
They run book reviews too... which I think I mentioned in my meta post.
Well, I am a current member of the IACR
I am not sure what we would want to say to the IACR, though
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.
some sites are "sponsered" by orgs I think... but I think it is too early for that
I am not worried about being shut down... just moving out of beta
and generally improving the site
On the other hand, upvoting good content is what should be done, independently of who answered/asked. This will give us our "avid users" by itself.
7:31 PM
@PaŭloEbermann No. Your site (last I checked) is in no danger of shutdown.
@PaŭloEbermann Exactly; if people aren't voting then they should be.
Another thing you can all do regardless of reputation is edit posts.
And tag wikis
@AarthiDevanathan Shutdown can happen ?
I always thought it was an empty threat just to keep people motivated
@ThomasPornin .......Yes.
if you have under some reputation (not sure what the exact figure is) and your edits are approved, you get +2 reputation.
@ThomasPornin Did happen with some sites already. Nobody remembers them, though ... which shows it is only done for sites nobody cares about.
7:34 PM
One thing we could do at some stage is have a "tag wiki editing spree" - here's an example tag wiki: crypto.stackexchange.com/tags/number-theory/info
@Shog9 out of interest, are tag wikis indexed by search engines? Can you say?
@Ninefingers It is +1k for a beta site
@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.
after that your edit goes through, no approval and no +2
@Ninefingers yes, they are
not by the internal search though
So as a broad introduction to the topics, properly written tag wikis will generate us traffic. So that's one thing we should definitely consider.
7:36 PM
@Ninefingers Looks like this
@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.
does mathjax work in tags?
I see now that it does
@PaŭloEbermann This is true - I was thinking more that we have two options - 1 link to great questions and 2 - link to great resources.
@PulpSpy Not in the excerpts, though (there is no formatting at all).
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.
7:43 PM
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!
@PaŭloEbermann Ah, maybe I should wait a bit before answering
I don't really have complaints of the moderating, at least when it comes down to edits and topic closings
not sure if that's what you're asking
I've enjoyed being on crypto.se. Have learned a ton.
@ThomasPornin I think the primary contribution of the site is getting timely, good questions, so I wouldn't hold off... stats are secondary
we can work on adding complementary information where ever possible... and make that a priority
@SamuelNeves That's good to know (excellent @mikeazo). It sounds like crypto.se is appealing then :)
7:48 PM
@Ninefingers Definitely is.
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?
@PaŭloEbermann Bumping old but good questions is rather nifty
Good questions on the front page is a good thing for the site appeal
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
I'm trying to limit it to not drive new questions completely off the front page, of course :-)
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!
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 ;)
7:53 PM
@Ninefingers So the challenges would go through chat ?
@ThomasPornin Well... I don't know yet actually. Maybe meta?
This looks like a blog job
I'm open to ideas/thoughts/people's reactions
You want a rather stable, accessible place for the current challenge
and a canonical place for the solution (published a few days / weeks afterwards)
Something like projecteuler would be optimal
7:55 PM
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
@PulpSpy I think historical challenges might be interesting too, personally; we had a question on the enigma I think.
@PulpSpy I have one proposal, @Ninefingers was supposed to review it (hint !)
@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
@Ninefingers I would be interested to try my teeth on such challenges, but I'm not the right person to think of new challenges.
@ThomasPornin Cool!
7:58 PM
@ThomasPornin sorry... I had to put 15k users live last week and I'm still firefighting dealing with the outcome
I will have a look, I promise :)
I could paste it here right away, though
@PulpSpy Is there any where we can brainstorm without giving answers away?
My proposal does not include any hint as to the solution
@mikeazo That is a good question... is there any private chats on SE?
There can be locked rooms
actually there is one called "Challenge construction room"
8:00 PM
@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.
meant precisely for that
Obviously, if you have access, you have to promise not to give the challenges away...!
remember that people with access to that room may see spoilers
8:01 PM
@ThomasPornin are you reading my mind? :P
[I have to leave now but will come back and read the transcript... it was fun... bye everyone]
@PulpSpy No problem, thanks for coming.
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??!!
"Book reviews", that's a hard one
Discussion about book reviews, or reviewing books in chat?
both, I think
but I was talking about the former
8:06 PM
Another thing: We could try to brainstorm a name for our chat room.
Q: Should we name our chat room?

NinefingersAs 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'...

Does anyone has any ideas?
Right now it is called "Cryptography" -- that's accurate
"The Puzzle Palace" :-)
(If not now, we can also do this in the next meeting.)
@poncho That's a bit less accurate ... as we are not (only) discussing puzzles here.
Something with "secret"?
challenges can be a good way to teach people about many implementation mistakes
low-exponent rsa, cbc-mac and cbc with same key, etc etc
@SamuelNeves Save your ideas for later, when you are constructing a challenge.
8:14 PM
@fgrieu, feel free to answer @Ninefingers' question above, too.
35 mins ago, by Ninefingers
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.
34 mins ago, by Ninefingers
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?
34 mins ago, by Ninefingers
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!
(Anyone else, too, of course.)
I think they're imports from sci.crypt
Yes, I came from sci.crypt
Ponco is on sci.crypt, for example, and fgrieu is also.
I find that site a wonderful upgrade from sci.crypt where I used to write, and am still wondering what kind of glue makes this miracle hold
So far every moderation I saw was kind of approriate, and I see nothing to change
8:22 PM
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)
@fgrieu crypto.SE is maintained. People are actively working on the technical details so that the user experience is smooth.
@fgrieu Looks like the Stack Exchange system works for some kind of topics. Or we are just lucky to not get the wrong experts yet.
Usenet in general has not yet finished its internal struggles to decide whether it should use ISO-8859-1 or UTF-8 as the next step beyond ASCII
@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.
The ability to use this tex-like thing for formulas is a great plus for crypto.
8:25 PM
Stack Exchange offers formatted text with bold, italics, bullet points, and, last but not least, inline LaTeX.
That's half of what makes it more pleasant than sci.crypt
Yes, I agree, Tex formatting is a great help
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.
Q: An existential forgery attack on ElGamal

Bobby SFrom 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.
The other half, in my opinion, is that the strict question-and-answers format, and the trigger-happy moderators, make Stack Exchange mostly crank-free
8:28 PM
@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.
42 mins ago, by Ninefingers
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??!!
8:47 PM
Q: Proofs involving Blom's Scheme

Bobby Shttp://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 ...

@PaŭloEbermann I usually just call them chat events. Chat-cast implies a 1-way flow of conversation (like broadcast) whereas this is a conversation.
(I'm off now, too ... have to buy ice-cream, shop is closing in 13 minutes.)
oh, hey, @ThomasPornin make sure you make the bookmark! :D
1 hour later…
10:13 PM

Chat-meeting #1

3 hours ago, 1 hour 35 minutes total – 176 messages, 12 users, 8 stars

Bookmarked 41 secs ago by Paŭlo Ebermann

For everyone who wants to reread everything.
You can find all bookmarks at the room info page.
2 hours later…
11:45 PM
Q: Why is MixColumns omitted from the last round of AES?

FixeeAll 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...


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