24.4.2012 22:22, pesco
A few years back I prepared a presentation on the so-called
Socialist Millionaires' Protocol (SMP) for a university seminar.
SMP is a solution to the problem of key authentication
devised for
OTR (Off-the-Record),
the system for instant-messaging encryption.
Today I held a short version of the presentation
for non-mathematicians at the
CCC Hamburg.
For the benefit of the Internet,
the awesomely hand-made
slides
are in English.
There is also a handy
hand-out
with a protocol diagram.
The
written presentation for the course
is
completely in German and math-rich.
I did try hard to make it a clear read for the so-inclined.
Have fun! :)
5.7.2011 10:30, pesco
tags: bitcoin talk slides
I held a little intro talk about
Bitcoin last night
at a local Linux meetup kinda thing. It was a light technical description of
what the system is and how it works.
Here are the
slides and
their LaTeX
sources. That is all.
29.4.2011 21:00, pesco
tags: crypto blindsigs chaum
I'm starting work on my diploma thesis this month.
The exact topic isn't set in stone yet,
but it will be something crypto.
If everything goes dreamy-awesome,
I'll find something nice to write about lattice-based
blind signatures or somesuch.
Background:
- Blind signatures are used for e-cash.
I'm fascinated with e-cash.
- Lattice-based methods are candidates for quantum-resistant systems.
Appearently there's lots of current research going on.
- I've done some lattice theory at Charles University in Prague.
Never thought I'd see it again, so wouldn't that be something.
- There's zero knowledge in there somewhere.
Another fascination.
So, time to sum up the basics.
As far as my history serves,
David Chaum invented blind signatures in the 80s for electronic voting
but nobody wanted to buy that,
so he also invented electronic cash.
Then he got really paranoid and didn't sell it either.
Real quick summary. ;)
Anyway…
The principle is to mix whatever you want signed
(electronic voting ballot, 100 EUR banknote)
with a random
blinding factor
and divide that out only after Trent
(your government, bank) has signed.
Thus Trent cannot recognize and connect the note to you
when it comes back to him later.
The classic algorithm is based on RSA and is painted up fast.
Unfortunately, my awesome markup language still has no fancy math support
so you have to live with ASCII art:
m = message to be signed
e = public "encryption" (i.e. verification) exponent
n = public modulus
d = secret "decryption" (i.e. signing) exponent
k = blinding factor (just a random number)
x^(de) = x^(ed) = x (mod n) -- RSA property
Alice prepares: mk^e -- blinded message
Trent signs: (mk^e)^d = m^d k
Alice unblinds: m^d k / k = m^d -- signed message
Bob can check: (m^d)^e = m
One might think that signing something completely blindly might be a bad idea.
After all, a bank needs to know the value of the note it is signing.
To ensure
any desired property of the signed document,
Trent can require a
cut-and-choose
step.
In this case Alice must give him
n different but equivalent messages.
He chooses one of them and asks Alice to unblind all the others.
Trent signs the remaining blinded one if
the others satisfy the desired property.
Alice's chance to cheat of
1:n can be made unattractive
by attaching a suitable penalty.
14.3.2011 22:13, pesco
tags: memory game javascript kompilierfreizeit
I used the weekend to code
a little memory game
in Javascript.
Apart from being pointless and annoying
(especially if your visual memory sucks as much as mine),
I think it turned out lovely!
I was hoping to gain some experience with user-facing Javascript
from it, as
previous excursions into the
misunderstood programming language
have been minimal in
one way
or
another.
So, this time I got to use some actual objects.
Structured data, woo!
I poked around the design space a little to see what was up with
Crockford's take on
prototypal inheritance
vs.
others' assertions
that his dislike of the
new-operator was ill-founded.
You can look at
the code
to see what I settled on in this instance,
but maybe I'll leave that discussion for another post.
Suffice it to say, it's a bit of a mish-mash
but I'm sure it will crystallize nicely.
Oh yeah, and this is going onto my
side project
(I desperately needed one!) site
kompilierfreizeit.de.
I'm going to collect some nice other time wasters there,
but won't say it out too loud, yet.
That would just make me feel obligated…
Have fun!
27.1.2011 0:30, pesco
tags: tron movie eastereggs perlin
I just (re)watched the original Tron. Highlights:
- Adam, Tron's user, has the phrase
gort klaatu barada niktu
posted up in large letters on his cubicle wall.
This is not a reference to Army of Darkness
(1992, duh) but to
The Day the Earth Stood Still
.
I should watch that.
- The screen in the control room of bad guy's ship shows pac-man in one scene
(see image above).
- The image of Moses in Southpark episode
Jewbilee
(s03e09) is modeled after
the Master Control Program (see image below).
- Spotted Kenneth Perlin
in the credits.