The Side Channel

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Maarten Bodewes

12:19 AM

@ZION Hmm, indicating what kind of trouble would be nice...

Running out of Pi?

ZION

Maarten don't worry I fixed it :)

mathb.in/134663

Q: Verifying the Indictor Function:$X_{[a,b]}$ can be expressed as a Fourier Series?

In the text "Fourier Analysis: An Introduction" by Elias M. Stein and Rami Shakarchi. I'm having trouble attempting to verify the that $f(x)$ can be written as a Fourier Series in $Propostion \, \, (1.2).$ Note my initial approach to verify $Proposition \, (1.2)$ can be seen within, $Lemma \, \,...

Maarten the question is up

Maarten Bodewes

Ugh, am I fortunate I'm not so much into math :P

But I can up it 1 of course :)

ZION

Thanks Maarten it's mathematically a very heavy question

Maarten do you do applied crypto

Maarten Bodewes

Yep. I do some math sometimes but I'm no theoretical cryptographer as such

Then again, most academical cryptographers cannot program worth a damn

And I'm OK with explaining things and reading papers and such like.

ZION

Maarten I'm interesting gin quantum cryptography

Maarten Bodewes

12:31 AM

Me too, but the math scares me a bit. I'll focus on the solution, i.e. quantum resistant cryptography; that's hard enough in itself.

ZION

Maarten math is about understanding

Maarten what makes the math scary if you are scared then it means you don't understand

Maarten Bodewes

It requires a lot of abstract thinking. I'm pretty good at that but there are limits. And I'm missing practice. Can't say I had good tutors either.

ZION

Maarten practice makes perfect keep going and you'll get it

Maarten Bodewes

Too much work, too little reward I'm afraid. I'm good at what I do, just couple me to somebody good at math and we'd make a perfect team.

I'm good with development, software architecture, standardization, common criteria certification, applied cryptography, secure programming practices and I'm trying teaching it as well. I mean, there is so much you can specialize in.

ZION

Maarten I used to do Vulnerability Research

but then I moved to Mathmatcal Physics/ Analysis

Maarten Bodewes

12:38 AM

Oh, cool. Like what Riscure does?

Or more software oriented?

ZION

Who's Riscure ?

Maarten Bodewes

Oh, they specialize in hardware side channel attacks

But I guess more white/grey/black hat stuff?

ZION

Maarten I mainly did CTF(hacking contests) and Malware stuff

I nearly got a job

Maarten Bodewes

Darn shame that you could not get it. I know Melanie Rieback. You could contact her if you want to do some hacking. She mainly manages her people online.

You probably need to show some skillz of course :)

ZION

Maarten I don't do the whole hacking thing anymore, I just don't do it

Maarten Bodewes

1:01 AM

OK - it just an idea. I'm off to bed, it's getting late here and I'm doing nothing productive anymore.

Then again, it is weekend :)

Talk to you later!

G'nite.

ZION

see ya

16 hours later…

Evinda

4:59 PM

Hello

I have a question about the number of steps that an algorithm that computes a discrete logarithm makes

SEJPM

@Evinda go ahead

Evinda

I want to give an upper bound for the number of operations in the group $\mathbb{Z}/n \mathbb{Z}$ that the algorithm makes.
We can find the multiplicative inverse $g^{-1}$ by applying the extended euclidean algorithm for g and n.

The time complexity of the extended euclidean algorithm is $O(\log{a} \log{b})$ when we apply it for a and b.

So we need in our case $O(\log{n} \log{g})=O(\log^2{n})$ time to compute $g^{-1}$.

After that it remains to compute the product $y \cdot g^{-1} \mod n$.

For this, we need $O(\log{y} \log{g^{-1}})=O(\log{n} \log{n})=O(\log^2{n})$ time.

SEJPM

5:14 PM

@Evinda note that $g<<n$ usually

the HAC should also have a section on algorithmic complexities

6 hours later…

Evinda

11:47 PM

@SEJPM Ok... But isn't the upper bound right?

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