# Lists 2010 : StackExchange sites

One of the trends of 2010 was the proliferation of StackExchange sites. I guess by now most of us visit MathOverflow along with the arXiv daily. But, there are plenty of other StackExchange sites around that may be of interest to the mathematics-community : Mathematics somewhat less high-brow than MathO. Physics still in the beta-phase (see below) Theoretical computer science… Read more →

# On2 : transfinite number hacking

Surely Georg Cantor’s transfinite ordinal numbers do not have a real-life importance? Well, think again. Read more →

# return of the cat ceilidh

I couldn’t believe my eyes. I was watching an episode of numb3rs, ‘undercurrents’ to be precise, and there it was, circled in the middle of the blackboard, CEILIDH, together with some of the key-exchange maps around it… Only, the plot doesn’t involve any tori-crypto… okay, there is an I-Ching-coded-tattoo which turns out to be a telephone number, but that’s all.… Read more →

# now what?

You may not have noticed, but the really hard work was done behind the scenes, resurrecting about 300 old posts (some of them hidden by giving them ‘private’-status). Ive only deleted about 10 posts with little or no content and am sorry I’ve self-destructed about 20-30 hectic posts over the years by pressing the ‘delete post’ button. I would have… Read more →

# the crypto lattice

Last time we have seen that tori are dual (via their group of characters) to lattices with a Galois action. In particular, the Weil descent torus $R_n=R^1_{\mathbb{F}_{p^n}/\mathbb{F}_p} \mathbb{G}_m$ corresponds to the permutation lattices $R_n^* = \mathbb{Z}[x]/(x^n-1)$. The action of the generator $\sigma$ (the Frobenius) of the Galois group $Gal(\mathbb{F}_{p^n}/\mathbb{F}_p)$ acts on the lattice by multiplication with… Read more →

# Weil descent

A classic Andre Weil-tale is his narrow escape from being shot as a Russian spy The war was a disaster for Weil who was a conscientious objector and so wished to avoid military service. He fled to Finland, to visit Rolf Nevanlinna, as soon as war was declared. This was an attempt to avoid being forced into the army, but… Read more →

# key-compression

The main application of tori to cryptography is to exchange keys more efficiently while preserving the same security standards. In the Diffie-Hellman key-exchange one interchanges elements of the finite field $\mathbb{F}_q$ where $q=p^N$ is a prime-power of a large prime number $p$. If we call an element of the prime field $\mathbb{F}_p$ a pit (similar to… Read more →

# tori & crypto : Diffie-Hellman or GCHQ?

Boris Kunyavskii arXived the paper Algebraic tori – thirty years after dedicated to the 80th anniversary of V. E. Voskresenskii. The goal is to give an overview of results of V. E. Voskresenskii on arithmetic and birational properties of algebraic tori which culminated in his monograph “Algebraic Tori” published in Russian 30 years ago. As Ive worked on this stuff… Read more →

Suppose for a moment that some librarian at the Bodleian Library announces that (s)he discovered an old encrypted book attributed to Isaac Newton. After a few months of failed attempts, the code is finally cracked and turns out to use a Public Key system based on the product of two gigantic prime numbers, $2^{32582657}-1$ and $2^{30402457}-1$, which were… Read more →