Want to read Slashdot from your mobile device? Point it at m.slashdot.org and keep reading!


Forgot your password?

Comment Re:Need a summary of the summary (Score 4, Informative) 194

No we don't.

Primality testing is easy - the problem is in P. Approximate methods for finding primes are very efficient. Exact checking is rarely used.

Modern security protocols rely on the problem of factoring a number into primes being difficult. Or on inverting exponentiation within a prime field.

Comment Re:Basic Math... (Score 1) 159

This is actually a pretty shit way of doing it; vehicles rarely hold a constant speed. If you build a database of locations and times for a vehicle doing the same route repeatedly then a more appropriate calculation is the median travel time from the given location.

Comment Re:Should be a tax on every transaction (Score 1) 251

Ok, so you seem to be more informed than I thought from your previous posts. In a market where the marketplace owner is a single central authority what you've said would hold about the privacy of bids / offers and instant settlement. But electronic traders are not working in those markets. For example, Nasdaq has distributed market making. The firms involved in trading are also making the market - this is a much closer model to a pre-electronic trading pit where the bids and offers were broadcast by shouting.

The actors in trading are the actors involved in making the market, so the signals and intentions are effectively public: or at least they are public to all of the major players in the market. One of the key behaviours that has been discussed is bots that try to identify arbitrage opportunities by leaping in to close bids before other actors, then hold the asset for microseconds before selling it in different sized parcels at different prices. They provide liquidity at the expense of widening spreads for traders. In the terms that you are described it these are middlemen, but in the case of markets like nasdaq they are also participants.

If this description does not convince you that the signals are public then I have a question for you: why do you think that firms pay so much to reduce latency to the exchange? Latency is only an issue in reaction times for deciding whether to trade or not, and the model that you've described so far with synchronous actions is non-interactive...

Comment Re:Should be a tax on every transaction (Score 2) 251

No, they don't. They don't have ESP. They can't see what you do on a market before you actually do something on the market.

That's a bit of a silly thing to say, unless you actually believe that ESP would be necessary to see what is about to happen in a market. I don't know if you've given any real thought to this at all: but before a buyer and a seller can meet to make a trade they both need to signal that they have the intention to do so.

Comment Re:Short memories (Score 1) 95

Are you confusing Yahoo with AltaVista?

There was a link on the AltaVista front page to add a site that was not in the index, and its robot spidered all the links from that starting URL. Their big boast at the time was they had a bigger index than any other search engine (something like 8 billion pages). That was one of the reasons that Google used to crow about how many pages they could spider in their first few years.

Comment Re:It doesn't pay to be the first (Score 1) 95

Google had two big improvements over AltaVista (which at that point was the market leader by far). Relevance and speed. By that stage SEO was alive and well (although probably not called that). The big trick for fooling search engines of the time was spaff filler at the bottom of a page that contained search terms to make the page seem more relevant. When Google started page rank was mostly immune to this technique so it returned much more relevant results, and that is why it spread so quickly and overtook AltaVista. The fast loading simple front page really helped as well. Of course now SEO is mainly aimed at Google's algorithm of the week and the relevance and quality of the results has gone downhill since those early days. Of yeah, and their various AJAX / caching technologies have broken the web completely and are the reason that every machine I've seen recently has a bunch of semi-permanent connections to Google edge points.

Comment Re:RSA = out of date (Score 1) 282

Whoops, was working from memory and it has been a looong time. DH key exchange is indeed completely different to what I said above - as you've said it is an alternative way to set up a secret channel. Certifying trust on a public key is indeed the important issue, and solved in a different way.

I'm guessing the alternative issues on IBE are the need to trust the CA, which puts it roughly in the same level of messiness as using digital signatures on public keys anyway. Is that Matt Palmer at the National Archive?

Comment Re:RSA = out of date (Score 1) 282

What you have described is true when both parties hold the relevant keys, and they believe that the keys have not been compromised - this is when I can trust that I really have your public key and not one substituted by an adversary. To solve this problem of key distribution the DH key exchange algorithm is normally used, and this relies on the hardness of discrete logs. If the DH problem is weak (which now appears to be the case) then RSA would be borken in the sense that you could not exchange keys to use it.

Slashdot Top Deals

The opposite of a correct statement is a false statement. But the opposite of a profound truth may well be another profound truth. -- Niels Bohr