## Comment broken link (Score 1) 344

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*Today, you probably pay a flat fee for your Internet service and, for the most part, you don't pay anything for the various Web sites you visit or services you use. In the pre-CIX Internet days, it was an entirely different story.*

*Unless you were lucky enough to live close to an online service point of presence you had to use a dial-up modem to call up an X.25 packet switched wide area network (WAN). This connection service alone could cost anywhere from an affordable $1 an hour to a wallet busting $30 an hour, which you could then use to connect with an online service. The online service would also typically charge you a monthly fee plus an additional fee of $1 to $6 an hour. And you thought your ISP was expensive!*

That's between $2 and $36 per hour. At the speeds mentioned, you could transfer 135,000 bytes per hour. That's $0.00237 to

$0.0427 per 160 bytes, which is much less than the $0.20 that we are charged today for text messaging without a plan. Incredible.

DVR

Apparently, it hasn't leared how to spell yet.

It's very possible that this is just a coincidence and that this has nothing to do with the meaning of the bits. Sure, it seems like there's no way it could be by accident that a number around 6.8 billion is prime, but there is:

The chances of a random number x being prime are about ln x. ln 6830770643 ~= 22.6, but it's possible that the first number had to be 1, which would mean (since it's palindromic) the last number has to be 1 (making the number odd), excluding 2 as a possible factor. This puts the chance at more like 11.3. It's quite possible that we're reading too much into this. This might've just been randomly picked by an artist, (and then made symmetrical by making it a palindrome) instead of designed by a geek (and intentionally including a hidden meaning or just making it a prime or something).

In searching for additional evidence that primes were an intentionally selected theme, I looked at:

11001011100100101

10100100111010011

0100100111010011

1100101110010010

(each half of the palindrome, with and without the 1 in the center)

One of these is prime: 0100100111010011_2=18899_10, 18899 is prime. I'm not sure what it means, but I doubt those substrings were chosen for their primality.

I'm from the UK, is 4+3+2=( )+2 a commonly used / commonly understood way of presenting the problem in the US?

No, that's not standard usage in the US or anywhere else that I'm aware of.

It's always possible the report was not properly representing what he was trying to convey, but the report definitely shows usage that isn't clear for anyone, unless it was explained on the test. No wonder people are confused.

Blizzard announced today that *StarCraft II: Wings of Liberty*, the first game in a series of three, will be released on July 27. The game will contain the Terran campaign (29 missions), the full multiplayer experience, and "several challenge-mode mini-games," with "focused goals designed to ease players into the basics of multiplayer strategies." It will launch alongside the revamped Battle.net, which we've previously discussed. Blizzard CEO Mike Morhaime said, "We've been looking forward to revisiting the *StarCraft* universe for many years, and we're excited that the time for that is almost here. Thanks to our beta testers, we're making great progress on the final stages of development, and we'll be ready to welcome players all over the world to *StarCraft II* and the new Battle.net in just a few months."

The first time you encounter the concept of factoring (as per OP's question) is probably not the best time to introduce mathematics requiring groups and rings.

Granted.

And while the GNFS is indeed magnificently superior to naive searching, it is not sufficiently fast to make a significant difference to the cryptographic strength of a system based on the difficulty of finding large factors - hence, I judged it was not worth mentioning.

While the fact remains that you can make the number large enough for it to be impractical even with GNFS, I must disagree that it makes no significant difference. If the only thing we could do was trial division by primes, a 44 digit RSA composite would need at most ~200 quintillion divisions to find the factors. (see http://primes.utm.edu/howmany.shtml, there are ~200 quintillion primes below 10^22) More than sufficient for safe encryption. Even if you could do 1 billion per second, you'd need almost 6400 years to crack it.

But since there's GNFS, a 309 digit (1024 bit) number is currently the standard, and is being phased out.

In any case, you could've said something along the lines of "There are some more efficient ways, but they are still difficult for large numbers." instead of "There are some tricks you can use to speed it up, but that's essentially it."

It is cryptographically useful because it doesn't have a short way of doing it: you have to simply try dividing by 2, 3, 4, 5, etc, till you get an answer. When you have a number that's several hundred digits long and only has two relatively large factors, this takes a very long time. There are some tricks you can use to speed it up, but that's essentially it.

This is very, very wrong. What you describe is the most naive possible way to factor a number, a.k.a. trial division (without an obvious "trick" to speed it up: not bothering dividing by composites). There are far more efficient ways to factor large numbers. The fastest, currently, for numbers over about 90 digits without any easily-found smaller factors, is the General Number Field Sieve.

http://en.wikipedia.org/wiki/Integer_factorization

http://en.wikipedia.org/wiki/Trial_division

http://en.wikipedia.org/wiki/General_number_field_sieve

you could crack a 768-bit RSA in... roughly guessed...

Sorry, no. That doesn't take into account the fact that some parts can't be run in parallel on many home computers. Not to mention that the longest part, sieving, for a number this size, needs about 1 GB of RAM free, which I'd think people would be likely to notice and shut down pretty quickly...

Sieving is the step that takes the most time, in this case 1500 CPU years ("On a single core 2.2 GHz AMD Opteron processor with 2 GB RAM per core, sieving would have taken about fifteen hundred years."), but can easily be run in parallel. Let's say you have access to 100,000 cores, each with at least 1 GB of RAM that you can use (read the PDF...). It will now take you 5.475 days to do the sieving.

Polynomial selection can, like sieving, be easily distributed, and is a relatively trivial task with 100,000 cores available. (roughly 20 CPU years, or under 2 botnet-hours, and a non-enormous amount of RAM)

The hard parts are the final steps: filtering, building a matrix, solving it, and finding the factors. You basically need one or more supercomputers to do it, with at least one of them having 1 TB of RAM and fast access to 5 TB of data. To do it like they did, you'd also need to write your own block Wiedmann implementation. If not, you'd have to use the block Lanczos, which can only be run on a single computer/supercomputer/cluster.

Doubtless, someone could botnet enough computing power to sieve for an RSA-768 key in a matter of weeks, but to actually finish it and get the factors would require an expensive supercomputer, be it purchased, (better hope whatever's behind that key is valuable...and thank goodness that they were stupid enough to use just a 768-bit key on it) botnetted, (good luck to get one and not have anyone notice!) or otherwise acquired.

What they did was factor a 768-bit number, like one that could be used as a 768-bit RSA public key. e.g. to factor 15, you need to find that it is equal to 3*5, which can be easily done by dividing the first few primes and finding that 3 divides 15. To factor a very large number, like a 768-bit number that is semiprime with the two factors both about the same size, (as is the case with RSA public keys) is a very difficult task. It is currently best done by the General Number Field Sieve (GNFS). For more info on any of these concepts, use Wikipedia.

This demonstrates the possibility of breaking any given 768-bit RSA key by factoring the public modulus, and shows how much work that takes. Note, however, that it is still very difficult, and in this case took multiple years of calendar time and hundreds of years of CPU time to crack.

This does not mean that every 768-bit RSA key can be cracked any more easily than it could before, it just demonstrates that we have the ability to crack any 768-bit RSA key (given the time and resources).

BlizzCon kicked off this morning with a keynote address that brought some major announcements for some of their games. First, *World of Warcraft's* third expansion, *Cataclysm*, was officially revealed. It differs from the previous expansions in that they will not be creating an entirely new continent for players to explore. Instead, the two huge continents from the original game will be going through a literal cataclysm, causing some zones to be destroyed, new ones to become available, and existing ones to be entirely revamped. Big news came for *Diablo III* as well, with the announcement of the Monk class and a trailer showing how it plays. More details for both games as well as *StarCraft II* will undoubtedly become available over the next few days, but read on for more about what we already know. If you have any questions, don't forget to post them here.

cheros writes *"NASA reports that the Spirit Mars lander is presently stuck in soft soil. The lander's wheels are halfway sunk into the soil and they are planning simulation tests to see if they can get it out again. I hope they can get it out of there because it's picking up enough new energy to operate; however, it only has 5 wheels left to get around on — one of the wheels hasn't been working for years. Fingers crossed."*

This is a bit more mathematics than general science, but I'd suggest GIMPS for a chance to find a huge prime or, if they're more interested in actually finding a prime than searching for an enormous one, I'd suggest No Prime Left Behind (NPLB).

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Murphy's Law, that brash proletarian restatement of Godel's Theorem. -- Thomas Pynchon, "Gravity's Rainbow"