Not radio-controlled, so someone's not likely to hack the contol signals
Well, it's not directly radio controlled, but I'm pretty sure the Air Force can issue new commands to divert the plane's course if they need to, or extract any kind of status information on how the plane is doing. On the other hand, we can safely assume they're using strong encryption, so you wouldn't have much of a chance breaking the code. This would be a perfect application for a one time pad (at least for the commands, the images might be a little too big for that)
The risks of explosion from fuel cell batteries is probably smaller than the risk that your Lithium-ion battery explodes.
Most fuel cell technology uses substances like methanol as a fuel, and this is pretty harmless stuff.
Lithium-ion batteries can potentially create metallic Lithium, and that would be a bad thing to have sprayed all over your lap. Try looking up 'lithium ion explosion' on google
The end user doesn't want to deal with security
on
New flaws in 802.11B
·
· Score: 1
No matter how strict you make your security, in the end it depends on the user.
If you take every attempt to provide good security, the customer will find your key management such a big hassle that they won't buy your products. Popular magazines will make fun of your complicated methods, and elaborate network setup, and will praise the Plug-and-Play method of your competitor. The only way to survive as a vendor is to make it easy on the user. Unfortunately, tight security and ease of use don't mix very well.
I'll bet that more 802.11 networks are broken into that are simply not using any security at all, than networks that have had their WEP security cracked. Just because the network manager couldn't be bothered to check the box that said 'use WEP security'. And even if people do enable WEP security, how many do you think will opt for a 128 bit hex string, as opposed to an easy to remember dictionary word ?
The 802.11 was designed for operation over short distances only. All the timing calculations assume that the air propagation delay is negligable.
If you're going to use 802.11 for outside links, you have to take the propagation delay into account. For every mile between the two stations, there is a >10 usecs round trip delay. The 802.11 standard uses a 20 usec time as a slot length. These slots are the basis for the random backoff procedure, and can also be found in the difference between the various inter frame spaces. When the total round trip delay (air+rx+tx delays) becomes greater than 20 usecs, you'll get (some) performance degradation.
The degradation in DCF mode is graceful, but the PCF will basically break down completely in the face of long delays. Fortunately, most vendors don't even support PCF.
Things get worse if you have more than a simple point-to-point link.
In short, 802.11 can work over long links, but don't bet the farm on it, and results may vary with equipment.
The WEP encryption works like this (assuming 128 bit version)
- every station has a 104 bit secret key
- every packet has a 24 bit IV (initialization vector) in the header.
The 24 bit IV and the 104 bit key are combined into a 128 bit key, which is used to seed a pseudo random generator based on RC4. The resulting stream of random numbers is then XOR-ed with the payload. To avoid tampering with the contents, there's also a 32 bit ICV (integrity check vector appended) which is a CRC on the plaintext.
Now, the short IV is vulnerable to attacks because if you ever find two packets with the same IV (and the same secret key), you know the contents have been XOR-ed with the same stream.
However, if all the packets you receive use different IV, your only way to find the contents is to crack the 104 bit secret key.
The proposed changes to WEP include a larger IV, that's not appended to the secret key, but XOR-ed.
This will still result in a total 128 bit key length to seed the RC4 engine, so this will be a firmware-only upgrade on most (all ?) hardware vendors.
I think that option 4 can be construed as a copyright violation.
If a server can MD5-sum any portion of the aim.exe file upon request, I could easily request MD5-sums of every single byte and reconstruct the original aim.exe image.
Of course that's why people are talking hydrogen rather than batteries and electric charge. Pumping gas into a car is equivalent
to "charging" it at a rate in the BILLIONS of watts. You're not going to pull an electric into a station and give it a quick charge.
You'd be using the entire output of a fossil fuel or nuclear plant to charge ONE car. The magnetic fields around the cable would
bend the sheet metal.
While I agree with most points you make, these numbers are not entirely realistic. A full tank of gasoline is about 2 MJ, but nobody is expecting that you can recharge an electric car in 1 second. If you take a more realistic number of about 2 minutes for a charge, you 'only' need about 15 MW. The best way to do this would be to exchange the batteries for fresh ones. This isn't really feasible with current battery technology, of course.
The heat wasted in the brakes of a car stopping from 50 MPH, once, could heat a snowbound four-bedroom house for half an hour
Sounds impressive, but is exaggerated. A 1000 kg car, running at 50 MPH has a kinetic energy of about 250kJ. Divide by 1800 seconds, and you'll get 140 Watts. This isn't going to heat a four-bedroom house. You'll need something closer to 25 kW for that.
I've always understood that this type of higher temperature superconductivity breaks down in the presence of strong magnetic fields, such as produced by strong currents in the material itself.
I think that the free internet will explode again when consumer bandwidth increases. When the average user has a 500Kb/s connection, the possiblities open up.
I think so too, but in the other direction. When people have cheap, high speed internet at home, they will start to run their own servers. Since they expenses are already paid, they don't need to generate income for their site and/or bandwith, and can focus on meaningful content. I don't think it will be easy for the big companies to create extremely flashy sites with little content, using unavoidable ads, to compete with the content-rich home user. Of course, the home user can never dream to built a site like CNN's, but like you said, CNN can afford not to have unavoidable ads, because they get enough hits (and their content is relatively cheap because the research has already been done for their TV channels).
For example, I run a rec.puzzles archive at home, no banners, no ads, simple makeup, just the content. Bandwith is limited, but will undoubtedly increase in the future. My bandwith requirements (due to lack of images) stay modest. Somebody with a commercial site, with similar content as mine is going to have a hard time getting viewers if they force the user to download tons of annoying ads before they can view the content.
It also doesn't matter that a big company can through money around to lure viewers to their site, because Google will advertise mine for free.
What I didn't get from the article is how they think they're going to fetch the asteroid, and move it into a proper orbit. Doesn't seem trivial to control a 100 km big rock.
And as they say, you don't want it actually hitting the earth.
For whatever it's worth, a Faraday cage only blocks electrical fields, not magnetic. Powerful magnets as used in the train will certainly penetrate the train itself. Whether this is dangerous is a completely different story of course.
Also, a Faraday cage needs to be closed all the way. You couldn't make a big window in it, and still effectively block ectrical fields. The size of the maximum holes you can have depends on the wavelengths you want to block, the bigger the holes, the longer the waves that can get through.
Also note that if the holes aren't circular, you have to take the longest dimension into account. This means that a long, narrow, slit in a Faraday case renders it useless.
Why doesn't Linus quit working on his kernel, and concentrate his efforts on gcc 3.0 ?
Why don't you sell your computer, and donate all the money to finding a cure for AIDS ?
This is a useless argument, and I wish people would drop it. There's always something more important (especially stuff that others find more important) than the stuff you're working on.
The symbols are designed to withstand some noise on the transmitted signal. They are sufficiently big, and different, that a few flipped pixels will not turn them into another symbol, and confuse the recipient.
Also, the code is sent in the form of simple images so that it is easy to include a few drawings. The invidual pages are also outlined by a single pixel, which should make it really easy to figure out that you're on the right track when you try to decode the message.
Using a balanced eco-system is not the ideal way to harvest energy. You still need to put in energy (i.e. light) for the algae to grow, and it would be easier and more effective to skip the entire eco-system, and use solar panels to create your energy directly from the light.
A balanced eco-system is useful for space travel, but only because humans are going to be part of the food cycle, because they depend on sugar, and can't survive on light alone. Plus the eco-system will take their waste products, which is nice. But it would be silly to have a sugar powered robot running around on a space ship/colony for example. Sugar costs more per joule than sunlight in that case.
(The robot is still cool, though, and this technology will certainly be useful).
I can't get excited about motion blur. It's a hack, and even though it can improve animation at low fps speeds, it's not natural.
The problem is that our eyes can track a moving object (even at pretty high speeds), and if you do, you'd expect the object to be sharp again, not blurry. With motion blur, the object will be blurry, even if you track it with your eyes, so it will be unnatural.
The only real solution is more frames per second. Now, this is not easily done on a TV screen for example, so I can see where motion blur in Toy Story animations is a good thing. But not for computer games, played on a monitor that's capable of high frame rates. Instead of using hard- and software to perform motion blur, use it to increase the frame rates...
Creditcards are by nature very unsafe, because their security depends on a single "public key" that's printed on the outside, and that's given out and stored by everyone that accepts payment with them. Moreover, they are handled in a very insecure way. Why do some on-line institutions insist on keeping their credit card database on an networked computer. Why do they insist on keeping the number anyway ? I'd rather type it in every time it was used, and then have it thrown away after the transaction. And why do they apparently store them in clear text ? It would be pretty easy to encrypt them using a cookie that's stored on my browser.
It's time to move towards a more cryptographically secure way of making payments. These secure methods have been developed years ago, and are still not being used on a wide scale. As long as the costs associated with the occasional credit card theft isn't too high, the banks will not take action. So, it's good that things like this happen once in a while, since the banks will take most of the damage anyway (their biggest loss is probably loss of confidence by big consumer groups).
You need a lot of extra energy to move something into infinite space. Don't forget that these satellites are still quite close to the earth, (about 100-200 miles from the surface). Compared to the size of the earth that is still pretty close, and gravity is still quite strong up there.
It may seem things are 'weightless' in orbit, but that's not true. The gravity is still present, but the satellites are basically in a never ending free fall. If you want to climb into a higher orbit, you'd still have to counteract 90% of the earth's gravity. Once you're a couple of thousand miles away, it gets a lot easier, though.
Moving them in a higher orbit has tremendous costs associated with them. If not, the space shuttle could just visit geostationary satellites. The space shuttle never does that. It only stays in the lower orbits, simply because it doesn't have the fuel to go up that high.
Thickness doesn't matter for the capability to withstand rotating at high speeds. As the thickness is reduced, the mass of the disk, and therefore the forces on the material will be reduced by the same amount. This compensates the decreased strenght of the material.
Of course, if there are small imperfections in the disk, those will become more problematic as the disk gets thinner, so the production process needs to be designed carefully so that the material has even thickness and strenght throughout the entire disk.
Slashdot Mirror
Not radio-controlled, so someone's not likely to hack the contol signals
Well, it's not directly radio controlled, but I'm pretty sure the Air Force can issue new commands to divert the plane's course if they need to, or extract any kind of status information on how the plane is doing. On the other hand, we can safely assume they're using strong encryption, so you wouldn't have much of a chance breaking the code. This would be a perfect application for a one time pad (at least for the commands, the images might be a little too big for that)
The risks of explosion from fuel cell batteries is probably smaller than the risk that your Lithium-ion battery explodes.
Most fuel cell technology uses substances like methanol as a fuel, and this is pretty harmless stuff.
Lithium-ion batteries can potentially create metallic Lithium, and that would be a bad thing to have sprayed all over your lap. Try looking up 'lithium ion explosion' on google
And amazingly enough, when drug users and prostitutes can't find a pay phone, they'll stop using drugs, and find a decent job. Imagine that!
This story from more than a year ago already mentions this technology. Apparently it's Lithium based.
Microsoft has admitted that the Xbox will not be released in Europe before 2002. Read this article:
http://www.vnunet.com/News/1115777
No matter how strict you make your security, in the end it depends on the user.
If you take every attempt to provide good security, the customer will find your key management such a big hassle that they won't buy your products. Popular magazines will make fun of your complicated methods, and elaborate network setup, and will praise the Plug-and-Play method of your competitor. The only way to survive as a vendor is to make it easy on the user. Unfortunately, tight security and ease of use don't mix very well.
I'll bet that more 802.11 networks are broken into that are simply not using any security at all, than networks that have had their WEP security cracked. Just because the network manager couldn't be bothered to check the box that said 'use WEP security'. And even if people do enable WEP security, how many do you think will opt for a 128 bit hex string, as opposed to an easy to remember dictionary word ?
Take a look at Western Multiplex gear sometime
They have nice stuff but it doesn't appear to be all standard 802.11b, which is what I was talking about.
Of course, the round trip delay effects are of little consequence if your MAC has been designed to take that into account. 802.11b has not.
In fact, standard 802.11b will fail completely at 50-60 miles distance, because every transmission will result in an ACK timeout.
Vendors of long-distance bridge links will either use a different MAC, or modify 802.11b in a non-standard way to increase things like ACK timeout.
The 802.11 was designed for operation over short distances only. All the timing calculations assume that the air propagation delay is negligable.
If you're going to use 802.11 for outside links, you have to take the propagation delay into account. For every mile between the two stations, there is a >10 usecs round trip delay. The 802.11 standard uses a 20 usec time as a slot length. These slots are the basis for the random backoff procedure, and can also be found in the difference between the various inter frame spaces. When the total round trip delay (air+rx+tx delays) becomes greater than 20 usecs, you'll get (some) performance degradation.
The degradation in DCF mode is graceful, but the PCF will basically break down completely in the face of long delays. Fortunately, most vendors don't even support PCF.
Things get worse if you have more than a simple point-to-point link.
In short, 802.11 can work over long links, but don't bet the farm on it, and results may vary with equipment.
That's not completely true.
The WEP encryption works like this (assuming 128 bit version)
- every station has a 104 bit secret key
- every packet has a 24 bit IV (initialization vector) in the header.
The 24 bit IV and the 104 bit key are combined into a 128 bit key, which is used to seed a pseudo random generator based on RC4. The resulting stream of random numbers is then XOR-ed with the payload. To avoid tampering with the contents, there's also a 32 bit ICV (integrity check vector appended) which is a CRC on the plaintext.
Now, the short IV is vulnerable to attacks because if you ever find two packets with the same IV (and the same secret key), you know the contents have been XOR-ed with the same stream.
However, if all the packets you receive use different IV, your only way to find the contents is to crack the 104 bit secret key.
The proposed changes to WEP include a larger IV, that's not appended to the secret key, but XOR-ed.
This will still result in a total 128 bit key length to seed the RC4 engine, so this will be a firmware-only upgrade on most (all ?) hardware vendors.
The fact that it is freely downloadable doesn't necessarily mean is freely distributable.
If it is freely distributable then you don't have to bother having the MD5 server in the first place.
I think that option 4 can be construed as a copyright violation.
If a server can MD5-sum any portion of the aim.exe file upon request, I could easily request MD5-sums of every single byte and reconstruct the original aim.exe image.
Of course that's why people are talking hydrogen rather than batteries and electric charge. Pumping gas into a car is equivalent
to "charging" it at a rate in the BILLIONS of watts. You're not going to pull an electric into a station and give it a quick charge.
You'd be using the entire output of a fossil fuel or nuclear plant to charge ONE car. The magnetic fields around the cable would
bend the sheet metal.
While I agree with most points you make, these numbers are not entirely realistic. A full tank of gasoline is about 2 MJ, but nobody is expecting that you can recharge an electric car in 1 second. If you take a more realistic number of about 2 minutes for a charge, you 'only' need about 15 MW. The best way to do this would be to exchange the batteries for fresh ones. This isn't really feasible with current battery technology, of course.
The heat wasted in the brakes of a car stopping from 50 MPH, once, could heat a snowbound four-bedroom house for half an hour
Sounds impressive, but is exaggerated. A 1000 kg car, running at 50 MPH has a kinetic energy of about 250kJ. Divide by 1800 seconds, and you'll get 140 Watts. This isn't going to heat a four-bedroom house. You'll need something closer to 25 kW for that.
I've always understood that this type of higher temperature superconductivity breaks down in the presence of strong magnetic fields, such as produced by strong currents in the material itself.
Any ideas how this has been solved ?
I think that the free internet will explode again when consumer bandwidth increases. When the average user has a 500Kb/s connection, the possiblities open up.
I think so too, but in the other direction. When people have cheap, high speed internet at home, they will start to run their own servers. Since they expenses are already paid, they don't need to generate income for their site and/or bandwith, and can focus on meaningful content. I don't think it will be easy for the big companies to create extremely flashy sites with little content, using unavoidable ads, to compete with the content-rich home user. Of course, the home user can never dream to built a site like CNN's, but like you said, CNN can afford not to have unavoidable ads, because they get enough hits (and their content is relatively cheap because the research has already been done for their TV channels).
For example, I run a rec.puzzles archive at home, no banners, no ads, simple makeup, just the content. Bandwith is limited, but will undoubtedly increase in the future. My bandwith requirements (due to lack of images) stay modest. Somebody with a commercial site, with similar content as mine is going to have a hard time getting viewers if they force the user to download tons of annoying ads before they can view the content.
It also doesn't matter that a big company can through money around to lure viewers to their site, because Google will advertise mine for free.
Here's an error message that was on the arrivals monitor at Schiphol Airport in the Netherlands.
What I didn't get from the article is how they think they're going to fetch the asteroid, and move it into a proper orbit. Doesn't seem trivial to control a 100 km big rock.
And as they say, you don't want it actually hitting the earth.
For whatever it's worth, a Faraday cage only blocks electrical fields, not magnetic. Powerful magnets as used in the train will certainly penetrate the train itself. Whether this is dangerous is a completely different story of course.
Also, a Faraday cage needs to be closed all the way. You couldn't make a big window in it, and still effectively block ectrical fields. The size of the maximum holes you can have depends on the wavelengths you want to block, the bigger the holes, the longer the waves that can get through.
Also note that if the holes aren't circular, you have to take the longest dimension into account. This means that a long, narrow, slit in a Faraday case renders it useless.
Because people can do whatever they want to do.
Why doesn't Linus quit working on his kernel, and concentrate his efforts on gcc 3.0 ?
Why don't you sell your computer, and donate all the money to finding a cure for AIDS ?
This is a useless argument, and I wish people would drop it. There's always something more important (especially stuff that others find more important) than the stuff you're working on.
The symbols are designed to withstand some noise on the transmitted signal. They are sufficiently big, and different, that a few flipped pixels will not turn them into another symbol, and confuse the recipient.
Also, the code is sent in the form of simple images so that it is easy to include a few drawings. The invidual pages are also outlined by a single pixel, which should make it really easy to figure out that you're on the right track when you try to decode the message.
Using a balanced eco-system is not the ideal way to harvest energy. You still need to put in energy (i.e. light) for the algae to grow, and it would be easier and more effective to skip the entire eco-system, and use solar panels to create your energy directly from the light.
A balanced eco-system is useful for space travel, but only because humans are going to be part of the food cycle, because they depend on sugar, and can't survive on light alone. Plus the eco-system will take their waste products, which is nice. But it would be silly to have a sugar powered robot running around on a space ship/colony for example. Sugar costs more per joule than sunlight in that case.
(The robot is still cool, though, and this technology will certainly be useful).
How many times have you yanked your CD player off the shelf ? Or your VCR ? I think the harddisk will survive normal household use.
I can't get excited about motion blur. It's a hack, and even though it can improve animation at low fps speeds, it's not natural.
The problem is that our eyes can track a moving object (even at pretty high speeds), and if you do, you'd expect the object to be sharp again, not blurry. With motion blur, the object will be blurry, even if you track it with your eyes, so it will be unnatural.
The only real solution is more frames per second. Now, this is not easily done on a TV screen for example, so I can see where motion blur in Toy Story animations is a good thing. But not for computer games, played on a monitor that's capable of high frame rates. Instead of using hard- and software to perform motion blur, use it to increase the frame rates...
Creditcards are by nature very unsafe, because their security depends on a single "public key" that's printed on the outside, and that's given out and stored by everyone that accepts payment with them. Moreover, they are handled in a very insecure way. Why do some on-line institutions insist on keeping their credit card database on an networked computer. Why do they insist on keeping the number anyway ? I'd rather type it in every time it was used, and then have it thrown away after the transaction. And why do they apparently store them in clear text ? It would be pretty easy to encrypt them using a cookie that's stored on my browser.
It's time to move towards a more cryptographically secure way of making payments. These secure methods have been developed years ago, and are still not being used on a wide scale. As long as the costs associated with the occasional credit card theft isn't too high, the banks will not take action. So, it's good that things like this happen once in a while, since the banks will take most of the damage anyway (their biggest loss is probably loss of confidence by big consumer groups).
You need a lot of extra energy to move something into infinite space. Don't forget that these satellites are still quite close to the earth, (about 100-200 miles from the surface). Compared to the size of the earth that is still pretty close, and gravity is still quite strong up there.
It may seem things are 'weightless' in orbit, but that's not true. The gravity is still present, but the satellites are basically in a never ending free fall. If you want to climb into a higher orbit, you'd still have to counteract 90% of the earth's gravity. Once you're a couple of thousand miles away, it gets a lot easier, though.
Moving them in a higher orbit has tremendous costs associated with them. If not, the space shuttle could just visit geostationary satellites. The space shuttle never does that. It only stays in the lower orbits, simply because it doesn't have the fuel to go up that high.
Thickness doesn't matter for the capability to withstand rotating at high speeds. As the thickness is reduced, the mass of the disk, and therefore the forces on the material will be reduced by the same amount. This compensates the decreased strenght of the material.
Of course, if there are small imperfections in the disk, those will become more problematic as the disk gets thinner, so the production process needs to be designed carefully so that the material has even thickness and strenght throughout the entire disk.