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Comment: One time pad (Score 1) 93

by Keith Henson (#48435939) Attached to: WhatsApp To Offer End-to-End Encryption

"End-to-end encryption is easy - you just need to send a courier with a one time pad."

Key management is a PITA. Still, making pairs of DVDs filled with random noise isn't that hard. If you seal them with glitter nail polish and send a picture of the sealing back, then you and the recipient can be fairly sure it wasn't intercepted and copied.

USB sticks are larger, but you need to completely erase the USB or DVD after copying to disk. Then the program needs to enforce that used blocks on the disk are erased.

Phil Z and one other name in the crypto biz thinks this is unneeded.

It doesn't work well for encrypting pirated movies, but for most stuff it's really secure.

Comment: Re:BLINDED BY SCIENCE !! (Score 1) 315

by Keith Henson (#47637577) Attached to: Why the "NASA Tested Space Drive" Is Bad Science

A simple thought experiment will tell you that if this thing works as stated, it's a source of free energy. I was amused by a post from a power satellite fan saying that the thing could be used to get parts from LEO to GEO to make power satellites economical.

It might make stuff cheaper to move in space, but the near free energy these things can generate eliminates the market for energy from space.

Comment: Re:And today (Score 1) 211

by Keith Henson (#47504521) Attached to: Apollo 11 Moon Landing Turns 45

I was in my last year of college when they landed. It's still one of my most intense memories.

It's worth keeping in mind that NASA is not the only game in town. The most interesting work right now is Skylon by Reaction Engines in the UK. Japan has the most interest in a commercial product, power satellites. Between them with China or Norway picking up much of the tab, we could see the first power satellite by 2023.

Artwork of a microwave ground station and and a vehicle to take 1000 15 ton Skylon payloads from LEO out to GEO to build power satellites.

Ground transmitter size

Microwave rockets 3 pixs

Comment: In the old days (Score 1) 125

by Keith Henson (#47490043) Attached to: FTC To Trap Robocallers With Open Source Software

In the long, long ago when telemarketers were humans and more often known as telephone solictors, I listed my phone number under a high school nickname, Heimdallr the Watcher., or Watcher, H.T.

That made it easy to sort out the telemarketers, it was a legit call if they asked from "the Watcher," but a dead giveaway if they asked for Mrs. Watcher.

So the standard rap would be, "Sorry, Mrs. Watcher is here but she can't speak to you."

Sometimes they would bite and ask "Why?"

"Well, you see, Mrs. Watcher used to be a telephone solicitor." [Dramatic pause]

"Until someone caught her." [Another dramatic pause]


Usually this got a laugh, but at least once the telemarketer said she was calling the cops.

Comment: The last days of XOC (Score 1) 90

by Keith Henson (#47187623) Attached to: Xanadu Software Released After 54 Years In the Making

I knew the people who worked on Xanadu though not quite back to the earliest days.

The design was largely completed by the time Autodesk got out of funding it. For a while the project continued under Memex (later Filoli over trademark issues). Memex had funding problems, the core group quit, and when Memex was funded again Roger Gregory (one of the original team members) and I were brought in to try to make sense of what they had. My experience was long out of date FORTRAN and more recent assembly. The majority of the code had been written in Smalltalk and auto translated to C++ as part of the compiling process. Memory was (by current standards) insanely limited. The clever part of the code was to pack and unpack a multi dimensional tree off disk. Fan out ran to around a thousand link pointers per 8k disk block meaning three disk reads could take you to a billion unique objects. The famous log N property.

The performance critically depended on a high performance system to reclaim abandoned parts of the tree in memory and that part was not finished. (It had been designed as an Ungar-Sather moving type garbage collector and partly written but not tested.) We got it going and it ran the regression test suite. One of the last tasks was to upgrade it from the Sun compiler. The most critical inner parts of the code depended on switching tree elements around to keep the tree balanced. It used the classic c=a, a =b and a=c where a and b were links. Bjarne Stroustrup had changed the definition of overriding equal between the two compilers making this a hard bug to find. I finally found it single stepping through the assembly language representation of the code. The tools are much better now, nobody would think of writing a garbage collector from scratch. It was only 20 years ago, but it feels like a lifetime.

Comment: Re:If you're just beaming it down to earth anyways (Score 1) 230

by Keith Henson (#46850327) Attached to: How Japan Plans To Build Orbital Solar Power Stations

Let's take a crack at putting numbers on your assumptions.

Assuming power satellite people want a large market share, they will have to set the cost lower than other sources. Say 2 cents per kWh. Hydro is lower, but there isn't enough of it.

If you go into the models for calculating levelized power, then to get 2 cents per kWh, the cost of the source can't be higher than $1600/kW (6.8% discount and 20 years). Even in China nuclear reactors are about $5000/kW. Ground PV can't get close, it might hit 8-10 cents per kWh, but at that cost the concrete and steel become bigger factors than the silicon.

The rectenna, the part on earth, will cost around a billion dollars for 5 GW. That's $200/kW. I have published the details on how I estimated the cost, can quote them if you want.

I favor thermal designs as they are a lot smaller, but even with PV, it should be possible to get the cost of panels and transmitter plus labor down around $900/kW referenced to the output of the rectenna. That's assuming microwave amplifier tubes cost about the same per kW as they do in microwave ovens.

So a reasonable cost for power satellites $200 plus $900 plus $500 for the transport to GEO.

I think it's reasonable to expect power satellites to mass around 5 kg/kW.

Thus the allowed transport cost to GEO is $100/kg, or $45/lb. But that's to GEO, not LEO.

Comment: Re:Satellites have eclipses (Score 1) 230

by Keith Henson (#46850003) Attached to: How Japan Plans To Build Orbital Solar Power Stations

"The problem with space elevators (and other sky-hooks) is that if the tonnage down doesn't, over time, match the tonnage up, the orbit decays."

That's not true. Long as the cable is tight, you can lift stuff forever without anything coming down. The cable does lean a little to the east, and it saps the earth's rotation to provide the velocity at GEO. Remember there is a rigid arm from the center of the earth to the base of the elevator. If the traffic tonnage is matched, the elevator will be straight, if more is coming down, it will lean to the east.

Comment: Re:Satellites have eclipses (Score 1) 230

by Keith Henson (#46849255) Attached to: How Japan Plans To Build Orbital Solar Power Stations

Musk is right.

A reasonable economic analysis of power satellites requires about $100/kg for the cost of parts lifted to GEO.

You can't get that with rockets, not even reusable ones.

The main reason is that low exhaust velocity leads to rotten payload fractions. It's just physics, the rocket equation.

The proposed Skylon gets around 9 km/s equivalent exhaust velocity till it runs out of air, and 4.5 km/s from there up. Still too expensive by a factor of 4-5.

Leaving the oxygen out and using a 3 GW laser to heat hydrogen gives around 7.5 km/s for the last 6 km/s to orbit. The laser is hugely expensive, but run 24/7 it costs only a few tens of dollars a kg for 500,000 tons per year.

More here:


Comment: Re:Maybe not extinction... (Score 1) 608

by Keith Henson (#46843651) Attached to: Are Habitable Exoplanets Bad News For Humanity?

It's still possible, though I don't see even the excellent work of SpaceX getting us there.

It's not a sure thing that additional development of chemical rockets will do the job. If you go through the math involved, it just doesn't look good.

Space based solar power, for example, has to substantially undercut existing and projected cost per kWh in order for the investment to be worth the trouble. Depends on the numbers you use, but I make a case that the cost of lifting power satellite parts to GEO has to come down to $100/kg for SBSP to make economic sense.

It takes less than a dollar of energy to get a kg to GEO, so the physics doesn't stand in our way. But I don't think you can make a case for rockets getting down to this cost, and if you could, then the volume needed, around 10 million tons per year, just makes rocket lift look really questionable.

The problem traces back to the rotten payload fraction and that's the direct result of low exhaust velocity. However, there may be another way to skin the cat.

Skylon gets the equivalent of 9 km/s to where it runs out of air, and laser heated hydrogen will get at least 7.5 km/s for the rest of the way to orbit. From there to GEO, a hydrogen/laser stage will deliver 2/3rds of a 30 ton second stage in LEO to GEO. Running the laser full time will get three 20 ton vehicles to GEO every hour or about half a million tons per year. Scrap the vehicles at GEO and they are all payload. More details here:

Keith Henson

Comment: Re:Farming (Score 1) 737

by Keith Henson (#46741853) Attached to: Ask Slashdot: Are You Apocalypse-Useful?

When I was much younger, we raised rabbits. For years they were most of the meat the family ate.

I also did every step in making bread. Growing a patch of wheat, harvesting it, thrashing out the grain, grinding grain to flour and baking flour into bread. I can tell you it's a pain.

The most likely thing to happen that would bring down civilization would be running out of cheap energy, especially liquid hydrocarbons for transport. There are several possible ways to get around that problem. This is my proposal.

Comment: Impressed by Tim Cook (Score 1) 348

If someone reading this knows Tim, please give him my regards.

Also, if he wants to talk about the whole world going off fossil fuels to a cheap form of solar, be happy to do so. If it can't make dollar a gallon gasoline, then the idea isn't ready for prime time.

Talk I gave at Google.

A laser 33 times larger than the propulsion laser I propose.

Comment: Re:I disagree (Score 1) 221

by Keith Henson (#46351099) Attached to: South Park Game Censored On Consoles Outside North America

"The things that are done in this World in the name of [insert religion - including Buddhists ] is appalling. "

I make a case it is the other way around.

In the former world of hunter-gatherers, the nut corp would fail or the game move away. When that happened ,it was necessary to go batshit crazy with xenophobic memes and kill the neighboring tribe. The trait was selected because it promoted genetic survival. It's the underlying resource crisis that causes the appalling behavior. The memes (religions) are in the chain, but not causal.

Comment: Re:Yes, and changing that is not an option (Score 1) 115

by Keith Henson (#46291621) Attached to: French, German Leaders: Keep European Email Off US Servers

"Only true end-to-end encryption can be a solution."

I doubt even that. If NAS can't break the encryption, they put a keylogger on your computer and break the encryption that way.

One time pad is a pain in the ass for key management, but it is impossible to break and the NSA may well waste a lot of cycles trying.

Key management here is to keep the keys on your hard drive and do a military grade erase on the blocks you have used.

Sending the key on three memory sticks by different routes and xoring them together seems like it might work. Then fill the sticks several times over with junk files, or if you are really paranoid, burn them. DVDs would work for those without a lot to say.

The question is not about being paranoid, the question is: Are you paranoid enough?

Dead? No excuse for laying off work.