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Journal Journal: Unix History

This guy has made a Unix Family History Page. Quoting:

This is a simplified diagram of unix history. There are numerous derivative systems not listed in this chart, maybe 10 times more! In the recent past, many electronic companies had their own unix releases. This diagram is only the tip of an iceberg, with a penguin on it ;-).

It is a very well written web page, with a lot of very informative links.


Journal Journal: Mail Signing to Prevent Spoofing, Spam 4

I just got an idea that might help in implementing spam filters. The idea is to use asymmetrical key cryptography to authenticate an outgoing message. We could have the mail server sign the message being sent, with its private mail key (which is ofcourse, kept private). Its public mail key should be posted in some standard place (such as http://<domain.com>/mailsign.txt).

Whenever the receiving mail server receives a message, it should verify that the message matches the signature, if it finds a mail signature. If it does not match the signature, the mail server must try to refresh the signature (from the standard location) before deciding that it is a spoofed address.

Unfortunately, I don't know much about the SMTP protocol. I vaguely recollect that mail servers can modify the message in small ways (such as changing lf->cr/lf, or adding more line breaks). If this is so, signing the whole message may not work. It might be useful to sign a part of the message. The main parts of the message - such as send date, message id, mail sender and recepients could be signed.

The message could contain two signatures - one for the entire message, and the other for the snapshot of the identity information. The receiving server could be configured to either mark or reject messages which don't match the signature obtained from accessing the standard location directly. There could be varying grades of marking a message:
1. The identity info does not match
2. The message does not match, but identity does
3. Both match
4. There is no signature
Case 1 is surely spoofed. Case 2 could be a replay of a message that was received earlier, with the message body modified - it still could be spam. Case 3 is definitely not spam (atleast the source is authentic). Case 4 is unkown.

If this system is widely adopted, hopefully case 4 will reduce and it will be easier for existing spam software to weed out spam, more accurately.

United States

Journal Journal: Freedom Quote

Although I am not an American, and I don't support everything the U.S. does, I have a lot of respect for the "Founding Fathers". Here is quote I really like:

They that can give up essential liberty to obtain a little temporary safety deserve neither liberty nor safety.

Benjamin Franklin, Historical Review of Pennsylvania, 1759

Update: I did a Google search on "Historical Review of Pennsylvania". It was amazing how I found so many like minded web posts. Most of them posted the same quote. Sadly, I did not find the actual document. I am interested in any information on how to get the document.


Journal Journal: Elevator Emergencies

Recently, I was in an elevator while the power went off. It was a local power outage - limited to the building I was in. The power returned in about 5 minutes, but during that time I was almost panic stricken. From inside, I could not make a call on my cell phone - I could not figure out whether this is a small or a big problem. There was no way of contacting people outside and telling them about my predicament.

It made me wonder about the large scale outage that happened in the U.S., and also about possible terrorist attacks. More specifically, it made me wonder why, in the 21st century, the elevator could not go the next floor and open the door. It is a simple idea that should lead to a much greater level of safety and convenience. I know there are ways of opening the elevator door without any power, but "technology" like this would require less attention by security personnel, during emergencies, hopefully allowing them to attend to more important things.

Implementation should not be too difficult. There are two ways I can think of doing this. One is to do this electronically, using a UPS, etc. The other is to do it mechanically.

The UPS system just needs to have enough backup power to keep the elevators running, during a power failure. As soon as there is a power failure, the elevator controllers should be able to sense the failure, and use this algorithm:
1. Reduce speed at the safest possible deceleration, until minimum speed is reached
2. Prepare to stop at the next floor
3. Open the doors - and keep them open until the system is reset.
See ? That's not too hard, is it ?

Actually, it is a little more problematic. Elevators consume too much power to be powered by a simple UPS. The UPS required would have to be quite expensive. An alternative would be to use a system that quickly switches to backup power supply during a power failure. Even with this, the problem is that a large amount of power is required suddenly. Such power systems are quite expensive and maybe unreliable.

An alternative is to use mechanical techniques to bring the elevator to a stop. Actually, it is not completely mechanical - it would require some electronics too. The electronics would have to be powered by a UPS. When a power failure occurs, the safety brakes should not be deployed unless the elevator's speed increases. Instead, a controlled brake should be applied. This controlled brake should be monitored by the controller to make the elevator stop at a floor end.

If the elevator does not have enough momentum to bring it to another floor, we can fall back to other techniques. Typically, elevators have a counterweight to balance the load in the elevator. If there is a way to "free up" the motor just enough to move the elevator (either to the next or the previous floor), it would be fantastic. Otherwise, the main motor could be freed and a less powerful backup motor deployed, using backup power supply. The backup motor could be substantially less powerful than the main motor, since we require the elevator to move a short distance.

Since I work in a technology field, I can imagine some of the problems that would be faced in implementing this. Quite often, it takes a lot of bureaucracy to change things. One might have to re-architect the system which can be very time (and manpower) consuming. Safety standards add a lot of problems, as well. It is such a pity that technology is not as malleable as I thought it would be.

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