Remark

This blog started with an old safe I bought with unknown content and combination. It describes the process of opening, finding the origins, contents and mechanics of the safe.

The posts are closely relate to each other and should probably be read in chronological order. Therefore, if you are visiting this blog for the first time you might want to start reading with the oldest entry and work your way back to the present time.

Wednesday, July 29, 2009

How I opened the safe

The first thing I tried was to follow the instructions given in "Safecracking for the computer scientist". If you are not an expert, you will have to read some parts of it if you want to understand the following in detail.

Essentially there should only one place where you feel a change in resistance when turning the dial, it is called the gate. The gate will be found at the same location each revolution. For this make and model of the combination lock (Sargent & Greenleaf, group 2, three wheel lock) it should be somewhere between the numbers 95 and 15. For a combination lock of this type and if it is in good condition it should be easy to found by feel (not so much sound). The lever nose drops into the gate each turn. If all the other wheels (three in this case) are aligned correctly the lever nose will drop into the gate all the way and enable the unlocking mechanism. The method of manipulating the combination lock (finding out the correct combination) relies on small imperfections of the wheels. Essentially one systematically dials in different combinations and measures how deep the lever nose dropped into the gate. This is done by finding the left and right contact points between the lever nose and the gate (they can be felt). The results are graphed and ideally one number of the combination can be read of that graph. Then a few experiments can indicate which place the number has in the sequence of the combination. The experiment is then repeated in the same fashion, only by presetting that found number while changing the others. If one is able to detect the locations of the left and right contact points accurately and repeatably one should be able to find the correct combination in less than an hour.

Well all that sounds reasonable straight forward, only that my dial was not turning easily and randomly sticking. I was able to find the gate and even get a reasonable idea where the left and right contact points were but a few experiments showed that my measurements were not reliably repeatable. It was just to difficult to turn the deal smoothly and feel the subtle change in resistance.

My next attempt was to apply some WD-40 to the combination lock and that improved things greatly. The dial was now turning smoothly and the change in resistance stood out very well. So I made some safe cracking graph paper and made a few runs of filling them in:



One has to look for where the left and right contact points are the closest to each other. I found some areas of interest and one place around numbers 70 to 75 were there was a big jump in the size (the nose lever is held higher above the gate), but I could not reproduce the areas of interest by closer investigation. Generally I found it difficult to determine the contact points to the required accuracy.

During my time of dialling in different combinations I noticed marks on the knob of the dial.




I had noticed them before, there were two sets of different marks (lines and round holes) with four marks for each of the sets. A safe expert on All Experts had already suggested to me to try these marked numbers. I discounted them since I was sure I only needed three numbers in my combination and it is very hard to tell to which exact number each mark belongs. I found however that the set of round marks had one mark on zero. I discounted the zero mark and rounded the remaining three marks to their closest multiple of 5 numbers. This gave me three numbers to work with for which there are nine different orders of dialling them in. I wrote all nine sequences down and started dialling them in systematically (see this entry on how to correctly dial in a combination). The lever nose clicked very audible into the gate after dialling in my third combination. I turned the handle and the safe opened revealing that is was stuffed full with things.

I will write more about the content and the safe soon. I want to have a look at the combination lock from the inside (see what happens between the numbers of 70 and 75) and maybe even set my own combination.

1 comment:

  1. You seem to be an expert at it. Your blog is very nice. God is Great. Best wishes.

    http://www.thedynamicnature.com

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