The price of cracking a combo vault

LiteS · 2014-02-07 02:43:58

Disclaimer: I think combo locks are lame.

Step 1: Disable all commitment gates between you and the combination buttons so you can exit the house safely.

Step 2: Disable all commitment gates between you and the thing the combination buttons open.

Step 3: Calculate the value of tools needed to do this. It may be cheaper to just saw your way to the vault and then ladder over the powered trapdoor, or at least saw your way to the inverter switches to learn the combination for next time.

Step 4: If it's cheap to try new combinations it's time to run some numbers. The builder of the combination lock is abusing the fact that adding a single button doubles the total possible combinations. But as a robber we can abuse the fact that it is possible to check multiple combinations per run, and then return to try again. The trick is to not check the same combination twice. In the following example, I'll use an 8 switch combo.

There are 2^8 (256) total possible combinations, which seems huge at first, but if you break it down it's really not.
There is 1 combination with no buttons pushed
There are 8 combinations with one button pushed
There are 28 combinations with two buttons pushed,
56 with 3,
70 with 4,
56 with 5,
28 with 6,
8 with 7, and
1 with all buttons pushed.

Which means if you devise a method for checking 8 different combinations each time, you will only have to visit the house 70 times to try every 4 button combination. Throw a little probability into the game and this is how much it costs to break an 8 switch combo if the solution is a 4 button combo:

Commit gate disablement cost (Absolute minimum is 100, so I'll assume that. In all likelyhood the total will be closer to 400) * 35 = $3500 + the time to actually do it
Cost of sawing through half the map and placing a ladder over the powered trapdoor to get to the vault: 12*400 +1800 = $6000

In conclusion, solving combination locks isn't feasible. It is unfortunate that there isn't an alternate way to solve them.

DaVinci · 2014-02-07 03:07:41

For low value houses, solving it is NOT feasible, but for high value houses chances are you are getting more than what you are giving it.

largestherb · 2014-02-07 05:05:57

my favourite is when the house has three or more combo locks

HaterSkater · 2014-02-07 06:54:14

Well, AFAIK, 8-bit combo lock with 4 correct keys can be bruteforced (i.e. to put your saw in, you know, wall) with chance of success 1/2. However, if only 1 key is correct chance is 1/8, but you never know. Actually OP gave me some thoughts about why this system isn't enough to defend high-tier house.

FYI: chance calculation based on bit-lock, in which breaking of wired-wall-tile will destroy whole circuit, so you need to choose correct wire at the start. If there is no such protection, you can saw it from behind, breaking through tons of concrete

UPD: isn't OP tactic works only if homeowner is in his bed IRL? He can change code between attempts

Last edited by HaterSkater (2014-02-07 07:00:31)

DaVinci · 2014-02-07 07:30:53

That is one of the reasons that comb locks are great at beggining, not worth the hassle and easily changed.

High tier house robbers can crack the stuff up no matter what. Infinite tools.

setz · 2014-02-07 08:57:53

I have never used one and will never. And although people can do what they want and I support their choice I will not be using them. They are a complete bore to me, BUT they are a good way to make ALOT of money and this is why people use them. They basically require brute-forcing or EXTREME luck.

Banakai · 2014-02-07 18:25:53

This actually made it seem easier to me. $6000 to potentially get several hundred grand.

DethBringa · 2014-02-07 22:54:00

I used one in a house once. I have tried almost everything once. I think the only thing I haven't incorporated is the magic dance. My current house I decided will have neither a combo lock or a magic dance since almost every house on the server as at least one of those 2.
My contest house was the house that had one and after the contest I issued a challenge and was quickly smashed into oblivion. I posted it on the forums for people to have a look at. It did a good job and got me to 15th place in 2 days from the start of that build. I think its one of those things that you should do to have a play with it, like the clock circuit. Its cool to play with and build. Probably best to put it close to the entrance rather than final defence, that way you can watch people walk in and play with it all day. Less likely to just be brute forced if its at the start and you can just keep coming back and attempting it for a 0 tool cost and little risk of death. If I ever do build another house with a combo lock I will put it up at the entrance just for fun.

jere · 2014-02-09 12:13:42

Just guessed a combo lock! It had about 7 sticking switches, so I hit 2, 3, skipped to 5 and started mashing buttons. Noticed somewhere in there a door opened but I had already closed it. Luckily, I could exit and come back.

I wonder if the owner thinks I've cheated.....

iceman · 2014-02-09 12:28:52

jere wrote:

Just guessed a combo lock! It had about 7 sticking switches, so I hit 2, 3, skipped to 5 and started mashing buttons. Noticed somewhere in there a door opened but I had already closed it. Luckily, I could exit and come back.
I wonder if the owner thinks I've cheated.....

I've actually guessed a few combo locks... it's always a fun feeling to cheat chance =P

jere · 2014-02-09 12:44:05

THIS TIME I'm not going to leave $8k of my chain robbing tools in my vault when I go back out to rob..... derp.

holy...... almost got CHARLES EDWARD KNIGHT, but.... stepped right on a pitbull for no reason

Last edited by jere (2014-02-09 13:14:58)

The Castle Doctrine Forums

#1 2014-02-07 02:43:58

The price of cracking a combo vault

#2 2014-02-07 03:07:41

Re: The price of cracking a combo vault

#3 2014-02-07 05:05:57

Re: The price of cracking a combo vault

#4 2014-02-07 06:54:14

Re: The price of cracking a combo vault

#5 2014-02-07 07:30:53

Re: The price of cracking a combo vault

#6 2014-02-07 08:57:53

Re: The price of cracking a combo vault

#7 2014-02-07 18:25:53

Re: The price of cracking a combo vault

#8 2014-02-07 22:54:00

Re: The price of cracking a combo vault

#9 2014-02-09 12:13:42

Re: The price of cracking a combo vault

#10 2014-02-09 12:28:52

Re: The price of cracking a combo vault

#11 2014-02-09 12:44:05

Re: The price of cracking a combo vault

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