msig 2-of-3 with one weak key? what service produces them?

[amaclin]

Just wondering...
There are some strange addersses in blockchain.
Look at these msig addresses:

3A2tqbPLPG248Bisqwo5YTc7qegz2NubSh
2-of-3 msig of { 1F3sAm6ZtwLAUnj7d38pGFxtP3RVEvtsbV, 1C6RiMmuiWEGfEatuLNmRYNG1kaQzUt1u9, 1283gYYX9R3CLEDHU31Wxy5bzpFknpDTUY }

36gYmoA5DrDEnvENNmyef4CyH9TDdsoXng
2-of-3 msig of { 1F3sAm6ZtwLAUnj7d38pGFxtP3RVEvtsbV, 1Nn5i5nXMUgDXktyiHhfRApHtvXfnBinGg, 1H7sZtTSgUq6Tv5ykr6mJDktAhoK5HMfFL }

34GU3ThG3sq2bAJHG6UWwhwKrPuWL2UDb3
2-of-3 msig of { 1F3sAm6ZtwLAUnj7d38pGFxtP3RVEvtsbV, 181m1p28X1TVC5eRd3HTUY45o9y2NLedvu, 1PVUmPa127qn55J6vH32wwWUcjVSSQWRYP }

There are several other examples in blockchain, these are the recent ones.
What is strange? 1F3sAm6ZtwLAUnj7d38pGFxtP3RVEvtsbV is compressed address of brainwallet ( "" )
So, in fact these addresses are not 2-of-3, but 1-of-2 (because one private key is well known)

There is no visible reason to use 2-of-3 keys in this case... 1-of-2 would be better. May be it is a bug on some (unknown by me) service?

upd: OK, may be it is some sort of counter, to make all 1-of-2 msig addresses used once 
related topic https://bitcointalk.org/index.php?topic=666016

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[Razick]

Strange. Just out of curiosity, how did you figure this out? What led you to notice that the address had a weak key?

[Peter R]

Strange. Just out of curiosity, how did you figure this out? What led you to notice that the address had a weak key?

Amaclin is a blockchain super-slueth.  He's found numerous very interesting blockchain anomalies, and probably a bit of loose change too.  

[amaclin]

Just out of curiosity, how did you figure this out?

Blockchain is public. I use the same sources of information that you can use also.

For example, let us take 34GU3ThG3sq2bAJHG6UWwhwKrPuWL2UDb3
Here are details for transaction http://webbtc.com/tx/f21d3e4507e0b3c41ef67b1af40e9145b6d0eddff8f01e33a3251b0b25012437
Look at the "Input" section (sorry, I do not know how to attach images to this forum)
In the right side there is "Script" section
And the last (longest) line in it is "522103a34b99f22c790c4e36b2b3c2c35a36db06226e41c692fc82b8...."
Remember the digits i have bolded for you.

Now the next step.
Open https://brainwallet.github.io/
Do not enter any passphrase, just push the button "Compressed" in "Point Conversion" section
Now scroll to the bottom
Do you see Public Key? It is the same digits! 03a34b99f22...

Isn't it easy?  

[Remember remember the 5th of November]

Just out of curiosity, how did you figure this out?

Blockchain is public. I use the same sources of information that you can use also.

For example, let us take 34GU3ThG3sq2bAJHG6UWwhwKrPuWL2UDb3
Here are details for transaction http://webbtc.com/tx/f21d3e4507e0b3c41ef67b1af40e9145b6d0eddff8f01e33a3251b0b25012437
Look at the "Input" section (sorry, I do not know how to attach images to this forum)
In the right side there is "Script" section
And the last (longest) line in it is "522103a34b99f22c790c4e36b2b3c2c35a36db06226e41c692fc82b8...."
Remember the digits i have bolded for you.

Now the next step.
Open https://brainwallet.github.io/
Do not enter any passphrase, just push the button "Compressed" in "Point Conversion" section
Now scroll to the bottom
Do you see Public Key? It is the same digits! 03a34b99f22...

Isn't it easy? 

So you do this manually for every single transaction?

[amaclin]

So you do this manually for every single transaction?

Suppose the answer is "yes". Will you trust me? Or will you demand more proofs? 
I gave you a method, which can be performed even by hands. Of course, computers are slightly better for such job