recover coinbase multisig wallet to electrum?

[o_e_l_e_o]

Yes, the encrypted shared seed starts with "6P".

In that case, just use a program such as https://btcrecover.readthedocs.io/ to try to brute force your unknown decryption key.

but I am thoroughly confused, there is a single vault password and single encrypted shared seed...    how does that correspond to two different public addresses?

As per the stack exchange answer from achow101 you linked to before, Coinbase turns the seeds in to BIP32 master keys and then uses them to create an HD wallet, which can therefore generate as many addresses as you want.

[o_e_l_e_o]

it's unlikely brute-force will success unless CoinBase used weak passphrase.

Users picked their own passphrase, so it depends on how good OP's password picking abilities at the time were. Also, there is hopefully a higher chance he remembers some of a password or passphrase he picked himself rather than one he was given.

Not ideal, but it doesn't look like he has any other options.

[effin_new_guy]

Users picked their own passphrase, so it depends on how good OP's password picking abilities at the time were. Also, there is hopefully a higher chance he remembers some of a password or passphrase he picked himself rather than one he was given.

In the event anyone else in the same boat is following this thread my post on stack exchange covers how to test decryption of shared seed for a multisig vault https://bitcoin.stackexchange.com/questions/111851/how-to-test-decryption-of-shared-seed-for-a-multisig-vault

Unfortunately, all my attempts at a password failed.   In addition to that, researching my email leads me to believe I was using a password manager that supports strong password creation at the time of the vault creation so I didn't pick a password.   That is what rubs me the wrong way in this situation since I stored (what I thought to be) all the essential information for the vault (user seed, shared seed, all three public keys, etc).  I was (and still am) a noob and didn't understand any of the working parts.  

Continuing down the rabbit hole...
On the topic of brute forcing, This YouTube video covers running BTCRecover with Vast.ai (rented servers) https://www.youtube.com/watch?v=8Zqc-2Te3zQ and in the first 10 seconds, he states that "In one 24 hour period, with $50 worth of hash power, this could knock over about as much as my CPU could do if it was running for 3 years straight"

I fully understand attempting BIP38 wallet recovery on rented servers is not secure, as there is no ability to do any kind of "Wallet Extract" or anything like that. The server owner would possess the key if decryption succeeds.  
My two questions are this:
As my wallet is multisig, does that decrease the risk dramatically?  
Assuming the answer to the above question is "yes", I'd be willing to throw a few hundred $$ at this which would get me over a decade of hashing power.  
Besides, it will make a funny story if nothing else.  
Assuming my password generator did a great job and produced a really awesome completely random password is a decade going to even come close or are we talking over 100 years to crack?
It is not easy to find answers on BIP38, everything seems to be focused on BIP39.

[o_e_l_e_o]

As my wallet is multisig, does that decrease the risk dramatically?

The risk of having your coins stolen is near zero. Even if the cloud computing is successful at decrypting your shared seed, then they only have access to one of the necessary seeds. As long as you don't mistakenly share or leak your user seed as well, then there is no chance of them being able to steal your coins.

Assuming my password generator did a great job and produced a really awesome completely random password is a decade going to even come close or are we talking over 100 years to crack?

I don't know how much power you could reasonable rent with vast.ai, but as pointed out above, BIP38 is specifically designed to be more difficult to brute force than, say, a seed phrase. Even if your password generator generated a weak password with only 60 bits of entropy, and even if you managed to rent enough computing power to give you 1 billion guesses a second (which is likely a gross overestimation and would be hugely expensive), then you are still looking at over 36 years of rented power to exhaust the search space. Most password generators today would generate a minimum of around 80 bits of entropy, which already takes us in to the area of millions of years.

If the password was randomly generated and you have absolutely no idea what it is, then you are wasting your time. The only other possible option I can think of is to contact Coinbase and see if they still have the Coinbase seed linked to your account stored somewhere and if they will provide it to you. Seems like a long shot though, given how terrible Coinbase support is and how little they care about their customers.

[effin_new_guy]

Thanks for saving me the couple hundred $$ trying to brute force it.   
 
I would, however, like to understand this post a little better
https://bitcoin.stackexchange.com/questions/57207/how-to-derive-the-private-key-associated-with-a-coinbase-multi-sig-vault-address

That seems pretty close to my situation, but I actually have more information than that user did.   I certainly don't have the comprehension of the problem that user does, unfortunately....   
This probably isn't the best place to ask but wanted to toss it out here.
He seemed to be able to obtain everything he needed from getting access to the master private key and the extended private key using ONLY the user seed.  Sorry, not trying to be dense, but I am not understanding the difference

I am attempting to contact the OP for that post as well
thanks

[o_e_l_e_o]

He seemed to be able to obtain everything he needed from getting access to the master private key and the extended private key using ONLY the user seed.  Sorry, not trying to be dense, but I am not understanding the difference

The user in that post does not reveal either his master public key nor the address he is trying to access, so I can't be sure, but it seems like he has used his user seed and user master public key on their own (i.e. as a single-sig wallet and without the multi-sig requirements of the shared seed or the Coinbase seed) to generate some addresses. Certainly the code provided by achow101 in response takes his user seed, uses it to derive a single master private key, a single master public key, and then a single address at a specific index, with no mention of the multi-sig requirements.

If you wanted, you could take your user public key and check the addresses it derives on its own, as has been done in the Stack Exchange post you linked to. There is no need to use python to do this. You can simply go to https://iancoleman.io/bip39/, paste your user public key in to the box named "BIP32 Root Key", select "BIP32" under the heading "Derivation Path", and then change the BIP32 Derivation Path to m from m/0. If any of those addresses hold a balance then you can access them only using your user seed, but it also means that Coinbase made a critical flaw that no one noticed when implementing their multi-sig vaults, which would be highly unlikely.

[effin_new_guy]

I'm not sure if this thread can be revived but I may have located what I need but have no idea how to use it.   

Long story short, I found an old dead android phone, ordered a battery for it, got it unlocked and while the device was disconnected from the internet, opened my password manager on this device and found an old entry for Coinbase labeled "cold key used to encrypt other keys"

I would like to test decryption of the encrypted shared seed with this key but the only decryption tools I am finding need the "encrypted seed"  and a "seed phrase"...  I don't have a seed phrase... I have an actual 30 character key.   no words, no spaces...   

Any suggestions for this situation would be appreciated.

[o_e_l_e_o]

As we discussed on the previous page, your encrypted seed starts with "6P", correct?

If it does, then it should be a BIP38 encrypted key, although these are supposed to be 58 characters long, not 30, so I'm not entirely sure what you have. The easiest way to decrypt a BIP38 key is going to be to download bitaddress.org from its GitHub (https://github.com/pointbiz/bitaddress.org), run it on an offline computer, click on "Wallet Details", enter your encrypted key beginning with "6P", click on "View Details", and then enter your decryption key in the new box which appears. I would try this first and see what happens.

[effin_new_guy]

Yes, the encrypted shared seed starts with 6P.

The encrypted shared seed is 58 characters in length.

the "cold key" that I found in an old version of my password manager is 30 random characters, not words like a "seed phrase".

regardless, I am getting a pop-up message stating: "Incorrect passphrase for this encrypted private key."

[o_e_l_e_o]

regardless, I am getting a pop-up message stating: "Incorrect passphrase for this encrypted private key."

Then either that decryption passphrase does not match that encrypted key (most likely), or Coinbase have done something weird and non-standard with their implementation of BIP38 (although that is highly unlikely to be the case). I suppose you could try installing the BIP38 library from https://github.com/bitcoinjs/bip38 and trying again to decrypt your encrypted key, but I doubt very much that you would have a different result.

[Rickorick]

you need these three things for recovery User key- Seed and Public key. Shared key- Seed (encrypted) and Public key. Coinbase key- Public key.