Quote from: hroub on May 21, 2018, 09:56:45 PM

I have the 3 private keys of the 3 participants (3-of-3). Is it possible to import the BTC from the multi-sig address to Electrum wallet?

As Abdussamad has said, if the "private keys" that you have are NOT Master Private Keys (ie. xprivs) then you cannot recreate the MultiSig in Electrum.

However, you can certainly get the funds to your Electrum wallet if you have the 3 private keys... One possible option would be to use a service like coinb.in to:

1. Replicate the 3-of-3 MultiSig using the "New -> MultiSig Address" feature of Coinb.in:

Enter the 3 public keys for the 3 private keys into the boxes provided
Set "Amount of Signatures required" to 3
Click Submit
Double check that the address generated matches the 3-of-3 MultiSig address
If the address does NOT match, alter the order of the public keys and try again. Continue trying different combinations until you get the correct MultiSig address generated
Once you have the correct address, make a copy the RedeemScript

and then you can...

2. Create a transaction that spends from that MultiSig Address

Copy/Paste the "RedeemScript" from Step 1. into the box and click "Load"
All available "Inputs" (ie. UTXOs) for that address should be loaded (see "Inputs" tab)
On the "Outputs" tab, enter the destination address (ie. the address from your Electrum wallet) into the Address Box and the amount you want to send
NOTE: Coinb.in simply uses whatever is NOT sent to Addresses as the fee, so you have to calculate manually. This also means that if you're not wanting to spend EVERYTHING from the MultiSig, you NEED to explicitly specify a Change Address as any unspent funds will be used as a fee!!!
Once you're happy with your Inputs and Outputs, click "Submit" and you'll get the unsigned transaction hex.
Copy the unsigned transaction hex
(Optional, but Recommended) You can input the unsigned hex on the "Verify" page to make sure it is sending the correct amount of coins to the correct addresses and paying the correct fee
Once you're satifisied, goto the "Sign" page and paste the unsigned hex into the box, and enter the first of your 3 private keys
Click submit and you'll get a "partially" signed transaction hex
Copy the partially signed hex
Again, goto the "Sign" page, but this time, put in the partially signed hex and the second of your 3 private keys
Click submit and you'll get a second "partially" signed transaction hex
Copy the second partially signed hex
Again, goto the "Sign" page, this time, put in the second partially signed hex and the last of your 3 private keys
Click submit and you'll get a fully signed transaction hex
(Optional, but Recommended) Double check the fully signed transaction hex on the "Verify" page once more
Once satisfied that all is OK, goto the "Broadcast" page, enter your fully signed transaction hex and click "Submit"
congrats, you just created, signed and broadcast a MultiSig transaction

NOTES: You should consider the MultiSig Address (and the 3 private keys used) compromised if you do this... I would not recommend using that address or the private keys again.