Quote from: zemario on March 08, 2015, 12:32:33 AM

I'm not sure what you are trying to achieve by posting that

Clearing up misinformation that Mycelium finds it ok to spread. Their feature is not "spending from cold storage," it's *AT BEST* "spending from a paper wallet" which does not imply cold storage.
If I spend coins from a paper wallet and send the change back to the same paper wallet, it is no longer cold. As my pubkey is exposed on the blockchain, and my private key has been exposed to an online device. The exact antithesis of cold storage.

Sure, maybe you can understand the intricacies of what's going on and you can understand that your paper wallet is no longer cold at all, and you accept that risk, but someday, someone won't, and they'll lose bitcoins with "no one to blame but themselves" (the chant everyone begins when someone not understanding every single aspect of Bitcoin loses coins due to error)

To answer your question:

Mycelium has no feature to spend from a BIP32 HD wallet xprv, nor exists there any protocol for encrypting an xprv like BIP38 (which only encrypts single private keys in WIF format (Starting with 5 or K or L))

This will likely never happen, as there are way too many factors of an HD wallet that are not encoded into the xprv that are needed to recover coins (like which path was used, which gap limit was used, etc. BIP44 aims to create a standard for all of these factors, but adoption by wallet apps is weak at best.)

However, this is also not a good idea either, as swiping a BIP32 key and sending change back to it would do that same thing that swiping a paper wallet and sending change back to it; give a false sense of security, when in actuality your setup is the same as a normal hot wallet.

If you think it's a great idea, bring it up on the bitcoin-development mailing list and see if anyone agrees with you. They'll give you a BIP number and everything.