Is there any deep reason not to support this? Or is this merely a "good idea, but no volunteers" situation?

By the way, although Bitcoin Core had supported BIP32 several years ago, it uses hardened derivation for addresses, which makes it impossible for the watch-only side to derive new addresses for receiving/change, or used addresses to watch transaction history and final balance.


Prior to segwit doing this securely required carrying around enormous prior transactions.

Prior to PBST there wasn't a standard serialization that covered all the interesting use-cases.

It's been possible to offline sign for years using the CLI and many people have been doing so.

More recently this PR adds a GUI for doing this using PSBT: https://github.com/bitcoin/bitcoin/pull/16944

  • Some update on this: unfortunately SegWit (v0) doesn't avoid the requirement of enormous prior transaction data: blog.trezor.io/… ( which was even discovered before SegWit activation actually: twitter.com/theinstagibbs/status/1268302648366624768 ) Even if SegWit/Taproot etc can fix it, IMHO it still doesn't fundamentally solves the problem, because even without the prior tx, the tx data itself can still be huge, at least exceeding capacity limit of one single QR code.
    – Chris Chen
    Nov 7 '20 at 17:14
  • PSBT makes multi-sig, offline signing easy (interoperable/compatible among vairous different types/models/brands of wallets), however, in my opinion PSBT still doesn't fix two problems: (1) the QR code data capacity limit mentioned above; (2) the wallet setup process, eg. mnemonic format, HD derivation path, script/address type, gap limit etc.
    – Chris Chen
    Nov 7 '20 at 17:19
  • I don't agree that it doesn't avoid the requirement-- the resign attack pattern is pretty contrived. Of course, better to have it fixed. I don't see why you're hung up on QR codes, -- don't use them.
    – G. Maxwell
    Nov 8 '20 at 18:30
  • To my understanding QR code is better than USB thumb drive/bluetooth etc, because the later two have their own attack surfaces. It's also slightly better than something like amodem probably, because sound "broadcasts" in air naturally.
    – Chris Chen
    Nov 9 '20 at 10:57

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