[bitcoin-dev] Proposal for a few IANA mime-types related to Bitcoin

Christopher Allen ChristopherA at lifewithalacrity.com
Tue Aug 31 20:02:44 UTC 2021

On Tue, Aug 31, 2021 at 12:18 PM Peter D. Gray <peter at coinkite.com> wrote:

> QR Codes do not use IANA mime-types.
> If anyone wanted to use UR encoding for PSBT data in a web context (http),
> NFC, or email, it would probably be best to discourage them.
> While I can understand the need for UR encoding in animated QR
> codes, I don't think any other use-case could justify introducing
> a new word list (ByteWords), a unique checksum algo (Xoshiro256),
> fountain codes (Luby Transform) and CBOR... just to wrap a few k
> of binary.
> I do love CBOR though. It's the best.

UR is more than just a QR, it is URL conformant text that is optimized for
compression in QRs.

In particular, take a look at the explanation of the UR format at the 20m0s
mark in this video:

The rest of the video explains why we made the choices we did. We wanted to
leverage existing standards, but there were too many compromises expecially
give QR requirements. See the section on “Why Another Standard” in our
overview at

Note that the UR specification just is not just being adopted by wallet
vendors, but also a number of online services / transaction coordinators
that only have access watch-only keys. These services can then do a
crypto-request for the airgapped wallet to sign the PSBT.

— Christopher Allen

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