Subject: [bitcoindev] Human meaningful witness versioning

From: Ethan Heilman <[email-masked]>
Date: Fri, 18 Jul 2025 17:58:46 -0400

I want to propose a new criteria for allocating Witness versions based on
human meaningfulness and see if there is support for this approach or if
the community is highly allergic to this idea.

Bech32 (BIP-0173
<https://github.com/bitcoin/bips/blob/master/bip-0173.mediawiki>) was
designed such that the Witness version is the first character in an address
after the “bc1” address prefix

Witness Version 0: bc1q…
Witness Version 1: bc1p…

Witness version 2: bc1z…

Witness version 3: bc1r…

Witness version 4: bc1y…
Witness version 5: bc19…

Witness version 6: bc1x…

Witness version 7: bc18…

Witness version 8: bc1g…

…

So far we have been allocating Witness Versions in incrementing numeric
order (0,1,...). I want to suggest we allocate Witness Versions mnemonic to
make it easier to look at an address and determine the output type.

This originally came up over the question of if BIP-360 should use Witness
Version 3 to get bc1r… for P2QRH (r for resistant) or the next numerically
available 2, but I want to see how the community feels about it as a
general pattern for future softforks (z for compressed/zipped output, y for
yield outputs, etc…).

Making it easier for users to understand the output type associated is
likely to grow in importance over time as we retire output types, add
policy restricting the relay of certain output types or output types become
insecure due to cryptanalytic breaks. While wallet software should flag
dangerous output types, some wallets may not invest in such functionality
or the user may be using a paper wallet. This is the same argument as
prefixing addresses with “bc” for mainnet and “tc” for testnet.

Note: the Witness version is sometimes called the SegWit version.

Thanks,
Ethan

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