CHIPs · CHIP-2021-01 · withdrawn
PMv3: Version 3 Transaction Format
A 2021 draft for a new transaction format to enable fixed-size inductive proofs for token covenants. Withdrawn in February 2022 in favour of CashTokens.
Summary
PMv3 proposed a version 3 transaction format for Bitcoin Cash. Its main goal was to let contracts build token systems inside the existing VM, “without requiring miners to track or validate new kinds of data.”
Note: PMv3 shares the “CHIP-2021-01” prefix with two unrelated CHIPs that activated in 2023 (Restrict Transaction Version and Minimum Transaction Size).
Motivation and design
From the January 2021 draft, the format would:
- Enable fixed-size inductive proofs for covenants, by letting transactions include a hash in place of any unlocking bytecode.
- Unify the four integer formats in transactions around Script Numbers.
- Define an upgrade path for fractional satoshis.
- Cut about 12 bytes from small transactions and about 3 bytes per input or output.
Current status
Withdrawn. On 22 February 2022, the same day CashTokens was published, Jason Dreyzehner wrote: “Because CashTokens could now enable more efficient, user-friendly decentralized prediction markets than PMv3, I’m withdrawing the PMv3 CHIP.” He hoped its other benefits (malleability protection, signature aggregation, fractional satoshis) would return in later proposals. Several of them reappear in TXv5.
Superseded in practice by CashTokens.