May 2023: CashTokens, P2SH32 and smaller transactions

What changed

Activation came when the median time past reached Unix time 1684152000 (15 May 2023, 12:00 UTC). The first block under the new rules is height 792,773. Test network chipnet ran the same rules six months early, from 15 November 2022.

Four CHIPs activated:

CashTokens (CHIP-2022-02)

CashTokens, by Jason Dreyzehner, adds two token types directly to UTXOs:

• Fungible tokens: interchangeable units, like a stablecoin or points. A category can have up to 9,223,372,036,854,775,807 units, all created in its genesis transaction.
• NFTs: each carries a commitment of 0 to 40 bytes, set by the issuer. An NFT can have the minting capability (create any number of new NFTs), the mutable capability (edit its own commitment), or neither (immutable).

Each token category ID is the transaction ID of an output-0 coin spent in the genesis transaction. So category IDs are unique and cannot be faked. Tokens sit in an output next to BCH, marked by a prefix byte (0xef).

Six new opcodes let contracts inspect tokens: OP_UTXOTOKENCATEGORY, OP_UTXOTOKENCOMMITMENT, OP_UTXOTOKENAMOUNT, OP_OUTPUTTOKENCATEGORY, OP_OUTPUTTOKENCOMMITMENT and OP_OUTPUTTOKENAMOUNT. The CHIP also adds a SIGHASH_UTXOS signing mode and token-aware CashAddress types.

P2SH32 (CHIP-2022-05)

P2SH32, by bitcoincashautist, adds a 32-byte version of pay-to-script-hash: OP_HASH256 <32-byte hash> OP_EQUAL. Classic P2SH uses a 20-byte hash, which is open to collision attacks at about 80-bit security. See P2SH.

Minimum transaction size (CHIP-2021-01)

The minimum size dropped from 100 bytes to 65 bytes. Proposed by Tom Zander.

Restrict transaction version (CHIP-2021-01)

Transaction versions other than 1 and 2 became invalid by consensus. Before, only relay policy enforced this.

Why

Contracts that can vouch for things. The CashTokens CHIP starts from a gap: before 2023, the only commitments a contract could check were signatures, and signatures need a private key. A contract cannot hold a key, so anything a contract “says” had to be signed by a trusted party. That ruled out decentralized oracles and many multi-contract designs. Token commitments give contracts their own verifiable messages, “without increasing transaction or block validation costs.”

Tokens validated by consensus. Token rules are enforced by every node, so contracts can read and control tokens directly. The CHIP also aims to support higher-level token standards on top of these primitives.

Contract security. P2SH32 grew out of a discussion titled “a long-term solution for 80-bit P2SH collision attacks”. A 20-byte hash gives only about 80 bits of collision resistance. That matters for multi-party contracts, where one party could try to craft two scripts with the same hash. A 32-byte hash closes that gap.

Housekeeping. The 100-byte minimum (from 2018) blocked some valid, useful small transactions and tripped up coinbase builders; 65 bytes still blocks the 64-byte SPV attack. Pinning versions to 1 and 2 means a future transaction format can claim a fresh version number that no old transaction has ever used.

What it enables

• Tokens that cost under a cent to mint or send. Anyone can issue a token or NFT collection with no contract to deploy, no approvals, and no admin keys. See CashTokens and the live token list at tokenstork.com.
• DEXes and DeFi in UTXOs. NFT commitments can hold contract state: ownership, authorizations, credit, debt. Contracts can recognise each other’s tokens and interact without shared global state. Apps such as Cauldron (DEX), Moria (borrow MUSD) and TapSwap (NFT market) build on this.
• Safer covenants. Contracts can use a 32-byte script hash for their address.
• Fewer lost tokens. Token-aware CashAddresses mark wallets that accept tokens. Token-aware wallets must refuse to send tokens to an ordinary address.
• Metadata. The separate BCMR standard lets issuers publish names, tickers and icons for a category.

Limits

NFT commitments were capped at 40 bytes. That cap was raised to 128 bytes in 2026.