Xiaohui Liu

OP_PUSH_TX and its applications in Bitcoin smart contracts

What if a Bitcoin contract could inspect its own spending transaction? Discover how OP_PUSH_TX enables stateful applications previously deemed impossible, from on-chain games to financial instruments.

OP_PUSH_TX and its applications in Bitcoin smart contracts
#1about 2 minutes

Introduction to OP_PUSH_TX and its applications

An overview of the OP_PUSH_TX technique, its internal implementation, and the smart contract applications it enables, including a live demo.

#2about 1 minute

Introducing the OP_PUSH_TX technique for smart contracts

The OP_PUSH_TX technique allows a smart contract to access the current transaction's data by pushing it onto the stack.

#3about 1 minute

Accessing transaction data via the SIGHASH pre-image

The technique pushes the SIGHASH pre-image, which contains transaction data like inputs and outputs, onto the stack for inspection.

#4about 3 minutes

Implementing OP_PUSH_TX as a pseudo-opcode

The technique is implemented as a pseudo-opcode using existing script commands to verify the SIGHASH pre-image is for the current transaction.

#5about 5 minutes

Controlling future spending with transaction introspection

By inspecting the transaction pre-image, smart contracts can enforce rules on future outputs, replicating features like CLTV and P2SH.

#6about 3 minutes

Maintaining state across transactions with OP_PUSH_TX

Stateful smart contracts are created by dividing the locking script into immutable code and mutable data, ensuring state transitions correctly in subsequent transactions.

#7about 2 minutes

Building on-chain games and tokens with stateful contracts

The ability to maintain state enables complex applications like fully on-chain games, fungible and non-fungible tokens, and financial instruments.

#8about 2 minutes

Demonstrating a fully on-chain Tic-Tac-Toe game

A live demo shows a Tic-Tac-Toe game where each move is a Bitcoin transaction, enforcing game rules on-chain and preventing cheating.

#9about 2 minutes

Summary and resources for building with sCrypt

A recap of the OP_PUSH_TX technique and its applications, with links to sCrypt's open-source code, documentation, and community channels.

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