Bitcoin's homegrown programming language

Bitcoin script is a programming language developed by Satoshi Nakamoto for the purpose of programatically declaring the conditions in which Bitcoin can be spent. Bitcoin script is a core component of the Bitcoin protocol and can be found in the source code of any protocol-compliant Bitcoin node software. Script was created as part of the first public implementation of the Bitcoin software released in 2008 and continues to be a vital part of the codebase today. The necessity for script came about when Satoshi acknowledged and tackled one of the limitations of developing a consensus protocol -- slow adoption to change. Thus, the long-term functionality of Bitcoin would be dependent on the design decisions of the initial protocol implementation. Following this thought process, 'script' was made to act as a robust way to specify the spending condition of coins and not limit how a user specifies who can spend their coins.

Bitcoin script is a stack-based programming language with no loops, therefore excluding it from membership in the turing-complete group of programming languages. A parser was built into Bitcoin's first implementation to support the evaluation of this language and now has its specification as part of the consensus protocol. Because Bitcoin script is used to specify the spending conditions of individual amounts of Bitcoin, it is stored on the blockchain as part of every transaction spending Bitcoin. Bitcoin script's usage is unavoidable and at a high level, Bitcoin cannot be sent to another individual without it. Although the development of Bitcoin script was used to support the more complex use-cases of payment Satoshi mentioned in the early days ("Escrow transactions, bonded contracts, third party arbitration, multi-party signature, etc."), most transactions follow the same structure of just attempting to send money to a particular address.

Today the Bitcoin script language is primarily maintained by the open source contributors to the Bitcoin core codebase, and changes to the script are proposed as rfc-like documents called Bitcoin improvement proposals (BIPs). The high-level Bitcoin script specification consists of operations in the format of OP\_{command} with each operation/keyword mapping to an unsigned integer. The parser for the language within the Bitcoin core codebase reads the operation-mapped integers as hex for it's input while the name for the operations aren't used in the script code itself over concern for the size of these transactions. Changes are typically proposed to the Bitcoin script language when new functionality is desired,or a security vulnerability with the existing language is found. Changes to script are imperative for the growth of Bitcoin as a protocol and to allow the use-cases of Bitcoin to grow along with the needs of its users. This blog will be dedicated to exploring all kinds of Bitcoin topics but I thought I should start off explaining where the name comes from, which is the programmatic name of the script spending condition -- 'scriptpubkey'. For these beginning posts at the very least I will discuss script more extensively and plan to look at Bitcoin code snippets, historical and otherwise. Look forward to more posts in the future!