This is the second article in a series deep diving into individual covenant proposals that have reached a point of maturity meriting an in-depth breakdown. 

CHECKSIGFROMSTACK (CSFS), put forward by Brandon Black and Jeremy Rubin with BIP 348, is not a covenant. As I said in the introductory article to this series, some of the proposals I would be covering are not covenants, but synergize or interrelate with them in some way. CSFS is the first example of that. 

CSFS is a very simple opcode, but before we go through how it works let’s look at the basics of how a Bitcoin script actually works. 

Script is a stack based language. That means that data is “stacked” together on top of…

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