Ever wonder how long it would take to mine a block into the Bitcoin blockchain by hand? Well, wonder no longer because blogger Ken Shirriff has done the work for you with a pencil and paper.

In an article entitled “Mining bitcoin with pencil and paper,” Shirriff provides a thorough explanation of what a lot of bitcoin users take for granted: how exactly bitcoin mining works. Mining, which is considered a bit oddly named by many outside of the Bitcoin community, consists of a type of proof-of-work that helps secure the Bitcoin block chain, the distributed ledger of every transaction made on the Bitcoin network.

According to Shirriff, doing a single round of SHA-256 hashing took him approximately 16 minutes and 45 seconds. This means approximately one hash every 1.49 days (at 128 rounds per block) or a hash rate of 0.67 hashes per day.

Of course, this doesn’t mean that the hash would be accepted at this rate, see below. So anyone actually interesting in manually mining bitcoins might want to read the rest first.

Mining: how does it work?

Bitcoin hashing works under an interesting principle. It uses a cryptographic method, the SHA-256 algorithm, twice on a series of variables that includes the hash of the previous block in the blockchain. As the previous block’s hash is needed for the new block’s hash this connects the two, forming the “chain.” However, even a full pass on a block is not enough to for the block to be accepted. First, its hash must been a particular rare criteria that cannot be predicted before running the hash—in Bitcoin’s case the hash must start with approximately 17 zeros to be accepted.

The result: to get a Bitcoin block accepted into the blockchain a mining machine must complete hash, after hash, after hash, until such time that a hash starts with approximately 17 zeros. Because it takes so much work to produce a proper hash, the discovery of an acceptable block works as a sort of proof-of-work that makes it impossible for any single person or machine to control the chain.

Above is a short, simplified version of how Bitcoin mining works (Shirriff does a great job of unrolling it a bit more in his article).

How does a human compare to a machine?

With his first attempt at hashing, Shirriff estimated that he could produce 0.67 hashes per day. Most modern Bitcoin mining machines (of the ASIC variety) sell in the gigahash per second range (or one billion hashes a second.) Needless to say, a single ASICMiner Block Erupter 30GH/s miner could blow a human out of the water in a mere second.

In energy as well. To humor a reddit user, Shirriff attempted to calculate his energy consumption per hash guessing about 10 megajoules per hash (using a 1500kcal/day sitting metabolism) versus 1000 1000 megahashes/joule for mining software. Making him about 10 quadrillion less efficient than a mining machine.

To calculate energy costs, he went with doughnuts as his go-to energy source at $0.26 per 200 kcalories; whereas electricity for a mining machine would be $0.15/kilowatt-hour. From this he estimated that his energy costs would be about 67 quadrillion times higher than those of mining hardware.

The comparison does make for a lot of doughnuts for the human mining machine.

Conclusion

The double-SHA-256 mining algorithm used to secure the Bitcoin blockchain is deceptively simple—after all, it can be done by hand—however, the specialized mechanism used to accept hashes (the rarity rule) is really what does the heavy lifting.

As expected, Shirriff concludes, “Needless to say, manual Bitcoin mining is not at all practical.”

The experiment, however, does a great job of revealing the under-the-hood function of the Bitcoin blockchain algorithm and is an excellent practical explanation of not just how, but why it works.

Image credit: Ken Shirriff, SHA-256 hash by hand, http://www.righto.com/2014/09/mining-bitcoin-with-pencil-and-paper.html