DOKK Library

Some Technicalitites Behind NFTs: Notes for a discussion of NFTs, Copyright, and CC Licenses

Authors Jonathan A. Poritz

License CC-BY-SA-4.0

                         Some Technicalitites Behind NFTs:
                             Notes for a discussion of
                         NFTs, Copyright, and CC Licenses

                                             Jonathan A. Poritz


                                                  16 December 2021

                        This slide deck, except where otherwise indicated, is by Jonathan Poritz and is released under a
                       Creative Commons Attribution-ShareAlike 4.0 International License.

                      These slides are available at .                  Some Technicalities Behind NFTs                                    16 December 2021   1 / 31
Land acknowledgement

           Before I begin, I need to say that while we are meeting in this vir-
           tual space from many geographic locations, I am myself physically
           located at this moment within the unceded territory of the Ute
           Peoples. The earliest documented people in this area also include
           the Apache, Arapaho, Comanche, and Cheyenne. An extended list
           of tribes with a legacy of occupation in this area can be found here:
           Colorado Tribal Acknowledgement List.    Some Technicalities Behind NFTs         16 December 2021   2 / 31
Origins of the Blockchain Whirlwind: Bitcoin

 In October 2009, the pseudonymous
 Satoshi Nakamoto posted a paper →
 to a cryptography mailing list.

 He or she shortly thereafter also
 posted, to a FLOSS sharing site,
 source code for a reference
 implementation of the proposed

            At which point, Yoda could be heard muttering, “Begun, the Bitcoin Wars have.”

      the full paper is here:
                    Some Technicalities Behind NFTs   16 December 2021   3 / 31
Some Bitcoin Hype

                                                  Maybe not a good currency?


      from coinbase, here; snapshot taken 10:10am MT 16 Dec 2021; used by fair use.
                      Some Technicalities Behind NFTs       16 December 2021   4 / 31
A Fly in the Ointment Here, a Few Megatons of CO2 , There



      from, here; snapshot taken 10:10am MT 16 Dec 2021; used by fair use.
                      Some Technicalities Behind NFTs         16 December 2021   5 / 31
Diving Into the Deep End: How a Blockchain Works
Why does it consume so much power?         I thought you’d never ask.

To answer, we must talk about how bitcoin works. Actually, the underlying technology is
called a blockchain, so we’ll talk for a few minutes about How a blockchain works.
Before you stick you fingers in your ears and start humming nervously, let’s remember
that almost everyone in this room has driven a car on the highway, where a lapse of
attention for a fraction of a second could have fatal consequences. And you all have
complex, sophisticated disciplinary knowledge. So bear with me for ten fucking minutes.
A blockchain is built out of three basic pieces:
  • digital signatures,
  • a cryptographic hash function, and
  • a distributed consensus protocol.

You’re probably already sweating... but chill: every academic discipline and every
commercial industry has terms of art. The above three pieces are basically
  • really distinctive personal style [for digital files],
  • a very effective blender [that grinds up digital files], and
  • an method for group decision-making [for groups that meet only on the ’net, never
    in person].   Some Technicalities Behind NFTs     16 December 2021   6 / 31
References for Cryptology

Crypto tends to intimidate users, because they hear that small mistakes can be fatal. But
that is also true of many things in life, and we don’t let it stop us.
The other problem with crypto is that it is fairly mathy. Which is a feature, not a bug ...
to a mathematician, but maybe not to others.4
The good news is that there are great free/open resources on the ’net. For example:
        Chapter 4 of my open textbook Yet Another Introductory Number Theory
        Textbook [YAINTT], which can be found at
        [although, being a math textbook, this is rather unabashedly mathy – even though
        that Chapter has a lot of history and terminology.]; or
        Ed Felton’s [Princeton professor of computer science and Deputy Chief Technology
        Officer under Obama] Nuts and Bolts of Encryption: A Primer for Policymakers,
        found at felten/encryption primer.pdf, which is not
        mathy at all.

      because the mathematical community has done a terrible job of sharing the joy and beauty of our subject!
                       Some Technicalities Behind NFTs                       16 December 2021   7 / 31
Our protagonists, and an adversary

Most works of cryptology speak of two star-crossed lovers, Alice and Bob, who attempt
to keep the guttering candle of their love alight, though distance separates them and
their communications are being monitored by the evil Eve.


[Extra credit if you can name the two famous mathematicians who acted as models for these pictures of Alice and Bob.]

        “Alice” and “Bob” images in the public domain; “Eve” from Pirate Riley. Aaarrhh Me Hearties! which is by peasap and is licensed under CC BY 2.0;
         thanks, CC Search!
                        Some Technicalities Behind NFTs                                  16 December 2021       8 / 31
Why is Eve so powerful?

It’s important to realize that in many – maybe most – situations, it is entirely
appropriate to assume that Eve can see all the communication between Alice and Bob
while it is in transit. All of the channels you are used to using suffer from this:
    A cell phone is basically a walkie-talkie with infrastructure [the infrastructure being
    all those cell towers all over the place]. Anyone with a radio receiver of the right
    type who is within the footprint of the same tower can hear the entire exchange.
    Satellite phones are much worse: the footprint is the size of a continent, often.
    Anything you do on the Internet is essentially public.
Here is a diagram with some basic terminology:
   Some Technicalities Behind NFTs         16 December 2021   9 / 31
Keys [for symmetric cryptosystems]

If we are to publish our encryption and decryption algorithms, the security must lie in
some other secret. This is an additional piece of information called the key, which is
input into those algorithms, as follows:

Using mathy notation:
  • x ∈ S means the thing x is in the set [collection of things] S, pronounced “x is in S”
  • o = a(i) means o is the output when the input i is fed into the algorithm a, pronounced
    “o equals a of i”    Some Technicalities Behind NFTs          16 December 2021   10 / 31
Notes on symmetric cryptosystems

The above is called symmetric (or private- or secret-key) cryptography.
Both the encryption ek and decryption dk use the same key k, which must be shared in
some private, pre-lapsarian moment. The keyspace K must be large, otherwise Eve can
just try all keys and see which works [which is called a brute-force attack].
Symmetric cryptosystems are fast — you can run a video stream through one without
noticing it on a consumer-grade PC.
The design of symmetric cryptosystems is something of a black art. There is little general
theory on the attack or defense side, and the algorithms tend just to be along the lines of
scramble the bits a lot. See, e.g., the pretty pictures on the Wikipdeia page for AES
Some examples:
    The Syctale – ancient Greece
    The Caesar cipher – actually used by Julius Caesar. [addition mod 26...]
    The Vigenère Cipher – thought to be unbreakable for centuries. Easy to break today.
    The one-time pad – completely unbreakable; hard to use in practice (but see Leo
    Marks’ Between Silk and Cyanide: A Code Maker’s War 1941-45)
    The Enigma machine – a German military coding device from WWII.
    Modern block ciphers like DES, triple-DES, AES, etc.   Some Technicalities Behind NFTs       16 December 2021   11 / 31
Asymmetric cryptosystems
If Alice and Bob want to be able to communicate securely without ever having met to
exchange the symmetric key, they can instead use asymmetric (or public-key)

That this is possible at all is very cool. There are a few ways we do it, now, including
RSA (named after Ron Rivest, Adi Shamir, and Leonard Adelman, who published this
idea in 1977) and elliptic curves (which are more efficient but less commonly used, since
their mathematics is significantly harder to chew that what is behind RSA).
All asymmetric crypto relies upon a mathematical function which is easy to compute in
one direction but difficult to invert. For RSA, this is essentially multiplication forward
[easy], but factoring backwards [hard]. For other asymmetric algorithms, there are other
of these one-way functions.   Some Technicalities Behind NFTs       16 December 2021   12 / 31
The “Man-in-the-middle attack”

A significant issue with asymmetric cryptosystems is a Public-key Infrastructure [PKI],
because of the dreaded man-in-the-middle attack:

   Some Technicalities Behind NFTs    16 December 2021   13 / 31
Digital Signatures

Therefore, we need to be sure that the public keys we use really do belong to the people
who we think they do. We do this either by getting the key from someone in person –
but that kind of ruins the whole idea of asymmetric crypto! – or we get a key in some
way that we are sure of its provenance. One way to be sure would be to have a digital
signature on the public key, signed by someone whom we trust. Signatures work like this:

   Some Technicalities Behind NFTs    16 December 2021   14 / 31
How to Think Critically About Security/Privacy/Cryptography

Things to think about when learning and critically assessing cryptological gizmos:
  • What exact problem was it designed to solve?
       ◦ What [exactly] are the inputs and outputs.
       ◦ What [precise] assumptions are made about who knows what, when?
       ◦ What [precise] assumptions are made about how the adversary will try to break the
         system – what is the threat [or attack] model?
       ◦ What computational power is available to the allies and to the adversaries?
  • How confident is the community in the effectiveness of the proposed technique?
       ◦ Is there a mathematical proof, based on just mathematical truths.
       ◦ Is there a mathematical proof that breaking the proposed technique would be
         equivalent to solving some well-studied problem?
       ◦ Does the security of the proposed technique rest on some engineering factors – e.g., is
         there a way known to break the technique if we could be a certain new kind of
and, often the most important issue by far:
  • How reasonable are the assumptions in a real-world context where we want to use
    this new technique?
    Some Technicalities Behind NFTs          16 December 2021   15 / 31
E.g., Thinking Critically About Digital Signatures

The problem: Bob has a secret key with corresponding public key that is reliably known
to the whole community as being his. He also has a message he wants to sign.
Bob will transmit to Larry the message along with an extra piece of data, the digital
signature. Larry can use the widely known public key associated to Bob, the message,
and the signature data to determine if only someone who knew Bob’s secret key could
have produced that signature on that message.
In the case of RSA-based digital signatures, there is a mathematical proof that breaking
this signature scheme would amount to figuring out how to factor large numbers quickly,
at which many mathematicians have been unsuccessful for many years.
There is a way to factor large numbers if engineers can build a quantum computer. This
used to be thought of as far in the future, if ever even possible; now we think it might be
25 years or fewer off. So it will be possible to forge RSA signatures in ≤ 25 years.6
In the real world, it is very hard to keep a secret key secret forever. It is also very hard to
associate public keys to a public identity reliably. Therefore a robust PKI is a essential
for digital signatures to work in practice, and it is hard to make one and keep it healthy.

      Actually, almost all digital signature schemes fall to quantum computers, not just RSA-based ones.
                        Some Technicalities Behind NFTs                16 December 2021   16 / 31
Cryptosystems: What to Remember

Encryption is important: messages on the Internet are as open as postcards.
Symmetric cryptosystems:
  • Are fast.
  • Have very little structure: “just fiddle with the bits.”
  • So our confidence on them is based on smart people trying hard to break them.
  • Require a previously shared secret key – key management.
Asymmetric cryptosystems:
  • Are slow.
  • Have a lot of mathy structure.
  • So our confidence in them is based on math, although we do know many of them
    break with quantum computers.
  • Key management is crucial, particularly a Public Key Infrastructure [PKI]
Digital signatures:
  • Are based on asymmetric cryptosystems.
  • Strongly link specific messages to specific (public, private)-key pairs.   Some Technicalities Behind NFTs        16 December 2021   17 / 31
Cryptographic Hash Functions

A cryptographic hash function is an algorithm which takes arbitrarily large chunks of data
as input, and produces a hash [sometimes called a digest] of a certain, fixed size – e.g.,
the most widely used cryptographic hash function today is called SHA-256 and it always
produces hashes consisting of 256 bits, no matter how big the input.
A hash function is called pre-image resistant if it is very hard7 given any particular
possible hash value, to find an input data chunk whose digest has that value.
A hash function is called second pre-image resistant if it is very hard, given one input
data chunk, to find a second which hashes to the same digest as that chosen first chunk.

Basically, a hash function is a blender into which you pour data, which blends all its input
thoroughly and produces a small output pellet. The pellet is almost unique to that set of
ingredients, in the sense that it would take many lifetimes of the universe for you to find
another set of input ingredients which would yield the same output pellet.

The problem is described above. Known hashing algorithms are quite complex and have
little mathematical structure. Therefore, it is very hard to attack them... but, also, there
are not any proofs that they do what we hope they will. Old hash functions, for example,
are no longer used because we now know how to break them.
      meaning that, essentially, one should just have to keep trying random inputs until one gets lucky.
                         Some Technicalities Behind NFTs               16 December 2021   18 / 31
Hash Functions As Message Digests and For Chains
Suppose I send you a big file and we want to be sure it didn’t get corrupted in transit. I
could compute a hash of that data on my end, you could do the same on yours, and I
could read you the digest over the phone – if they agree, we’d be quite certain the files
agree as well.

You can use hash functions to make immutable chains. Suppose we all agree on some
block of starting data, called the genesis block in the blockchain community. Then we
start attaching new blocks to the list of official, on-chain blocks, by some sort of
distributed agreement process, and also putting the hash of the previous block into each
new block on the chain – this is called a hash chain. If, afterwards, we have a dispute
about what the whole chain is, we could each run down the whole chain, checking that
each hash value in the nth block is equal to the hash of the (n − 1)st block. Since it is
hard to find second-preimages for good hash functions, this is impossible to forge, and
thus it is impossible to change the old blocks on an existing chain: hash chains are

   Some Technicalities Behind NFTs       16 December 2021   19 / 31
Hash Functions to Slow Computers Down

Suppose you want to slow someone down. You could had them a chunk of data and ask
them to find some other piece of data to add to that such that when they hashed the
big, joined data chunk, the output hash would end in at least five (or seven or ten or
whatever, depending upon how much you want to slow them down) 0s.
You couldn’t ask for them to find data which will make the hash value exactly equal
some given value, but instead this task of working to get a certain number of 0s can be
done, only with a lot of computation, by just trying over and over again.
The bitcoin protocol uses this method to slow down – and randomly assign a winner,
whoever found the second piece of data which makes the whole thing have a hash ending
in a certain number of 0s – all of the people working around the globe to verify
transactions made on the bitcoin network. The number of 0s needed to win this
competition can be changed as the total amount of computational power on planet Earth
dedicated to doing this (stupid, useless, but un-short-cut-able) work increases, so that
even with all that power, there will only be winner about once every ten minutes.
The total hashing power on planet Earth right now can do about 152.67 quintillion
SHA-256 hashes per second8 – that’s 1.5 × 1020 hashes per second. Much if this is in
special hardware in hashing farms which used to be in China.
      see Bitcoin Hashrate Chart
     Some Technicalities Behind NFTs   16 December 2021   20 / 31
Hash Functions: What to Remember

Hash functions crunch arbitrarily large input data files into a digest (think of it as a
fingerprint) which cannot be predicted and pretty much is unique to that input data
compared to all other datasets the human race is likely to create until the heat death of
the universe.
  • They are fast.
  • They have very little structure: “just fiddle with the bits.”
  • So our confidence on them is based on smart people trying hard to break them.
  • The community is pretty confident at the moment about SHA-256 (although md5
    died a while ago and SHA-1 is considered too shakey to be trustworthy).

   Some Technicalities Behind NFTs      16 December 2021   21 / 31
Distributed Consensus
Suppose you have a block of transactions – maybe people submitting records of buying or
selling goods by transferring some artificial cryptocurrency among users – you want to
submit to a global, public ledger. It is important that everyone agrees upon what are the
valid blocks, because otherwise a bad actor could spend some cryptocurrency on one
transaction in one block, and the same cryptocurrency in another transaction with
someone else: this is the double-spend problem.
The easiest way for this to work is if there is a central party who collects all proposed
blocks and simply decides which ones will go on the chain, perhaps by
first-come-first-served, perhaps by playing favorites (or so people fear). Such a central
decision-maker is called a trusted third party [TTP] by cryptologists. Distributed
consensus is very easy, fast, and efficient with a TTP.
Without a TTP, as bitcoin tries to go, much more work is required. The bitcoin approach
is to make everyone do the “hash to get a certain number of 0s” game, and then publish
their winning extra bit of junk data. Whoever wins can prove it, with that data, and gets
to submit their preferred block to the global public ledger.
Sometimes, two people will win at the same time in different places, and the chain will
split. But if half of the network works on growing one chain and half works on the other,
pretty quickly it will be very likely that one will be quite a bit longer than the other, and
everyone will go over to the longer valid chain at that point.   Some Technicalities Behind NFTs        16 December 2021   22 / 31
Wrapping Up The Blockchain Bow

The term blockchain is used to describe a hash chain whose globally recognized
individual blocks are agreed upon by a distributed consensus protocol.
Generally, those who can submit blocks come from a very open group – potentially
anyone 9 – and follow some internal rules such as for maintaining a cryptocurrency ledger
or running an on-chain Turing-complete programming language [Ethereum, a company
based in the Crypto Valley, calls these on-chain programs smart contracts in an
essentially meaningless bit of excellent marketing].
Another differentiator between different blockchains is how the individuals in the group of
participants identify themselves. Generally, the choice is with some identity strictly
coupled (hopefully) to a real-world individual or entity or one where individuals act
through pseudonymous (hopefully10 IDs. Both require some kind of reliable PKI, however!
Different blockchains use different consensus protocols: bitcoin’s proof of work has a
horrible carbon cost, is slow, etc. Another protocol is based on proof of stake, which is
less energy-intensive but amounts to formalizing a strategy of the rich always get richer.

      Some people restrict this group and then talk about permissioned blockchains, but I think that is pretty much the same as freeze-dried water.
      This has turned out to be much harder that it seemed it would be, e.g., in bitcoin’s case.
                         Some Technicalities Behind NFTs                                 16 December 2021         23 / 31
Thinking Critically About Blockchains
Whatever particular version of a blockchain, the solution it provides [in the spirit of our
Thinking Critically About Security... strategy above] involves these key features:
  • A chain of linked, sequential public records.
  • This [hash] chain is immutable.
  • Individuals participate in the blockchain through either pseudonymous or
    intentionally real world-linked IDs supported by a robust PKI.
  • The progress of the blockchain is realized by a distributed consensus protocol which
    avoids putting its trust in any particular [third] party.
In short, blockchains are characterized as
   • public
   • immutable
   • relying on a robust PKI
   • eschew TTPs.
The constituent cryptographic pieces that realize these characteristics may or may not be
generally thought of as reliable, but the ways these blocks are combined is not much
subject to debate.
Whether the above characteristics are reasonable assumptions in any particular real-world
context is much more questionable....   Some Technicalities Behind NFTs        16 December 2021   24 / 31
Blockchains ... Of Limited Use?

The integrity of the bitcoin ledger is based on a huge amount of (useless) work, needed
because cryptocurrency fanatics don’t trust the government: it’s all about the TTP.
Now what about other use-cases?
Educational institutions should “put student credentials on the blockchain:” it’s
public, immutable, and not subject to any single party’s control.
But this is nonsense. There is a natural TTP for a credential: the issuing institution!
OK, we need a functioning PKI, but so does a blockchain-based credential system (the
credential would have to be signed, in its form “on the chain,” as well).
Walmart will “put its supply chain on the blockchain.”
But this is nonsense. There is a natural TTP for a Walmart’s supply chain: Walmart
trusts Walmart!
Marijuana producers in Colorado will put their production records on a blockchain
so that the state marijuana oversight organization will be able to check that it has all
been produced according to state law.
But this is nonsense. There is a natural TTP here as well: that state supervisory agency!
Also, just having a cryptographically verified blockchain doesn’t mean that the data
entered in its blocks corresponds correctly with the real world: this is a misreading of the
idea of “trust” here.   Some Technicalities Behind NFTs       16 December 2021   25 / 31

Cryptocurrencies at blockchains which allow actors to perform transactions which add or
subtract to their accounts.
“Actors” are defined as (public, private)-key pairs [!!!].
Those accounts are like bank accounts, they just have a number in them.
The transactions will deduct a number from an input account (or accounts) and credit it
to an output account (or accounts), often owned by different actors.
Since the numbers being added and subtracted are all just numbers, the units of this
“currency” are all fungible, one of the defining properties of an actual currency.
The consensus protocol makes sure the global community agrees upon the current values
of all accounts.
Doing the work to run the consensus protocol is called “mining,” and usually the actor
who succeeds in validating a block of transactions gets a reward of some amount of the
The full hash chain, which records all transactions that have achieved consensus, is often
enormous: the Bitcoin blockchain is 380.24GB as of 15 December 202111 .
       see Bitcoin Blockchain Size
    Some Technicalities Behind NFTs   16 December 2021   26 / 31
Finally, NFTs

NFTs put either entire digital objects into some blockchain, or, much, much more often,
just a reference such as a URL or an identifier on the IPFS (which is an Internet-wide
distributed storage mechanism that is something like a grown-up version of bit torrent).

The protocol does not treat these objects as numbers in an account like for a
cryptocurrency, so there is nothing at all like splitting up an object and depositing it in
some other accounts. In this sense, the objects are non-fungible.

Blockchains for NFTs have a special operation (in addition to something like mining for
cryptocurrency blockchains) called minting an NFT. This involves creating a block on
the chain which has the digital object in it, with some actor as the “owner.” Other actors
can then do transactions which transfer “ownership” of that data block to another actor
when compensated by real- or cryptocurrency. (Remember: here, “actor”=”key pair.”)

Additionally, the “owner” of a minted NFT can issue a transaction to the corresponding
blockchain, using the power that actor [key pair!]has to issue valid digital signatures,
transferring the ownership to another actor. This is often done in exchange for the
transfer of cryptocurrency (maybe even on the same blockchain), or simply a check for
real currency.   Some Technicalities Behind NFTs         16 December 2021   27 / 31
Copyright and CC Licensing Issues for NFTs

As far as I understand things (but IAmNotALawyer!), minting an NFT is almost exactly
like putting some URL on a website I own along with a bit of text that says “I like the
artwork [or whatever] is at the end of this link.”
There should be no copyright consequences for that, it is not a copy!
Licensing that NFT would be very odd: does that short web page with URL and
statement even have enought creativity even to have a copyright? Rights for that page
should be (unless there are some platfrom Terms of Service or otherwise other contracts
signed) completely independent of rights over the object at the end of the link.
Of course, the platform that runs that blockchain [but wait a second, the whole point of
blockchains is that they are decentralized! ... but in practice, most NFts are on particular
platforms] may have Terms of Service, or an auction house which helps inflate the price
of a NFTs may have contracts which buyers and sellers have to sign, that require some
intellectual property rights over the material at the end of the URL, and/orwhich transfer
those rights upon sale of the NFT.
Absent such legal instruments external to the NFT platform (which externalities really
give up on Lessig’s famous “code as law” approach to technology), the NFT per se seems
to be merely a way of publicly registering one’s patronage of an artist or artistic work12 .
       If this is true, then there really should be no re-sale market in NFTs: “owning” the NFT is all about public support of the artist, so a third party
       buying it from the original patron would notd support the artist, nor would it gain the purchaser anything.
                           Some Technicalities Behind NFTs                                    16 December 2021            28 / 31
The Blockchain’s New Clothes

I love the technology in blockchains. It is very beautiful computer science.
But I don’t think Emperor Blockchain, in any of his forms (cryptocurrencies, “academic
credentials on the chain,” NFTs, etc.) has any clothes on.
I think approximately 100% of proposed blockchain applications make absolutely no sense.
I have been told by some blockchain enthusiasts that blockchains have magical properties
which I know for a fact they absolutely do not have. I don’t know if these people are
good or bad actors (the downfall of prominent blockchain enthusiast Alex Tapscott
proves that there are at least some bad actors), or have simply been mininformed.
It’s possible that this is case of regulatory capture by metaphor : computer scientists use
“trust” and many related words when talking about these topics – “trusted third party,”
“proof [of work, etc.],” “verifiable signature,” ... – but those are just metaphors! It is a
mistake to take them too literally, as seems to be done nearly universally in the
blockchain world.

   Some Technicalities Behind NFTs        16 December 2021   29 / 31

 I NFT Gains Mostly Go to Small Group of Whitelisted Investors: Study [Bloomberg]
 I Mapping the NFT revolution: market trends, trade networks, and visual features —
   Scientific Reports [From Nature]
 I Non-fungible tokens (NFTs) [Slides from a presentation to the European
   Observatory on Infringements of IP Rights
 I Right-Clicker-Mentality [great short commentary by Cory Doctorow]
 I Stephen Diehl’s Blog [a very insightful techie]
 I Attack of the 50 Foot Blockchain [“Blockchain and cryptocurrency news and
   analysis by David Gerard”]
 I There’s No Good Reason to Trust Blockchain Technology [Wired article by Bruce
 I Blockchains and Cryptocurrencies: Burn It With Fire [video of great talk by Nicholas
 I Blockchain Pixie Dust [website by JP]
 I Twitter feeds @davidgerard @smdiehl @ncweaver   Some Technicalities Behind NFTs    16 December 2021   30 / 31
Discussion and Contact Info

Contact info:
Email: ; Tweety-bird: @poritzj .
Get these slides at and all files for remixing13 at .
If you don’t want to write down that full URL, just remember
  or [then click Always SHARE]
  or [then click Always SHARE]
  or scan −−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−→
       [then click Always SHARE]

       subject to CC-BY-SA 4.0
     Some Technicalities Behind NFTs       16 December 2021   31 / 31