I am not an expert on the subject of cryptocurrency, a very complex issue with many details, but the other day, talking to my friend Jaime Zarucki, I had an Aha! Moment that I would like to share.
Jaime mentioned an article published by Magalí Piastri and Leonardo Akerman  where they discuss legal issues when acquiring a property in exchange for cryptocurrency. Is it considered a sale or barter?
They quote a consultation made to the Uruguayan Tax Authorities by a notary inquiring how to calculate the relevant taxes that the seller should pay.
The conclusion in their articles is that both the Tax Authority and the notary public agreed that the transaction in question should be considered an exchange and not a real estate sale, because, according to the Uruguayan civil code, in order for a sale to occur a price must be agreed upon and in this case being that cryptocurrency will be used, which does not qualify as money but as a movable asset, to be exchanged for a real estate asset, it cannot be considered to be a sale.
In a different article in that magazine, Dr. Jorge Pereyra presents a broader view regarding the criteria that would determine if cryptocurrencies are to be considered currency or chattel. Among several considerations, he compares it to foreign currencies. He cites China, Germany and El Salvador as examples of the wide range of criteria currently applied. China does not accept it as a means of payment and at the other extreme we have El Salvador, which as of September 2021 includes Bitcoin, the best known cryptocurrency, among the currencies of legal tender. 
There is nothing that is not alluded to in the Torah . Our sages see the Torah as blueprints according to which G-d created the world. Everything that one sees in a building is represented in the blueprints. Likewise, G-d created the world according to the "blueprints" of the Torah. Everything that happens in our tangible reality has its roots in the Torah. To better understand the essential hows, whys and wherefores of everything, we turn to the Torah and by extension, the Talmud.
What can the Talmud, authored some two millennia ago, contribute to our understanding and definition of cryptocurrency?
We find in the Bible, and more extensively in the Talmud and codified in the Halacha, detailed laws regarding sales, purchases and other types of transactions and acquisitions.
The most common methods of acquiring an object in exchange for something are: purchase and barter.
They each have their own dynamics. For example: according to Talmudic law (Halachah), if one pays for goods, he does not acquire ownership until he performs a “chazakah” or a physical act of acquisition that draws it out from the seller's domain and physically brings it into the buyer's. The logic of this rabbinic rule is the following: Let us suppose that the merchandise that one purchased is stored in the warehouse of the seller. If we were to consider that upon payment the merchandise automatically belongs to the buyer, in the event of a flood or fire, the seller will not have any personal incentive to hurry or even bother at all to save the merchandise. The goods are no longer his and he is not liable for the damages, since he did nothing to cause them. It is quite a different matter, however, if the goods paid for still belong to the seller until they leave his property and are transferred to the buyer’s. In that case, in the event of a flood or fire, the seller has every incentive to move to save the merchandise, as it is still his and he will have to absorb the loss. In the case of barter, however, as soon as I deliver my object of value to the owner of the other object, the other object becomes mine, although it still finds itself in the property of the other.
Another practical difference between these two methods of acquisition is regarding the moment when the transaction is considered closed and irreversible. In the case of payment, since, as we have seen, transference of ownership of the goods does not occur until they come into the physical possession of the buyer, either party may renege and the seller must reimburse the buyer . In the case of barter, however, as soon as one of the parties takes possession of the goods from the other, the other’s goods automatically becomes the property of the first party and the transaction is closed and irreversible.
What would we say, then, in the case of acquisition of property in exchange for cryptocurrency? When transferring the sum of cryptocurrency to the “wallet” of the seller, can they still renege on the deal as would be the case of a sale being that nothing other than "money" changed hands, or can they no longer renege because it is considered barter and one party has already delivered their goods, namely the cryptocurrency?
The Talmud discusses at length the criteria that determine whether something is to be considered chattel or currency.
It is not the purpose of this article to address the subject exhaustively, I’d just like to share some basic concepts in order to pique the reader's interest and motivate him or her to delve deeper into the subject.
For a precious metal to be considered currency the Talmud discusses three conditions: 1. It has intrinsic value; 2. It is minted by and has the backing of the government; 3. It is a recognized and accepted means of acquisition.
These are not such simple and absolute criteria, to be sure, since there are coins that are valued more because of their intrinsic value than for their value as currency. The Talmud  discusses the case of one who has gold coins and exchanges them for silver coins or vice versa. Would this transaction be considered a sale or a barter (with the respective practical implications mentioned above)?
The answer is classic Talmud: it depends. The relationship between gold, silver and copper coins is relative. A silver coin is considered “currency” in relation to the gold coin that would be considered “chattel” in such a transaction.
The reasoning is: Silver coins are easier and more practical for use in commerce, as it is not as easy for a seller to receive a gold coin as a means of payment. A gold coin is more often used as a means of storing value. In the specific case mentioned, if the owner of the silver coins, which is considered “currency”, gave them to the owner of the gold coins, it would mean that he made a “payment” to “buy” the gold coins. Since it is a purchase, the transaction is not finalized until the gold coins —the “merchandise”— is physically transferred to him. On the other hand, if the owner of the gold coins is the first to deliver them to the owner of the silver coins, the transaction is considered closed, since the “merchandise” has been delivered, and neither party can now renege. The owner of the silver coins now has an irreversible obligation to deliver the stipulated silver coins as payment for the goods received.
There are, in fact, not one but two types of barter or exchange: 1. When the exchange is made without defining a monetary value for the items exchanged: “I want to exchange my bike for your horse”; 2. When the exchange is made after defining a monetary value: “my bike is worth $100 and your horse is worth $100, shall we exchange one for the other?” Each of the two cases has different halachic implications.
We might want to consider whether such criteria would be relevant when defining the “monetary” nature of cryptocurrency. One possible application might be the following:
If one acquires cryptocurrency for speculative purposes —investment— it could be considered chattel, similar to the Talmudic gold coin, as opposed to the case where one acquires it not in order to store it or speculate with its value but to use it as a means of payment —with a defined and stable value— to acquire goods, services or property as if it were fiat currency. In that case it would be more similar to the talmudic silver coin.
In fact, there already exist two different types of cryptocurrencies: 1. the speculative one, which is evaluated by its own value, which fluctuates according to market dynamics. The best known in this category are Bitcoin and Ethereum. 2. The so-called “stablecoin” class, whose value is fixedly and stably linked to fiat currencies. The pioneers in that class are known as USDT and BUSD. Might we compare Bitcoin to the talmudic gold coin and Stablecoin to the silver coin? This fascinating subject is just getting off the ground.
We see here a small example of the sophistication of the Talmudic perspective regarding currencies and transactions. It would be interesting to see which of the Talmudic criteria regarding this subject can shed light on the new legal realities related to cryptocurrency and the different questions that they generate.
So far, we have examined two sides of the coin, the Talmudic side and the monetary system side. Although based on different premises, both address practical and tangible definitions. There is, however, a third side of the coin (did you know that a coin had more than 2 sides?): the spiritual side.
A coin, by definition, has a limited commercial value, which is what allows you to acquire goods in exchange for it. But this is so only true when it is used to acquire something of material value, since everything material is limited and has a limited value. There is, however, a way to acquire something of infinite and eternal value in exchange for a coin of limited monetary value: when one allocates money to help someone else, Tzedakah, one achieves an effect and acquires a merit of infinite value that does not expire, neither in this life nor in the next. Its value endures for all of eternity.
Appears in Panorama Económico y Empresarial, No. 26 (December, 2021) pages 6-7. Published by the Cr. Alfredo Kaplan studio. Accessible online: https://bit.ly/32DbROG
It is noteworthy that although it is legal to renege on the agreement until the delivery of the goods, even though payment has been rendered, it is not considered ethical and one who does so incurs the curse known as “Mi Shepara”.
Bava Metzia,beginning on page 45a.
Based on the original lecture delivered in Spanish on January 26, 2022 at the virtual annual summer symposium titled, Is there nothing new under the Sun?, organized by Chabad of Uruguay in conjunction with Escuelas Oholei Jinuj of Chabad of Argentina. https://youtu.be/N-npRG0e2bE (30:00). Spanish version published originally in Revista Kesher No. 78, Fall 2022.