Recently, the technology giant Google launched a quantum chip called Willow. The processing power of this chip has been described in an attractive marketing way, saying that it can solve in 5 minutes a mathematical problem “that would take a supercomputer 10 septillion years (i.e. 10 25 ), a number that far exceeds the age of the Universe.” Although this technology is in the experimental phase and has no practical applications, its existence is estimated to be decisive for the future of computing systems and cryptography.  

Satoshi Nakamoto had already foreseen something like this in 2010, when he imagined the possibility of the SHA-256 algorithm being destroyed . The creator of Bitcoin does not mention what or how this hash function could be destroyed, but he sets out the consequences of any technology rendering this algorithm obsolete. 

SHA-256 , which stands for Secure Hash Algorithm 256, is a cryptographic function that converts any block of data into a fixed-length 256-bit character string. This algorithm has two features that make it highly secure.  

One is that it is irreversible, since the original data cannot be recreated in reverse from the data encrypted by the hash. Another is that it is resistant to collisions: it is designed to prevent two different inputs from producing the same numerical string. The collision or repetition of these numerical series would have consequences such as the replication of bitcoin addresses, which would undermine the integral functioning of the network and its capacity to safeguard digital property. 

According to Satoshi, SHA-256 was already “pretty strong” in 2010, sensing that this algorithm could remain valid for several decades if a massive attack on the network did not occur. In fact, it has remained valid for a decade and a half, and it would have to last at least two decades for the Bitcoin creator’s prediction to come true.  

In any case, Satoshi considered that if there were a technology capable of breaking the hash function, such as quantum computing, whose processing capacity is superior to anything currently known, this would not mean the end of the world for Bitcoin, which is an open, free system that can be modified on the fly to overcome difficulties of all kinds. 

If SHA-256 were completely broken, I think we could come to some agreement on what the legitimate blockchain was before the problems started, fix it, and continue from there with a new hash function. 

Satoshi Nakamoto, creator of Bitcoin. 

Selecting a new starting point for Bitcoin after its algorithm is destroyed would imply that all nodes and participants in the network would accept one chain as the true one, and that they have the incentives to do so.  

Satoshi then goes into technical details about how to preserve the network after a SHA-256 breach:  

“If the hash break were to occur gradually, we could transition to a new hash in an orderly fashion. The software would be programmed to start using a new hash after a certain block number. Everyone would have to update their bitcoin client at that time. The software could save the new hash for all old blocks to make sure a different block with the same old hash couldn’t be used.” 

Satoshi Nakamoto, creator of Bitcoin.

Bitcointalk is a forum with essential records for the history of bitcoin. Source: Bitcointalk

Other Bitcoiners weighed in on the hash function and Bitcoin 

Theymos, a well-known figure in the Bitcointalk community who has served as a forum administrator since its inception, agreed with Satoshi that “broken cryptography” could not be the end of bitcoin if the currency were to become popular, which it eventually did.  

Since the blockchain can be forked without losing too much data, modifications are possible to all aspects of BitCoin. If SHA-256 were to be breached, a new version of BitCoin would be released that would use a more robust hash function for addresses. 

Theymos, Bitcointalk moderator.

collisions known for the year 2010, fifteen years after its publication, suggesting that this family of hash functions is quite robust and resistant to the passage of time, even if they become outdated. 

Luke Dashjr, another still active Bitcoin developer , commented in 2011 that the solutions proposed by Satoshi and other commentators a year earlier were somewhat simplified. Especially since in just one year, Bitcoin had changed considerably: 

“'Switching' to a new hash means creating a new protocol (possibly derived from the existing one) and a completely new network (possibly based on a genesis block that offers bitcoin funds to SHA-256 addresses that had them pending). In 2010, there was only a single client, and reinventing everything may have seemed like a simple solution. But starting in 2011, we're starting to see alternative Bitcoin implementations, and by the time SHA-256 is broken, we'll no doubt have many different possibilities.

Luke Dashjr, Bitcoin developer.

Both Satoshi and Bitcointalk contributors agree that the Bitcoin protocol, and especially its developers, have the ability to fully preserve and move ownership records within the system while “hashing” the network onto a new hash function, likely triggering a fork of the protocol. This new hash function would be quantum-proof.  

Efforts in this direction have been made by cryptographers, and their results are the SHA-3 function, in whose family of algorithms there is at least one pair with more than 300 bits, and therefore capable of creating longer numerical series with a greater number of possible combinations.  

But the most important set of developments in future-proofing cryptography comes from “ post-quantum cryptography” (PQC) , which has given rise to new hashing algorithms such as lattice -based hashing algorithms, hash-based cryptography, including modern versions of systems such as Lamport signatures and the Merkle signature scheme; and code-based cryptography.