4 ms·

An orthogonal question I’ve always had is what happens if SHA-256 is broken?

_cenw 2y ago
With the current compute density of Bitcoin (which now runs mostly on purpose-built hardware) it'd still take longer than the universe has existed to find even one collision and the actual process of computing SHA256 is simple enough that we're not likely to find a shortcut.
- jandrewrogers 2y ago
  I think you missed the “broken” part. A lot of simple cryptographic hash functions have been broken. There is a community of people with some semblance of credibility that believe it is just a matter of time for SHA-256. The creation of SHA-3 wasn’t entirely for no reason. I’m not saying it will happen but it is plausible. The question is what is the effect of that happening to bitcoin.
  - adastra22 2y ago
    Who? I don’t know any cryptographers that think this anymore.
- UltraSane 2y ago
  Broken in this context means being able to determine the input nonce that generates a hash with enough leading zeros to mine a bitcoin block with much less energy and time than brute forcing random nonces does now. Then you could mine bitcoin blocks with no power expense and always be first. You would have to be careful about how many blocks you mine to not make people suspicious.
grapesodaaaaa 2y ago
Much worse things than fraudulent cryptocurrency transactions.
salynchnew 2y ago
Fundamentally, just one update to the protocol (becuase code kind of is actually law, insofar that code is overseen by a group of humans capable of collective action and coordination around documentation and if-then statements) will circumvent any concerns about that particular bugaboo.
hannob 2y ago
I couldn't care less about Bitcoin's use of SHA-256, but based on experience: First of all, it's quite unlikely that this is going to happen at all. There are no signs of significant weaknesses in SHA-256. But if it's going to happen, in all likelyhood, you'll get preliminary results long before any actual breakage. (For both MD5 and SHA1, you had around a decade of warnings between "this looks insecure / broken in theory" and "we now have an actual collission".) Anyone paying attention and moving away from algorithms already known to be broken was unaffected by the MD5/SHA1 weaknesses. Of course, there will be those who will wait until an actual breakage, and a few years more, before they act. (As we've seen particularly with MD5.)
t_mann 2y ago
The article is about stablecoins, which mainly live on smart-contract-enabled blockchains (ie, not Bitcoin). I don't think there are many (if any) major smart contract chains out there still using PoW, which I assume your concern is about. Solana's PoH also uses hashes, but I'm not sure what kind of threat that would be (would probably depend on the exact nature of the 'breaking'). Most other major chains such as Ethereum use PoS. The bigger concern would be breaking the asymmetric cryptography those chains use. That would absolutely kill the protocols in their current form (but could probably be fixed by switching to a different crypto standard).
jl6 2y ago
We may never find out. The financial incentive to keep it secret is too great. If someone broke SHA-256, they could generate blocks directing all coins to their own address and thus destroy the entire system. However, in that scenario it is likely that everybody else would roll the chain back to before the break and restart it with a different algorithm (likely SHA-3). In summary, an obvious compromise would get caught and neutralized. So a wily possessor of an SHA-256 break would use it subtly. Most likely they would target “lost” coins that haven’t moved in decades that nobody will notice are missing. Not Satoshi’s though. Too much heat.
- deleted 2y ago
  [deleted]
- UltraSane 2y ago
  If someone broke SHA-256 the best way to use it would be to mine blocks vastly cheaper than anyone else can, and you can choose how many blocks you "win" to control suspicion.
Ferret7446 2y ago
If someone broke SHA-256, a lot of modern crypto is broken. I would worry about all of your sensitive accounts like your bank, government before worrying about cryptocurrency.
UltraSane 2y ago
If the person who breaks it keeps it secret they become very rich or if the method becomes public then bitcoin quickly crashes to be worth $0 per bitcoin. I don't know if bitcoin could migrate to a different hash if the flaw as disclosed to them first.

With the current compute density of Bitcoin (which now runs mostly on purpose-built hardware) it'd still take longer than the universe has existed to find even one collision and the actual process of computing SHA256 is simple enough that we're not likely to find a shortcut.

jandrewrogers 2y ago
I think you missed the “broken” part. A lot of simple cryptographic hash functions have been broken. There is a community of people with some semblance of credibility that believe it is just a matter of time for SHA-256. The creation of SHA-3 wasn’t entirely for no reason. I’m not saying it will happen but it is plausible. The question is what is the effect of that happening to bitcoin.
- adastra22 2y ago
  Who? I don’t know any cryptographers that think this anymore.
UltraSane 2y ago
Broken in this context means being able to determine the input nonce that generates a hash with enough leading zeros to mine a bitcoin block with much less energy and time than brute forcing random nonces does now. Then you could mine bitcoin blocks with no power expense and always be first. You would have to be careful about how many blocks you mine to not make people suspicious.

grapesodaaaaa 2y ago

Much worse things than fraudulent cryptocurrency transactions.

salynchnew 2y ago

Fundamentally, just one update to the protocol (becuase code kind of is actually law, insofar that code is overseen by a group of humans capable of collective action and coordination around documentation and if-then statements) will circumvent any concerns about that particular bugaboo.

hannob 2y ago

I couldn't care less about Bitcoin's use of SHA-256, but based on experience: First of all, it's quite unlikely that this is going to happen at all. There are no signs of significant weaknesses in SHA-256. But if it's going to happen, in all likelyhood, you'll get preliminary results long before any actual breakage. (For both MD5 and SHA1, you had around a decade of warnings between "this looks insecure / broken in theory" and "we now have an actual collission".) Anyone paying attention and moving away from algorithms already known to be broken was unaffected by the MD5/SHA1 weaknesses. Of course, there will be those who will wait until an actual breakage, and a few years more, before they act. (As we've seen particularly with MD5.)

t_mann 2y ago

The article is about stablecoins, which mainly live on smart-contract-enabled blockchains (ie, not Bitcoin). I don't think there are many (if any) major smart contract chains out there still using PoW, which I assume your concern is about. Solana's PoH also uses hashes, but I'm not sure what kind of threat that would be (would probably depend on the exact nature of the 'breaking'). Most other major chains such as Ethereum use PoS. The bigger concern would be breaking the asymmetric cryptography those chains use. That would absolutely kill the protocols in their current form (but could probably be fixed by switching to a different crypto standard).

jl6 2y ago

We may never find out. The financial incentive to keep it secret is too great. If someone broke SHA-256, they could generate blocks directing all coins to their own address and thus destroy the entire system. However, in that scenario it is likely that everybody else would roll the chain back to before the break and restart it with a different algorithm (likely SHA-3). In summary, an obvious compromise would get caught and neutralized. So a wily possessor of an SHA-256 break would use it subtly. Most likely they would target “lost” coins that haven’t moved in decades that nobody will notice are missing. Not Satoshi’s though. Too much heat.

deleted 2y ago
[deleted]
UltraSane 2y ago
If someone broke SHA-256 the best way to use it would be to mine blocks vastly cheaper than anyone else can, and you can choose how many blocks you "win" to control suspicion.

Ferret7446 2y ago

If someone broke SHA-256, a lot of modern crypto is broken. I would worry about all of your sensitive accounts like your bank, government before worrying about cryptocurrency.

UltraSane 2y ago

If the person who breaks it keeps it secret they become very rich or if the method becomes public then bitcoin quickly crashes to be worth $0 per bitcoin. I don't know if bitcoin could migrate to a different hash if the flaw as disclosed to them first.