Hash() function not secure

[knightmb]

I'm not particularly sold on the technical soundness of this program, honestly. Why use SHA256 rather than Whirlpool or SHA512?

For the same reason they didn't use SHA1024 or SHA2048 or SHA4048 or SHA1000000000000000000000000000000000

There are lots of theoretical attacks that can be done against it, but if a program or new math proof can half the amount of time it takes to crack it, are we really worried about the encryption taking 100 billion years to crack but now with this new attack (insert math,attack,flaw) it's only going to take only 1 billion years to crack? How about a million years? Even one-hundred thousand years?

When they can crack SHA256 in under 10 minutes, I'll be worried, but until then, time is on your side.

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[Some Mouse]

For the same reason they didn't use SHA1024 or SHA2048 or SHA4048 or SHA1000000000000000000000000000000000

No. SHA512 and Whirlpool exist, are well defined, well supported, well analyzed, and they exist for a reason.

There are lots of theoretical attacks that can be done against it, but if a program or new math proof can half the amount of time it takes to crack it,

Reversible computing techniques 'cheat' around the entropy limit. This means they can reach effective speeds far, far beyond what are possible with current computers, as they are effectively capable of performing nondeterministic operations.

You are basically betting the entire economy (if you believe bitcoins will succeed anyway) on no one developing a means to halve the effective bit length as has been done with e.g. AES.

It's careless.

are we really worried about the encryption taking 100 billion years to crack but now with this new attack (insert math,attack,flaw) it's only going to take only 1 billion years to crack? How about a million years? Even one-hundred thousand years?

Ten years, assuming only minor flaws in SHA256.

If there is a major flaw (again, see the push for SHA-3) there is a much more serious problem. There does not appear to be a clear mechanism for handling a compromise of the basic algorithm, and there should be.

[knightmb]

For the same reason they didn't use SHA1024 or SHA2048 or SHA4048 or SHA1000000000000000000000000000000000

No. SHA512 and Whirlpool exist, are well defined, well supported, well analyzed, and they exist for a reason.

I'm sure the same was said back when 40, 64, 128, and 256 bit encryption was coming out. SHA512 is part of SHA2, I remember when everyone was talking about how insecure SHA1 was with that significant *flaw* and how we all need to move to SHA2 because it was well defined, well supported, and well analyzed; sound familiar?

There are lots of theoretical attacks that can be done against it, but if a program or new math proof can half the amount of time it takes to crack it,

Reversible computing techniques 'cheat' around the entropy limit. This means they can reach effective speeds far, far beyond what are possible with current computers, as they are effectively capable of performing nondeterministic operations.

You are basically betting the entire economy (if you believe bitcoins will succeed anyway) on no one developing a means to halve the effective bit length as has been done with e.g. AES.

It's careless.

I'm not betting anything for the simple fact that unless you can see into the future, we work with what we have in front of us. We can debate all day that in the future computers will be a million times faster or that some math genius is going to discover a flaw in the system that would bring everything down. I'm well aware of many peer reviewed papers and tech journals, even blogs about encryption. Not everything in existence, as I don't have the time for all of it, but enough practical experience to be able to visualize what it would really take to do what you propose.

are we really worried about the encryption taking 100 billion years to crack but now with this new attack (insert math,attack,flaw) it's only going to take only 1 billion years to crack? How about a million years? Even one-hundred thousand years?

Ten years, assuming only minor flaws in SHA256.

If there is a major flaw (again, see the push for SHA-3) there is a much more serious problem. There does not appear to be a clear mechanism for handling a compromise of the basic algorithm, and there should be.

10 years is a good a guess as my 1 million years. SHA1 still has not been broken, but you can brute force/exploit flaws on a super-computer in under 60 hours if you have $35 million to throw at it.

Overall, I hear what you say and if BitCoin jumped in the SHA3 realm, I would sleep just as well at night as I did with it using the older SHA2 realm of technology.

I'm not trying to nitpick your post, just offering up my opinion and I certainly respect yours. I think we can both agree that if the encryption is bumped up another notch in the future, it would be a good thing for the system and community as a whole.

[Some Mouse]

I'm sure the same was said back when 40, 64, 128, and 256 bit encryption was coming out. SHA512 is part of SHA2, I remember when everyone was talking about how insecure SHA1 was with that significant *flaw* and how we all need to move to SHA2 because it was well defined, well supported, and well analyzed; sound familiar?

I'm not aware of any 40 bit hash length. The reason for SHA512 and Whirlpool's excessive bit lengths are just for such future proofing. A collision has a 50% chance of occurring at half of the bit length (roughly), so weak hashes such as MD5 would have problems at around 2^64 elements, this was well known and few people thought this was impossible to achieve in the future.

So no, it's not exactly familiar. Wanting to double it again because the idea is to form a basis for a new economy is not crazy talk - there is no technical reason not to use Whirlpool or SHA512 (or both). The only hurt would be a lower hash generation rate... which isn't exactly a problem.

I'm not betting anything for the simple fact that unless you can see into the future, we work with what we have in front of us. We can debate all day that in the future computers will be a million times faster or that some math genius is going to discover a flaw in the system that would bring everything down. I'm well aware of many peer reviewed papers and tech journals, even blogs about encryption. Not everything in existence, as I don't have the time for all of it, but enough practical experience to be able to visualize what it would really take to do what you propose.

Your participation is your bet.

10 years is a good a guess as my 1 million years. SHA1 still has not been broken, but you can brute force/exploit flaws on a super-computer in under 60 hours if you have $35 million to throw at it.

$35 million to swipe any single person's bank account.

I'm not trying to nitpick your post, just offering up my opinion and I certainly respect yours. I think we can both agree that if the encryption is bumped up another notch in the future, it would be a good thing for the system and community as a whole.

I'm honestly rather keen on exploring alternative possibilities for generation. As one Slashdotter put it, the current scheme is like claiming a forest of unknown size as currency, burning it down, then proclaiming the most select 21 tons of ash as the representative medium. I have an idea but I have no clue about who would be interested.

[knightmb]

That's why I'm glad we have people like you here to participate in the discussion as well. A room full of "yes men" is a dangerous thing. 

[D҉ataWraith]

Reversible computing techniques 'cheat' around the entropy limit. This means they can reach effective speeds far, far beyond what are possible with current computers, as they are effectively capable of performing nondeterministic operations.

Wait, what? I thought reversible computation just uses less energy. Where does the non-determinism come in?

Anyway, about the hashing being insecure: Wikipedia says that attacks on SHA-256 still take on the order of 2²⁵⁰ operations. And unless I made a big thinko here, doesn't the hash target change every ~10 minutes? Wouldn't that throw of an attacker? And if it was possible to break SHA faster, wouldn't the system adjust by raising the difficulty level?

[Some Mouse]

Wait, what? I thought reversible computation just uses less energy. Where does the non-determinism come in?

It's the theoretical limit of how far you can go with it. When doing a brute force search, you can reverse back to any previous state and try new states.

Anyway, about the hashing being insecure: Wikipedia says that attacks on SHA-256 still take on the order of 2²⁵⁰ operations. And unless I made a big thinko here, doesn't the hash target change every ~10 minutes? Wouldn't that throw of an attacker? And if it was possible to break SHA faster, wouldn't the system adjust by raising the difficulty level?

It's doubtful that SHA2 would be that broken before all coins have been minted. The issue is it then becomes a question of how much it costs to hijack someone's bank account.

[satoshi]

SHA256 is not like the step from 128 bit to 160 bit.

To use an analogy, it's more like the step from 32-bit to 64-bit address space.  We quickly ran out of address space with 16-bit computers, we ran out of address space with 32-bit computers at 4GB, that doesn't mean we're going to run out again with 64-bit anytime soon.

SHA256 is not going to be broken by Moore's law computational improvements in our lifetimes.  If it's going to get broken, it'll be by some breakthrough cracking method.  An attack that could so thoroughly vanquish SHA256 to bring it within computationally tractable range has a good chance of clobbering SHA512 too.

If we see a weakness in SHA256 coming gradually, we can transition to a new hash function after a certain block number.  Everyone would have to upgrade their software by that block number.  The new software would keep a new hash of all the old blocks to make sure they're not replaced with another block with the same old hash.

[dete]

I don't want to sound disrespectful, Satoshi (after all, you're the reason we're all here!), but I'm not sure that "it's probably good enough" is a sufficient answer!

I hear you saying that SHA-256 isn't much better than SHA-128, but what I think we need to hear is why SHA-128 is BETTER than SHA-256...

(Also: Is there a planned mechanism in place to switch to a new hashing scheme?  Seems like a good thing to plan for early, even if it seems unlikely to be necessary...)