I might be confused as to how Bitcoin works, but as far as I can tell, ASIC miners are getting better every year and faster at cracking SHA-256 encryption. Won't this cause the eventual complete obsolescence of SHA-256 encryption entirely, much faster than previously estimated?
Another way to look at it is to take a look at a recent block that was mined, for example, block 388368. Looking at this block on blockchain.info, you can see that the hash for this block is:
It took roughly 10 minutes for all of the miners (doing a combined 700,000,000 giga-hashes per second) to find the above hash which has enough leading zeroes (17) to meet the difficulty requirement of the network at that time. Since the remaining digits after the first 17 leading zeroes could have been anything, there are 16^47 (i.e.16^(64-17)) possible hashes that could have been found which would have satisfied the difficulty requirement (which is 3.92 * 10^56), yet it took
all of the mining power of the entire bitcoin network ~10 minutes to find just one hash that met the requirement.
To crack a hash, you need not just the first 17 digits to match the given hash, but all 64 of the digits to match. So, extrapolating from the above, it would take 10 * 3.92 * 10^56 minutes to crack a SHA256 hash using all of the mining power of the entire bitcoin network. That's a long time.
TL;DR: No, but if the hashes were collected, one might be able to better tell as to whether or not the SHA256^2 algorithm is broken.
If one can find a way to produce desired outputs from specific inputs, then a hashing algorithm is considered "broken". Both MD5 and SHA1 are know to be broken in this way. Theoretically, running an algorithm over and over again over a set of random inputs (exactly what mining is), could provide insight into patterns produced by the algorithm, thereby allowing one to prove whether or not it's broken. However, this insight would only come through statistical analysis of data gathered, and since most of the data is thrown out -- of the trillions of hashes per second only the ones corresponding to minded blocks are recorded -- this isn't feasible.
Another subtlety: because the algorithm in question is specifically SHA256 applied twice and not simply SHA256, even if the data were collected and analyzed, it may not tell us anything directly about SHA256.
I understand. 2^255 is indeed an incredibly large number. Not only is SHA-256 not an encryption algorithm, it is a cryptographic hash function, so my question was a little flawed to begin with, but the amount of time it would take to brute-force a single SHA256 hash is (currently) much too long even with the most advanced ASIC miners available today. To brute-force a single SHA256 hash, we would need ASIC miners that are a trillion trillion trillion times faster than the hash rate of the entire bitcoin network.