I understand the output of the SHA-256 hashing function is a random number between 0 and 2^256. Does the randomness of this output imply that there cannot be a, so to say, honey hole in the hashing.

For instance this reddit post, http://www.reddit.com/r/BitcoinMining/comments/1rysqh/is_there_something_strange_about_block_272754_and/

They point out that someone relayed two blocks very close together, approximately 10s apart. Could they have found an occurrence where two block solving hashes sit close to each other?

I guess this kind of doesn't make sense though. Once a block is found, or a transaction is accepted, and even for each 3 seconds(timestamp) the block header is changed. So you would really could never find a block with the same hash just one number off (same block header, with two blocks one with nonce and the other nonce+1), because the first block will not be included in the second one, the second will become a dead fork in the blockchain?

1 Answer 1


No, the SHA2 hashing function is not vulnerable to any known attack that significantly reduces the difficulty of finding a block, but it is a highly random process.

Randomness is funny sometimes. Statistically it it works out to be even over a longer time period or larger population, but if you focus in on a small set of samples sometimes you see a cluster or a gap. This is why the estimated hash rate of the network on blockchain.info is woefully inaccurate on anything less than a multi-day average, and bitcoin is based on a 2 week correction period instead of a smaller number.

(which is why the unlucky miner can't expect to find 2 blocks quickly "because" he had a drought, and you should not expect a gap to "make up for" earlier luck, it's the population that matters.)

  • I think this answer is correct, but I'd like to add a comment regarding potential foul play with quick consecutive blocks by the same miner/pool. The vulnerability, already widely discussed, is where a block found by the miner is kept private and not broadcast immediately, giving the miner/pool a slight head start on the next block, at the potential risk of having the original block go orphaned.
    – ktorn
    Commented Dec 3, 2013 at 6:01
  • I agree, that the luck will even out in the end, but that doesn't show that you couldn't find a block every hash right? You have the same chance each block, isn't there then a chance that you could find n blocks in a row? Though the chance is probably amazingly incomprehensibly low.
    – KDecker
    Commented Dec 3, 2013 at 6:24

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