Quote from: Amitabh S on December 21, 2015, 08:22:10 PM

Quote from: Jan on August 08, 2013, 04:48:15 PM

One is the ASCII-HEX byte-wise reverse of the other.

But why?

Thats how transaction IDs appear in the Bitcoin protocol, where they are represented by byte-reversed transaction hashes.

I was curious and did some googling a while ago. There have been discussions on this topic, but apparently, nobody knows why Satoshi chose it to be this way.

Heres one possible explanation. Internally, the SHA-256 algorithm works with 32-bit numbers rather than bytes. Its specification says that when the hashing itself is done, the resulting numbers are converted to a byte sequence in big-endian byte order, and this byte sequence is the official SHA-256 hash. Now, the Bitcoin protocol is little-endian. So Satoshi may have decided to change this last step of SHA-256 to use little endian for consistency with the rest of the protocol. (The order of words would have to change as well to preserve continuity.) Also, because the most widely used processor architectures are little endian (x64, x86, ARM), Satoshis representation is simply a dump of the internal state of the hashing algorithm on these machines, without the additional byte swapping that would be required by the specification.