Why do we use Double-Hashing(SHA256) in Bitcoin?
Where is it used?
What is the benefit?
SHA256 is designed & patented (released royalty-free), by the NSA.
Even though paranoia is a minimal requirement in cryptography, I don't think there are backdoors here.
Satoshi may have had his doubts.
Whenever hashing is performed in Bitcoin is done 2 times.
The most obvious use of SHA256 is when doing the PoW, but it is used a a LOT of other places.
All of the done 2 times.
The theory is that Satoshi though it prevents certain( length extension attacks) attacks.
But the reality is it does not really add any benefits.
Even though this fact became more obvious, the double-hashing trend continued with future things that were built.
It seemed it was easier to subscribe to the "superstition", rather than convenience people that hashing once is safe.
The "modern" changes use single hashing, and in some cases, hashing was dropped altogether.
The design choices made by Satoshis are consensus-breaking, which means that changing them would cause a fork, so they will probably stay like this forever.
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