Quote from: Rick Storm on May 09, 2016, 07:27:46 AM

I think this is relevant to the question:

http://crypto.stackexchange.com/questions/779/hashing-or-encrypting-twice-to-increase-security

The relevant bit:

Quote

SHA-256(SHA-256(x)) was proposed by Ferguson and Schneier in their excellent book "Practical Cryptography" (later updated by Ferguson, Schneier, and Kohno and renamed "Cryptography Engineering") as a way to make SHA-256 invulnerable to "length-extension" attack. They called it "SHA-256d".
...
I wouldn't be surprised if the inventors of Bitcoin used it for similar reasons.

You did not read carefully. Try again by clicking the last link in the quote below:

Quote from: sockpuppet1 on May 08, 2016, 04:01:13 PM

I am speaking on behalf of TPTB_need_war aka AnonyMint, who is quoted in the OP, because he is currently banned for 9 more days due to calling theymos and gmaxwell out on their censorship of a potential technical back door in Bitcoin. There is a simpler explanation of Satoshi's obviously intentional technical error. It is obviously intentional because it was quite well known by 2009 that the HMAC formulation is more secure yet Satoshi used the more suspect double hashing everywhere in BitCON.