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Title: Bitcoin header help... Post by: ck3po on January 10, 2024, 02:21:39 AM So... I was going through the CPUMiner code (... YES, I know CPU mining is dead, I'm just using this code as an educational way to learn how BTC blocks and transactions are assembled) and was wondering about these two lines:
work->data[20] = 0x80000000; work->data[31] = 0x00000280; in the block header setup. Any idea why these values are important to set? From reading the BTC specs, I thought the header padding from +20 onwards was all supposed to be 0's..? So confused newbie to the bowels of BTC... any help appreciated, thanks. Title: Re: Bitcoin header help... Post by: pooya87 on January 10, 2024, 04:22:11 AM This looks like SHA256 related values.
The first one 0x80 is the SHA-2 specific padding used at the end of the message (1 followed by m 0)[1]. The second one (0x0280) is the message length in bits added at the end of the final [SHA2] block. We have an 80-byte header so 80 byte message * 8 = 640 bits or 0x0280 [1] https://datatracker.ietf.org/doc/html/rfc6234#section-4 Title: Re: Bitcoin header help... Post by: ck3po on January 19, 2024, 06:16:07 PM Brilliant, thank you. I had no clue these were SHA256 prefix/suffix-related. I really appreciate it, thanks!
This looks like SHA256 related values. The first one 0x80 is the SHA-2 specific padding used at the end of the message (1 followed by m 0)[1]. The second one (0x0280) is the message length in bits added at the end of the final [SHA2] block. We have an 80-byte header so 80 byte message * 8 = 640 bits or 0x0280 [1] https://datatracker.ietf.org/doc/html/rfc6234#section-4 |