Showing my work:
/:~~.hex_header
0123456789abcdef
#:i.16
0 0 0 0
0 0 0 1
0 0 1 0
0 0 1 1
0 1 0 0
0 1 0 1
0 1 1 0
0 1 1 1
1 0 0 0
1 0 0 1
1 0 1 0
1 0 1 1
1 1 0 0
1 1 0 1
1 1 1 0
1 1 1 1
'0123456789abcdef'i.hex_header
0 1 0 0 0 0 0 0 8 1 12 13 0 2 10 11 7 14 5 6 9 14 8 11 12 13 9 3 1 7 14 2
15 14 9 9 15 2 13 14 4 4 13 4 9 10 11 2 11 8 8 5 1 11 10 4 10 3 0 8 0 0 0 0
0 0 0 0 0 0 0 0 14 3 2 0 11 6 12 2 15 15 15 12 8 13 7 5 0 4 2 3 13 11 8 11
1 14 11 9 4 2 10 14 7 1 0 14 9 ...
So,
,(#:i.16){~'0123456789abcdef'i.hex_header
0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0
0 1 1 1 0 0 1 1 0 1 0 0 0 0 0 0 1 0 1 0 1 0 1 0 1 1 0 1 1 1 1 1 1 0 0 1 0 1
0 1 1 0 1 0 0 1 1 1 1 0 1 0 0 0 1 0 1 1 1 1 0 0 1 1 0 1 1 0 0 1 0 0 1 1 0 0
0 1 0 1 1 1 1 1 1 0 0 0 1 0 ...
On Sun, Apr 12, 2020 at 4:40 AM bill lam <bbill....@gmail.com> wrote:
> try
> _3&(128!:6)^:2 bfh header_hex
>
> On Sun, Apr 12, 2020, 3:50 PM Thomas McGuire <tmcguir...@gmail.com> wrote:
>
> > In a round about way (it started with reading slashdot) I was researching
> > Bitcoin hashing. I came across a python explanation of taking a bitcoin
> > header and SHA256 hashing it twice to see if it produces the desired
> number
> > of leading (or terminating depending on the endian of your machine) '0’s.
> >
> > The snippet of python code is here at a bitcoin wiki site:
> > https://en.bitcoin.it/wiki/Block_hashing_algorithm <
> > https://en.bitcoin.it/wiki/Block_hashing_algorithm>
> >
> > I won’t reproduce it in its entirety here since it’s only a few lines of
> > code I figured I should be able to do the same in J.
> >
> > First I grabbed the header as ascii hex
> >
> > hex_header =:
> >
> '0100000081cd02ab7e569e8bcd9317e2fe99f2de44d49ab2b8851ba4a308000000000000e320b6c2fffc8d750423db8b1eb942ae710e951ed797f7affc8892b0f1fc122bc7f5d74df2b9441a42a14695'
> >
> > Then came the issue of turning this into binary. After reviewing the J
> > programming archives finding a thread on packed python structures, a few
> > attempts in J and some code in C to make sure I was doing it right, I
> came
> > to the realization that I only had to index pairs of hex characters into
> > ‘a.’ After using the ‘dfh’ function to convert the pair. So I made a bfs
> > tacit to do the work:
> >
> > bfh =: a. {~ [: dfh _2 ]\ ]
> >
> > (As an aside I cheated and used the 13 : functional form and let J figure
> > out the tacit.)
> >
> > NB. Python double hash:
> > hashlib.sha256(hashlib.sha256(header_bin).digest()).digest().
> >
> > 3&(128!:6)^:2 bfh header_hex NB. Seemingly direct implementation
> in J
> > 8ac7142a625bdd47e177ab584d60de449d0a844eb56173bd1c9aa0dbe69b61a4
> >
> > Now the above is the incorrect answer. The reason being is that our SHA
> > foreigns convert the answer from underlying binary to a hex string
> > representation. I need to convert the answer with ‘bfh’ and then call the
> > SHA256 algorithm again:
> >
> > 3&(128!:6) bfh 3&(128!:6) bfh header_hex
> > 1dbd981fe6985776b644b173a4d0385ddc1aa2a829688d1e0000000000000000
> >
> > This is the correct double hash that is agreement with the wiki article
> > listed above.
> >
> > So 2 questions from all of this:
> >
> > 1) is there a more efficient way of converting a string of hex characters
> > into a binary character array?
> >
> > 2) Shouldn’t the SHA algorithms send the raw binary back so that you can
> > use the power conjunction with it to do multiple hashes?
> > ----------------------------------------------------------------------
> > For information about J forums see http://www.jsoftware.com/forums.htm
> >
> ----------------------------------------------------------------------
> For information about J forums see http://www.jsoftware.com/forums.htm
>
--
Devon McCormick, CFA
Quantitative Consultant
----------------------------------------------------------------------
For information about J forums see http://www.jsoftware.com/forums.htm
