[Cryptography] SHA-256 challenge

[Michael Kjörling]

On 28 Mar 2024 10:42 +0000, from cryptography at metzdowd.com (McDair via cryptography):
> Find a full-fledged preimage that matches output hash:
> 
> deb360ae3c1ff7a29f83731b33dcd4bf354a5e80de2dc50370ebf55a14216b85
> 
> Tip: the original message size is 32 bytes.
> 
> Here are the results I can share at the moment:
> 
> - With respect to the overall hash function (including additional 'one' bit, zero padding, message length and derived words):

> Preimages of 64 rounds
> ----------------------

> Full block of 64 words containing the custom 56 values AT THE END and resolving to the desired hash:
> 1137559525, 3265777086, 3513913394, 2594848941, 129008566, 107100536, 378474686, 8040043, 1096971124, 1918985076, 773865760, 1886745189, 1819877488, 1701147181, 1953443184, 1701147168, 1986359923, 1768910368, 1868963941, 1818583924, 1919905385, 1663066977, 1936203895, 1869966436, 543255660, 1870078063, 1852598638, 1696624737, 2037212526, 1953702004, 1864393317, 544433518, 1948279913, 1919247220, 1819877478, 1919905056, 1869505824, 1885434484, 2032170095, 543256175, 1952998770, 544696692, 1752135028, 543649641, 1852252276, 1752330101, 1734877281, 543582574, 1634624361, 1634476137, 1853060201, 1953854569, 1869491744, 1147758441, 1952541728, 1936287598, 1635022194, 1702043760, 1919907433, 1684349040, 1634890784, 1868963956, 1751457907, 1869378932

At least treating these numbers as base 10 representations of 32-bit
integers representing a preimage, having tried several times, I cannot
get a hash matching the specified SHA-256 hash.

The closest I can get is to recover the text you reference, by:

$ printf '%s\n' 1137559525, 3265777086, 3513913394, 2594848941, 129008566, 107100536, 378474686, 8040043, 1096971124, 1918985076, 773865760, 1886745189, 1819877488, 1701147181, 1953443184, 1701147168, 1986359923, 1768910368, 1868963941, 1818583924, 1919905385, 1663066977, 1936203895, 1869966436, 543255660, 1870078063, 1852598638, 1696624737, 2037212526, 1953702004, 1864393317, 544433518, 1948279913, 1919247220, 1819877478, 1919905056, 1869505824, 1885434484, 2032170095, 543256175, 1952998770, 544696692, 1752135028, 543649641, 1852252276, 1752330101, 1734877281, 543582574, 1634624361, 1634476137, 1853060201, 1953854569, 1869491744, 1147758441, 1952541728, 1936287598, 1635022194, 1702043760, 1919907433, 1684349040, 1634890784, 1868963956, 1751457907, 1869378932 | tr -d , | perl -e '$n = 0; while(<>) { $v = $_; $v1 = ($v & 0xff000000) >> 24; $v2 = ($v & 0x00ff0000) >> 16; $v3 = ($v & 0x0000ff00) >> 8; $v4 = ($v & 0x000000ff); printf "%08x: %02x %02x %02x %02x\n", $n, $v1, $v2, $v3, $v4; $n+=4; }' | xxd -r

but using the output of the above as a preimage, it SHA-256 hashes to
d084a44d89a2ce255743f551c92e018f5ddcc5b98a3adfddd2edd4b109b6b379, not
deb360ae3c1ff7a29f83731b33dcd4bf354a5e80de2dc50370ebf55a14216b85.

(Note to anyone executing this: keep in mind that the first several
bytes of the output are non-ASCII. You probably don't want to send the
output directly to a terminal.)

So _either_ I am making a mistake when converting your string of
numbers to something which actually can be hashed in a meaningful way
(which seems relatively unlikely given that it does correctly include
the text you reference and the number of bytes appears to be correct),
_or_ it doesn't actually as a preimage hash to the specified hash.

To fully rule out the former, please rather post a plain binary file
containing exactly your proposed preimage with no gratuitous encoding.

You are the one making a claim here. If your claim is accurate, I do
believe it would be in your interest to make it easy for people to
verify the correctness of your claim.

-- 
Michael Kjörling                     🔗 https://michael.kjorling.se
“Remember when, on the Internet, nobody cared that you were a dog?”