Re: The SHA256 of "xy\n" (ASCII, no CRLF) contains 1337, ACBAD in za, and I am 1aa

From: Jeff King <peff@peff.net>
Date: Jan 24, 2026, 07:28 UTC
Message-ID: <20260124072814.GA3455597@coredump.intra.peff.net>
In-Reply-To: <xmqq8qdogdmu.fsf@gitster.g>

On Fri, Jan 23, 2026 at 02:36:41PM -0800, Junio C Hamano wrote:

Show 21 quoted lines

> Jeff King <peff@peff.net> writes:
> 
> > On Fri, Jan 23, 2026 at 09:16:46PM +0100, Klaus Sembritzki wrote:
> >
> >> $ # My initials (ks): 1aa
> >> $ echo ks | sha256sum
> >> $ 1aa44e718d5bc9b7ff2003dbbb6f154e16636d5c2128ffce4751af5124b65337
> >> 
> >> $ # 50566750337
> >> $ echo thinking | sha256sum
> >> $ 50566750337beb9e98e553fd9196d10576f9eb0cbc6b66e2586b9d73af4f352f
> >
> > Oh man, I've got deadbeef!
> >
> >   $ echo jk35252822 | sha256sum
> >   33f1a74529870456c56ad97c59cfed6bdeadbeef9b9bc3f4ff49bb203e36f96b
> >
> > What could it all mean?
> 
> Sorry, but I have to admit that I completely lack humor receptor
> cells.

Probably because it was not that funny. :)

The original message seemed to be looking for Numerology-style meanings in random data. I wasn't sure if it was serious or not, but I could not resist either playing along (if not) or trolling (if so).

But here's my deadbeef brute-force program for fun.

-Peff

-- >8 -- #include <stdio.h> #include <string.h> #include <openssl/evp.h>

int main(int argc, const char **argv)
{
	const char needle[] = { 0xde, 0xad, 0xbe, 0xef };
	const EVP_MD *algo = EVP_sha256();
	EVP_MD_CTX *ctx = EVP_MD_CTX_new();

	EVP_DigestInit_ex(ctx, algo, NULL);
	while (*++argv)
		EVP_DigestUpdate(ctx, *argv, strlen(*argv));

	for (unsigned i = 0; ; i++) {
		char buf[16];
		char *p;
		unsigned char digest[32];
		EVP_MD_CTX *copy = EVP_MD_CTX_dup(ctx);

		p = buf + sizeof(buf);
		for (unsigned v = i; v; v /= 10)
			*--p = '0' + (v % 10);
		EVP_DigestUpdate(copy, p, buf + sizeof(buf) - p);
		EVP_DigestUpdate(copy, "\n", 1);
		EVP_DigestFinal_ex(copy, digest, NULL);
		EVP_MD_CTX_free(copy);
		if (memmem(digest, sizeof(digest), needle, sizeof(needle)))
			printf("%d\n", i);
	}
}