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I sign Floppy PNGs with the same private key associated with this npub.

My entire software repo is inside my banner PNG. It can be extracted with this script:

Deno.writeFileSync("f.z",Deno.readFileSync("f.png").slice(41,-16))
new Deno.Command('pigz',{args:['-d','-f','-k','f.z']}).outputSync()
let extracted_data=Deno.readFileSync('f')
const data_length=parseInt(new TextDecoder().decode(extracted_data.slice(65,4120)).split('\n')[0])
const unfiltered=new Uint8Array(extracted_data.length)
let f=0,p=0,r=0
do{if(r==4140||f==0){f++;r=0;} else {unfiltered[p]=extracted_data[f];r++;f++;p++;}}while(f<extracted_data.length)
let site_text=(new TextDecoder().decode(unfiltered.slice(542340,542340+data_length)))
Deno.writeTextFileSync('site.txt',site_text)

This should be verified. I sign the data part of the PNG and use the top row to store the secp256k1 signature. This can be verified with this script:

import { sha256 } from "@noble/hashes/sha2";
import { schnorr } from "@noble/curves/secp256k1";
import * as pako from "pako";
try {
let f = 0, p = 0, r = 0;
const fpng_img = Deno.readFileSync(Deno.args[0]);
const pub = Deno.readTextFileSync(Deno.args[1]).trim();
const zdat = pako.inflate(fpng_img.slice(41, -16));
const u = new Uint8Array(zdat.length);
do {
if (r == 4140 || f == 0) {
f++;
r = 0;
} else {
u[p] = zdat[f];
r++;
f++;
p++;
}
} while (f < zdat.length);
const dl=parseInt(new TextDecoder().decode(zdat.slice(65,4140)).split('\n')[0])
console.log(schnorr.verify(
new Uint8Array(zdat.slice(1, 65)),
sha256(u.slice(542340, dl + 542340)),
pub,
));
} catch {
console.log("Usage: lverify [Floppy PNG] [144MB Hex Public Key]");
}

The extract script itself can be extracted from the Floppy PNG using the instructions on the header of the banner of the PNG in my profile banner. It is all so wonderfully self-referential, no?

Note that to use the verify script you need something like this package.json:
{
"name": "anything",
"version": "1.0.0",
"dependencies": {
"@noble/curves": "^1.9.2",
"@noble/hashes": "^1.8.0",
"pako": "^2.1.0"
}
}

Later versions of noble/curves need a different import. Also, if you want to use that same site.txt file to load a web page, you can use this:

<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8">
<title>Floppy PNG</title>
<meta name="viewport" content="width=device-width,initial-scale=1">
</head>
<body>
<div id="l"></div>
<script>
fetch('site.txt').then((resp) => {
resp.text().then((t)=>{
s = document.createElement("script");
s.appendChild(document.createTextNode(t));
document.body.appendChild(s);
})})
</script>
<div id="main"></div>
</body>
</html>

You need to remove the verify() command for it to work as a live web page. Verify the sig separately, remove the line, and spin up some kind of local web server. Most of the time the verify() command is the last line of site.txt. The web application for all browsers is listed in the floppypng.com repo (src/browser.js).
Public Key
npub1a2g7uthlp9ppzk64zkaahmsjtx703x0cm3umx02c2fx3qn3at66spp9ssf
Profile Code
nprofile1qqsw4y0w9mlsjss3td23tw7macf9n08cn8udc7dn84v9yngsfc74adgpzemhxue69uhhyetvv9ujuurjd9kkzmpwdejhgtdfvpf
Publishing to
Author Public Key
npub1a2g7uthlp9ppzk64zkaahmsjtx703x0cm3umx02c2fx3qn3at66spp9ssf