Nico Weber nico

Unexpected Uses for the Galois Field Affine Transformation Instruction

Intel added the Galois Field instruction set (GFNI) extensions to their Sunny Cove and Tremont cores. What’s particularly interesting is that GFNI is the only new SIMD extension that came with SSE and VEX/AVX encodings (in addition to EVEX/AVX512), to allow it to be supported on all future Intel cores, including those which don’t support AVX512 (such as the Atom line, as well as Celeron/Pentium branded “big” cores).

I suspect GFNI was aimed at accelerating SM4 encryption, however, one of the instructions can be used for many other purposes. The extension includes three instructions, but of particular interest here is the Affine Transformation (GF2P8AFFINEQB), aka bit-matrix multiply, instruction.

There have been various articles which discuss out-of-band

So you want to modify the text of a PDF by hand...

If you, like me, resent every dollar spent on commercial PDF tools, you might want to know how to change the text content of a PDF without having to pay for Adobe Acrobat or another PDF tool. I didn't see an obvious open-source tool that lets you dig into PDF internals, but I did discover a few useful facts about how PDFs are structured that I think may prove useful to others (or myself) in the future. They are recorded here. They are surely not universally applicable --
the PDF standard is truly Byzantine -- but they worked for my case.

Command line tools

Cairo is a 2D graphics library with support for multiple output devices. Currently supported output targets include the X Window System (via both Xlib and XCB), Quartz, Win32, image buffers, PostScript, PDF, and SVG file output. Experimental backends include OpenGL, BeOS, OS/2, and DirectFB.
Ghostscript is an interpreter for the PostScript language and for PDF.
MuPDF is an open source software framework for viewing and converting PDF, XPS, and E-book documents.
- mutool draw - This is the more customizable tool, but also has a more difficult set of command line options. It is primarily used for rendering a document to image files.
- mutool convert - This tool is used for converting documents into other formats, and is easier to use.
- mutool trace - This is a debugging tool used for printing a trace of the graphics device calls on a page.
mutool show - A tool for displaying the inter

58 bytes of CSS to look great nearly everywhere

When making this website, i wanted a simple, reasonable way to make it look good on most displays. Not counting any minimization techniques, the following 58 bytes worked well for me:

main {
  max-width: 38rem;
  padding: 2rem;
  margin: auto;
}

Recon and Attack Vectors from My Logs

This document contains excerpts from my web server logs collected over a period of 7 years that shows various kinds of recon and attack vectors.

There were a total of 37.2 million lines of logs out of which 1.1 million unique HTTP requests (Method + URI) were found.

$ sed 's/^.* - - \[.*\] "\(.*\) HTTP\/.*" .*/\1/' access.log &gt; requests.txt

	global.THREE = require("three");

	const canvasSketch = require('canvas-sketch');
	const Random = require('canvas-sketch-util/random');

	const gradientHeight = 512;
	const settings = {
	dimensions: [ 2048, gradientHeight * 2 ]
	};

	// To see this run, you first stub out these imports. Then put the file in a Uint8Array.
	// let slice = new Slice(array);
	// let font = new OTFFont(slice);
	// Then you can call methods like font.drawText(canvasContext, )
	//
	//
	import { ICanvasContext } from "./ICanvasContext"
	import { log as Log } from "./log"

	const log = Log.create("OPENTYPE");

	struct Adjacency
	{
	struct Vertex
	{
	// Vertices are shared by a variable number of edges. This indexes the global EdgeRef array.
	uint32_t edgeStartRef;
	uint32_t nbEdges;
	};

	union EdgeRef

	Code from PyCon India 2019 Keynote Talk
	David Beazley (https://www.dabeaz.com)
	======================================

	This code is presented "as is" and represents what was live-coded
	during my closing keynote presentation at PyCon India, Chennai,
	October 13, 2009. I have made no changes to the files.

	Requires: Python 3.6+, numpy, pygame

	from __future__ import print_function

	# the string to check is in 'candidate'
	if isinstance(candidate, type(u"")):
	print("This is a unicode string")
	else:
	# if it's a Py2 'str' or a Py3 'bytes' object, this will convert
	# otherwise it'll raise an exception
	candidate = candidate.decode('utf8')