Ciro Santilli @cirosantilli 37

section .data
    hello_world db "Hello world!", 10
    hello_world_len  equ $ - hello_world
section .text
    global _start
    _start:
        mov rax, 1
        mov rdi, 1
        mov rsi, hello_world
        mov rdx, hello_world_len
        syscall
        mov rax, 60
        mov rdi, 0
        syscall

Compiled with:

nasm -w+all -f elf64 -o 'hello_world.o' 'hello_world.asm'
ld -o 'hello_world.out' 'hello_world.o'

TODO: use a minimal linker script with -T to be more precise and minimal.

Versions:

NASM 2.10.09
Binutils version 2.24 (contains ld)
Ubuntu 14.04

We don't use a C program as that would complicate the analysis, that will be level 2 :-)

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Yeast artificial chromosome Updated 2025-07-16

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ELF Hello World Tutorial / How to learn Updated 2025-07-16

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Spin like mad between:

standards
high level generators. We use the assembler as and linker ld.
hexdumps
file decompilers. We use readelf. It makes it faster to read the ELF file by turning it into human readable output. But you must have seen one byte-by-byte example first, and think how readelf output maps to the standard.
low-level generators: stand-alone libraries that let you control every field of the ELF files you generated. github.com/BR903/ELFkickers, github.com/sqall01/ZwoELF and many more on GitHub.
consumer: the exec system call of the Linux kernel can parse ELF files to starts processes: github.com/torvalds/linux/blob/v4.11/fs/binfmt_elf.c, stackoverflow.com/questions/8352535/how-does-kernel-get-an-executable-binary-file-running-under-linux/31394861#31394861

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ELF Hello World Tutorial / Index 0 section Updated 2025-07-16

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Contained in bytes 0x40 to 0x7F.

The first section is always magic: www.sco.com/developers/gabi/2003-12-17/ch4.sheader.html says:

If the number of sections is greater than or equal to SHN_LORESERVE (0xff00), e_shnum has the value SHN_UNDEF (0) and the actual number of section header table entries is contained in the sh_size field of the section header at index 0 (otherwise, the sh_size member of the initial entry contains 0).

There are also other magic sections detailed in Figure 4-7: Special Section Indexes.

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Skew-symmetric form Updated 2025-07-16

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CAIDA/commoncrawl-host-ip-mapper Updated 2025-07-16

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github.com/CAIDA/commoncrawl-host-ip-mapper

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Baker-Campbell-Hausdorff formula Updated 2025-07-16

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Solution

Z

for given

X

and

Y

of:

e^{Z} = e^{X} e^{Y}

(1)

where

e

is the exponential map.

If we consider just real number,

Z = X + Y

, but when X and Y are non-commutative, things are not so simple.

Furthermore, TODO confirm it is possible that a solution does not exist at all if

X

and

Y

aren't sufficiently small.

This formula is likely the basis for the Lie group-Lie algebra correspondence. With it, we express the actual group operation in terms of the Lie algebra operations.

Notably, remember that a algebra over a field is just a vector space with one extra product operation defined.

Vector spaces are simple because all vector spaces of the same dimension on a given field are isomorphic, so besides the dimension, once we define a Lie bracket, we also define the corresponding Lie group.

Since a group is basically defined by what the group operation does to two arbitrary elements, once we have that defined via the Baker-Campbell-Hausdorff formula, we are basically done defining the group in terms of the algebra.

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Barn (unit) Updated 2025-07-16

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Battle of Algiers (1966) Updated 2025-07-16

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There's nothing like seeing the hypocrisy of the "Liberté, Égalité, Fraternité" people destroyed.

Interesting how Algeria now supports China's Xinjiang policy in 2019. But of course, dictatorships tend to work together

Ciro Santilli's father, an avid history reader, and in particular interested in the military dictatorship in Brazil through which he lived, once told Ciro how the French torture doctrine was directly adopted by Brazillian military, e.g. then even invited general Paul Aussaresses who had served in Algeria, to help them out with intelligence operations and give courses. Bro, fuck that.

But of course, the Americans weren't too far behind in Guantanamo.

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Potassium Updated 2025-07-16

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BB84 Updated 2025-07-16

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Does not require entangled particles, unlike E91 which does.

en.wikipedia.org/w/index.php?title=Quantum_key_distribution&oldid=1079513227#BB84_protocol:_Charles_H._Bennett_and_Gilles_Brassard_(1984) explains it well. Basically:

Alice and Bob randomly select a measurement basis of either 90 degrees and 45 degrees for each photon
Alice measures each photon. There are two possible results to either measurement basis: parallel or perpendicular, representing values 0 or 1. TODO understand better: weren't the possible results supposed to be pass or non-pass? She writes down the results, and sends the (now collapsed) photons forward to Bob.
Bob measures the photons and writes down the results
Alice and Bob communicate to one another their randomly chosen measurement bases over the unencrypted classic channel.
This channel must be authenticated to prevent man-in-the-middle. The only way to do this authentication that makes sense is to use a pre-shared key to create message authentication codes. Using public-key cryptography for a digital signature would be pointless, since the only advantage of QKD is to avoid using public-key cryptography in the first place.
they drop all photons for which they picked different basis. The measurements of those which were in the same basis are the key. Because they are in the same basis, their results must always be the same in an ideal system.
if there is an eavesdropper on the line, the results of measurements on the same basis can differ.
Unfortunately, this can also happen due to imperfections in the system.
Alice and Bob must decide what level of error is above the system's imperfections and implies that an attacker is listening.

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Bell's theorem Updated 2025-07-16

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Basically a precise statement of "quantum entanglement is spooky".

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Spinor Updated 2025-07-16

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TODO understand a bit more intuitively.

Video 1.

The Mystery of Spinors by Richard Behiel

. Source.

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Biconvex spherical lens Updated 2025-07-16

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Focal length

Each side is a sphere section. They don't have to have the same radius, they are still simple to understand with different radiuses.

The two things you have to have in mind that this does are:

converges parallel light to a point at center at distance $f$ known as the focal length.
This is for example why you can use lenses to burn things with Sun rays, which are basically parallel.
Conversely, if the input is a point light source at the focal length, it gets converted into parallel light.
image formation: it converges all rays coming from a given source point to a single point image. This amplifies the signal, and forms an image at a plane.
The source image can be far away, and the virtual image can be close to the lens. This is exactly what we need for a camera.
For each distance on one side, it only works for another distance on the other side. So when we set the distance between the lens and the detector, this sets the distance of the source object, i.e. the focus. The equation is:
$\frac{1}{f} = \frac{1}{S _{1}} + \frac{1}{S _{2}}$
(1)
where $S_{1}$ and $S_{2}$ are the two distances.

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