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brohee

3,042 karma · joined June 21, 2011

Random hacker, Paris, France.

Contact me at bruno@rohee.com

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brohee··on The state of SIMD in Rust in 2026
"The ARM-based CPU manufacturers make this worse by posting almost no low-level documentation for their CPUs."

Are those not based on standard ARM cores or ARM documentation on its cores not deep enough for your purpose?

brohee··on Italian parliament votes for return to nuclear energy
They are in valleys and I think the risk assessment was heavily influenced by https://en.wikipedia.org/wiki/Cumbre_Vieja_tsunami_hazard which has been toned down quite a bit since... But IRSN (now ASNR) studies all kind of risks seriously...
brohee··on Agents Build Chess Engines from Scratch in Rust, C++, Rocq, LaTeX, Brainfuck
Title edited for length from "Coding Agents Build Chess Engines From Scratch in Rust, C++, COBOL, Rocq, LaTeX, Brainfuck, and More"

He also has dedicated entries on two very special case, the engine running within pdflatex https://blog.mathieuacher.com/TeXCCChessEngine/ and the one in Brainfuck https://blog.mathieuacher.com/BFChessChessEngineBrainfuck/ which are seemingly the first of their kind.

brohee··on Factoring RSA 260
The discussion on the cost of the attack needs an addendum. The lattice sieving part would be free for an an attacker with a big enough botnet or enough cloud computing stolen credentials.

Maybe it could even be practical to run it on browser in parallel to video streaming on a free video site...

brohee··on RSA-260 Factorized
Not all attackers pay for compute. With enough stolen compute, breaking RSA-1024 is free and not that slow...
brohee··on AI models ran real businesses: They sent $12,431 in fake invoices, lost $3,200
Yeah I really wonder what makes them think they are legally insulated from the actions of the agents they ran...

The crimes were relatively benign but Grok going the Silkroad way would be on brand...

brohee··on The largest electric aircraft just flew [video]
Efficiency is not that that important in an era of negative price electricity.

Synfuel made just from air and electricity is doable (both water and carbon dioxyde can be extracted from the atmosphere). And with 10% of what's spend on IA we'd be way out of the lab...

Thankfully there are military budgets (synfuel makes sense on a nuclear carrier)

brohee··on FDA authorizes first wearable device that monitors ketone and blood sugar levels
I've fairly good control over not running my car out of the road, yet I have airbags...
brohee··on SeL4 security proofs now complete on AArch64
A backdoor in physics would be interesting indeed, but not as likely as a rogue agent in a TSMC fab...
brohee··on SeL4 security proofs now complete on AArch64
Security-partition switches that carefully reset all shared micro-architectural state, while making switch times completely deterministic, and in particular, independent of previous execution history.

I'm afraid it means clearing all caches at each context switch. The performance penalty is really high.

brohee··on SeL4 security proofs now complete on AArch64
I don't think you can ignore memory access. The whole "hyperthreading considered harmful" was because of shared cache between contexts. That's why I think a proof is in reach without cache, much harder with one...
brohee··on SeL4 security proofs now complete on AArch64
I'm not so sure. It's pretty hard to know how many cycles a register load instruction will take if there is a cache, or worse a cache hierarchy. That's why I think it will be a lot easier to have a proof on simple cache less designs...

Your version is likely good enough in practice though.

brohee··on SeL4 security proofs now complete on AArch64
To add to that, the only way I see proof of absence of timing channels is by proving both the software and the hardware design side by side, and then the proof would hold only for a specific core. Something that would look both at the code manipulating secrets and at the Verilog for the specific core/memory chips. I've not been working in that space in a long while but AFAIK such a thing is nowhere near ready. I suspect it will be a lot easier if the hardware design is optimised for provability, which won't be good at all for performance. But there are plenty of contexts where security matters a lot more than performance (SMC, BMC, RoT and co at the very least).

And then you'd need assurance that the Verilog is faithfully transcribed in the silicon, which is a can of worms in itself.

brohee··on SeL4 security proofs now complete on AArch64
The assumptions the proof makes are pretty clearly listed: https://sel4.systems/Verification/assumptions.html

The one covering side channels is pretty honest:

Information side-channels: this assumption applies to the confidentiality proof only and is not present for functional correctness or integrity. The assumption is that the binary-level model of the hardware captures all relevant information channels. We know this not to be the case. This is not a problem for the validity of the confidentiality proof, but means that its conclusion (that secrets do not leak) holds only for the channels visible in the model. This is a standard situation in information flow proofs: they can never be absolute. As mentioned above, in practice the proof covers all in-kernel storage channels but does not cover timing channels.

So the proof won't be invalidated at it does not cover that particular threat.

Now the question is how useful the is a proof not covering side channels? I'd say pretty useful and it doesn't mean they don't have counter measures for to counter their exploitation, nor that they are not effective, just that a proof of efficiency is out of reach for now.

brohee··on A joke domain purchase turned in geopolitical warfare
I suspect a lot of software does not behave well at negative altitude. I heard of an ECU having trouble on one of the rare negative altitude roads.
brohee··on Show HN: We Implemented the IPv8 Internet-Draft in Linux, Libc, and BGP
SCEP was (and still is) a very deployed protocol yet took 20 years for the draft to be published...
brohee··on Single log line is 49KB+ (ext4) / 110KB+ (btrfs) of systemd-journald disk writes
Writing multiple pages for a few hundred actual bytes also thrashes the OS cache...
brohee··on Single log line is 49KB+ (ext4) / 110KB+ (btrfs) of systemd-journald disk writes
Ah, the Ulrich Drepper school of dealing with reported issues. Time for esystemd ;)
brohee··on Tl;dv: Over 180k meetings left wide open
Now let's see if European users get their GDPR article 33 notification of the breach...
brohee··on Human mathematicians are being outcounterexampled
The most astonishing thing is that she still holds the PhD whose thesis was the basis of the book. A stain on Oxford reputation.
brohee··on Who are the fire-tamers?
Since data is now the plural of anecdote... Frenchman here. Someone I knew fell from his bike without appropriate gear and ended up in the burn ward. His wife was very into the fire tamer thing and sent him a few practitioners...

He took the morphine.

On another note, I had respect for Aeon as a publication, and now I got a lot less.

brohee··on 45°C cooling design cuts data center water use to near zero
In the most nuclear country, France, power plants can't rise the river temperature by too much legally and yes it is an issue in summer with less water flowing.
brohee··on The founder's playbook: Building an AI-native startup
I know in which DC you are hosted and will cut your electricity off.
brohee··on Tracing a powerful GNSS interference source over Europe
Celestial Navigation is also doable even in daylight nowadays, e.g. https://sodern.com/en/ranges/astradia
brohee··on Higher usage limits for Claude and a compute deal with SpaceX
Because you'd need to trash the old GPUs in order to make room for new GPUs. Right now new GPUs get online mostly in new DCs. TSMC fab capacity is much more limiting than DC building and it will likely keep being the case. It's much easier to build a DC than a fab.
brohee··on Spirit Airlines Is Winding Down All Operations
Europe has passenger trains that work. What would be a short flight in the US, e.g. London to Paris is done more my train through the chunnel than flying unless you got a connecting flight.
brohee··on Spirit Airlines canceled all flights and is going out of business
It's quite possible other carriers would have gone around the worst and that the economy airline saved fuel.
brohee··on I built my own hair electrolysis machine
Step 2, put the needle on a gantry (I suspect you'd need more like 5D CNC to enter the pore with the right angle) and seek and destroy hairs... As it is it saves money but not time nor skill...
brohee··on GoDaddy gave a domain to a stranger without any documentation
That's one of the reasons I can walk in the main office of my registrar within an hour. It's clearly not available to everyone but it's especially important that if you can't do that you can at least conveniently sue your registrar... So at the very least in your jurisdiction.

So much is tied to DNS and particularly email...

brohee··on Amateur armed with ChatGPT solves an Erdős problem
In the end "proofs" that are not machine checked will be left unread unless submitted by someone very respected in the field...
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