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Comment by Sanzig | Hacker News Reader

> Even the tiniest MCU can typically perform more than one cryptographic operation per second. If your MCU has any cycles to spare at all it usually has enough cycles for cryptography.

Well, no. If you can do 1 AES block per second, that's a throughput of a blazing fast 16 bytes per second.

I know that's a pathological example, but I do understand your point - a typical workload on an MCU won't have to do much more than encrypt a few kilobytes per second for sending some telemetry back to a server. In that case, sure: ChaCha20-Poly1305 and your job is done.

However, what about streaming megabytes per second, such as an uncompressed video stream? In that case, lightweight crypto may start to make sense.

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1 operation per second would refer to cryptographic signatures. If you are doing Chacha, the speeds are more like 1 mbps. AES is probably closer to 400 kbps.

An uncompressed video stream at 240p, 24 frames per second is 60 mbps, not really something an IoT device can handle. And if the video is compressed, decompression is going to be significantly more expensive than AES - adding encryption is not a meaningful computational overhead.

If it's compressed you don't need to decompress it first.

on the receiving end.

The device doing the decryption may not be the same device that does the decompression.

Eg a small edge gateway could be doing the VPN, while the end device is decoding the video.

A VPN’s encryption is different than a streaming platform’s encryption. The streamer’s encryption is their form of rights management. So the device/app decompressing the video very much is the point of decryption. If not, the rights management is very broken. If the small edge gateway is somehow decrypting the video stream, you’d have a very rogue device that lots of people would be curious to learn more

CCTV doesn’t need rights management. Nor do advertising billboards.

Why would you compare an uncompressed video stream to anything in this discussion? Especially at such a small frame size in modern video usage.

Modern encrypted streaming uses pre-existing compressed video where the packets are encrypted on the way to you by the streaming server. It would have to uniquely encrypt the data being sent to every single user hitting that server. So it's not just a one and done type of thing. It is every bit of data for every user. So that scales to a lot of CPU on the server side to do the encryption. Yes, on the receiving side while your device is only dealing with the one single stream, more CPU cycles will be spent decompressing the video compared to decrypting. But again, that's only have of the encrypt/decrypt cycle

>Even the tiniest MCU can typically perform more than one cryptographic operation per second. If your MCU has any cycles to spare at all it usually has enough cycles for cryptography.

>1 operation per second would refer to cryptographic signatures. If you are doing Chacha, the speeds are more like 1 mbps. AES is probably closer to 400 kbps.

It sounds to me like you, sir or madame, have not worked with truly tiny MCUs. :-)

But yes, there are inexpensive MCUs where you can do quite a bit of crypto in software at decent speeds.

This whole framing is weird, because you can't spend $0.50 per already-deployed part to upgrade to something that can viably do AES.

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