# Tiny Bytes: Figuring out a misunderstanding

By [ldnovak](https://paragraph.com/@ldnovak) · 2022-08-03

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Hi,

Tonight I wasn’t sure what I wanted to write about. That’s not quite true. I wanted to write about quantum computers but to do that I need to understand elliptical curves. And that’s going to take too much time.

However, in trying to figure out what to write I stumbled onto a misunderstanding.

Next Steps
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The plan is to write about how quantum computers break key generation and signatures. This is going to require writing about elliptical curves and RSA first.

When reading through the cloudflare article, I realized that the key generation mentioned Diffie-Hellman but the signature mentioned RSA. I was confused as I thought they could be used for both.

This got me going down a bit of a rabbit hole.

The problem
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I realized that my understanding of signing and encrypting was fundamentally flawed. I thought the same key was generated, encrypt/decrypt, and sign/verify.

Instead, there’s an encryption and a signature scheme. So there’s gen, encrypt, and decrypt AND gen, sign, verify. Some schema you can technically use both (e.g., RSA) but it is considered bad to do.

[https://crypto.stackexchange.com/questions/12090/using-the-same-rsa-keypair-to-sign-and-encrypt#:~:text=Longer%20Answer%3A%20You%20are%20true,key%20pair%20for%20both%20operations.](https://crypto.stackexchange.com/questions/12090/using-the-same-rsa-keypair-to-sign-and-encrypt#:~:text=Longer%20Answer%3A%20You%20are%20true,key%20pair%20for%20both%20operations.)

Fallout
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This really helped put what I was reading fall better into place. Not a lot of words for today, but I can guarantee I did a bunch of research to figure this and other problems out.

The problem I now have is how do MACs play into this? Are they used for symmetric encryption (e.g., after the TLS handshake)?

I get wanting to use key generation schemes (involving public and private key encryption and signing) to generate the symmetric keys. I’m just curious on how devices talk after.

Night,

Lucas

ps

Quantum computing come on my mind tonight because it looks like a quantum algorithm in the 4th round (i.e., where alternative algorithms that weren’t selected in round 3 are evaluated) was found to be broken. I don’t understand how but want to.

[https://arstechnica.com/information-technology/2022/08/sike-once-a-post-quantum-encryption-contender-is-koed-in-nist-smackdown/](https://arstechnica.com/information-technology/2022/08/sike-once-a-post-quantum-encryption-contender-is-koed-in-nist-smackdown/)

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*Originally published on [ldnovak](https://paragraph.com/@ldnovak/tiny-bytes-figuring-out-a-misunderstanding)*
