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Comment by aufhebung | Hacker News Reader

As someone who isn't in the jailbreaking space I don't really know what this means. Can you sign your own PS5 code and run it on the hardware?

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These keys are symmetric, so they can be used for decryption. With these symmetric keys you might be able to decrypt games, videos, save files etc sitting on the disk. I don't believe signing will be possible, nobody uses symmetric keys for signing games.

What this does is increase the possibility of someone finding how to bypass the signature verification check and then running their own code.

Why don't they use asymmetric keys for everything?

Symmetric keys means that anyone with the key can do everything the key allows one to do. That's bad if you're building consumer devices that contain the key. Signing with public key cryptography, which allows only verification with the end-user key, is much more secure in this scenario.

This isn't a good answer for "Why don't they use asymmetric keys for everything?" as you basically just explained that it would be more secure to use asymmetric keys.

You're right. I misread the question and thought they asked why they weren't using symmetric keys for everything. My bad.

If you need to encrypt and decrypt your data, on the same device, asymmetric is only more complex.

Because we don't generally use asymmetric keys for much data encryption. The operations are (IIRC) comparatively computationally expensive.

First of all, we are talking about on-device decryption, so there is no difference in terms of security whether people extract a symmetric secret key or an asymmetric secret key.

Secondly, yes, asymmetric encryption is slower, so you almost always use hybrid scheme: asymmetric scheme (ElGamal, for instance) for encrypting the symmetric key, and then a symmetric scheme (e.g. AES) for the bulk of the data.

Only in very exotic protocols such as digicash blind signatures or anonymous credentials with "algebraic MACs", you want your actual content encrypted directly via ElGamal or RSA, so that you can do some operations or proofs about the ciphertext — in those cases you can't encrypt symmetrically as that would erase all the algebraic relations.

> First of all, we are talking about on-device decryption, so there is no difference in terms of security whether people extract a symmetric secret key or an asymmetric secret key.

Sure, but we might (potentially) be interested in the encryption part later on too, and having a symmetric key will make that easier (though of course it won't get you past any signature checks.

I've never come across those more exotic protocols, but I'm familiar with symmetric kex under public/private encryption.

For that reason, the usual trick is to use asymmetric encryption to protect a symmetric key (a fresh one per payload) that is then used for the actual payload. That way you get the speed of symmetric encryption with the benefits of asymmetric ones. (Though evidently that's not what the PS5 uses here, otherwise it would be useless to read out one symmetric key).

And to add to that: you should use as many different symmetric keys as possible as long as asymmetric decryption of the key doesn't overly degrade performance.

As your sibling post technically notes, asymmetric vs symmetric is a wash, here. To use asymmetric encryption for saves, the PS5 would need to know the public and private keys, so you would be able to extract those and still have the same access.

Of course, there are still advantages to having the symmetric key not be used as is, but there are many solutions other than asymmetric encryption.

The most common asymmetric encryption algorithm (RSA) can only encrypt a plaintext of limited size. Depending on padding scheme, a 2048 bit RSA key can encrypt a message of up to ~245 bytes.

Typically to securely encrypt a message you use symmetric key encryption. Then to allow a third party to decrypt that message, you encrypt the symmetric key using the third party's asymmetric key.

AES can only encrypt a limited size too

No, signing is done with asymmetric keys. Someone sign with their private key so you can verify it with their public key, basically. Symmetric keys are used to encrypt the code for updates, generally to prevent unintentional leak of secrets or just to prevent reverse engineering.

I'm not in the jailbreaking space, but I guess that what it means here is that some people may find flaws in the code and leverage them to potentially bypass the signature verification, although this might prove very difficult to do. It might also help emulating the PS5 behavior which in turns could lead to some modding/cheating for some games. Who knows ?

I hope they also get the asymmetric keys once. I'll buy the thing then. I'm not buying hardware I can't patch to have root access and run custom firmwre on.

It's almost certainly impossible.

With symmetric encryption, both the encryptor and decryptor need a copy of the same key- that's what makes it 'symmetric'.

But with asymmetric encryption, the keys do not match. This means you can encrypt or sign the data with your private key, and then keep it private. The matching pubic key will decrypt or verify.

The device would not have a copy of the private key in it, so it's unlikely it will ever leak.

I know but everything is likely to leak sooner or later.

PS5 is too attractive a target, anyone who cracks it will be etched in history forever.

The hackers will come up with a workaround, they always do. I eagerly await the 33c3 presentation.

Does this mean I can buy a PS5 now?

Absolutely not

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