Most of these attack vectors have been known for 10 years, and yet researchers keep finding bugs in major implementations to this day. Here's one from last week: https://portswigger.net/research/the-fragile-lock

> How would you digitally sign a Json document and embed the signature in the document?

You would not, because that's exactly how you get these bugs. Fortunately serialization mechanisms, whether JSON or Protobuf or XML or anything else, turn structured data into strings of bytes, and signature schemes operate on strings of bytes, so you'll have a great time signing data _after_ serializing it.

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BaconVonPork 2 days ago | parent [-]

This seems like a distinction without meaning. The question is whether JSON serializations intended for canonical signing would be somehow safer than those XML serializations. Obviously people would like all the same features that caused problems before.

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aleksejs 2 days ago | parent [-]

That is not, in fact, the question. The whole point of storing signatures separately from the serialized bytes they sign is not having to rely on any properties of the serialization scheme. It does not matter whether your serialization is canonical or not if you don't need to parse the document before you've verified the signature on it. XML-DSig, to the contrary, requires that you parse the document, apply complex transformations to it, and then reserialize it before you can verify anything, which is what makes bugs like "oops the canonicalization method errored and now my library will accept a signature over the empty string as valid for any document" (https://portswigger.net/research/the-fragile-lock#void-canon...) possible.

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BaconVonPork 2 days ago | parent [-]

You are saying people shouldn't want what they want and since JSON has no standards for it you assume it won't happen. Not even X509 is interested in working with detached signatures.

> It does not matter whether your serialization is canonical or not if you don't need to parse the document before you've verified the signature on it.

It most certainly does. First or last duplicate key?

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aleksejs 2 days ago | parent [-]

I am comfortable saying that, when designing a signature scheme, people should not want features that are known to consistently lead to catastrophic vulnerabilities.

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BaconVonPork 2 days ago | parent [-]

When I look at JSON related crypto, say JWT or WebAuthn, I am (un)comfortable saying the CVE causing complexities are there but repeating and not consolidated on a standard layer.

	▲	aleksejs 2 days ago \| parent [-]
		I'm not sure why you take me for a JSON/JWT fan (I'm happy to agree they've had their own share of implementation bugs), or what that has to do with signature wrapping bugs in XML-DSig, which is what I've been talking about this entire time.