ecdsa keyval.public format is hex-encoded DER, should be PEM

[jku]

It looks like the ecdsa-sha2-nistp256 keytypes keyval.public value is incorrectly the hex encoded raw bytes of the key, instead of PEM. Spec says:

The "ecdsa-sha2-nistp256" format is:

{
  "keytype" : "ecdsa-sha2-nistp256",
  "scheme" : "ecdsa-sha2-nistp256",
  "keyval" : {
    "public" : PUBLIC
  }
}

PUBLIC: PEM format and a string.

I'm looking at e.g the sigstore metadata https://github.com/sigstore/root-signing/blob/main/repository/repository/2.root.json#L36 where the value does not seem to be PEM.

Related:

• Spec issue to clarify key format Clarify key format specification#201
• python-tuf interop issue: compatibility: go-tuf ecdsa key format is incompatible python-tuf#1859
• maybe this issue is a duplicate of Is ecdsa verifier implemented according to the specification? #127 ?

[asraa]

I think the big problem was that newlines inside JSON couldn't be handled well with go. I pulled a PEM encoded public key string from python repository testadata and you'll usually get invalid chars trying to unmarshal:
https://go.dev/play/p/WikoJBIBMRo

[jku]

I realize the following is not useful to solve the problem that we have now but I'll say this to any future developers thinking of a similar workaround: Redefining an existing keytype is not the best solution to this problem. The specification supports new keytypes just fine.

I don't have ideas to fix the issue at hand: I'm not very familiar with the go deployment styles but I suppose we are now in a situation where:

• current clients only accept hex ecdsa keys
• even if client code is updated to support both, there is no guarantee that clients are updated
• even if the metadata generating code is fixed, repositories currently serving hex ecdsa keys might not want to switch to PEM keys because of above point

What the project can definitely do is document the issue: "go-tuf does X in a non-compliant way: it works fine but may prevent using other TUF implementations with the same metadata"

[toby-jn]

Implemented a fix for this in: #270