🆕 blog!
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I'm going to try and keep a record of all the bugs, errors, and inconsistencies I've reported in #ActivityPub and #Mastodon documentation.
First up, how big are the limits on what you can federate?
Mastodon lists some limits in KB/MB, but others are just raw numbers. That might make sense for an ASCII world - but emoji complicate everything.
Next is slightly more trivial - a broken internal link in the Mastodon documentation.
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Next is slightly more trivial - a broken internal link in the Mastodon documentation.
I think the #RFC9421 HTTP Signature algorithm should be explicitly included in #Mastodon's requests.
Feedback welcome - especially those explaining politely why I'm a wrong about this.
https://github.com/mastodon/mastodon/issues/29905#issuecomment-5440336919
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I think the #RFC9421 HTTP Signature algorithm should be explicitly included in #Mastodon's requests.
Feedback welcome - especially those explaining politely why I'm a wrong about this.
https://github.com/mastodon/mastodon/issues/29905#issuecomment-5440336919
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@Edent Currently on vacation so I might misremember, but afair the algorithm is already determined by the key used. So including it would do no harm, but is kind of redundant.
@dave I'm not sure I understand.
The *digest* says what algorithm it uses, but it isn't a given that the same algo will be used for the signature, right?I can't find another reference to the algorithm in the public key.
Very happy to be told I'm missing something obvious
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@dave I'm not sure I understand.
The *digest* says what algorithm it uses, but it isn't a given that the same algo will be used for the signature, right?I can't find another reference to the algorithm in the public key.
Very happy to be told I'm missing something obvious
@Edent RFC9421 only lists a handful of possible algorithms. IIRC if your key is ed25519 only one of them applies, similarly if the key is ecdsa. I think there are two possibilities for RSA keys, but we only support one for legacy reasons and do not plan to encourage future use of RSA so will likely never implement the other. So in practice looking at the key type should be sufficient to determine the algorithm used.
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@Edent RFC9421 only lists a handful of possible algorithms. IIRC if your key is ed25519 only one of them applies, similarly if the key is ecdsa. I think there are two possibilities for RSA keys, but we only support one for legacy reasons and do not plan to encourage future use of RSA so will likely never implement the other. So in practice looking at the key type should be sufficient to determine the algorithm used.
@dave ah, I think i get it.
Enjoy your holiday
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I think the #RFC9421 HTTP Signature algorithm should be explicitly included in #Mastodon's requests.
Feedback welcome - especially those explaining politely why I'm a wrong about this.
https://github.com/mastodon/mastodon/issues/29905#issuecomment-5440336919
@Terence Eden If the verifier chooses which algorithm to use from this header, without double-checking it against the key, there's a chance it'll be vulnerable to an "algorithm confusion attack".
Here's what that looks like in the case of JWTs; the same problem could happen with RFC9421.
The safe way to work out which algorithm to use is to dereference thekeyidand then choose the algorithm which matches the type of the returned key. -
@Terence Eden If the verifier chooses which algorithm to use from this header, without double-checking it against the key, there's a chance it'll be vulnerable to an "algorithm confusion attack".
Here's what that looks like in the case of JWTs; the same problem could happen with RFC9421.
The safe way to work out which algorithm to use is to dereference thekeyidand then choose the algorithm which matches the type of the returned key. -
@fentiger I think that's where I'm getting confused.
I'm getting the public key from the Mastodon user - but how do tell what algorithm the key itself uses?
@Terence Eden You should be able to find out from your crypto library after you've decoded the key from PEM.
(I don't think anyone uses anything other than RSA in thepublicKeyPemfield, but I'm not sure it's safe to assume that.) -
@Terence Eden You should be able to find out from your crypto library after you've decoded the key from PEM.
(I don't think anyone uses anything other than RSA in thepublicKeyPemfield, but I'm not sure it's safe to assume that.)@fentiger
If I decode the PEM, all I get is
Type: RSA Public Key
Key Size: 2048 bitsNothing to say which algorithm it uses.
Feel free to tell me what incredibly obvious thing I'm missing
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