Support host certificates in client - #752
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Five coupled pieces. The exchange hash now uses the blob the server actually sent: for a certificate the parsed form is only the key inside it, and re-encoding that hashes something the server never sent — a failure that looks like a bad signature and is computed entirely locally, so there is nothing on the wire to compare against. The key exchange is verified with the key the certificate contains; the certificate's own signature is a separate proof, left to the client and its trusted authorities. Collapsing them would accept a certificate nobody vouched for. check_server_certificate replaces check_server_key rather than adding to it — the key inside a certificate is not something a client was ever told to trust, and asking about it as well invites answering the wrong question. It defaults to refusing: a client that has not been taught which authorities it trusts cannot answer, and answering wrongly accepts any machine whose operator can get a certificate from anyone at all. Certificate algorithms are a parallel list because Algorithm cannot represent one — it maps ssh-ed25519-cert-v01@openssh.com back to Ed25519, so a certificate placed in `key` would be advertised under the plain name. Empty by default: advertising it makes servers present certificates to clients that may have no idea who is allowed to have signed them.
Two literals build it field-by-field, so a new field is a breaking change for them. Noted in the pull request: downstream code that does the same needs the one-line addition, which is why the field carries an empty default and nothing else changes.
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Would this also add support for servers to authenticate users that provide a signed certificate. |
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@oni303 no worries - I've seen all 3 PRs - I'll merge client support here since and then merge your server support on top with a few changes |
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#748 + fixes