KRL extensions and signing #19
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Defines KRL extension sections that may be marked optional or mandatory for support. Will allow graceful extension of the format in the future.
factor out signature verification and trusted key checking into separate functions.
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This changeset contains three patches for the OpenSSH KRL code:
This takes the form of new (sub-)section types that contain named extensions. These may be flagged as "critical" which causes the KRL parser to treat them as mandatory-to implement. If they aren't flagged as critical then they are ignored.
Unfortunately KRLs with extensions are not backwards-compatible, as the parser treats unknown section types as a fatal error. They are forwards-compatible though. I didn't update the KRL format version because I couldn't see any practical difference between "KRL parsing fails because of an unknown section type" and "KRL parsing fails because the format version is wrong".
This simplifies and splits the KRL parsing logic into three phases: signature verification, key trust verification and everything else. The idea is to make this easier to read and verify, but also to allow reuse of the first two steps in other contexts (e.g. a KRL parser that just tests a single key, instead of trying to load the whole KRL into RAM).
The KRL format has supported signing of KRLs and verification of KRL signatures for a long time, but there is currently no way to generate a signed KRL or check the signature on one. The final patch hooks this up for
ssh-keygen(1)at least.