Before anyone says it, i'd be more than willing to work on the code for
this myself but would like feedback on the idea.

Essentially as follows:

1 - A sysctl variable stores a public key that can only be written to once
at startup
2 - All executables on the system must be signed with that public key
3 - Any executable not signed is essentially chmod -x

Of course that's the simple basic idea, there are obvious performance
issues to consider and this system would have to be optional, but for truly
paranoid installs it could be a wonderful feature.

More complex policies are easily imagined, but for a first version, simply
refusing to run executables without signing seems worthwhile.

The performance issues could be partly addressed by only signing hashes of
the executables, the unsigned hashes would be stored all in one file that
is supplied with the install sets and signed the first time this feature is
enabled. Signing can take place on another machine and only the signature
file copied over, or signing can take place locally with the private key
later removed - or simply left in place for slightly lower levels of
security.

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