If all authorities restart at once right before a consensus vote, nobody
will vote about "Running", and clients will get a consensus with no usable
relays. Instead, authorities refuse to build a consensus if this happens.
The first happens on an error case when a controller wants an
impossible directory object. The second happens when we can't write
our fingerprint file.
The code for these was super-wrong, but will only break things when we
reset an option on a platform where sizeof(time_t) is different from
sizeof(int).
See task 1114. The most plausible explanation for someone sending us weak
DH keys is that they experiment with their Tor code or implement a new Tor
client. Usually, we don't care about such events, especially not on warn
level. If we really care about someone not following the Tor protocol, we
can set ProtocolWarnings to 1.
The old flavored consensus URL format made it harder to decode URLs
based on their prefixes, and didn't take into account our "only give
it to me if it's signed by enough authorities" stuff.
The point of doing SHA256 twice is, generally, is to prevent message
extension attacks where an attacker who knows H(A) can calculate
H(A|B). But for attaching a signature to a document, the attacker
already _knows_ A, so trying to keep them from calculating H(A|B) is
pointless.
This patch introduces a new type called document_signature_t to represent the
signature of a consensus document. Now, each consensus document can have up
to one document signature per voter per digest algorithm. Also, each
detached-signatures document can have up to one signature per <voter,
algorithm, flavor>.
Previously, we insisted that a valid signature must be a signature of
the expected digest. Now we accept anything that starts with the
expected digest. This lets us include another digest later.
When we tried to use the deprecated non-threadsafe evdns
interfaces in Libevent 2 without using the also-deprecated
event_init() interface, Libevent 2 would sensibly crash, since it
has no guess where to find the Libevent library.
Here we use the evdns_base_*() functions instead if they're
present, and fake them if they aren't.
