An override for the wallet to daemon connection is provided, but not for
other SSL contexts. The intent is to prevent users from supplying a
system CA as the "user" whitelisted certificate, which is less secure
since the key is controlled by a third party.
This allows "chain" certificates to be used with the fingerprint
whitelist option. A user can get a system-ca signature as backup while
clients explicitly whitelist the server certificate. The user specified
CA can also be combined with fingerprint whitelisting.
The former has the same behavior with single self signed certificates
while allowing the server to have separate short-term authentication
keys with long-term authorization keys.
If the verification mode is `system_ca`, clients will now do hostname
verification. Thus, only certificates from expected hostnames are
allowed when SSL is enabled. This can be overridden by forcible setting
the SSL mode to autodetect.
Clients will also send the hostname even when `system_ca` is not being
performed. This leaks possible metadata, but allows servers providing
multiple hostnames to respond with the correct certificate. One example
is cloudflare, which getmonero.org is currently using.
If SSL is "enabled" via command line without specifying a fingerprint or
certificate, the system CA list is checked for server verification and
_now_ fails the handshake if that check fails. This change was made to
remain consistent with standard SSL/TLS client behavior. This can still
be overridden by using the allow any certificate flag.
If the SSL behavior is autodetect, the system CA list is still checked
but a warning is logged if this fails. The stream is not rejected
because a re-connect will be attempted - its better to have an
unverified encrypted stream than an unverified + unencrypted stream.
Using `verify_peer` on server side requests a certificate from the
client. If no certificate is provided, the server silently accepts the
connection and rejects if the client sends an unexpected certificate.
Adding `verify_fail_if_no_cert` has no affect on client and for server
requires that the peer sends a certificate or fails the handshake. This
is the desired behavior when the user specifies a fingerprint or CA file.
Currently if a user specifies a ca file or fingerprint to verify peer,
the default behavior is SSL autodetect which allows for mitm downgrade
attacks. It should be investigated whether a manual override should be
allowed - the configuration is likely always invalid.
Currently a client must provide a certificate, even if the server is
configured to allow all certificates. This drops that requirement from
the client - unless the server is configured to use a CA file or
fingerprint(s) for verification - which is the standard behavior for SSL
servers.
The "system-wide" CA is not being used as a "fallback" to verify clients
before or after this patch.
Specifying SSL certificates for peer verification does an exact match,
making it a not-so-obvious alias for the fingerprints option. This
changes the checks to OpenSSL which loads concatenated certificate(s)
from a single file and does a certificate-authority (chain of trust)
check instead. There is no drop in security - a compromised exact match
fingerprint has the same worse case failure. There is increased security
in allowing separate long-term CA key and short-term SSL server keys.
This also removes loading of the system-default CA files if a custom
CA file or certificate fingerprint is specified.
