Some more from mailing list to make it easier for people:
F L
Bitcoin XT contains an unmentioned addition which periodically downloads
lists of Tor IP addresses for blacklisting, this has considerable privacy
implications for hapless users which are being prompted to use the
software. The feature is not clearly described, is enabled by default,
and has a switch name which intentionally downplays what it is doing
(disableipprio). Furthermore these claimed anti-DoS measures are
trivially bypassed and so offer absolutely no protection whatsoever.
Connections are made over clearnet even when using a proxy or
onlynet=tor, which leaks connections on the P2P network with the real
location of the node. Knowledge of this traffic along with uptime metrics
from bitnodes.io can allow observers to easily correlate the location and
identity of persons running Bitcoin nodes. Denial of service can also be
used to crash and force a restart of an interesting node, which will
cause them to make a new request to the blacklist endpoint via the
clearnet on relaunch at the same time their P2P connections are made
through a proxy. Requests to the blacklisting URL also use a custom
Bitcoin XT user agent which makes users distinct from other internet
traffic if you have access to the endpoints logs.
https://github.com/bitcoinxt/bitcoinxt/commit/73c9efe74c5cc8faea9c2b2c785a2f5b68aa4c23Christophe Biocca
Todd
Christophe Biocca via bitcoin-dev wrote:
> So I checked, and the code described *does not* run when behind a
> proxy of any kind, including tor:
>
>
https://github.com/bitcoinxt/bitcoinxt/commit/73c9efe74c5cc8faea9c2b2c785a2f5b68aa4c23#diff-11780fa178b655146cb414161c635219R265>
> At least based on my admittedly weak understanding of how the internal works.
>
> Hopefully I save the next reader of your post from also having to dig
> around to find the code and realize this is a false alert.
That's not entirely correct.
The code does disable downloading of the Tor exit node list if fListen
is false, or if there is a proxy setup, this means the statement:
> Connections are made over clearnet even when using a proxy or
> onlynet=tor,
is false. However, in the common scenario of a firewalled node, where
the operator has neglected to explicitly set -listen=0, the code does
still download the Tor exit node list, revealing the true location of
the node. This is contrary to the previous behavior of not revealing any
IP information in that configuration.
FWIW Gregory Maxwell removed the last "call home" feature in pull-req
#5161, by replacing the previous calls to getmyip.com-type services with
a local peer request. Similarly the DNS seeds use the DNS protocol
specifically to avoid leaking IP address information.
tl;dr: Yes, Bitcoin XT has a privacy problem with the automatic Tor exit
node list download.
Gregory Maxwell
It's not a bug, it's a feature: These concerns and others were
specifically called out when we rejected this submission to Bitcoin
Core in favor of a more generic approach that lacks the privacy
problems and avoids being explicitly punitave to the use of Tor.
At least it's not a full on block as soon a the node fills for the
first time like the first implementation.
Peter Todd
This is why Bitcoin XT will fail in my opinion.... It's not a fork being done in the interest of a global need, but to satisfy the USA government and all it's regulations.