working on computers outside imperial network about hpce-2013-cw6

[m8pple]

Well you don't need to be able to connect to the exchange
in order to check correct operation, it's more just to check
things against slightly different code once you are happy
with it the test env.

That said, assume you have:

• IMPERIAL_HOST : a machine you can ssh into from outside college
• EXCHANGE_HOST : a machine inside college where an exchange is running
• EXCHANGE_PORT : a port on the machine running the exchange
• LOCAL_PORT : a port on your machine (can probably use EXCHANGE_PORT).

then you should be able to set up an ssh tunnel using:

ssh -L $LOCAL_PORT:$EXCHANGE_HOST:$EXCHANGE_PORT $IMPERIAL_HOST

That will open up an ssh session, but behind the scenes it will also
tunnel port $EXCHANGE_PORT on the localhost to $EXCHANGE_PORT on the
remote host. So in a different (local) shell, you can run:

./bitecoin_miner MyId 4 tcp-client localhost $LOCAL_PORT

However, you may find you get the error (depends on where you ssh to):

open failed: administratively prohibited: open failed

which means your ssh provider is "security conscious".

So, you can get more clever, and use netcat (nc), to get
past that, as if you have stdin and stdout you can always
push a socket over them.

So, you can do:

rm .backwards
mkfifo .backwards
REMOTE_CMD="nc $EXCHANGE_HOST $EXCHANGE_PORT";
FORWARD_CMD="ssh -v -T -x $IMPERIAL_HOST ${REMOTE_CMD}";
nc -lk $LOCAL_PORT 0<.backwards | ${FORWARD_CMD} 1>.backwards

That lets me get in via most ssh hosts. Good luck working out
why it works :)

A possibly more understandable version:

rm .send .recv;
mkfifo .send .recv;
0<.send
ssh -v -T -x $IMPERIAL_HOST nc $EXCHANGE_HOST $EXCHANGE_PORT
1>.recv &
./bitecoin_client MyId 4 file .recv .send

You'll want passwordless authentication, which you should probably
be using anyway. So you'd want to be using ssh-agent, ssh-add, and
friends (or pageant under windows with putty).

A much simpler method to is to just connect to the imperial
VPN. That should allow you to connect directly to any tcp
socket on an internal computer.

David Thomas

On 2014-03-16 23:08, dimchrist89 wrote:

i wanted to ask if it is possible to work on our computers for cw6. You
mention in the description that this can be done via ssh. Could you give
us some details on that? (The problem is the limited time, since the
premises of the college are open untill 12pm)

Thank you in advance,

Dimitrios Christopoulos

—
Reply to this email directly or view it on GitHub
#3.