Here’s the info we found from Professor Varghese’s notepad:
NETSIFT CONFIDENTIAL
varghese
netsift 2005
From this, we can deduce that we need to connect to [email protected] with password varghese. The next step is to connect to host netsift port 2005.
# Get the IP address of netsift
$ dig netsift
# Solve phase
$ ./socket
> socket
> connect 3 10.0.124.247 2005
> send 3 GET /
> recv 3 2000
> close 3
> ^D
We get our response:
HTTP/1.0 200 OK
Content-Type: text/plain
NETSIFT INTERNAL DOCS
<REDACTED>
DATA LINK PROTOCOLS DISCUSSION:
FRAMING:
PAGE 20 OF LECTURE NOTES BIT STUFFING
<REDACTED>
Hint: Check Tuesday's lecture notes on Bit Stuffing (page 20).
The next host you should connect to is a protocol that's 4 characters long.
The port is the year that this protocol was created. (Check Wikipedia.)
From the response, we know to check BruinLearn and Tuesday's lecture slides on Bit Stuffing. Check page 20. We see that the only 4 letter protocol is HDLC, and it was created in 1979—so, our host is hdlc and port is 1979.
$ dig hdlc
$ ./socket
> socket
> connect 3 10.0.78.200 1979
> send 3 GET /
> recv 3 2000
> ^D
We get our response:
HTTP/1.0 404 Not Found
Content-Type: text/plain
NETSIFT INTERVIEW PROBLEM (CONFIDENTIAL):
Here's a sequence of bits from a (modified) HDLC connection (beginning/end stripped):
00110011 001101110 00110011 001110000
From left to right, these bits form an ASCII string.
HDLC uses bit stuffing with a sentinel pattern 011110.
Any time it sees a sequence of 3 1s in a row, it inserts a 0.
Your job is to "unstuff" these bits.
Hint: If the answer is 2467, send GET /2467
Unfortunately, this is not as easy as phase 1—we have a problem to solve.
We know that anytime there’s a sequence of 3 1s, we should remove a 0. In our sequence of bits, we see that there are 2 triplets of 1s:
00110011 00110***111***0 00110011 00***111***0000
We can now remove the 0 right after:
00110011 00110***111*** 00110011 00***111***000
Converting to decimal, we get: