GIAC Exams - Calculators

laughing_man

Okay, paranoid question:

So I am sitting for the GSEC soon and have been studying big time on packet analysis, just because it is one of the more in depth sections of the books. I am more than comfortable converting hex to binary/hex to decimal, etc. I was told in the OnDemand lecture that we would have a calculator with hex/binary/decimal conversion. i just email SANS to confirm and they said this is not true.

Here is the paranoid part - I have no issue converting smaller hex values to decimal, say a signle byte in lenght. But when you get into sequence/acknowledgement numbers (4 bytes long), I get quickyly lost in the manual calculations. Am I being paranoid? Is the GSEC even going to ask me to convert a sequence number, or merely identify it? I can assume I would need to convert smaller values for TTL's, protocol type, checksums.

I think I need to take a break.

dover

Laughing_man,

I haven't taken the GSEC but I have taken the GCIA exam. I can confirm that you only have access to a simple add/sub/mult/div calculator on the exam. I can't imagine you would be asked to convert a large sequence or ack field - though I could be wrong. Even if they do, just use your scratch paper to keep track and you'll be fine. If you understand the concept of conversion you'll have no troubles.

laughing_man

Well for example a sequence number might be 0xa432274f. Going to binary is easy enough, using the 8,4,2,1 notation.

10(a) = 1010
4 = 0100
etc.

Now I have my 32 binary digits; 1010 0100 0011 0010 0010 0111 0100 1111
Easy enough.

From here, though I need a quick way to convert such a large number to decimal.

Or should I go right from hex to decimal, multiplying by the following notation: 16^7 - 16^0

JDMurray

Why do you need to convert the sequence numbers from hex to dec?

laughing_man

Well, the SANS material converts the seq/ack numbers from hex to dec, so I was doing the same. Frankly, I agree that I am being too nitpicky. I was more interested in finding a way to quickly convert hex to decimal.

Currently I do this:

4ABE: I write out each nibble in decimal format = 4 10 11 14

Multiply each value as follows:

4(16^3) + 10(16^2) + 11(16^1) + 14(16^0) = 19134

So I am assuming for a 4 byte value, I would do this:

n(16^7) + n(16^6) + n(16^5) +n(16^4) + n(16^3) + n(16^2) + n(16^1) + n(16^0)

beads

Your thinking a little too hard about the exam here. Took GSEC a couple of years ago and do not remember having to much if any math. SANS has been pretty reasonable about not putting items on the exam that require heavy math. Probably used slow on screen calculator no more than a handful of times.

Given that I will be taking my GCPM (Project Management) exam Tuesday and I am willing to bet there won't be much in the way of higher math there and the PM piece can get into all kinds of mid level math like standard deviation and such. You really think anyone is going to figure out square roots on that dinky little on screen calculator? Doubtful. Know the material but its been too boring to review. I'll post a follow up if I am wrong.

- beads