Wanted: a clue for using encrypt with DES

[Ben Rubinstein]

I'm trying to implement a protocol which uses DES encryption to send a
password across the network.  And I know nothing about encryption.

In the protocol I'm working with, the approach is that one side sends a random
16-byte "challenge"; the other end encrypts this data "with DES using the
password as key", and sends the 16 byte encrypted result back to the server.

I captured this exchange between two existing apps that implement the
protocol, ie I got the 16 byte challenge, and the 16 byte response (and of
course I already know the password).  So now I'm attempting to implement code
in Rev that will generate the same 16 byte response, given that 16 byte
challenge and the password.

My first attempt:

   encrypt tChallenge using "des" with password tPassword

This returned 16 bytes, but they were the wrong ones.

I went back to the documentation and saw that it said "using the password as
key"; my second attempt therefore:

   encrypt tChallenge using "des" with key tPassword

This time I get an error "invalid keystring for specified keysize".


I saw that "the ciphernames" tells me the default key length for DES is 64
bits.  My password is four characters.  I changed my code to pad the password
to eight bytes, using numtochar(0). Now I didn't get an error, but I get the
wrong byte sequence back.  Just for fun, I tried spaces instead of zero bytes
for the padding; different data, still wrong.

So then I decided that while I'd like to understand this, it was an 
unnecessary distraction; and changed the password to be exactly eight 
characters, and captured a new challenge and response.  Feeding this to the 
script, the first byte of the Rev-calculated response (possibly the first 12 
bits depending on endian issues) matches the correct response, but perhaps 
that's just coincidence.

Can someone kindly point me in the right direction?  Have I just misunderstood
something simple?

TIA,

Ben