Hi,
AFAIK, the problem with using rainbowtables for cracking kerberos hashes, is that kerberos uses a salt value to hash the password.
This means that for every one password, there are now 4096 possible different hashes. This means that for a dictionary or brute force attack, you will need to hash each password 4096 times based upon a further brute force of the 12 bit salt value. That isn't much of a problem for cracking techniques that create hashed 'on the fly' like the dictionary/brute force, it will just slow it down slightly.
For a system that pre-computes the hashes, like rainbow tables, the size of that table will now be 4096 times bigger! I have 47GB of LM hashing tables! The kerberos hashing algorithm is much more complex and will require a much bigger set of tables, then multiply that by 4096!!!
It really makes the use of rainbow tables inneffective.
But that is only my current knowledge, if someone knows something different, please let use know.
l8r,
xatar.