AES for Kerberos (RFC3962)

[Anderson Luiz Brunozi]

Hello,

I'm implementing a Java kerberos client to be used in a mobile application. I already have a working version, using DES keys. 
But now, I'm required to change it to use AES, instead of DES. I have started it by trying to follow what is described in RFC3962.
The text says the key generation is done by these two steps:

   tkey = random2key(PBKDF2(passphrase, salt, iter_count, keylength))
   key = DK(tkey, "kerberos")

And, following the example below, I have already been able to generate the "128-bit PBKDF2 output".

   Iteration count = 1200
   Pass phrase = "password"
   Salt = "ATHENA.MIT.EDUraeburn"
   128-bit PBKDF2 output:
       5c 08 eb 61 fd f7 1e 4e 4e c3 cf 6b a1 f5 51 2b
   128-bit AES key:
       4c 01 cd 46 d6 32 d0 1e 6d be 23 0a 01 ed 64 2a

Now I'm stuck at how I could generate the "128-bit AES key". If I have understood it, that should be what the DK() function does. 
So, could anyone tell me what, exactly, does this DK() function do? 

Thanks,

Anderson Luiz Brunozi