How to extract MAC and AES keys using x9.63 based kdf For trying ECIES, I need to derive keys for MAC and AES from the shared secret using ANSI x9.63 based KDF. The information on key derivation I got it from Section 3.6.1 of http://www.secg.org/sec1-v2.pdf. 

What is the standard procedure to extract/separate the keys for MAC and AES from the Key derived using KDF?
For that standard, it is covered in Section 5.1.3:


  
  Use the key derivation function KDF established during the setup procedure to generate keying data K of length enckeylen + mackeylen
  octets from Z and [SharedInfo1 ]. If the key derivation function
  outputs “invalid”, output “invalid” and stop.
  Parse the leftmost enckeylen octets of K as an encryption key EK and the rightmost mackeylen octets of K as a MAC key MK. If symmetric
  encryption method is XOR and backwards compatibility mode is not
  selected, then instead parse the rightmost enckeylen octets of K as an
  encryption key EK and the leftmost mackeylen octets of K as a MAC key
  MK.
  


In the end, it depends on the parameters enckeylen and mackeylen, which define the sizes of the keys for the symmetric encryption and the MAC, respectively.