padding in ESP

[Lokesh <lokeshnb@intotoinc.com>]

Hi all
One questions each on ESP and AH protocols:

1] why do we need to adjust ESP packet size by padding to be aligned to 4 
byte boundary in case of
null encryption? can we bypass padding for null encryption?

2] AH RFC says ICV can be of variable size, and is normally taken as 12 
bytes, in case if someone
wants > 12 bytes of ICV how he/she can intimate other party of new size of 
the ICV?

Thanks
Lokesh