Cryptography Stack Exchange is a question and answer site for software developers, mathematicians and others interested in cryptography. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

Dan Boneh's courersa lecture on format preserving encryption at 5.50 mins , talks about truncating a PRF on $n$ bits to PRF on $t$ bits.

The approach is by appending $(n-t)$ zeros to input $t$ bits then applying AES on $n$ bits and truncating it back to $t$ bits . He says there are better ways to do it but does not mention how . anybody has idea on better ways to truncating PRF on $t$ bits when $t \ll n$ .

share|improve this question

closed as unclear what you're asking by D.W., e-sushi, DrLecter, otus, poncho Jun 26 '14 at 15:45

Please clarify your specific problem or add additional details to highlight exactly what you need. As it's currently written, it’s hard to tell exactly what you're asking. See the How to Ask page for help clarifying this question.If this question can be reworded to fit the rules in the help center, please edit the question.

Better, in what way? The construction Boneh provides is a perfectly reasonable choice. Unless you can define in what objective metric/criteria you would use to define "better", I don't think this question is well-defined. – D.W. Jun 23 '14 at 1:43
@D.W even i was not clear by Boneh's comment that there are better ways to do it . so thought of checking with the community – sashank Jun 23 '14 at 6:24