# how to truncate a PRF on n bits to PRF on t bits where t < n? [closed]

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 $t \ll n$ .

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

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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 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 at 6:24