1

Suppose I apply a PRF to a secure MAC. Do I still have a secure MAC?

Demi
  • 4,853
  • 1
  • 22
  • 40

2 Answers2

3

Yes.

A secure PRF is a secure MAC. A secure MAC of a secure MAC is a secure MAC. Therefore, applying a PRF to a MAC still gives you a MAC.

Depending on the length of the inner MAC and the PRF you may lose security bits, but if they are long enough it works.

otus
  • 32,462
  • 5
  • 75
  • 167
-2

Assuming you're asking if PRF(MAC) can be used as MAC (message authentication code)? Depends on the PRF. MAC is de-factor PRF too with several properties in mind (collision resistance, pre-image resistance, avalanche effect, non-linearity...).

Until your PRF keeps these properties, you should be ok. The basic idea is you should not weak the strength (length) of the MAC.

gusto2
  • 1,194
  • 7
  • 14