Consider the following message authentication code that on input a message m$,$

produces a tag for the message as follows

t$($m$)=$ F$\backslash$kappa $($m$)||$F$\backslash$kappa $($m $$ r$)$

where F is a PRF that is known to be secure$,$ r is fixed and known to the adversary,

and $||$ is appending F$\backslash$kappa $($m $$ r$)$ to F$\backslash$kappa $($m$).$ Do you think this is a secure MAC? If not, what

property is this construction violating? Can you show an example where this property is

being violated?