Take the 2-minute tour ×  Suppose the Hill cipher were modified
to something like a one-time pad cipher, where Alice wants to
send a message to Bob, and she chooses a key matrix randomly
everytime a new message is sent (and the inverse of the key
matrix is sent to Bob by other means everytime - just as in the
one-time pad). Would this yield perfect secrecy or at least
$\mathsf{IND-CCA}$?  Any thoughts on how to proceed with the
security analysis of this?  share|improve this question  1
Answer 1  Expand the equation system corresponding to the matrix
multiplication:  $c_j = \sum_{i=0}^{n-1}k_{i,j}p_i$  In other
words, each element of the cipher text corresponds to the sum of
the cipher text elements of an OTP encryption of the input plain
text. If the matrix is never reused, it should be fairly easy to
go from here. You are basically using $n$ one time pads to
encrypt the message instead of a single one. - Almost, since the
$k_{i,j}$ values of the matrix have to be selected in such way
that the determinant is