–dissipates
statistical structure of plaintext over bulk of ciphertex
•Where
did we see this?
•We saw
that the Hill cipher has
this property.
–This means
that frequency statistics of letters, [digraphs], etc. in the plaintext are
diffused over several characters in the ciphertext, which means that much more ciphertext is
needed to do a meaningful statistical attack.
•Confusion means that the key does not relate in a simple way to the ciphertext.
–each character of the ciphertext should depend on several
parts of the key.
–makes
relationship between ciphertext and
key as complex as possible
•For example,
suppose we have a Hill cipher with an n*n
matrix, and suppose we have a plaintext-ciphertext pair of length n2 with which we are able to solve for the
encryption matrix.
–If we
change one character of the ciphertext, one column of the matrix can change
completely.
•When a
situation like that happens, the cryptanalyst would probably need to solve for
the entire key simultaneously, rather than piece by piece.
