🚀 go-pugleaf

The question arose in a previous reply to this posting of whether
triple, double or any other repeated DES encryption was stronger than a
single encryption.  The previous reply indicated that the question was
still open.  It is not open ... it has been settled and the results
presented at CRYPTO 92.

Essentially the question about the strength of double encryption is the
same as the question about whether DES is or is not a group.

If DES were a group then for two keys K1 and K2

       DES( DES(Plaintext, K1), K2) == DES(Plaintext, K3) for some

K3 which presumably the eavesdropper is trying to discover ... the point
being that they would not have to find K1 and K2, but only a kind of
"combination" K3.

The recently demonstrated fact that DES is *not* a group indicates that
a double encryption *is* stronger than single encryption.