wouter van ooijen & floortje hanneman <wf@XS4ALL.NL> wrote:
> On the problem of distributing a new hex image: with a few checks &
> procedures you could distrubute the XOR of the old and the new image.
> Cryptographically this is (almost?) equal to the 'one time pad', the
> strongest possible cypher. Of course this requires that the loader can
> read the old content....

That depends on the relative sizes of them. One time pads rely on the
Shannon (information entropy) law by using more than one bit of pad per
bit of data (the more than one can come from the decision on which bit of
pad to use for which bit of data if the apparent data quantity is 1:1).
Thus the fundamental condition for using one time pads is that the pad be
at least the size of the data to be sent. Otherwise you are trying to
redefine what a 'bit' is in your context. And if the update is smaller
than what is inside there will be a way to crack it ...

Peter

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