Re: Rather Newb-ish Question


Paul Rubin wrote:
> "ncf" <nothingcanfulfill@xxxxxxxxx> writes:
> > Assuming that "c = p and k", how would the reciever decipher p from c,
> > knowing k?
>
> Normally you'd use "c = p xor k", not "p and k" ("xor" is short for
> "exclusive or"). That's because xor is reversible, unlike "and" and
> "or".
>
> Alternatively you could use addition: "c = p + k", which you can
> reverse with subtraction. Xor is just addition in a special number
> system where addition and subtraction are the same.

Sadly, the xor and basic addition/subtraction/multiplication/division
is what I was trying to get away from. I've read and have a general
understanding of the concepts put forth in _Applied Cryptography_ and
_Practical Cryptography_, however, my knowledge in entirity is still
lacking as to how to pull off any more advanced bit-wise operations
than xor in en/de-cryption.

However, you noted that "and" and "or" are not reverseable, so I may
just be wrong in my recalling that they were used to create c from p in
more advanced algorithms.

> > Also, are there any books that are very practical for teaching bit-wise
> > math and the like?
>
> Hmm, that's a very basic topic in programming. Anyway, try here:
>
> http://en.wikipedia.org/wiki/Binary_arithmetic
>
> You might also like "The Code Book", by Simon Singh. It's a general
> intro to cryptography, mostly not too technical, but covers methods
> from ancient times to the present.

Thanks for the pointer, although basic aspects of it were not so
useful, it was very gladdening to finally see the electronic method of
addition and such operations.

.

Relevant Pages

  • Re: rotor alternative?
    ... The idea of cryptography now is to keep the data secure as long as the ... Rotor fails in that criterion. ... > very little difference to use base64 and a xor or something similar. ...
    (comp.lang.python)
  • Re: Question about bit strength
    ... about cryptography into a coherant form. ... character key grabs an 8 character block of data and does an XOR between ... kind of like a cross between blowfish and 3DES (blowfish uses xor and ... Blowfish uses Xor, you use Xor; 3DES uses multiple keys, you use multiple keys ...
    (sci.crypt)
  • Re: Rather Newb-ish Question
    ... reverse with subtraction. ... Xor is just addition in a special number ... system where addition and subtraction are the same. ... You might also like "The Code Book", ...
    (sci.crypt)
  • Re: The strength of "post-encryption encryption"?
    ... since it didn't have subtraction, either, an XOR was actually ... TAD A ... DCA result ...
    (sci.crypt)
  • Re: Fast DES IP implementation
    ... > On some machines you can use a variant, the subtraction trick. ... I'd say that the XOR is just a specific case of this more general --+ ...
    (sci.crypt)