XOR is perfectly fine as an encryption technique, provided that the
sequence being XORed with is sufficiently strongly pseudorandom.
This is known as a “stream” cipher. Basically, any “block” cipher can be
turned into a stream cipher by using it to generate the XOR sequence.
One threat exists with using XOR, even with a good sequence. If you have a
way of already knowing what the plaintext is, you will know which bits to
invert in order to forge a different message.
Also, "sufficiently strongly pseudorandom" would normally mean having good
statistical properties, resembling those of a genuine random sequence.
That's not the same as cryptosecure. A sequence could be ideal from that
point of view, and yet completely predictable. For example, produce your
stream by the XOR of the binary digits of pi with a linear congruential
generator. That eliminates the statistical flaws of the linear
congruential generator, but since everybody knows pi, it's still not
secure.
John Savard
| Date | Sujet | # | Auteur | |
| 27 Jun 25 |  Re: Zen Microcode | 2 | John Savard | |
| 27 Jun 25 |   Re: Zen Microcode | 1 | BGB |
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