Re: A twist on OTP for an outstandingly secure channel?


"Jean-François Michaud" <cometaj@xxxxxxxxxxx> wrote in
message
news:1168208626.673690.99840@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

John E. Hadstate wrote:
Does this sound similar to what you're trying to achieve?

Very similar indeed! I'm trying to clarify the idea by
using the
perfect case of the OTP. I'm not so much concerned
wheather and OTP is
deemed unbreakable or not; it simply offers a good
platform for
thinking about the concepts involved.

Here's the problem with this discussion: you can not improve
the security of a perfectly random OTP. Once you invoke the
random OTP for a stream cipher, you might as well have
invoked God. If the random OTP is used for encryption,
every decryption is equally likely to be the original
plaintext. There is very little more to say (except for
techniques for encrypting very short plaintexts, which was
mentioned in another part of this thread).

Now, if your OTP is based on a PRNG, it's a whole different
ballgame, and there is then some room for discussion. I
actually proposed this idea in sci.crypt twice. The first
time, it was roundly ignored (and after re-reading it, I can
see why). The second time, someone was good enough to
actually analyze the effect of pseudo-randomly dispersing
plaintext in a background of pseudo-random bits. As I
recall, it turned out that if you allow a bandwidth
expansion of 2:1, you only add a bit or two to the effective
key size. All things considered, there are undoubtedly more
efficient and effective ways to improve the security of a
PRNG-based stream cipher.


.

Relevant Pages

  • Re: Chosen plaintext attacks
    ... the plaintext you have the OTP stream. ... "The known-plaintext attack or crib is an attack model for ... "In cryptography, the one-time pad (OTP) is a type of encryption, ... the same length as the plaintext, resulting in a ciphertext. ...
    (sci.crypt)
  • Re: Chosen plaintext attacks
    ... You are just confused a OTP uses a XOR on a plaintext, ... same for an OTP if you have an OTP stream of 10GB ... XOR to get the OTP numbers used to XOR the plaintext. ...
    (sci.crypt)
  • Re: quantum computing
    ... very fast (Shor's algorithm is one type of search). ... grover unstructured search algorithm is only a square root speedup, ... Nothing works against OTP since any message is a potentially valid mesage. ... once the entire plaintext is know it is possible to recover the key ...
    (sci.crypt)
  • Re: Encryption key longer than text to encrypt
    ... have OTP in mind, would ... generate a sequence entirely of zeros. ... look like any other plaintext of similar size given a proper key. ... and in normal use does not give very much information to the attacker. ...
    (sci.crypt)
  • Re: A twist on OTP for an outstandingly secure channel?
    ... Imagine an OTP. ... character from the plaintext message are inserted where the missing 24 ... bits would be (assuming 8 bit characters. ... You've not mentioned any missing bits? ...
    (sci.crypt)