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Re: Researches in quantum computing seem to progress only extremely slowly

Cross-posted to 2 groups.

Followups directed to: comp.programming

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On 2015-09-01, Mok-Kong Shen <mok-kong.shen@t-online.de> wrote:
> Am 01.09.2015 um 16:23 schrieb Kaz Kylheku:
>> On 2015-09-01, Mok-Kong Shen <mok-kong.shen@t-online.de> wrote:
>>>
>>> http://www.theplatform.net/2015/07/22/google-sees-long-expensive-road-ahead-for-quantum-computing/
>>>
>>> The article doesn't seem to be much more optimistic than reports on
>>> other well-known currently running big projects of physics, e.g.
>>> nuclear fusion.
>>>
>>> This means that there is in the foreseeable future no danger of the
>>> currently used asymmetric encryption schemes being broken by quantum
>>
>> Phew! Your python-PRNG-based security schemes is safe!
>
> In another thread I asked you to provide a reference to support your
> claim there but you still kept silence on that!

The reference is that the entire sequence coming out of a PRNG only contains as
much information as its seed. For instance, a 32 bit seed means that the
entire sequence contains at most 32 bits of information. (This is true even if
the PRNG is a good one with a big state vector, and a long period.)
The seed is effectively a selector which chooses one of 2**32 different
sequences.

If you generate, say, a 1024 bit key with a PRNG that is seeded with, say, 64
bits, then it's effectively a 64 bit key. Given a known plaintext and
ciphertext pair, we only have to search a 64 bit space to recover the key.
The encryption algorithm might be RSA-1024, but it's not really because
of the weak seeding; it is a misleading lie and "security through obscurity"---
you hope that the scheme is secure because the attacker doesn't know
that a particular weekly-seeded PRNG was used.

Do you also require a reference for the claim that water is wet?

Moreover, a PRNG may have other problems with it even if the state space is
large enough and the seed has enough entropy for the given crypto use.


About stream ciphers; yes they are lot like PRNG's where the encryption key
is a seed. The seed has an appropriate size to achieve a given security
level, and no misleading claims are made about the space from which it
is chosen. If we use a 256 bit stream cipher, but seed it with a PRNG
that uses a 32 bit seed, we have the same problem: the cipher is effectively
32 bit (but the users are duped into believing that it's the 256
bit real thing).

No, key entropy does not dilute with the increasing length of an encrypted
message.  Suppose we have a very good symmetric cipher against which there is
no known attack other than brute force.  Suppose the attacker knows all of our
plaintext.  It does not help the attacker to have a large quantity of known
plaintext.  In fact using more plaintext/ciphertext pairs only slows down the
brute force search. For each key which is tried, it is enough to try a single
known ciphertext/plaintex pair.

Encryption does not work by spreading key entropy across a message.
The entropy in a key is important, however, for obvious reasons:
more entropy means a larger key space.

If an encryption algoirthm requires keys with a certain amount of entropy,
and is given less entropy, it is incompetently implemented. Its security
is weakened.

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Thread

Researches in quantum computing seem to progress only extremely slowly Mok-Kong Shen <mok-kong.shen@t-online.de> - 2015-09-01 13:09 +0200
  Re: Researches in quantum computing seem to progress only extremely slowly Kaz Kylheku <kaz@kylheku.com> - 2015-09-01 14:23 +0000
    Re: Researches in quantum computing seem to progress only extremely slowly Mok-Kong Shen <mok-kong.shen@t-online.de> - 2015-09-01 20:00 +0200
      Re: Researches in quantum computing seem to progress only extremely slowly Kaz Kylheku <kaz@kylheku.com> - 2015-09-01 18:43 +0000
        Re: Researches in quantum computing seem to progress only extremely slowly Mok-Kong Shen <mok-kong.shen@t-online.de> - 2015-09-02 10:56 +0200
          Re: Researches in quantum computing seem to progress only extremely slowly William Unruh <unruh@invalid.ca> - 2015-09-02 16:24 +0000
            Re: Researches in quantum computing seem to progress only extremely slowly Mok-Kong Shen <mok-kong.shen@t-online.de> - 2015-09-03 05:58 +0200
              Re: Researches in quantum computing seem to progress only extremely slowly Mok-Kong Shen <mok-kong.shen@t-online.de> - 2015-09-04 18:34 +0200
                Re: Researches in quantum computing seem to progress only extremely slowly William Unruh <unruh@invalid.ca> - 2015-09-04 18:32 +0000
                Re: Researches in quantum computing seem to progress only extremely slowly Mok-Kong Shen <mok-kong.shen@t-online.de> - 2015-09-05 20:50 +0200
                Re: Researches in quantum computing seem to progress only extremely slowly Mok-Kong Shen <mok-kong.shen@t-online.de> - 2015-09-28 11:30 +0200
                Re: Researches in quantum computing seem to progress only extremely slowly Mok-Kong Shen <mok-kong.shen@t-online.de> - 2015-10-08 18:28 +0200
  Re: Researches in quantum computing seem to progress only extremely slowly "Chris M. Thomasson" <nospam@nospam.nospam> - 2015-09-01 13:23 -0700
    Re: Researches in quantum computing seem to progress only extremely slowly Mok-Kong Shen <mok-kong.shen@t-online.de> - 2015-09-02 11:04 +0200
  Re: Researches in quantum computing seem to progress only extremely slowly Robert Wessel <robertwessel2@yahoo.com> - 2015-09-02 02:22 -0500

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