Re: [BORKED] IACR eprint: SHADOW NUMBERS PUBLIC KEY ENCRYPTION

From	Peter Pearson <pkpearson@nowhere.invalid>
Newsgroups	sci.crypt
Subject	Re: [BORKED] IACR eprint: SHADOW NUMBERS PUBLIC KEY ENCRYPTION
Date	2021-10-05 20:32 +0000
Message-ID	<is3r38FtujjU1@mid.individual.net> (permalink)
References	(2 earlier) <sj9p51$5mq$1@gioia.aioe.org> <irrcgkFam13U1@mid.individual.net> <sjfrge$94g$1@gioia.aioe.org> <is38q9Fq8ouU1@mid.individual.net> <sji8ra$qh4$1@gioia.aioe.org>

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For reference sake, message m is encrypted to produce ciphertext e
by e = (m * Sara) mod Bra.

On Tue, 5 Oct 2021 14:26:32 -0500, 711 Spooky Mart <711@spooky.mart> wrote:
[snip]
>
> Thanks for cracking at this. Do you notice any more ways to break this
> system?
>

First, note that cryptologists use a much broader definition of "break"
than simply "I can find the plaintext from a single ciphertext."  One
demanding example, for example, is: given a paintext and two ciphertexts,
one of which will decrypt to that plaintext, it should be computationally
infeasible to guess, with probability greater than 1/2, which ciphertext 
works.  (Not all interesting ciphers meet that demand, but it illustrates
the neighborhood in which discussion takes place.)

Advice of a more practical nature: the field or ring in which your
encryption and decryption happen has far more "structure" than is
required to encrypt and decrypt, and that extra structure, while it
does nothing for you, is useful to the attacker.  The fact that
encrypt(m1+m2) = encrypt(m1) + encrypt(m2) mod Bra would worry me
a lot.

-- 
To email me, substitute nowhere->runbox, invalid->com.

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IACR eprint: SHADOW NUMBERS PUBLIC KEY ENCRYPTION 711 Spooky Mart <711@spooky.mart> - 2021-09-30 12:43 -0500
  Re: IACR eprint: SHADOW NUMBERS PUBLIC KEY ENCRYPTION Peter Pearson <pkpearson@nowhere.invalid> - 2021-10-01 15:52 +0000
    Re: IACR eprint: SHADOW NUMBERS PUBLIC KEY ENCRYPTION 711 Spooky Mart <711@spooky.mart> - 2021-10-02 05:41 -0500
    Re: IACR eprint: SHADOW NUMBERS PUBLIC KEY ENCRYPTION 711 Spooky Mart <711@spooky.mart> - 2021-10-02 09:08 -0500
      Re: IACR eprint: SHADOW NUMBERS PUBLIC KEY ENCRYPTION Peter Pearson <pkpearson@nowhere.invalid> - 2021-10-02 15:34 +0000
        Re: [BORKED] IACR eprint: SHADOW NUMBERS PUBLIC KEY ENCRYPTION 711 Spooky Mart <711@spooky.mart> - 2021-10-04 16:25 -0500
          Re: [BORKED] IACR eprint: SHADOW NUMBERS PUBLIC KEY ENCRYPTION Peter Pearson <pkpearson@nowhere.invalid> - 2021-10-05 15:20 +0000
            Re: [BORKED] IACR eprint: SHADOW NUMBERS PUBLIC KEY ENCRYPTION 711 Spooky Mart <711@spooky.mart> - 2021-10-05 14:26 -0500
              Re: [BORKED] IACR eprint: SHADOW NUMBERS PUBLIC KEY ENCRYPTION Peter Pearson <pkpearson@nowhere.invalid> - 2021-10-05 20:32 +0000

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