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From: tanveer on 6 Dec 2009 19:07
Hi all,

I am new to this cryptography world and getting interest in it.
Recently I came through a software where it can decipher a
monoalphabetic substitution cipher.
In theory it says that:
The SCBSolvr essentially does this very thing. It begins with a random
KEY, which is the 26 letters of the alphabet arranged in any order.
It then decrypts the ciphertext (Ct) according to this KEY and 'looks'
at the result. The program then makes a one letter change to the KEY,
by exchanging one of the letters with the letter next to it (flips a
pair of letters).
It decrypts the ciphertext with this KEY and 'looks' at the result.
The program then decides, 'better or worse.'

http://www.secretcodebreaker.com/scbsolvr.html

but now my question is after an initial random guess of key when we
decipher the cipher text how to verify how close it is to the original
plain text as a intruder don't know the plaintext. because the machine
is doing this deciphering not human.

Thanks in advance.
From: Ilmari Karonen on 7 Dec 2009 02:58
On 2009-12-07, tanveer <tanveer.chowdhury(a)gmail.com> wrote:
>
> but now my question is after an initial random guess of key when we
> decipher the cipher text how to verify how close it is to the original
> plain text as a intruder don't know the plaintext. because the machine
> is doing this deciphering not human.

It's probably looking at letter and letter pair (or possibly even
triplet) frequencies and comparing those with a statistical model of
English text. That the usual way of doing it, at least for computer
implementations.

--
Ilmari Karonen
To reply by e-mail, please replace ".invalid" with ".net" in address.
From: Globemaker on 8 Dec 2009 05:33
On Dec 6, 2:07 pm, tanveer <tanveer.chowdh...(a)gmail.com> wrote:
> Hi all,
>
> I am new to this cryptography world and getting interest in it.
> Recently I came through a software where it can decipher a
> monoalphabetic substitution cipher.
Seap Wp. Hivin0p,

Y0u gam cen wy bp0cpaw j0p a1btapenig vupvninuni0m an :
tnnb://cpeeba1btapen.p10cvb0n.g0w/
In iv jpee ams j1elip1e. Tahe jum npyimc n0 peas ntiv. 3eab gpybn0 gam
pe peas py a npaimes bepv0m xuigb1y, pun v1031y py 1aywem.

C10pewabep, Segewpep 8, 2008, B0ma, Ta3aii, UVA
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