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From: "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com>
Newsgroups: sci.crypt
Subject: Re: an scos2 test...
Date: Tue, 30 Jul 2024 21:08:34 -0700
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On 7/27/2024 12:20 AM, Richard Harnden wrote:
> On 27/07/2024 01:20, Ben Bacarisse wrote:
>> "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> writes:
>>
>>> On 7/26/2024 2:32 AM, Richard Harnden wrote:
>>>> On 26/07/2024 06:15, Chris M. Thomasson wrote:
>>>>> On 7/25/2024 8:54 PM, Rich wrote:
>>>>>> scos2 65 33
>>>>>>
>>>>>> 0ZGS XB sJ@ lH ~i<8/
>>>>>
>>>>> For some reason I am getting a plaintext of:
>>>>>
>>>>> ~U9o My 8/g v[ Ym9\;
>>>>>
>>>>> using my impl and Rich's original scos2 impl.
>>>> The key is wrong, try:
>>>> 28 60
>>>> 0ZGS XB sJ@ lH ~i<8/
>>>
>>> Indeed it works like a charm. It had to be a "key issue". Humm... That
>>> would be a fun test? Try different keys and log "readable" results wrt
>>> decrypted plaintext? ;^)
>>
>> Yes.  Somewhere I have a program that just tries all keys.  I was going
>> to get it to stop when English (or C) letter frequencies were found but
>> it turned out simpler just to eyeball the output.  As a human, you can
>> spot a decrypt a mile off and, if I remember correctly, SCOS has "close
>> decrypts" that I could spot but which would look, statistically, like
>> plaintext.
>>
> 
> I have one that tries to find consistent incr's in 3-letter word-blocks. 
>   Hopefully the correct base and incr bubble to the top.
> 
> It's better with longer texts, but ...
> 
> $ cat test.scos
> 0ZGS XB sJ@ lH ~i<8/
> 
> $ ./decode_scos test.scos | ./scos
> ./decode_scos: Not sure, but ...
>  > -28 -60
>  > Yes, it can be read.
> 
>  > -71 -60
>  > =~Bu :C ]}, [~ A~}#s
> 
> 

The key space is not that massive, so it can be brute forced for sure. 
However, its interesting wrt the plaintext. What if the plaintext is 
generated from a random source?