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What type of cipher could give ciphertext where for example random ASCII chars between say F-z (symbols and numerals inclusive), but with only a few spaces? Frequency of chars shows some similarities to alphabetic frequency and is 200 chars in length.

I've been reading up on ciphers and have not come across any common ones that would work.

Can someone enlighten me how a seemingly random group of ASCII chars in the given range could be encoded?

Yes, I understand this is broad, so I'm asking what cipher or combination of ciphers could present these observations? I'm happy to research from a jumping off point if someone can point out any thoughts that come to mind

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    $\begingroup$ Any modern cipher operates on bytes, and not characters. You are likely either working with a classical cipher (in which case you have a wide range of cryptanalysis options) or an ASCII encoding of a modern cipher, in which case you're likely out of luck (the output of a modern cipher should be indistinguishable from random data; the ability to distinguish it would be considered a serious break in the algorithm). $\endgroup$ – Stephen Touset Oct 31 '14 at 15:05
  • $\begingroup$ Right, so ASCII is just representing a range of bytes here? That makes sense. What prominent cryptology methods return cipher text with no spaces? $\endgroup$ – Aussie Cryptocurrency Nov 1 '14 at 4:53
  • $\begingroup$ Do you want to make the ciphertext look like a classical cipher with random letters grouped like words and spaces between the words? You could use a strong symmetric cipher, convert it to Base64 encoding, then randomly add spaces throughout so it looks like words to an attacker. Though if the protocol is public, then it doesn't add any value, as the attacker will just ignore the spaces. $\endgroup$ – NDF1 Nov 1 '14 at 5:29

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