[RC5] What does finding the contest key prove?

Bjoern Labitzke hermit at labitzke.isdn.cs.tu-berlin.de
Sat Apr 17 01:46:44 EDT 1999


On Thu, 15 Apr 1999 Matthew_Webber at cca-int.com wrote:

| What does this tell us about a read-world cracking example, where we do NOT
| know any part of the plaintext message (we may not even know what language
| or characterset it is in)? If I have mis-understood the issue, please
| clarify!

The knowledge of a part of the text is just a convenience. For your "real
world cracking" you normally will know at least _something_ about the
decrypted thing, e.g. that it is indeed plain text or some special format
or ...  Without any such knowledge I guess it to be completely impossible
to decrypt anything. (I could e.g. create a text in a painting program and
send a picture with the text or code it in EBCDIC (extended binary coded
decimal interchange code) instead of ASCII or ...).

So let´s assume you know your searched for decrypted thing is a plain
text. Then you can just generate decrypted variants and check the results
for special constraints (like: Only character codes upto 128; later you
would check texts that fullfill that constraint against a dictionary etc.)
Your decryption would just get a bit more complex, but at least the
principle stays the same.

-- 
Bjoern Labitzke  <hermit at cs.tu-berlin.de>
   Use PGP! (Don't you use envelopes for your letters?)
   9B00 9D82 A087 DC20 7293  BB27 0174 0C15 78AB A9FE

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