Breaking DES

[an41418@anon.penet.fi (wonderer)]

My understanding of how an exhaustive search on the key space
can be used to break DES is that for every key, K, D(K,Cipher)
is applied until the output matches something legible.

Say that some random string, to be thrown out, is added
to the beginning of the plain text, and that DES is applied
in cbc mode, then how could such an attack work? 

My point, I don't see how DES can be broken if the initial
block is a grabage block, and cipher block chaining is used.
Please enlighten me (gently).

One other point... is the decision to encrypt - decrypt -encrypt
when applying triple des arbitrary? Why not just encrypt
with k1 and then encrypt with k2. Isn't the effect the same?

Thanks a lot,
Wonderer
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