Encrypting same data with many keys...

[Ray Arachelian]

What are the dangers of taking a small block of data - say upto 1K in
size, then producing many files, each being the same data encrypted by
other keys? 

i.e.:
	Plain data: 1K in size or smaller
	
	File 1: Data encrypted with Key1
	File 2: Data encrypted with Key2
	File 3: Data encrypted with Key3
	File 4: Data encrypted with Key4
	File 5: Data encrypted with Key5
	File 6: Data encrypted with Key6
	File 8: Data encrypted with Key8
		....
	File N: Data encrypted with KeyN

A known plaintext attack won't help you to break the keys unless you have
one of the eight keys, but will having many keys that encrypt the same
data significanltly weaken the security of that tiny chunk of data?

And no, I don't mean, there's N keys so the odds of brute forcing the data
is now N times easier.  Assume we're using 128 bit Blowfish/Idea or
better, and discarding weak keys.  Are there any differential or other
cryptanalysis methods to use the eight resulting cyphertexts to get at the
data other than brute forcing it if you don't know any of the keys?

What if instead of using a private key cypher, we used a public key
cypher?  Would that make any difference in attack methods?

The data won't contain any text, or identifiers (i.e "GIF89" in GIF files,
"MZ" in wintel executables, etc...)  known or guessable to the attacker...

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