Encrypting same data with many keys...

nospam-seesignature at ceddec.com nospam-seesignature at ceddec.com
Wed Aug 13 14:36:30 PDT 1997

On Wed, 13 Aug 1997, Ray Arachelian wrote:

> On Wed, 13 Aug 1997 nospam-seesignature at ceddec.com wrote:
> In terms of padding does it matter WHERE I put the padding info?  Is it
> better to put random stuff in the front or at the end?  The reason I ask,
> say that you're going to encrypt an N byte block where N is bigger than
> your block cypher's key size?
> If my intution is correct, and you have the same data encrypted with many
> keys (even RSA) but have the padding at the end, the 1st block would still
> be breakable.  I suppose putting the data at the end would also result in
> the same kind of problem, though it might be a bit harder to attack than
> putting the data 1st...
> Would it not make sense to scatter the random padding throughout the
> block?   How is this normally done?  Front?  Back?  Middle?  Scattered?

The location does not matter.  The standard RSA libs place the padding at
the front - it is one of those PKCS specifications.

You would simply need to break the conventional key down to a few bytes
smaller than the modulus size, so each would be padded with a few random

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