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From: Andre MariŽn (andre.marien_at_ubizen.com)
Date: Thu Jan 09 2003 - 03:47:55 CST
Tom Arseneault wrote:
> As for the usage of the key in encryption and decryption, public key
> encryption is very compute intensive so while you could do bulk encryption
> with it whould be very slow.. The usual way things are done is that a
> symmetrical encryption will be used to encrypt a document (DES, 3DES,
> BLOWFISH, etc..., very fast) with a randomly generated key and that key is
> then encrypted with the public key of the person you sending the document
> to. Since only he, through the use of his private key, can decrypt the
> symmetrical key only he can decrypt the document.
Please do not use public key encryption for bulk data, even if
you accept the long times. It is a bad idea. If there are n
possible messgaes, it only takes at most n trials to decrypt
the message, no matter your key size (if the encrypting key is known;
typically it is the public key and it is known).
This problem is justification in itself to have a two stage system
for encryption of bulk data.
(there is someone at counterpane that can explain it in more detail ;-)