I once read a usenet thread discussing this issue - Bruce Schneider posted and said that multiple encryption with the same algorithm could actually weaken the encryption if there was a defect in that algorithm. He gave an explanation which I can't recall.
I do recall that the conclusion of the posters in the thread seemed to be that, if using multiple encryption, it is best to use two different algorithms from two different sources to avoid the abovementioned multiplicative effect of a defect in either one of the algorithms.
You can probably find this thread on google groups if you search for Bruce Schneider's posts - perhaps post a link if you can find it.
I do recall that the conclusion of the posters in the thread seemed to be that, if using multiple encryption, it is best to use two different algorithms from two different sources to avoid the abovementioned multiplicative effect of a defect in either one of the algorithms.
You can probably find this thread on google groups if you search for Bruce Schneider's posts - perhaps post a link if you can find it.
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