It has been frequently asked whether DES encryption is closed under composition; i.e., is encrypting a plaintext under one DES key and then encrypting the result under another key always
Trang 15.6 Is DES a group?
It has been frequently asked whether DES encryption is closed under composition; i.e., is encrypting a plaintext under one DES key and then encrypting the result under another key always equivalent to a single encryption under a single key? Algebraically, is DES a group?
If so, then DES might be weaker than would otherwise be the case; see [39] for a more complete discussion However, the answer is no, DES
is not a group [18]; this issue was settled only recently, after many years of speculation and circumstantial evidence This result seems to imply that techniques such as triple encryption do in fact increase
the security of DES
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Answers To
FREQUENTLY ASKED QUESTIONS
About Today's Cryptography
Paul Fahn
RSA Laboratories
100 Marine Parkway
Redwood City, CA 94065
Copyright (c) 1993 RSA Laboratories, a division of RSA Data Security, Inc All rights reserved
Version 2.0, draft 2f
Last update: September 20, 1993
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