Timeline for Why does consecutive permutations or consecutive substitutions not enhance security?
Current License: CC BY-SA 3.0
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| Mar 15, 2015 at 14:20 | comment | added | fgrieu♦ | @PaŭloEbermann: a public/unkeyed permutation/substitution is not, by itself, safe. It can lead to safety of a cryptographic algorithm embedding it (and that's the context of the question). In that context, for some permutation/substitution and cryptographic algorithm, iterating the permutation/substitution can increase safety, as illustrated in the second paragraph of my answer. While the example detailed is contrived, I could construct a natural one, with a simple public/unkeyed permutation/substitution increasing security when iterated. | |
| Mar 15, 2015 at 13:20 | comment | added | Paŭlo Ebermann | @fgrieu I guess this could be meant to apply to unkeyed permutations/substitutions only? | |
| Mar 15, 2015 at 12:36 | comment | added | fgrieu♦ | I disagree with the answer, which as written would allow to wrongly conclude that 3DES is no safer than DES, on the grounds that 3DES is 3 times DES performed in sequence and is a permutation (or substitution) since DES is one. $\;$ Also I'm reading the question as about the different assertion that iterating the same permutation (or substitution) does not increase security (which is wrong). | |
| Mar 15, 2015 at 5:45 | history | answered | cpast | CC BY-SA 3.0 |