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Eccouncil 212-81 Exam - Topic 5 Question 7 Discussion

If the round function is a cryptographically secure pseudorandom function, then ___________ rounds is sufficient to make the block cipher a pseudorandom permutation.
D) 3
A) 2
B) 15
C) 16

Eccouncil 212-81 Exam - Topic 5 Question 7 Discussion

Actual exam question for Eccouncil's 212-81 exam
Question #: 7
Topic #: 5
[All 212-81 Questions]

If the round function is a cryptographically secure pseudorandom function, then ___________ rounds is sufficient to make the block cipher a pseudorandom permutation.

Show Suggested Answer Hide Answer
Suggested Answer: D

3

https://en.wikipedia.org/wiki/Feistel_cipher

Michael Luby and Charles Rackoff analyzed the Feistel cipher construction, and proved that if the round function is a cryptographically secure pseudorandom function, with Ki used as the seed, then 3 rounds are sufficient to make the block cipher a pseudorandom permutation, while 4 rounds are sufficient to make it a 'strong' pseudorandom permutation (which means that it remains pseudorandom even to an adversary who gets oracle access to its inverse permutation). Because of this very important result of Luby and Rackoff, Feistel ciphers are sometimes called Luby--Rackoff block ciphers.


by Leslie at Aug 20, 2022, 07:46 AM

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Cecilia
10 months ago
I heard 15 rounds is actually the sweet spot.
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Jospeh
10 months ago
3 rounds? That can't be right...
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Leanna
10 months ago
Wait, are we sure 16 is enough? Seems high.
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Natalya
10 months ago
Definitely agree with that! 16 rounds is solid.
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Natalya
11 months ago
I think 16 rounds is the standard for security.
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Julie
11 months ago
I’m really uncertain here; I thought 3 rounds were way too few, but I can't remember the exact number that is recommended.
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Fernanda
11 months ago
I’m leaning towards 16 rounds too, but I remember some discussions about how even 10 could be enough for certain algorithms.
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Charlette
11 months ago
I feel like 15 rounds might be a common answer in practice questions, but I can't recall if that's for all block ciphers or just specific ones.
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Adelina
11 months ago
I think I remember reading that 16 rounds is often considered sufficient for security in block ciphers, but I'm not entirely sure.
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Helga
11 months ago
Okay, let me think this through. Virtual environments help keep my Python projects separate and avoid issues with incompatible packages, right? I'll make sure to choose the two most relevant options.
upvoted 0 times
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Chandra
11 months ago
Okay, I know SELinux needs to be in enforcing mode, so I'll scan the config file for that.
upvoted 0 times
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