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What does modular protocol design mean? Why does TLS not have modular protocol design?
What protocols have modular design? (IPSec, SSH)

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up vote 3 down vote accepted

By the definition given there, in a modular protocol design,

each method or scheme used in the protocol (such as the use of nonces or the application of a cryptographic schemes) has a clear goal which it is proven to achieve, and sub-protocols can be replaced without re-proving the security of the remaining protocol steps.

That's also the meaning used there.

The word modular is used with the meaning it has for an engineer: the ideal of building trustable complex systems from smaller trusted and well understood components, in a way such that a component can be replaced with any other having the required, stated properties. That is actually seldom done in real complex systems.

I pass as to if and why TLS, IPSec, SSH... follow, or try to follow, the modular protocol design principle, or not.

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I would pass on that last question as well, it would be highly debatable - you cannot prove if something has a modular design or not. E.g. "has a clear goal" is highly subjective. If this question is asked for a test you should give your own opinion and reasons why you think it is or is not modular instead. Then the given reasoning behind your decission could be evaluated. – Maarten Bodewes Mar 17 '14 at 13:18

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