Score:1

Implementation of a "running hash" on constrained devices

tr flag

The following link documents a proposal for a TLS-like alternative for constrained devices. https://github.com/lake-wg/edhoc/blob/4f56898808989e449cc412a8b136674202a0ddce/draft-ietf-lake-edhoc.md#implementation-considerations-impl-cons

Unlike TLS1.3, the proposal does not make use of running hashes. Citing the proposal:

The sequence of transcript hashes in EHDOC (TH_2, TH_3, TH_4) do not make use of a so-called running hash, this is a design choice as running hashes are often not supported on constrained platforms.

Why is it infeasible to implement a running hash in a constrained environment?

I can only think of an increased memory requirement to keep the state and input buffer, but it doesn't seem worse than hashing protocol messages separately in the context of such a protocol.

poncho avatar
my flag
My guess (and this is a guess, hence this is a comment, not an answer) is that some low end platforms don't have the crypto API's available to do it; they have an API to do a full hash, but not a running one...
Marc Ilunga avatar
tr flag
@poncho, thanks for the feedback. Seems like a reasonable explanation. Which makes me curious now as to why? Could it be the need for code/area efficiency? As in, more API would require more code etc? ¯\_(ツ)_/¯
poncho avatar
my flag
My guess: the buy their cryptolibrary from a third party, and that library doesn't provide the necessary functionality. I've seen this sort of thing too often in my day job...
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