Is rubberhose cryptanalysis a sidechannel - formally? I recently was engaged in a discussion in Sec.SE where somebody used the term "sidechannel" to actually mean "circumvent the encryption".

By what he said it was clear, that he wanted to not bother with crypto at all and this is - in my view - not a sidechannel. However, rubberhose cryptanalysis was also mentioned and it was argued that rubberhose cryptanalysis is a sidechannel because the definition of sidechannel includes the physical implementation of the cryptosystem and the human is part of the physical implementation.

So ultimately my question:
Can rubberhose cryptanalysis formally be considered a sidechannel?



The definition of sidechannel quoted in this context:


  In cryptography, a side-channel attack is any attack based on
  information gained from the physical implementation of a cryptosystem,
  rather than brute force or theoretical weaknesses in the algorithms
  (compare cryptanalysis).


I've also seen Wikipedia:


  Attempts to break a cryptosystem by deceiving or coercing people with
  legitimate access are not typically called side-channel attacks


But I'm asking if it is allowed by the definition of sidechannel attacks to include rubberhose cryptanalysis.
Yes. A human surely is a physical component of the cryptosystem. Even if we ignore the "physical" aspect, we have 


  implementation of a cryptosystem, other than brute force or theoretical weaknesses in the algorithms.


If a key is not secure (ie. in the mind of a human who can be persuaded to divulge it), acquiring this password and bypassing the crypto would be a side-channel attack IMO.