[Cryptography] block size / block cipher versus stream cipher

[Peter Gutmann]

Phillip Hallam-Baker <phill at hallambaker.com> writes:

>Of the 300+ devices I can control through the home automation system, only 
>100 or so have that degree of processing capability.

When we get an inquiry about running some crypto capability on an embedded
system, our first response is always "which CPU, how fast is it clocked, how
much RAM, and how much flash?"  The percentage of times when the answer
equates to "enough" is rare enough ("a megabyte of RAM? Wow, that's luxury,
way more than needed") that it's almost a cause for celebration.  More 
usually it's a case of figuring out what's possible given the hardware 
they've got.

In same cases I have no idea how people are doing what they're doing on
said hardware, e.g. running SSH on a 16-bit CPU.  They bank-switch the
RAM to make things fit, but how they do SHA-256 at any kind of reasonable
speed is a puzzle.

Peter.