QUOTE (kzt @ Jul 14 2008, 07:31 AM)

It's an interesting approach. I've seen some articles discussing doing reversible block cypher systems to avoid some side channel attacks based on power consumption. However encryption is computationally a lot easier than breaking encryption.
The italicized limitation in "The existence of logically reversible automata suggests that physical computers might be made thermodynamically reversible, and hence capable of dissipating an arbitrarily small amount of energy per step if operated sufficiently slowly" suggest some minor issues if you are intending to perform an exercise that requires 1.7 * 10^38 operations on average and plan on success before the sun becomes a red giant. And that's 128 bits, it's perfectly possible to do a 1024 bit or longer crypto system.
And storage of 1.7*10^38 copies of the message with the current key try sounds like it might occupy a lot of storage too.
This might be better than the previous one:
hereQuote concerning your point, pg. 503:
"The second objection, that even logically reversible data-processing operations
cannot be accomplished in a thermodynamically reversible fashion, I believe has
largely been overcome by explicit models, proposed by myself and others, of physical
mechanisms, which obey the accepted conventions of thermodynamic or mechanical
thought experiments, and which accomplish reversible computation at zero cost (socalled
ballistic computers, such as the Fredkin-Toffoli hard sphere model; Fredkin &
Toffoli, 1982), or at a per-step cost tending to zero in the limit of slow operation (socalled
Brownian computers, discussed at length in my review article; Bennett, 1982).
These questions were revisited and vigorously debated in an exchange in Physics
Reviews & Letters (Porod, Grondin, Ferry, & Porod, 1984). Of course, in practice,
almost all data processing is done on macroscopic apparatus, dissipating
macroscopic amounts of energy far in excess of what would be required by
Landauer’s principle. Nevertheless, some stages of biomolecular information
processing, such as transcription of DNA to RNA, appear to be accomplished by
chemical reactions that are reversible not only in principle but in practice."