[Cryptography] Finding undocumented opcodes

[Dave Horsfall]

On Sat, 5 Aug 2017, Bob Wilson wrote:

> With all the apparently random opcodes I saw generated, on different 
> processors, by students in my CS classes and by the programmers I 
> managed in industry, it is hard to believe there can be many (on those 
> processors) that have not already beet tested!

The classic undocumented instruction set would have to be that of the 
Z-80, as in e.g. http://www.z80.info/z80undoc.htm.  I can't believe that 
people went to so much trouble to explore every bit pattern!

But speaking of weird opcodes, there is the "population count" instruction 
on the CDC series; it counted the number of "1" bits in a (60-bit) word, 
and was known as the "NSA Instruction" (at first glance, it appeared to 
have no use at all, but Seymour Cray wouldn't have included it for no 
reason).

-- 
Dave Horsfall DTM (VK2KFU)  "Those who don't understand security will suffer."