[Cryptography] Finding undocumented opcodes

[Thierry Moreau]

On 06/08/17 03:54 AM, Dave Horsfall wrote:
>
> 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).
>

This is a speedup instruction for the Berlekamp-Massey algorithm that 
recovers the parameters and state of LFSR-based ciphers, which were 
present in the military crypto "culture" (hearsay). This instruction is 
present in a high end DSP architecture that I reviewed for RSA 
acceleration suitability.

- Thierry