At 12:35 PM -0800 1/28/1999, Steve Bellovin said:
For years, I had heard the story about NSA liking that instruction.
But I never understood why, until I started working on plaintext
recognizers,
and independently derived the need for it. See, for example,
http://www.research.att.com/~smb/papers/probtxt.ps.
There are other instruction types that are useful for cryptanalysts.
The CDC Star had a lovely set of vector operations under masks. And
the Harvest add-on to the IBM 7030 (Stretch), described in a book by
Buchholz ("Planning a Computer System", McGraw-Hill, 1962) was intended
for NSA as well.
For what it's worth, the same instruction was taken out of the
widely-released versions of the VAX, at the request of the NSA. Allegedly,
there were versions that had the opcode in the machine for that same
customer.
Jon
