[Cryptography] Skylake fails on Mersenne Prime 14942209 exponent

[Henry Baker]

FYI -- The fishy part of this story is the fact that Intel claims this bug can be fixed with a "BIOS update".  If true, this is proof positive that the arithmetic unit of these Intel processors can be hacked in essentially invisible ways by (van) Nessa.

http://arstechnica.com/gadgets/2016/01/intel-skylake-bug-causes-pcs-to-freeze-during-complex-workloads/

https://communities.intel.com/mobile/mobile-access.jspa#jive-content?content=%2Fapi%2Fcore%2Fv3%2Fcontents%2F524553

Simple instructions for freezing a Skylake Processor.

Henk_NL

on Dec 14, 2015 in Processors

The people at the community over at http://www.mersenneforum.org have found what appears to be a bug in the new Skylake architecture that can freeze any system that has a Skylake processor.

The Mersenne community are a bunch of mathematicians and other folks that use Intel processors to find record prime numbers. They have found all the record prime numbers of the last 20 years.

The main website of the community is http://www.mersenne.org where they keep track of all progress in searching for a new record prime number.

Owners of Skylake systems have found out that the software package that they use to hunt for prime numbers will freeze their system if they use particular settings. Since this bug is reproducible and has been confirmed on motherboards of many different suppliers and with RAM modules of different suppliers the bug seems to be tied to the processor architecture. The bug is reproducible under Windows and Linux.

This software works perfectly normal on all other Intel processors of past generations.

Steps to freeze your Skylake system:

- Download and install Prime95 for Windows on a Skylake system from the website at http://www.mersenne.org/download/
  (If you want to familiarize yourself with the software use the readme, a background in math will be helpful, but is not needed.)
- In the menu go to 'Advanced | Test' and fill in the number 14942209 in the box labeled 'Exponent to test'
- Let the program run for some time and at some point, minutes or hours, the system will freeze.

The prime95 software does multiplications of extreme high numbers using the Fast Fourier Transformation. The implementation of these FFT's in prime95 is handcoded in assembly by George Woltman, and is the most efficient implementation available. This project runs for more than 20 years now and has always been carefully maintained. Tens of thousands of machines run this software 24 hours a day.
For optimization, different FFT sizes have been implemented in Prime95, only the FFT with length 768K freezes the Skylake.

It is my fear that like the infamous FDIV bug this issue will require a new stepping and a product recall, since this has security implications as well.

If you have a Skylake system I invite you to try out the steps above. Please post your findings here and in the mersenneforum at http://mersenneforum.org/showthread.php?t=20714

Regards,