[Cryptech Tech] ent for rosc entropy in the Xilinx FPGA

[Joachim Strömbergson]

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Russ Housley wrote:
> The FIPS 140 testing includes the Consecutive Value Test.  It
> compares consecutive blocks within the random data.  The test fails
> if the blocks are equal.  Looking for repeated bytes in the first
> 40,000,000 bits in the provided data showed a few more failures than
> I expected.  So, I took a look at each place in the file where this
> this happened, and I found a pattern that is troublesome.
> 
> See these small chunks (in hex) from rosc_data.bin...
> 
> ... 79 f4 3e 1c 3e 3e fd b7 63 9b f2 1a ...

I've done some discussions with a colleague and done some testing.
The pattern we are seeing should appear p(1/2**16) i.e. with a frequency
0.000015.

I tested this by dumping out 450 MByte from
/dev/random in OSX and gets:

[~/tmp]$ tribytes.py testdata.bin
Analyzed file: testdata.bin
Total number of bytes: 498135040
Number of patterns:    7460
Frequency in file:     0.000015

That is, the frequency found in the rosc entropy which is 0.000014,
which is very close to expected frequency in random data.

- -- 
Med vänlig hälsning, Yours

Joachim Strömbergson - Alltid i harmonisk svängning.
========================================================================
 Joachim Strömbergson          Secworks AB          joachim at secworks.se
========================================================================
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