ID 772987
Date 12/04/2020
Public

Birthday Spacing Test

Test Purpose

The test uses simulation to evaluate the randomness of groups of 24 sequential bits of the integer output of a BRNG. The test analyzes all possible groups of the kind, that is, for example, from 0 to 23 bit, from 1 to 24 bit, and so on.

First Level Test

The first level test selects at random m = 210 ”birthdays” from a ”year” of n = 224 days. Then the test computes the spacing between the birthdays for each pair of sequential birthdays. The test then uses the spacings to determine the K value, that is, the number of pairs of sequential birthdays with the spacing of more than one day. In this case K should have the distribution close to the Poisson distribution with the l = 16 parameter. The first level test determines 200 values of Kj (j = 1, 2, ..., 200). To obtain the p-value p, the test applies the chi-square goodness-of-fit test to the determined values.

The integer output lists different interpretations for each BRNG. In the table below, NB stands for the number of bits required to represent a random number in integer arithmetic, WS stands for the machine word size, in bits, used in integer random number generation.

BRNG Integer Output Interpretation
MCG31m1

Array of 32-bit integers. Each 32-bit integer uses the following bits:

0-30. NB=31, WS=32.

R250

Array of 32-bit integers. Each 32-bit integer uses the following bits:

0-31. NB=32, WS=32.

MRG32k3a

Array of 32-bit integers. Each 32-bit integer uses the following bits:

0-31. NB=32, WS=32.

MCG59

Array of 64-bit integers. Each 64-bit integer uses the following bits:

0-58. NB=59, WS=64.

WH

Array of quadruples of 32-bit integers. Each 32-bit integer uses the following bits:

0-23. NB=24, WS=32.

MT19937

Array of 32-bit integers. Each 32-bit integer uses the following bits:

0-31. NB=32, WS=32.

MT2203

Array of 32-bit integers. Each 32-bit integer uses the following bits:

0-31. NB=32, WS=32.

SFMT19937

Array of quadruples of 32-bit integers. Each 32-bit integer uses the following bits:

0-32. NB=32, WS=32.

PHILOX4X32X10

Array of 32-bit integers. Each 32-bit integer uses the following bits:

0-31. NB=32, WS=32.

ARS5

Array of 32-bit integers. Each 32-bit integer uses the following bits:

0-31. NB=32, WS=32.

The test generates the dates of the birthdays in the following way:

1. Selects the bs, bs +1, ..., bs +23 bits from the next WS-bit integer of the integer output of viRngUniformBits.

2. Treats the selected bits as a 24-bit integer, that is, the number of the date on which the next birthday takes place and thus generates a birthday.

3. The test performs the steps 1 and 2 m times to generate m birthdays taken that the year consists of n days. The legitimate values s are different for each base generator (see the table above):  0 £ s £ NB - 24.

Second Level Test

The second level test performs the first level test ten times for the fixed s. The test applies the Kolmogorov-Smirnov goodness-of-fit test with Anderson-Darling statistics to the obtained set of pj(j = 1, 2 , ..., 10). If the resulting p-value is p < 0.05 or p > 0.95, the test fails for the given s.

Final Result Interpretation

The second level test performs ten times for each 0 £ s £ NB - 24. The test computes the FAILs percentage for the failed second level tests. The final result is the minimal percentage of the failed tests FAIL = min(FAIL0, FAIL1, ..., FAILNB-24) for 0 £ s £ NB - 24. The applicable result is the value of FAIL < 50%. Thus, the test determines if it is possible to select 24 random bits from every element of the integer output of the generator.

1. The integer output for the WH generator is the quadruples of the 32-bits values (xi, yi, zi, wi). In each 32-bit value only the lower 24 bits are significant.

2. The second level test performs ten times for the xi element. Then the test computes the FAILx percentage the failed second level tests.

3. The second level test performs ten times for the yi. Then the test computes the FAILy percentage for the failed second level tests.

4. The test performs the same procedure to compute the FAILz and FAILw values.

The final result is the minimal percentage of the failed tests FAIL = min(FAILx, FAILy, FAILz, FAILw). The acceptable result is the value of FAIL < 50%.

The test determines if it is possible to select 24 random bits from the fixed element x, y, z or w for each element of the integer output of the generator.

Tested Generators

Function Name Application
vsRngUniform
not applicable
vdRngUniform
not applicable
viRngUniform
not applicable
viRngUniformBits
applicable