How to limit the Bcrypt library generated random numbers range?

Question

How to limit the Bcrypt library generated random numbers range?

Zsolt Kántor 80

Hello!

I'm using the Bcrypt library BCryptGenRandom function to generate random numbers.

The BCryptGenRandom function generates UCHARs with range 0-255.

I need a range of 1-50. I know I can use the formula: rand_num % (MAX_NUM + 1 - MIN_NUM) + MIN_NUM. But this formula is not as precise as eventually setting a range and generating random numbers with that range directly from the Windows API.

Is there a way to configure and set a range using the Bcrypt interface?

Xiaopo Yang - MSFT 12,731 Reputation points Microsoft External Staff

2024-09-30T02:59:27.0566667+00:00

There are BCryptQueryContextFunctionProperty and BCryptSetContextFunctionProperty functions that may set the value of a named property for a random number generator function but there is no more information about if the system-preferred random number generator algorithm supports or not and how to do this if it supports.
Zsolt Kántor 80 Reputation points

2024-09-30T19:08:41.3433333+00:00

Thanks. Do you know, is there a way to contact the developers, or the department to give more info about these function parameters?
Zsolt Kántor 80 Reputation points

2024-10-03T21:40:55.0133333+00:00

P.S. I just found a solution to avoid bias. By using the so called "rejection sampling" method.

Your answer

Xiaopo Yang - MSFT 12,731 Reputation points Microsoft External Staff

2024-09-30T02:59:27.0566667+00:00

There are BCryptQueryContextFunctionProperty and BCryptSetContextFunctionProperty functions that may set the value of a named property for a random number generator function but there is no more information about if the system-preferred random number generator algorithm supports or not and how to do this if it supports.
Zsolt Kántor 80 Reputation points

2024-09-30T19:08:41.3433333+00:00

Thanks. Do you know, is there a way to contact the developers, or the department to give more info about these function parameters?
Zsolt Kántor 80 Reputation points

2024-10-03T21:40:55.0133333+00:00

P.S. I just found a solution to avoid bias. By using the so called "rejection sampling" method.

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How to limit the Bcrypt library generated random numbers range?

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