The BCryptGenRandom function generates a random number.

Syntax

NTSTATUS WINAPI BCryptGenRandom(
  __inout  BCRYPT_ALG_HANDLE hAlgorithm,
  __inout  PUCHAR pbBuffer,
  __in     ULONG cbBuffer,
  __in     ULONG dwFlags
);

Parameters

hAlgorithm [in, out]

The handle of an algorithm provider created by using the BCryptOpenAlgorithmProvider function. The algorithm that was specified when the provider was created must support the random number generator interface.

pbBuffer [in, out]

The address of a buffer that receives the random number. The size of this buffer is specified by the cbBuffer parameter.

cbBuffer [in]

The size, in bytes, of the pbBuffer buffer.

dwFlags [in]

A set of flags that modify the behavior of this function. This parameter can be zero or the following value.

Value	Meaning
BCRYPT_RNG_USE_ENTROPY_IN_BUFFER 0x00000001	This function will use the number in the pbBuffer buffer as additional entropy for the random number. If this flag is not specified, this function will use a random number for the entropy.
BCRYPT_USE_SYSTEM_PREFERRED_RNG 0x00000002	Use the system-preferred random number generator algorithm. The hAlgorithm parameter must be NULL. Windows Vista:  This flag is not supported.

 

Return Value

Returns a status code that indicates the success or failure of the function.

Possible return codes include, but are not limited to, the following.

Remarks

The default random number provider implements an algorithm for generating random numbers that complies with the NIST SP800-90 standard, specifically the CTR_DRBG portion of that standard.

Windows Vista:  Prior to Windows Vista with Service Pack 1 (SP1) the default random number provider implements an algorithm for generating random numbers that complies with the FIPS 186-2 standard.

Depending on what processor modes a provider supports, BCryptGenRandom can be called either from user mode or kernel mode. Kernel mode callers can execute either at PASSIVE_LEVEL IRQL or DISPATCH_LEVEL IRQL. If the current IRQL level is DISPATCH_LEVEL, the handle provided in the hAlgorithm parameter must have been opened by using the BCRYPT_PROV_DISPATCH flag, and any pointers passed to the BCryptGenRandom function must refer to nonpaged (or locked) memory.

Note  The Microsoft provider in Windows Vista does not support calling at DISPATCH_LEVEL.

Requirements

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Build date: 11/19/2009