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4/8/2010

This function fills a buffer with random bytes.

Syntax 

BOOL CRYPTFUNC CryptGenRandom( 
  HCRYPTPROV 
hProv,
  DWORD 
dwLen, 
  BYTE* 
pbBuffer
);

Parameters

hProv

[in] An HCRYPTPROVhandle to a cryptographic service provider created by a call to CryptAcquireContext.

dwLen

[in] The length, in bytes, of the random data to generate.

pbBuffer

[in, out] Pointer to the buffer containing the random data. This buffer must be at least dwLenbytes in length.

On input, the application must fill the buffer with data to use as an auxiliary random seed. The cryptographic service provider will use this data to further randomize its internal seed.

Return Value

TRUE indicates success. FALSE indicates failure. To get extended error information, call the GetLastErrorfunction.

The following table shows the common values for the GetLastErrorfunction. The error values prefaced by NTE are generated by the particular cryptographic service provider you are using.

Value Description

ERROR_INVALID_HANDLE

One of the parameters specifies an invalid handle.

ERROR_INVALID_PARAMETER

One of the parameters contains an invalid value. This is most often an illegal pointer.

NTE_BAD_UID

The hProvparameter does not contain a valid context handle.

NTE_FAIL

The function failed in some unexpected way.

Remarks

The data produced by this function is cryptographically random. It is far more random than the data generated by the typical random number generator, such as the one shipped with your C compiler.

This function is often used to generate random initialization vectors and salt values.

All software random number generators work in fundamentally the same way. They start with a random number, known as the seed, and then use an algorithm to generate a pseudo-random sequence of bits based on it. The most difficult part of this process is to get a seed that is truly random. This is usually based on user input latency, or the jitter from one or more hardware pieces.

If your OS design does not include the Cryptography Services feature, you can use CeGenRandomto generate random numbers. CeGenRandomis only available if the OS design includes the File System feature.

Example Code

Requirements

Header wincrypt.h
Library coredll.lib
Windows Embedded CE Windows CE 2.10 and later
Windows Mobile Windows Mobile Version 5.0 and later

See Also