API based random number generator for VB6

[Ben321]

The built-in one in VB6 isn't all that good at creating highly random numbers (at least for cryptographic purposes). The crypto API is much better at this. Below is some sample code that you can put in a module that will let you use the Microsoft CryptoAPI random number generator.

Private Declare Function CryptAcquireContext Lib "advapi32.dll" Alias "CryptAcquireContextA" (ByRef phProv As Long, ByVal pszContainer As String, ByVal pszProvider As String, ByVal dwProvType As Long, ByVal dwFlags As Long) As Long
Private Declare Function CryptReleaseContext Lib "advapi32.dll" (ByVal hProv As Long, ByVal dwFlags As Long) As Long
Private Declare Function CryptGenRandom Lib "advapi32.dll" (ByVal hProv As Long, ByVal dwLen As Long, ByRef pbBuffer As Any) As Long

Private Const PROV_RSA_FULL As Long = 1
Private Const VERIFY_CONTEXT As Long = &HF0000000


Public Function GenRandom(ByVal ptrMemory As Long, ByVal lenMemory As Long)
    Dim hProv As Long
    CryptAcquireContext hProv, vbNullString, vbNullString, PROV_RSA_FULL, VERIFY_CONTEXT
    CryptGenRandom hProv, lenMemory, ByVal ptrMemory
    CryptReleaseContext hProv, 0
End Function

I use actual numerical pointers passed ByVal, instead of something like "ByRef MyArrayFirstCell As Byte" because the ByRef alternative would require passing it something specifically Byte-type and if I had a Long-type array (or any other type) it wouldn't work, and I can't use ByRef As Any with VB functions (it only works with DLL functions). This allows it to access ANY kind of variable to be used for holding the memory, with the one caveat that you will need to use VarPtr to get the actual memory address of the variable, in order to pass it to this function.