A classy cryptographic PRNG

[David Roberts]

What I mean, of course, is a Cryptographic PRNG as a Class.

The internal function RtlGenRandom is used and since it flies below the CrytoAPI radar we can avoid all the usual initialization provided, of course, that we don't need the CryptoAPI for anything else. More details in an earlier Source Code thread post #3 here. The error checking there is PBWin based and stripped out here. The function coded there is fine but multiple calls will see a library being loaded in and out like a yoyo. We can code to avoid that but a Class comes into its own for multiple calls.

Usage: RandCrypto.Bytes( n, flag ) where n is the number of bytes required and flag = 0 will generate a binary string of length n. With flag <> 0 a hex string of length 2n will be generated.

' CRandCrypto.inc
 
Declare Function RtlGenRandom( RandomBuffer As Byte, ByVal RandomBufferLength As Dword ) As Long
 
Class CRandCrypto
 
  Instance hLib, hProc As Dword
 
  Class Method Create
    hLib = LoadLibrary( "advapi32.dll")
    hProc = GetProcAddress(hLib, "SystemFunction036")
  End Method
 
  Class Method Destroy
    FreeLibrary hLib
  End Method
 
  Interface IRandCrypto: Inherit IUnknown
 
    Method Bytes( ByVal BinarySize As Dword, ByVal Flag As Long ) As String
      Local i As Long
      Dim BinaryByte( )	As Byte
      Dim HexByte( ) As String * 2
      Local hexString	As String
 
      ReDim BinaryByte( BinarySize - 1 ) As Byte
 
      Call Dword hProc Using RtlGenRandom( BinaryByte(0), ByVal BinarySize )
 
      If Flag = 0 Then
        Method = Peek$( VarPtr( BinaryByte(0) ), BinarySize )
      Else
      	hexString = Space$( 2 * BinarySize )
      	ReDim HexByte( BinarySize - 1 ) As String * 2 At StrPtr( hexString )
      	' Overlay hexString with HexByte()
      	For i = 0 To BinarySize - 1
      		HexByte( i ) = Hex$( BinaryByte(i), 2 )
      	Next
      	Method = hexString
      End If
    End Method
 
  End Interface
 
End Class

Example use.

#Compile Exe
#Optimize speed
#Dim All
#Tools Off
#Register None

#Include "WIN32API.INC"

%NOMMIDS  = 1
%NOGDI    = 1

#Include "CRandCrypto.inc"

Global RandCrypto As IRandCrypto ' to give access to method anywhere in application

Function PBMain

  Local i As Long

  Let RandCrypto = Class "CRandCrypto"
  
  ? RandCrypto.Bytes(16,1)
    
  RandCrypto = Nothing
  
  #If %Def(%Pb_Cc32)
    WaitKey$
  #EndIf

End Function