Cryptographically secure random number generator

unit Random;
{
(C) Copyright Y2K Software 2004
Italy
All Rights Reserved
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Subject: SecureRandom
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}
interface
function	SecureRandom(): Integer; stdcall;
implementation
{
Generates a cryptographically secure random number.
A cryptographically secure random number has to be generated from hardware and
its sequence must not be predictable.
At least under Windows, which uses preemptive multitasking, the only reliable
and always present hardware device which changes its state in that manner, is
the inbuilt timestamp counter of Pentium IV+ processors. Instead of the TSC, we
also could try to access the Sound Blaster device and read the white noise
generated by the microphone/line input, but this could be unreliable, since a
plugged and stable sound source could give reproduceable patterns.
Since the TSC value could range from 0 to 0FFFFFFFFh in eax, we need to scramble
it a bit, to get an uniform distribution of the bits all over.
This random number generator returns a scrambled TSC value and does not need to
be seeded. Actually, the seed is taken each time from the processor, and the
overall speed is noticeably higher than any other known random number generator.
}
function	SecureRandom(): Integer; stdcall;
asm
	push	ebx
	rdtsc								// read timestamp counter (seed in eax:edx)
	mov		ebx,127773
	xor		edx,edx
	div		ebx
	mov		ecx,eax
	mov		eax,16807
	mul		edx
	mov		edx,ecx
	mov		ecx,eax
	mov		eax,2836
	mul		edx
	sub		ecx,eax
	mov		eax,ecx
  pop		ebx
end;
end.

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