Date: Sun, 01 Oct 1995 14:30:50 +0200 From: Mark Murray <mark@grondar.za> To: Bruce Evans <bde@zeta.org.au> Cc: hackers@freebsd.org, mark@grondar.za Subject: Re: How to get to the hardware? Message-ID: <199510011230.OAA04285@grumble.grondar.za>
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> This is much the same as calling microtime() or gettimeofday() and > and getting "random" bits from (tv_usec & 1) and (tv_usec & (1 << 7)) > (here 7 is an approximation to (1e6 / TIMER_FREQ) * 8)). These bits > are actually extremely non-random. They can be predicted as accurately > as the current time if their values at a previous time are known. Thus > they are insignificantly more random than the current time in > microseconds. More investigation is required to find a source of > random bits. I suspected so. I think the code had better stay out as time is already used. More questions; where would be a good place to call these: (I am having a large problem with the add_interrupt_randomness one) * Exported interfaces ---- input * ============================== * * The two current exported interfaces for gathering environmental * noise from the devices are: * * void add_keyboard_randomness(unsigned char scancode); * void add_interrupt_randomness(int irq); * * The first function uses the inter-keypress timing, as well as the * scancode as random inputs into the "entropy pool". * * The second function uses the inter-interrupt timing as random * inputs to the entropy pool. Note that not all interrupts are good * sources of randomness! For example, the timer interrupts is not a * good choice, because the periodicity of the interrupts is to * regular, and hence predictable to an attacker. Disk interrupts are * a better measure, since the timing of the disk interrupts are more * unpredictable. The routines try to estimate how many bits of * randomness a particular interrupt channel offers, by keeping track * of the first and second order deltas in the interrupt timings. BTW - would you be prepared to review this code before committal? M -- Mark Murray 46 Harvey Rd, Claremont, Cape Town 7700, South Africa +27 21 61-3768 GMT+0200 Finger mark@grumble.grondar.za for PGP key
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