I'm not especially familiar with /dev/urandom but I understand that it can "run out" of randomness and have to wait for some more to be "collected". As such it should be used sparingly, but you're tossing out over 50% of the random chars that you fetch from it.

Since you wont be using high bit ascii, you could zero out the most significant bit, mapping it 1 to 1 with the low bit ascii. This would significantly reduce the amount of randomness that you have to throw out.

This works on my x86 linux machine.... endianness might matter, but I'm not sure.

read( R, $char, 1 ) or die "Failed to read 1 char from @{[SRC]}: $!\n"
+;
vec($char, 7 , 1) = 0;  # map high-bit ascii to low-bit ascii
[download]

Update: As stefan k pointed out to me, /dev/urandom doesn't block when the entropy pool runs out. Instead, when no true random bits are available it will return pseudorandom bits instead. Its still probably a good idea to avoid pulling more bits than necessary though, just to keep the entropy pool happy and the pseudorandoms at bay ;-)

-Blake

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