Comments on Effective Perl by Joseph N. Hall: Tip: Creating a String of Random Hex Digits

my $0,2perl -e 'print ((0..9,a..f)[rand(16)]) for ...

2006-02-19T01:20:00.000-08:00

my $0,2

perl -e 'print ((0..9,a..f)[rand(16)]) for 1..32'

Of course it's a random string. However, it doesn'...

2006-02-03T21:02:00.000-08:00

Of course it's a random string. However, it doesn't have 128 bits of entropy.

It's also unlikely that glomming together hex digits resulting from repeated calls to rand will really produce 128 bits of randomness - because the pseudorandom number generator on your favorite platform is probably not cryptographically strong.

md5_hex(rand) will not give you a string of random...

2006-02-03T20:30:00.000-08:00

md5_hex(rand) will not give you a string of random hex digits. In fact, it's considerably less than random, since rand() gives 32, 48, or 64 bits of randomness, but a md5 hash is 128 bits. So there are 2^128 possible md5 hashes but your md5_hex(rand) will choose from only at most 2^64 of them. So it only looks random -- be careful!