This is most of the documentation on the subject

perl581delta#Hash Randomisation

perlsec#Algorithmic Complexity Attacks

perlrun#PERL_HASH_SEED,

perl-5.17.6/pod/perldelta.pod

New hash function Murmurhash-32 (v3)

Per process hash randomization

PERL_HASH_SEED enviornment variable now takes a hex value

Output of PERL_HASH_SEED_DEBUG has been changed

perl-5.17.6/MANIFEST

t/op/hash.t See if the complexity attackers are repelled