I don't know if this is the fastest way, but I've used this before and it doesn't seem to be too slow. It will use a bit of memory though, as you end up with a hash that has a union of the keys off all the hashes.

# untested, supports the interface you describe
sub commonkeys {
        my $number_of_hashes = scalar(@_);

        my %union;
        my @result;
        foreach (@_) {
                foreach (keys %{$_}) {
                        $union{$_}++;
                }
        }

        while (my ($key,$count) = each %union) {
                if ($count == $number_of_hashes) {
                        # a key which has appeared the same number of 
+times as we have hashes, is present in every hash.
                        push(@result,$key);
                }
        }

        return @result;
}
[download]

Odds are if you do a super search or look in Q/A, somebody else has had to do this too.

HTH

/\/\averick
perl -l -e "eval pack('h*','072796e6470272f2c5f2c5166756279636b672');"