use strict;
my %hash1 = (
	A => 5,
	B => 7,
	C => 2,
	D => 8,
);
my %hash2 = (
	1234 => "A,C",
	4567 => "A,D",
	5678 => "C",
);

my @a = split ",", join ',', values %hash2;
my $found = 0;
foreach my $key ( keys %hash1 )
{
	$found = 0;
	foreach my $val ( @a )
	{
		$found = 1 if $val eq $key;
	}
	print "$key => $hash1{$key}\n" if !$found;
}