use XML::Rules;

my (@keys, @values);

my $parser = XML::Rules->new(
	rules => {
		_default => '',
		Key => sub {push @keys, $_[1]->{_content}},
		Value => sub {push @values, $_[1]->{_content}},
	},
);
$parser->parse(\*DATA);

use Data::Dumper;
print Dumper(\@keys);
print Dumper(\@values);

__DATA__
<root>
<SigData>
<KVPair>
<Key>eb08f9990ae6545f9ea625412c71f24f7bf007ed</Key>
<Value>c73df5228c35c419f884ba9571310cd7</Value>
</KVPair>
<bogus>sdf sdhf nsdfg sdfgh nserg sfgdfgh</bogus>
</SigData>
<SigData>
<KVPair>
<Key>EB08F9990AE6545F9EA625412C71F24F7BF007ED</Key>
<Value>C73DF5228C35C419F884BA9571310CD7</Value>
</KVPair>
</SigData>
</root>