:-))

If you are sure each <KVPair> contains both <Key> and <Value> and is always in <SigData> you can use something as simple as this:

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>
[download]

If there is more in the XML you may skip some tags and their children by adding

  start_rules => {
    'the,list,of,such,tags' => 'skip'
  },
[download]

into the XML::Rules constructor.

If you do not want to use the globals, you may do something like:

my $parser = XML::Rules->new(
    stripspaces => 3,
    rules => {
        _default => '',
        Key => 'content',
        Value => 'content',
        KVPair => 'pass',
        SigData => sub {return '@keys' => $_[1]->{Key}, '@values' => $
+_[1]->{Value}},
        root => 'pass',
    },
);
my $data = $parser->parse(\*DATA);

use Data::Dumper;
print Dumper($data);
[download]

(assuming there is exactly one <KVPair> in each <SigData>! You'd have to add a test if it was optional.).

Actually are you sure you want to build two interrelated arrays? Wouldn't it make more sense to create a single hash? Or maybe process the pair as soon as you read it instead of keeping them all in memory?

The first would be

my $parser = XML::Rules->new(
    stripspaces => 3,
    rules => {
        _default => '',
        Key => 'content',
        Value => 'content',
        KVPair => sub {return $_[1]->{Key} => $_[1]->{Value}},
        SigData => 'pass',
        root => 'pass',
    },
);
my $data = $parser->parse(\*DATA);
[download]

the other just means that you change the anonymous subroutine specified in the rule for <KVPair> or <SigData> to do the processing and to return nothing. That way you only need memory proportional to the size of the individual keys and values.