1) know your tools 
    # Convert the decimal to hexadecimal and pad the result with a lea
+ding
    # zero if needed.
    my $hex = sprintf("%x", $dec);
    $hex = length( $hex ) == 1 ? "0".$hex : $hex;

[download]
way too complicated 
    my $hex = sprintf '%02x', $dec;

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conversion table 
  0 -> 00
  1 -> 01
 15 -> 0f
 20 -> 14
255 -> ff
256 -> 100    # garbage in, garbage out
2) nesting subs does not work: 
sub basicSNTPSetup {
  ...   
  sub keyDifference {
    ..
  };
};

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is equivalent to 
sub basicSNTPSetup {
  ...   
};

sub keyDifference {
  ..
};

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3) dead code / sub-ref / conditional 
my $verify_port = sub {
  my $port = shift;
  if ( defined $port && $port =~ /^[0-9]+$/ ) {
    if ( $port >= MIN_UDP_PORT || $port <= MAX_UDP_PORT ) {
      return FALSE;
    }
  }
  return TRUE;
};

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This functions does not seem to be referenced anywhere in your code. Additionally: Why do you code it as a sub reference instead of an actual function? 
sub verify_port {
  ...
};

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inside verify_port you are using the wrong conditional 
  if ( $port >= MIN_UDP_PORT || $port <= MAX_UDP_PORT ) {

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This will happily allow 10000000000 as a valid port. At the very least you should replace || with &&. I'm to lazy too look up operator precedence, but you may also need to replace && with 'and' or put the conditions into parenthesis. 
either:
  if ( ($port >= MIN_UDP_PORT) && ($port <= MAX_UDP_PORT) ) {
or:
  if ( $port >= MIN_UDP_PORT and $port <= MAX_UDP_PORT ) {

[download]

Resumee:

I would not want to touch this module with a ten-foot pole. I wasn't even looking very hard.

In reply to Re: RFC: Net::SNTP::Server v1 by Monk::Thomas
in thread RFC: Net::SNTP::Server v1 by thanos1983

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