Non the less, you would think it up to the person providing the data.

Btw, that was why I had the (subtle) invitation to golf a ciphering/deciphering algorithm which allowed for different "salts".

Never used golf before… but something else that might work is to use the Xor operator. If you Xor something twice you get the original value.

my $passphrase = "I love group ABC";
…
$text ^= $passphrase;
$line = $groupID . "\|" . $text;
print "$line\n";

…
if($group eq $myGroup) {
  $data ^= $passphrase;
}
print "$data\n";
[download]

Read that in a Steven Holznar book ...I think.
update: Although that may be less obscure than my first idea.