die( sprintf "usage: %s <tripkey>\n", __FILE__ ) unless @ARGV;
my $tripkey = $ARGV[0];
my $salt = substr substr( $tripkey, 1, 2 ) . "H.", 0, 2;
$salt =~ tr{:;<=>?\@[\\]^_`}{ABCDEFGabcdef};
$salt =~ s{[^./0-9A-Za-z]}{.}g;
my $trip = substr crypt( $tripkey, $salt ), -10;
printf "◆%s", $trip;

このperlをC#に変換してください