my $secret="(binary garbage here)";
sub checkSecurity;
sub decodeSecret;
sub reencode;
if (checkSecurity()) {  # <--- bypass the function call or make the function return TRUE
    my $plaintext=decodeSecret($secret);
    # breakpoint here
    say $plaintext;
    # or, if you like:
    say reencode($plaintext);
} else {
    die "Insecure condition found, won't tell you the secret!\n";
}