All decryption filters work on the principle of "security through
obscurity." Regardless of how well you write a decryption filter and
-how strong your encryption algorithm, anyone determined enough can
+how strong your encryption algorithm is, anyone determined enough can
retrieve the original source code. The reason is quite simple - once
the decryption filter has decrypted the source back to its original
form, fragments of it will be stored in the computer's memory as Perl
An alternative to writing the filter in C is to create a separate
executable in the language of your choice. The separate executable
reads from standard input, does whatever processing is necessary, and
-writes the filtered data to standard output. C<Filter:cpp> is an
+writes the filtered data to standard output. C<Filter::cpp> is an
example of a source filter implemented as a separate executable - the
executable is the C preprocessor bundled with your C compiler.