There are many possible things you could mean, and they have very different answers. For instance you could be looking for an encryption module, of which there are several on CPAN. Or you might be looking for pack and unpack. If you are on Windows try this:

perl -ne "print unpack("B*", $_)" input_file > output_file
[download]

You can reverse it with:

perl -ne "print pack("B*", $_)" input_file > output_file
[download]