This is Perl module Encode::Base58.
INSTALLATION
Encode::Base58 installation is straightforward. If your CPAN shell is set up,
you should just be able to do
    % cpan Encode::Base58
Download it, unpack it, then build it as per the usual:
    % perl Makefile.PL
    % make && make test
Then install it:
    % make install
DOCUMENTATION
Encode::Base58 documentation is available as in POD. So you can do:
    % perldoc Encode::Base58
to read the documentation online with your favorite pager.
Tatsuhiko Miyagawa