I think I am using ruby that came with the distribution. I had to apt-get some addtional packages. I'm attaching a list of the ruby related packages that I have installed.
ns-001.log
Mon Mar 5 11:30:20 2012.372772 DEBUG Connection from 127.0.0.1
Mon Mar 5 11:30:20 2012.373528 INFO Waiting for Unsniff to initiate SSL/TLS handshake...
Mon Mar 5 11:30:20 2012.473544 INFO Certificate verify ok
Mon Mar 5 11:30:20 2012.474090 INFO Certificate verify ok
Mon Mar 5 11:30:20 2012.519144 ERROR SSL/TLS Client produced an unauthorized certificate
Mon Mar 5 11:30:20 2012.520115 INFO Waiting to accept connections from Unsniff instances
ruby packages:
libdrb-ruby 4.2
liberb-ruby 4.2
libopenssl-ruby 4.2
libopenssl-ruby1.8 1.8.7.249-2ubuntu0.1
libreadline-ruby1.8 1.8.7.249-2ubuntu0.1
libreadline-ruby1.9.1 1.9.1.378-1
libruby 4.2
libruby1.8 1.8.7.249-2ubuntu0.1
libruby1.9.1 1.9.1.378-1
libyaml-ruby 4.2
libzlib-ruby 4.2
rdoc 4.2
ruby 4.2
ruby-dev 4.2
ruby1.8 1.8.7.249-2ubuntu0.1
ruby1.8-dev 1.8.7.249-2ubuntu0.1
ruby1.9.1 1.9.1.378-1
rubygems 1.3.5-1ubuntu2
rubygems1.8 1.3.5-1ubuntu2
rubygems1.9.1 1.3.5-1ubuntu2