Comment 8 for bug 516032

Ubuntu keyserver now accepts connections in port 80. See: https://answers.launchpad.net/ubuntu-website/+question/79193
Behind a firewall that blocks port 11371 the following step fails:

gpg --ignore-time-conflict --no-options --no-default-keyring --secret-keyring /etc/apt/secring.gpg --trustdb-name /etc/apt/trustdb.gpg --keyring /etc/apt/trusted.gpg --primary-keyring /etc/apt/trusted.gpg --keyserver keyserver.ubuntu.com --recv B305FC46C55F531512AFA579D6B6DB186A68F637
gpg: requisitando chave 6A68F637 de servidor hkp - keyserver.ubuntu.com
gpgkeys: HTTP fetch error 7: couldn't connect to host
gpg: nenhum dado OpenPGP válido encontrado.
gpg: Número total processado: 0

Changing the keyserver to "hkp://keyserver.ubuntu.com:80" does the trick:
gpg --ignore-time-conflict --no-options --no-default-keyring --secret-keyring /etc/apt/secring.gpg --trustdb-name /etc/apt/trustdb.gpg --keyring /etc/apt/trusted.gpg --primary-keyring /etc/apt/trusted.gpg --keyserver hkp://keyserver.ubuntu.com:80 --recv-keys B305FC46C55F531512AFA579D6B6DB186A68F637
gpg: requisitando chave 6A68F637 de servidor hkp - keyserver.ubuntu.com
gpg: chave 6A68F637: chave pública "Launchpad JDownloader PPA" importada
gpg: Número total processado: 1
gpg: importados: 1 (RSA: 1)

add-apt-repository should be aware of that and try the port 80 if 11371 fails (or simply use 80 by default). Alternatively, it could add an option to switch the keyserverport in command line.