$ gpg --keyserver hkp://pool.sks-keyservers.net --recv-keys 0x4E2C6E8793298290
$ gpg --keyserver hkp://pool.sks-keyservers.net --recv-keys 0x910397D88D29319A

if this gives a problem do this

$ cd ~/.gnupg
$ rm dirmngr.conf
$ rm dirmngr_ldapservers.conf
$ echo " " >> dirmngr.conf
$ echo " " >> dirmngr_ldapservers.conf

and retry

$ cd ~/tor
$ gpg --verify tor-0.2.7.6.tar.gz.asc tor-0.2.7.6.tar.gz

etc.