Recently I read that Tor switched from TAP handshake requests to NTor handshake requests. This seems to improve the performance and doesn't put such a high load on relays (because of Mevade). However I couldn't find a description what TAP and NTor is. Could you provide an explanation and tell the difference between both?
TAP is the original Tor Authentication Protocol, the one described in the original Tor paper (html). A security proof was later done by Goldberg at PET2006 and I think this is where the name of the scheme and the TAP acronym comes from.