The classic Trithemius cipher (using a shift of one) is equivalent to a Vigenère cipher with ABCDEFGHIJKLMNOPQRSTUVWXYZ as the key. It is also equivalent to a Caesar cipher in which the shift is increased by 1 with each letter, starting at 0.
ThE classic TrIThEmius CipHer (Using A sHiFt oF one) is EquivalEnT tO a vIGenèRe cIPher WitH aBcDEfGhiJklMnoPqrstuvwxyz as the key. iT is ALsO EQuIvalenT TO a caeSAr CIPheR In wHich the sHift is iNcReaseD By 1 witH eAcH letteR, sTaRtinG aT 0.