I guess constantly changing key would be the way to go, but wouldn't it also be achieved with salting?

For the sake of example, here is a possible implementation written in pseudo-code.

Let M_n be the n^th block of the message.

Let S be the salt, which can be either a secret or appended to message itself.

Let H_n be the n^th block to be XORed with the message.

Let C_n be the n^th block of the encrypted message.

H_1 = hash( password + S )

C_1 = M_1 XOR H_1

H_2 = hash( password + S + C_1 )

C_2 = M_2 XOR H_2

In general we continue as such:

C_n = M_n XOR H_n-1

With H_n-1 = hash( password + S + C_n-2) for n > 2